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curl_easy_setopt(3) libcurl Manual curl_easy_setopt(3)
NAME
curl_easy_setopt - set options for a curl easy handle
SYNOPSIS
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLoption option, parameter);
DESCRIPTION
curl_easy_setopt() is used to tell libcurl how to behave. By using the appropriate options
to curl_easy_setopt, you can change libcurl's behavior. All options are set with the
option followed by a parameter. That parameter can be a long, a function pointer, an
object pointer or a curl_off_t, depending on what the specific option expects. Read this
manual carefully as bad input values may cause libcurl to behave badly! You can only set
one option in each function call. A typical application uses many curl_easy_setopt() calls
in the setup phase.
Options set with this function call are valid for all forthcoming transfers performed
using this handle. The options are not in any way reset between transfers, so if you want
subsequent transfers with different options, you must change them between the transfers.
You can optionally reset all options back to internal default with curl_easy_reset(3).
Strings passed to libcurl as 'char *' arguments, are copied by the library; thus the
string storage associated to the pointer argument may be overwritten after
curl_easy_setopt() returns. Exceptions to this rule are described in the option details
below.
Before version 7.17.0, strings were not copied. Instead the user was forced keep them
available until libcurl no longer needed them.
The handle is the return code from a curl_easy_init(3) or curl_easy_duphandle(3) call.
BEHAVIOR OPTIONS
CURLOPT_VERBOSE
Set the parameter to 1 to get the library to display a lot of verbose information
about its operations. Very useful for libcurl and/or protocol debugging and under-
standing. The verbose information will be sent to stderr, or the stream set with
CURLOPT_STDERR.
You hardly ever want this set in production use, you will almost always want this
when you debug/report problems. Another neat option for debugging is the CUR-
LOPT_DEBUGFUNCTION.
CURLOPT_HEADER
A parameter set to 1 tells the library to include the header in the body output.
This is only relevant for protocols that actually have headers preceding the data
(like HTTP).
Custom headers are sent in all requests done by the easy handles, which implies
that if you tell libcurl to follow redirects (CURLOPT_FOLLOWLOCATION(3)), the same
set of custom headers will be sent in the subsequent request. Redirects can of
course go to other hosts and thus those servers will get all the contents of your
custom headers too.
Starting in 7.58.0, libcurl will specifically prevent "Authorization:" headers from
being sent to other hosts than the first used one, unless specifically permitted
with the CURLOPT_UNRESTRICTED_AUTH(3) option.
CURLOPT_NOPROGRESS
Pass a long. If set to 1, it tells the library to shut off the progress meter com-
pletely. It will also prevent the CURLOPT_PROGRESSFUNCTION from getting called.
Future versions of libcurl are likely to not have any built-in progress meter at
all.
CURLOPT_NOSIGNAL
Pass a long. If it is 1, libcurl will not use any functions that install signal
handlers or any functions that cause signals to be sent to the process. This option
is mainly here to allow multi-threaded unix applications to still set/use all time-
out options etc, without risking getting signals. (Added in 7.10)
If this option is set and libcurl has been built with the standard name resolver,
timeouts will not occur while the name resolve takes place. Consider building
libcurl with c-ares support to enable asynchronous DNS lookups, which enables nice
timeouts for name resolves without signals.
Setting CURLOPT_NOSIGNAL to 1 makes libcurl NOT ask the system to ignore SIGPIPE
signals, which otherwise are sent by the system when trying to send data to a
socket which is closed in the other end. libcurl makes an effort to never cause
such SIGPIPEs to trigger, but some operating systems have no way to avoid them and
even on those that have there are some corner cases when they may still happen,
contrary to our desire. In addition, using CURLAUTH_NTLM_WB authentication could
cause a SIGCHLD signal to be raised.
CURLOPT_WILDCARDMATCH
Set this option to 1 if you want to transfer multiple files according to a file
name pattern. The pattern can be specified as part of the CURLOPT_URL option, using
an fnmatch-like pattern (Shell Pattern Matching) in the last part of URL (file
name).
By default, libcurl uses its internal wildcard matching implementation. You can
provide your own matching function by the CURLOPT_FNMATCH_FUNCTION option.
This feature is only supported by the FTP download for now.
A brief introduction of its syntax follows:
* - ASTERISK
ftp://example.com/some/path/*.txt (for all txt's from the root directory)
? - QUESTION MARK
Question mark matches any (exactly one) character.
ftp://example.com/some/path/photo?.jpeg
[ - BRACKET EXPRESSION
The left bracket opens a bracket expression. The question mark and asterisk
have no special meaning in a bracket expression. Each bracket expression
ends by the right bracket and matches exactly one character. Some examples
follow:
[a-zA-Z0-9] or [f-gF-G] - character interval
[abc] - character enumeration
[^abc] or [!abc] - negation
[[:name:]] class expression. Supported classes are alnum,lower, space,
alpha, digit, print, upper, blank, graph, xdigit.
[][-!^] - special case - matches only '-', ']', '[', '!' or '^'. These char-
acters have no special purpose.
[\[\]\\] - escape syntax. Matches '[', ']' or '\'.
Using the rules above, a file name pattern can be constructed:
ftp://example.com/some/path/[a-z[:upper:]\\].jpeg
(This was added in 7.21.0)
CALLBACK OPTIONS
CURLOPT_WRITEFUNCTION
Pass a pointer to a function that matches the following prototype: size_t function(
char *ptr, size_t size, size_t nmemb, void *userdata); This function gets called by
libcurl as soon as there is data received that needs to be saved. The size of the
data pointed to by ptr is size multiplied with nmemb, it will not be zero termi-
nated. Return the number of bytes actually taken care of. If that amount differs
from the amount passed to your function, it'll signal an error to the library. This
will abort the transfer and return CURLE_WRITE_ERROR.
From 7.18.0, the function can return CURL_WRITEFUNC_PAUSE which then will cause
writing to this connection to become paused. See curl_easy_pause(3) for further
details.
This function may be called with zero bytes data if the transferred file is empty.
Set this option to NULL to get the internal default function. The internal default
function will write the data to the FILE * given with CURLOPT_WRITEDATA.
Set the userdata argument with the CURLOPT_WRITEDATA option.
The callback function will be passed as much data as possible in all invokes, but
you cannot possibly make any assumptions. It may be one byte, it may be thousands.
The maximum amount of body data that can be passed to the write callback is defined
in the curl.h header file: CURL_MAX_WRITE_SIZE (the usual default is 16K). If you
however have CURLOPT_HEADER set, which sends header data to the write callback, you
can get up to CURL_MAX_HTTP_HEADER bytes of header data passed into it. This usu-
ally means 100K.
CURLOPT_WRITEDATA
Data pointer to pass to the file write function. If you use the CURLOPT_WRITEFUNC-
TION option, this is the pointer you'll get as input. If you don't use a callback,
you must pass a 'FILE *' as libcurl will pass this to fwrite() when writing data.
The internal CURLOPT_WRITEFUNCTION will write the data to the FILE * given with
this option, or to stdout if this option hasn't been set.
If you're using libcurl as a win32 DLL, you MUST use the CURLOPT_WRITEFUNCTION if
you set this option or you will experience crashes.
This option is also known with the older name CURLOPT_FILE, the name CURLOPT_WRITE-
DATA was introduced in 7.9.7.
CURLOPT_READFUNCTION
Pass a pointer to a function that matches the following prototype: size_t function(
void *ptr, size_t size, size_t nmemb, void *userdata); This function gets called by
libcurl as soon as it needs to read data in order to send it to the peer. The data
area pointed at by the pointer ptr may be filled with at most size multiplied with
nmemb number of bytes. Your function must return the actual number of bytes that
you stored in that memory area. Returning 0 will signal end-of-file to the library
and cause it to stop the current transfer.
If you stop the current transfer by returning 0 "pre-maturely" (i.e before the
server expected it, like when you've said you will upload N bytes and you upload
less than N bytes), you may experience that the server "hangs" waiting for the rest
of the data that won't come.
The read callback may return CURL_READFUNC_ABORT to stop the current operation
immediately, resulting in a CURLE_ABORTED_BY_CALLBACK error code from the transfer
(Added in 7.12.1)
From 7.18.0, the function can return CURL_READFUNC_PAUSE which then will cause
reading from this connection to become paused. See curl_easy_pause(3) for further
details.
Bugs: when doing TFTP uploads, you must return the exact amount of data that the
callback wants, or it will be considered the final packet by the server end and the
transfer will end there.
If you set this callback pointer to NULL, or don't set it at all, the default
internal read function will be used. It is doing an fread() on the FILE * userdata
set with CURLOPT_READDATA.
CURLOPT_READDATA
Data pointer to pass to the file read function. If you use the CURLOPT_READFUNCTION
option, this is the pointer you'll get as input. If you don't specify a read call-
back but instead rely on the default internal read function, this data must be a
valid readable FILE *.
If you're using libcurl as a win32 DLL, you MUST use a CURLOPT_READFUNCTION if you
set this option.
This option was also known by the older name CURLOPT_INFILE, the name CURLOPT_READ-
DATA was introduced in 7.9.7.
CURLOPT_IOCTLFUNCTION
Pass a pointer to a function that matches the following prototype: curlioerr func-
tion(CURL *handle, int cmd, void *clientp);. This function gets called by libcurl
when something special I/O-related needs to be done that the library can't do by
itself. For now, rewinding the read data stream is the only action it can request.
The rewinding of the read data stream may be necessary when doing a HTTP PUT or
POST with a multi-pass authentication method. (Option added in 7.12.3).
Use CURLOPT_SEEKFUNCTION instead to provide seeking!
CURLOPT_IOCTLDATA
Pass a pointer that will be untouched by libcurl and passed as the 3rd argument in
the ioctl callback set with CURLOPT_IOCTLFUNCTION. (Option added in 7.12.3)
CURLOPT_SEEKFUNCTION
Pass a pointer to a function that matches the following prototype: int func-
tion(void *instream, curl_off_t offset, int origin); This function gets called by
libcurl to seek to a certain position in the input stream and can be used to fast
forward a file in a resumed upload (instead of reading all uploaded bytes with the
normal read function/callback). It is also called to rewind a stream when doing a
HTTP PUT or POST with a multi-pass authentication method. The function shall work
like "fseek" or "lseek" and accepted SEEK_SET, SEEK_CUR and SEEK_END as argument
for origin, although (in 7.18.0) libcurl only passes SEEK_SET. The callback must
return 0 (CURL_SEEKFUNC_OK) on success, 1 (CURL_SEEKFUNC_FAIL) to cause the upload
operation to fail or 2 (CURL_SEEKFUNC_CANTSEEK) to indicate that while the seek
failed, libcurl is free to work around the problem if possible. The latter can
sometimes be done by instead reading from the input or similar.
If you forward the input arguments directly to "fseek" or "lseek", note that the
data type for offset is not the same as defined for curl_off_t on many systems!
(Option added in 7.18.0)
CURLOPT_SEEKDATA
Data pointer to pass to the file seek function. If you use the CURLOPT_SEEKFUNCTION
option, this is the pointer you'll get as input. If you don't specify a seek call-
back, NULL is passed. (Option added in 7.18.0)
CURLOPT_SOCKOPTFUNCTION
Pass a pointer to a function that matches the following prototype: int func-
tion(void *clientp, curl_socket_t curlfd, curlsocktype purpose);. This function
gets called by libcurl after the socket() call but before the connect() call. The
callback's purpose argument identifies the exact purpose for this particular
socket:
CURLSOCKTYPE_IPCXN for actively created connections or since 7.28.0 CURLSOCK-
TYPE_ACCEPT for FTP when the connection was setup with PORT/EPSV (in earlier ver-
sions these sockets weren't passed to this callback).
Future versions of libcurl may support more purposes. It passes the newly created
socket descriptor so additional setsockopt() calls can be done at the user's dis-
cretion. Return 0 (zero) from the callback on success. Return 1 from the callback
function to signal an unrecoverable error to the library and it will close the
socket and return CURLE_COULDNT_CONNECT. (Option added in 7.16.0)
Added in 7.21.5, the callback function may return CURL_SOCKOPT_ALREADY_CONNECTED,
which tells libcurl that the socket is in fact already connected and then libcurl
will not attempt to connect it.
CURLOPT_SOCKOPTDATA
Pass a pointer that will be untouched by libcurl and passed as the first argument
in the sockopt callback set with CURLOPT_SOCKOPTFUNCTION. (Option added in 7.16.0)
CURLOPT_OPENSOCKETFUNCTION
Pass a pointer to a function that matches the following prototype: curl_socket_t
function(void *clientp, curlsocktype purpose, struct curl_sockaddr *address);. This
function gets called by libcurl instead of the socket(2) call. The callback's pur-
pose argument identifies the exact purpose for this particular socket: CURLSOCK-
TYPE_IPCXN is for IP based connections. Future versions of libcurl may support more
purposes. It passes the resolved peer address as a address argument so the callback
can modify the address or refuse to connect at all. The callback function should
return the socket or CURL_SOCKET_BAD in case no connection could be established or
another error was detected. Any additional setsockopt(2) calls can be done on the
socket at the user's discretion. CURL_SOCKET_BAD return value from the callback
function will signal an unrecoverable error to the library and it will return
CURLE_COULDNT_CONNECT. This return code can be used for IP address blacklisting.
The default behavior is:
return socket(addr->family, addr->socktype, addr->protocol);
(Option added in 7.17.1.)
CURLOPT_OPENSOCKETDATA
Pass a pointer that will be untouched by libcurl and passed as the first argument
in the opensocket callback set with CURLOPT_OPENSOCKETFUNCTION. (Option added in
7.17.1.)
CURLOPT_CLOSESOCKETFUNCTION
Pass a pointer to a function that matches the following prototype: int func-
tion(void *clientp, curl_socket_t item);. This function gets called by libcurl
instead of the close(3) or closesocket(3) call when sockets are closed (not for any
other file descriptors). This is pretty much the reverse to the CURLOPT_OPENSOCKET-
FUNCTION option. Return 0 to signal success and 1 if there was an error. (Option
added in 7.21.7)
CURLOPT_CLOSESOCKETDATA
Pass a pointer that will be untouched by libcurl and passed as the first argument
in the closesocket callback set with CURLOPT_CLOSESOCKETFUNCTION. (Option added in
7.21.7)
CURLOPT_PROGRESSFUNCTION
Pass a pointer to a function that matches the following prototype: int func-
tion(void *clientp, double dltotal, double dlnow, double ultotal, double ulnow); .
This function gets called by libcurl instead of its internal equivalent with a fre-
quent interval during operation (roughly once per second or sooner) no matter if
data is being transferred or not. Unknown/unused argument values passed to the
callback will be set to zero (like if you only download data, the upload size will
remain 0). Returning a non-zero value from this callback will cause libcurl to
abort the transfer and return CURLE_ABORTED_BY_CALLBACK.
If you transfer data with the multi interface, this function will not be called
during periods of idleness unless you call the appropriate libcurl function that
performs transfers.
CURLOPT_NOPROGRESS must be set to 0 to make this function actually get called.
CURLOPT_PROGRESSDATA
Pass a pointer that will be untouched by libcurl and passed as the first argument
in the progress callback set with CURLOPT_PROGRESSFUNCTION.
CURLOPT_HEADERFUNCTION
Pass a pointer to a function that matches the following prototype: size_t function(
void *ptr, size_t size, size_t nmemb, void *userdata);. This function gets called
by libcurl as soon as it has received header data. The header callback will be
called once for each header and only complete header lines are passed on to the
callback. Parsing headers is very easy using this. The size of the data pointed to
by ptr is size multiplied with nmemb. Do not assume that the header line is zero
terminated! The pointer named userdata is the one you set with the CURLOPT_WRITE-
HEADER option. The callback function must return the number of bytes actually taken
care of. If that amount differs from the amount passed to your function, it'll sig-
nal an error to the library. This will abort the transfer and return
CURL_WRITE_ERROR.
A complete HTTP header that is passed to this function can be up to
CURL_MAX_HTTP_HEADER (100K) bytes.
If this option is not set, or if it is set to NULL, but CURLOPT_HEADERDATA (CUR-
LOPT_WRITEHEADER) is set to anything but NULL, the function used to accept response
data will be used instead. That is, it will be the function specified with CUR-
LOPT_WRITEFUNCTION, or if it is not specified or NULL - the default, stream-writing
function.
It's important to note that the callback will be invoked for the headers of all
responses received after initiating a request and not just the final response. This
includes all responses which occur during authentication negotiation. If you need
to operate on only the headers from the final response, you will need to collect
headers in the callback yourself and use HTTP status lines, for example, to delimit
response boundaries.
When a server sends a chunked encoded transfer, it may contain a trailer. That
trailer is identical to a HTTP header and if such a trailer is received it is
passed to the application using this callback as well. There are several ways to
detect it being a trailer and not an ordinary header: 1) it comes after the
response-body. 2) it comes after the final header line (CR LF) 3) a Trailer: header
among the regular response-headers mention what header(s) to expect in the trailer.
For non-HTTP protocols like FTP, POP3, IMAP and SMTP this function will get called
with the server responses to the commands that libcurl sends.
CURLOPT_WRITEHEADER
(This option is also known as CURLOPT_HEADERDATA) Pass a pointer to be used to
write the header part of the received data to. If you don't use CURLOPT_WRITEFUNC-
TION or CURLOPT_HEADERFUNCTION to take care of the writing, this must be a valid
FILE * as the internal default will then be a plain fwrite(). See also the CUR-
LOPT_HEADERFUNCTION option above on how to set a custom get-all-headers callback.
CURLOPT_DEBUGFUNCTION
Pass a pointer to a function that matches the following prototype: int
curl_debug_callback (CURL *, curl_infotype, char *, size_t, void *); CURLOPT_DEBUG-
FUNCTION replaces the standard debug function used when CURLOPT_VERBOSE is in
effect. This callback receives debug information, as specified with the curl_info-
type argument. This function must return 0. The data pointed to by the char *
passed to this function WILL NOT be zero terminated, but will be exactly of the
size as told by the size_t argument.
Available curl_infotype values:
CURLINFO_TEXT
The data is informational text.
CURLINFO_HEADER_IN
The data is header (or header-like) data received from the peer.
CURLINFO_HEADER_OUT
The data is header (or header-like) data sent to the peer.
CURLINFO_DATA_IN
The data is protocol data received from the peer.
CURLINFO_DATA_OUT
The data is protocol data sent to the peer.
CURLOPT_DEBUGDATA
Pass a pointer to whatever you want passed in to your CURLOPT_DEBUGFUNCTION in the
last void * argument. This pointer is not used by libcurl, it is only passed to the
callback.
CURLOPT_SSL_CTX_FUNCTION
This option does only function for libcurl powered by OpenSSL. If libcurl was built
against another SSL library, this functionality is absent.
Pass a pointer to a function that matches the following prototype: CURLcode sslctx-
fun(CURL *curl, void *sslctx, void *parm); This function gets called by libcurl
just before the initialization of a SSL connection after having processed all other
SSL related options to give a last chance to an application to modify the behaviour
of openssl's ssl initialization. The sslctx parameter is actually a pointer to an
openssl SSL_CTX. If an error is returned no attempt to establish a connection is
made and the perform operation will return the error code from this callback func-
tion. Set the parm argument with the CURLOPT_SSL_CTX_DATA option. This option was
introduced in 7.11.0.
This function will get called on all new connections made to a server, during the
SSL negotiation. The SSL_CTX pointer will be a new one every time.
To use this properly, a non-trivial amount of knowledge of the openssl libraries is
necessary. For example, using this function allows you to use openssl callbacks to
add additional validation code for certificates, and even to change the actual URI
of a HTTPS request (example used in the lib509 test case). See also the example
section for a replacement of the key, certificate and trust file settings.
CURLOPT_SSL_CTX_DATA
Data pointer to pass to the ssl context callback set by the option CUR-
LOPT_SSL_CTX_FUNCTION, this is the pointer you'll get as third parameter, otherwise
NULL. (Added in 7.11.0)
CURLOPT_CONV_TO_NETWORK_FUNCTION
CURLOPT_CONV_FROM_NETWORK_FUNCTION
CURLOPT_CONV_FROM_UTF8_FUNCTION
Pass a pointer to a function that matches the following prototype: CURLcode func-
tion(char *ptr, size_t length);
These three options apply to non-ASCII platforms only. They are available only if
CURL_DOES_CONVERSIONS was defined when libcurl was built. When this is the case,
curl_version_info(3) will return the CURL_VERSION_CONV feature bit set.
The data to be converted is in a buffer pointed to by the ptr parameter. The
amount of data to convert is indicated by the length parameter. The converted data
overlays the input data in the buffer pointed to by the ptr parameter. CURLE_OK
should be returned upon successful conversion. A CURLcode return value defined by
curl.h, such as CURLE_CONV_FAILED, should be returned if an error was encountered.
CURLOPT_CONV_TO_NETWORK_FUNCTION and CURLOPT_CONV_FROM_NETWORK_FUNCTION convert
between the host encoding and the network encoding. They are used when commands or
ASCII data are sent/received over the network.
CURLOPT_CONV_FROM_UTF8_FUNCTION is called to convert from UTF8 into the host encod-
ing. It is required only for SSL processing.
If you set a callback pointer to NULL, or don't set it at all, the built-in libcurl
iconv functions will be used. If HAVE_ICONV was not defined when libcurl was
built, and no callback has been established, conversion will return the
CURLE_CONV_REQD error code.
If HAVE_ICONV is defined, CURL_ICONV_CODESET_OF_HOST must also be defined. For
example:
#define CURL_ICONV_CODESET_OF_HOST "IBM-1047"
The iconv code in libcurl will default the network and UTF8 codeset names as fol-
lows:
#define CURL_ICONV_CODESET_OF_NETWORK "ISO8859-1"
#define CURL_ICONV_CODESET_FOR_UTF8 "UTF-8"
You will need to override these definitions if they are different on your system.
CURLOPT_INTERLEAVEFUNCTION
Pass a pointer to a function that matches the following prototype: size_t function(
void *ptr, size_t size, size_t nmemb, void *userdata). This function gets called by
libcurl as soon as it has received interleaved RTP data. This function gets called
for each $ block and therefore contains exactly one upper-layer protocol unit (e.g.
one RTP packet). Curl writes the interleaved header as well as the included data
for each call. The first byte is always an ASCII dollar sign. The dollar sign is
followed by a one byte channel identifier and then a 2 byte integer length in net-
work byte order. See RFC2326 Section 10.12 for more information on how RTP inter-
leaving behaves. If unset or set to NULL, curl will use the default write function.
Interleaved RTP poses some challenges for the client application. Since the stream
data is sharing the RTSP control connection, it is critical to service the RTP in a
timely fashion. If the RTP data is not handled quickly, subsequent response pro-
cessing may become unreasonably delayed and the connection may close. The applica-
tion may use CURL_RTSPREQ_RECEIVE to service RTP data when no requests are desired.
If the application makes a request, (e.g. CURL_RTSPREQ_PAUSE) then the response
handler will process any pending RTP data before marking the request as finished.
(Added in 7.20.0)
CURLOPT_INTERLEAVEDATA
This is the userdata pointer that will be passed to CURLOPT_INTERLEAVEFUNCTION when
interleaved RTP data is received. (Added in 7.20.0)
CURLOPT_CHUNK_BGN_FUNCTION
Pass a pointer to a function that matches the following prototype: long function
(const void *transfer_info, void *ptr, int remains). This function gets called by
libcurl before a part of the stream is going to be transferred (if the transfer
supports chunks).
This callback makes sense only when using the CURLOPT_WILDCARDMATCH option for now.
The target of transfer_info parameter is a "feature depended" structure. For the
FTP wildcard download, the target is curl_fileinfo structure (see curl/curl.h).
The parameter ptr is a pointer given by CURLOPT_CHUNK_DATA. The parameter remains
contains number of chunks remaining per the transfer. If the feature is not avail-
able, the parameter has zero value.
Return CURL_CHUNK_BGN_FUNC_OK if everything is fine, CURL_CHUNK_BGN_FUNC_SKIP if
you want to skip the concrete chunk or CURL_CHUNK_BGN_FUNC_FAIL to tell libcurl to
stop if some error occurred. (This was added in 7.21.0)
CURLOPT_CHUNK_END_FUNCTION
Pass a pointer to a function that matches the following prototype: long func-
tion(void *ptr). This function gets called by libcurl as soon as a part of the
stream has been transferred (or skipped).
Return CURL_CHUNK_END_FUNC_OK if everything is fine or CURL_CHUNK_END_FUNC_FAIL to
tell the lib to stop if some error occurred. (This was added in 7.21.0)
CURLOPT_CHUNK_DATA
Pass a pointer that will be untouched by libcurl and passed as the ptr argument to
the CURL_CHUNK_BGN_FUNTION and CURL_CHUNK_END_FUNTION. (This was added in 7.21.0)
CURLOPT_FNMATCH_FUNCTION
Pass a pointer to a function that matches the following prototype: int func-
tion(void *ptr, const char *pattern, const char *string) prototype (see
curl/curl.h). It is used internally for the wildcard matching feature.
Return CURL_FNMATCHFUNC_MATCH if pattern matches the string, CURL_FNMATCH-
FUNC_NOMATCH if not or CURL_FNMATCHFUNC_FAIL if an error occurred. (This was added
in 7.21.0)
CURLOPT_FNMATCH_DATA
Pass a pointer that will be untouched by libcurl and passed as the ptr argument to
the CURL_FNMATCH_FUNCTION. (This was added in 7.21.0)
ERROR OPTIONS
CURLOPT_ERRORBUFFER
Pass a char * to a buffer that the libcurl may store human readable error messages
in. This may be more helpful than just the return code from curl_easy_perform. The
buffer must be at least CURL_ERROR_SIZE big. Although this argument is a 'char *',
it does not describe an input string. Therefore the (probably undefined) contents
of the buffer is NOT copied by the library. You must keep the associated storage
available until libcurl no longer needs it. Failing to do so will cause very odd
behavior or even crashes. libcurl will need it until you call curl_easy_cleanup(3)
or you set the same option again to use a different pointer.
Use CURLOPT_VERBOSE and CURLOPT_DEBUGFUNCTION to better debug/trace why errors hap-
pen.
If the library does not return an error, the buffer may not have been touched. Do
not rely on the contents in those cases.
CURLOPT_STDERR
Pass a FILE * as parameter. Tell libcurl to use this stream instead of stderr when
showing the progress meter and displaying CURLOPT_VERBOSE data.
CURLOPT_FAILONERROR
A parameter set to 1 tells the library to fail silently if the HTTP code returned
is equal to or larger than 400. The default action would be to return the page nor-
mally, ignoring that code.
This method is not fail-safe and there are occasions where non-successful response
codes will slip through, especially when authentication is involved (response codes
401 and 407).
You might get some amounts of headers transferred before this situation is
detected, like when a "100-continue" is received as a response to a POST/PUT and a
401 or 407 is received immediately afterwards.
NETWORK OPTIONS
CURLOPT_URL
Pass in a pointer to the actual URL to deal with. The parameter should be a char *
to a zero terminated string which must be URL-encoded in the following format:
scheme://host:port/path
For a greater explanation of the format please see RFC3986.
If the given URL lacks the scheme, or protocol, part ("http://" or "ftp://" etc),
libcurl will attempt to resolve which protocol to use based on the given host mame.
If the protocol is not supported, libcurl will return (CURLE_UNSUPPORTED_PROTOCOL)
when you call curl_easy_perform(3) or curl_multi_perform(3). Use curl_ver-
sion_info(3) for detailed information on which protocols are supported.
The host part of the URL contains the address of the server that you want to con-
nect to. This can be the fully qualified domain name of the server, the local net-
work name of the machine on your network or the IP address of the server or machine
represented by either an IPv4 or IPv6 address. For example:
http://www.example.com/
http://hostname/
http://192.168.0.1/
http://[2001:1890:1112:1::20]/
It is also possible to specify the user name and password as part of the host, for
some protocols, when connecting to servers that require authentication.
For example the following types of authentication support this:
http://user:password AT www.com
ftp://user:password AT ftp.com
pop3://user:password AT mail.com
The port is optional and when not specified libcurl will use the default port based
on the determined or specified protocol: 80 for HTTP, 21 for FTP and 25 for SMTP,
etc. The following examples show how to specify the port:
http://www.example.com:8080/ - This will connect to a web server using port 8080
rather than 80.
smtp://mail.example.com:587/ - This will connect to a SMTP server on the alterna-
tive mail port.
The path part of the URL is protocol specific and whilst some examples are given
below this list is not conclusive:
HTTP
The path part of a HTTP request specifies the file to retrieve and from what direc-
tory. If the directory is not specified then the web server's root directory is
used. If the file is omitted then the default document will be retrieved for either
the directory specified or the root directory. The exact resource returned for each
URL is entirely dependent on the server's configuration.
http://www.example.com - This gets the main page from the web server.
http://www.example.com/index.html - This returns the main page by explicitly
requesting it.
http://www.example.com/contactus/ - This returns the default document from the con-
tactus directory.
FTP
The path part of an FTP request specifies the file to retrieve and from what direc-
tory. If the file part is omitted then libcurl downloads the directory listing for
the directory specified. If the directory is omitted then the directory listing for
the root / home directory will be returned.
ftp://ftp.example.com - This retrieves the directory listing for the root direc-
tory.
ftp://ftp.example.com/readme.txt - This downloads the file readme.txt from the root
directory.
ftp://ftp.example.com/libcurl/readme.txt - This downloads readme.txt from the
libcurl directory.
ftp://user:password AT ftp.com/readme.txt - This retrieves the readme.txt file
from the user's home directory. When a username and password is specified, every-
thing that is specified in the path part is relative to the user's home directory.
To retrieve files from the root directory or a directory underneath the root direc-
tory then the absolute path must be specified by prepending an additional forward
slash to the beginning of the path.
ftp://user:password AT ftp.com//readme.txt - This retrieves the readme.txt
from the root directory when logging in as a specified user.
SMTP
The path part of a SMTP request specifies the host name to present during communi-
cation with the mail server. If the path is omitted then libcurl will attempt to
resolve the local computer's host name. However, this may not return the fully
qualified domain name that is required by some mail servers and specifying this
path allows you to set an alternative name, such as your machine's fully qualified
domain name, which you might have obtained from an external function such as geth-
ostname or getaddrinfo.
smtp://mail.example.com - This connects to the mail server at example.com and sends
your local computer's host name in the HELO / EHLO command.
smtp://mail.example.com/client.example.com - This will send client.example.com in
the HELO / EHLO command to the mail server at example.com.
POP3
The path part of a POP3 request specifies the mailbox (message) to retrieve. If
the mailbox is not specified then a list of waiting messages is returned instead.
pop3://user:password AT mail.com - This lists the available messages
pop3://user:password AT mail.com/1 - This retrieves the first message
SCP
The path part of a SCP request specifies the file to retrieve and from what direc-
tory. The file part may not be omitted. The file is taken as an absolute path from
the root directory on the server. To specify a path relative to the user's home
directory on the server, prepend ~/ to the path portion. If the user name is not
embedded in the URL, it can be set with the CURLOPT_USERPWD or CURLOPT_USERNAME
option.
scp://user AT example.com/etc/issue - This specifies the file /etc/issue
scp://example.com/~/my-file - This specifies the file my-file in the user's home
directory on the server
SFTP
The path part of a SFTP request specifies the file to retrieve and from what direc-
tory. If the file part is omitted then libcurl downloads the directory listing for
the directory specified. If the path ends in a / then a directory listing is
returned instead of a file. If the path is omitted entirely then the directory
listing for the root / home directory will be returned. If the user name is not
embedded in the URL, it can be set with the CURLOPT_USERPWD or CURLOPT_USERNAME
option.
sftp://user:password AT example.com/etc/issue - This specifies the file /etc/issue
sftp://user AT example.com/~/my-file - This specifies the file my-file in the user's
home directory
sftp://ssh.example.com/~/Documents/ - This requests a directory listing of the Doc-
uments directory under the user's home directory
LDAP
The path part of a LDAP request can be used to specify the: Distinguished Name,
Attributes, Scope, Filter and Extension for a LDAP search. Each field is separated
by a question mark and when that field is not required an empty string with the
question mark separator should be included.
ldap://ldap.example.com/o=My%20Organisation - This will perform a LDAP search with
the DN as My Organisation.
ldap://ldap.example.com/o=My%20Organisation?postalAddress - This will perform the
same search but will only return postalAddress attributes.
ldap://ldap.example.com/?rootDomainNamingContext - This specifies an empty DN and
requests information about the rootDomainNamingContext attribute for an Active
Directory server.
For more information about the individual components of a LDAP URL please see
RFC4516.
NOTES
Starting with version 7.20.0, the fragment part of the URI will not be sent as part
of the path, which was previously the case.
CURLOPT_URL is the only option that must be set before curl_easy_perform(3) is
called.
CURLOPT_PROTOCOLS can be used to limit what protocols libcurl will use for this
transfer, independent of what libcurl has been compiled to support. That may be
useful if you accept the URL from an external source and want to limit the accessi-
bility.
CURLOPT_PROTOCOLS
Pass a long that holds a bitmask of CURLPROTO_* defines. If used, this bitmask lim-
its what protocols libcurl may use in the transfer. This allows you to have a
libcurl built to support a wide range of protocols but still limit specific trans-
fers to only be allowed to use a subset of them. By default libcurl will accept all
protocols it supports. See also CURLOPT_REDIR_PROTOCOLS. (Added in 7.19.4)
CURLOPT_REDIR_PROTOCOLS
Pass a long that holds a bitmask of CURLPROTO_* defines. If used, this bitmask lim-
its what protocols libcurl may use in a transfer that it follows to in a redirect
when CURLOPT_FOLLOWLOCATION is enabled. This allows you to limit specific transfers
to only be allowed to use a subset of protocols in redirections. By default libcurl
will allow all protocols except for FILE and SCP. This is a difference compared to
pre-7.19.4 versions which unconditionally would follow to all protocols supported.
(Added in 7.19.4)
CURLOPT_PROXY
Set HTTP proxy to use. The parameter should be a char * to a zero terminated string
holding the host name or dotted IP address. To specify port number in this string,
append :[port] to the end of the host name. The proxy string may be prefixed with
[protocol]:// since any such prefix will be ignored. The proxy's port number may
optionally be specified with the separate option. If not specified, libcurl will
default to using port 1080 for proxies. CURLOPT_PROXYPORT.
When you tell the library to use a HTTP proxy, libcurl will transparently convert
operations to HTTP even if you specify an FTP URL etc. This may have an impact on
what other features of the library you can use, such as CURLOPT_QUOTE and similar
FTP specifics that don't work unless you tunnel through the HTTP proxy. Such tun-
neling is activated with CURLOPT_HTTPPROXYTUNNEL.
libcurl respects the environment variables http_proxy, ftp_proxy, all_proxy etc, if
any of those are set. The CURLOPT_PROXY option does however override any possibly
set environment variables.
Setting the proxy string to "" (an empty string) will explicitly disable the use of
a proxy, even if there is an environment variable set for it.
Since 7.14.1, the proxy host string given in environment variables can be specified
the exact same way as the proxy can be set with CURLOPT_PROXY, include protocol
prefix (http://) and embedded user + password.
Since 7.21.7, the proxy string may be specified with a protocol:// prefix to spec-
ify alternative proxy protocols. Use socks4://, socks4a://, socks5:// or socks5h://
(the last one to enable socks5 and asking the proxy to do the resolving, also known
as CURLPROXY_SOCKS5_HOSTNAME type) to request the specific SOCKS version to be
used. No protocol specified, http:// and all others will be treated as HTTP prox-
ies.
CURLOPT_PROXYPORT
Pass a long with this option to set the proxy port to connect to unless it is spec-
ified in the proxy string CURLOPT_PROXY.
CURLOPT_PROXYTYPE
Pass a long with this option to set type of the proxy. Available options for this
are CURLPROXY_HTTP, CURLPROXY_HTTP_1_0 (added in 7.19.4), CURLPROXY_SOCKS4 (added
in 7.10), CURLPROXY_SOCKS5, CURLPROXY_SOCKS4A (added in 7.18.0) and CURL-
PROXY_SOCKS5_HOSTNAME (added in 7.18.0). The HTTP type is default. (Added in 7.10)
If you set CURLOPT_PROXYTYPE to CURLPROXY_HTTP_1_0, it will only affect how libcurl
speaks to a proxy when CONNECT is used. The HTTP version used for "regular" HTTP
requests is instead controlled with CURLOPT_HTTP_VERSION.
CURLOPT_NOPROXY
Pass a pointer to a zero terminated string. The string consists of a comma sepa-
rated list of host names that do not require a proxy to get reached, even if one is
specified. The only wildcard available is a single * character, which matches all
hosts, and effectively disables the proxy. Each name in this list is matched as
either a domain which contains the hostname, or the hostname itself. For example,
example.com would match example.com, example.com:80, and www.example.com, but not
www.notanexample.com. (Added in 7.19.4)
CURLOPT_HTTPPROXYTUNNEL
Set the parameter to 1 to make the library tunnel all operations through a given
HTTP proxy. There is a big difference between using a proxy and to tunnel through
it. If you don't know what this means, you probably don't want this tunneling
option.
CURLOPT_SOCKS5_AUTH
Pass a long as parameter, which is set to a bitmask, to tell libcurl which authen-
tication method(s) are allowed for SOCKS5 proxy authentication. The only supported
flags are CURLAUTH_BASIC, which allows username/password authentication,
CURLAUTH_GSSAPI, which allows GSS-API authentication, and CURLAUTH_NONE, which
allows no authentication. Set the actual user name and password with the CUR-
LOPT_PROXYUSERPWD(3) option. Defaults to CURLAUTH_BASIC|CURLAUTH_GSSAPI. (Added
in 7.55.0)
CURLOPT_SOCKS5_GSSAPI_SERVICE
Pass a char * as parameter to a string holding the name of the service. The default
service name for a SOCKS5 server is rcmd/server-fqdn. This option allows you to
change it. (Added in 7.19.4)
CURLOPT_SOCKS5_GSSAPI_NEC
Pass a long set to 1 to enable or 0 to disable. As part of the gssapi negotiation a
protection mode is negotiated. The RFC1961 says in section 4.3/4.4 it should be
protected, but the NEC reference implementation does not. If enabled, this option
allows the unprotected exchange of the protection mode negotiation. (Added in
7.19.4).
CURLOPT_INTERFACE
Pass a char * as parameter. This sets the interface name to use as outgoing network
interface. The name can be an interface name, an IP address, or a host name.
Starting with 7.24.0: If the parameter starts with "if!" then it is treated as only
as interface name and no attempt will ever be named to do treat it as an IP address
or to do name resolution on it. If the parameter starts with "host!" it is treated
as either an IP address or a hostname. Hostnames are resolved synchronously.
Using the if! format is highly recommended when using the multi interfaces to avoid
allowing the code to block. If "if!" is specified but the parameter does not match
an existing interface, CURLE_INTERFACE_FAILED is returned.
CURLOPT_LOCALPORT
Pass a long. This sets the local port number of the socket used for connection.
This can be used in combination with CURLOPT_INTERFACE and you are recommended to
use CURLOPT_LOCALPORTRANGE as well when this is set. Valid port numbers are 1 -
65535. (Added in 7.15.2)
CURLOPT_LOCALPORTRANGE
Pass a long. This is the number of attempts libcurl will make to find a working
local port number. It starts with the given CURLOPT_LOCALPORT and adds one to the
number for each retry. Setting this to 1 or below will make libcurl do only one try
for the exact port number. Port numbers by nature are scarce resources that will be
busy at times so setting this value to something too low might cause unnecessary
connection setup failures. (Added in 7.15.2)
CURLOPT_DNS_CACHE_TIMEOUT
Pass a long, this sets the timeout in seconds. Name resolves will be kept in memory
for this number of seconds. Set to zero to completely disable caching, or set to -1
to make the cached entries remain forever. By default, libcurl caches this info for
60 seconds.
The name resolve functions of various libc implementations don't re-read name
server information unless explicitly told so (for example, by calling res_init(3)).
This may cause libcurl to keep using the older server even if DHCP has updated the
server info, and this may look like a DNS cache issue to the casual libcurl-app
user.
CURLOPT_DNS_USE_GLOBAL_CACHE
Pass a long. If the value is 1, it tells curl to use a global DNS cache that will
survive between easy handle creations and deletions. This is not thread-safe and
this will use a global variable.
WARNING: this option is considered obsolete. Stop using it. Switch over to using
the share interface instead! See CURLOPT_SHARE and curl_share_init(3).
CURLOPT_BUFFERSIZE
Pass a long specifying your preferred size (in bytes) for the receive buffer in
libcurl. The main point of this would be that the write callback gets called more
often and with smaller chunks. Secondly, for some protocols, there's a benefit of
having a larger buffer for performance. This is just treated as a request, not an
order. You cannot be guaranteed to actually get the given size. This buffer size
is by default CURL_MAX_WRITE_SIZE (16kB). The maximum buffer size allowed to set is
CURL_MAX_READ_SIZE (512kB). (Added in 7.10)
CURLOPT_PORT
Pass a long specifying what remote port number to connect to, instead of the one
specified in the URL or the default port for the used protocol.
CURLOPT_TCP_NODELAY
Pass a long specifying whether the TCP_NODELAY option is to be set or cleared (1 =
set, 0 = clear). The option is cleared by default. This will have no effect after
the connection has been established.
Setting this option will disable TCP's Nagle algorithm. The purpose of this algo-
rithm is to try to minimize the number of small packets on the network (where
"small packets" means TCP segments less than the Maximum Segment Size (MSS) for the
network).
Maximizing the amount of data sent per TCP segment is good because it amortizes the
overhead of the send. However, in some cases (most notably telnet or rlogin) small
segments may need to be sent without delay. This is less efficient than sending
larger amounts of data at a time, and can contribute to congestion on the network
if overdone.
CURLOPT_ADDRESS_SCOPE
Pass a long specifying the scope_id value to use when connecting to IPv6 link-local
or site-local addresses. (Added in 7.19.0)
CURLOPT_TCP_KEEPALIVE
Pass a long. If set to 1, TCP keepalive probes will be sent. The delay and fre-
quency of these probes can be controlled by the CURLOPT_TCP_KEEPIDLE and CUR-
LOPT_TCP_KEEPINTVL options, provided the operating system supports them. Set to 0
(default behavior) to disable keepalive probes (Added in 7.25.0).
CURLOPT_TCP_KEEPIDLE
Pass a long. Sets the delay, in seconds, that the operating system will wait while
the connection is idle before sending keepalive probes. Not all operating systems
support this option. (Added in 7.25.0)
CURLOPT_TCP_KEEPINTVL
Pass a long. Sets the interval, in seconds, that the operating system will wait
between sending keepalive probes. Not all operating systems support this option.
(Added in 7.25.0)
CURLOPT_UNIX_SOCKET_PATH
Pass a path to a UNIX domain socket. This enables the use of UNIX domain sockets as
connection end point and sets the path to path. If path is NULL, then UNIX domain
sockets are disabled. An empty string will result in an error at some point.
When enabled, cURL will connect to the UNIX domain socket instead of establishing a
TCP connection to a host. Since no TCP connection is established, cURL does not
need to resolve the DNS hostname in the URL.
The maximum path length on Cygwin, Linux and Solaris is 107. On other platforms
might be even less.
NAMES and PASSWORDS OPTIONS (Authentication)
CURLOPT_NETRC
This parameter controls the preference of libcurl between using user names and
passwords from your ~/.netrc file, relative to user names and passwords in the URL
supplied with CURLOPT_URL.
libcurl uses a user name (and supplied or prompted password) supplied with CUR-
LOPT_USERPWD in preference to any of the options controlled by this parameter.
Pass a long, set to one of the values described below.
CURL_NETRC_OPTIONAL
The use of your ~/.netrc file is optional, and information in the URL is to
be preferred. The file will be scanned for the host and user name (to find
the password only) or for the host only, to find the first user name and
password after that machine, which ever information is not specified in the
URL.
Undefined values of the option will have this effect.
CURL_NETRC_IGNORED
The library will ignore the file and use only the information in the URL.
This is the default.
CURL_NETRC_REQUIRED
This value tells the library that use of the file is required, to ignore the
information in the URL, and to search the file for the host only.
Only machine name, user name and password are taken into account (init macros and similar
things aren't supported).
libcurl does not verify that the file has the correct properties set (as the standard Unix
ftp client does). It should only be readable by user.
CURLOPT_NETRC_FILE
Pass a char * as parameter, pointing to a zero terminated string containing the
full path name to the file you want libcurl to use as .netrc file. If this option
is omitted, and CURLOPT_NETRC is set, libcurl will attempt to find a .netrc file in
the current user's home directory. (Added in 7.10.9)
CURLOPT_USERPWD
Pass a char * as parameter, which should be [user name]:[password] to use for the
connection. Use CURLOPT_HTTPAUTH to decide the authentication method.
When using NTLM, you can set the domain by prepending it to the user name and sepa-
rating the domain and name with a forward (/) or backward slash (\). Like this:
"domain/user:password" or "domain\user:password". Some HTTP servers (on Windows)
support this style even for Basic authentication.
When using HTTP and CURLOPT_FOLLOWLOCATION, libcurl might perform several requests
to possibly different hosts. libcurl will only send this user and password informa-
tion to hosts using the initial host name (unless CURLOPT_UNRESTRICTED_AUTH is
set), so if libcurl follows locations to other hosts it will not send the user and
password to those. This is enforced to prevent accidental information leakage.
CURLOPT_PROXYUSERPWD
Pass a char * as parameter, which should be [user name]:[password] to use for the
connection to the HTTP proxy. Use CURLOPT_PROXYAUTH to decide the authentication
method.
CURLOPT_USERNAME
Pass a char * as parameter, which should be pointing to the zero terminated user
name to use for the transfer.
CURLOPT_USERNAME sets the user name to be used in protocol authentication. You
should not use this option together with the (older) CURLOPT_USERPWD option.
In order to specify the password to be used in conjunction with the user name use
the CURLOPT_PASSWORD option. (Added in 7.19.1)
CURLOPT_PASSWORD
Pass a char * as parameter, which should be pointing to the zero terminated pass-
word to use for the transfer.
The CURLOPT_PASSWORD option should be used in conjunction with the CURLOPT_USERNAME
option. (Added in 7.19.1)
CURLOPT_PROXYUSERNAME
Pass a char * as parameter, which should be pointing to the zero terminated user
name to use for the transfer while connecting to Proxy.
The CURLOPT_PROXYUSERNAME option should be used in same way as the CURLOPT_PROX-
YUSERPWD is used. In comparison to CURLOPT_PROXYUSERPWD the CURLOPT_PROXYUSERNAME
allows the username to contain a colon, like in the following example:
"sip:user AT example.com". The CURLOPT_PROXYUSERNAME option is an alternative way to
set the user name while connecting to Proxy. There is no meaning to use it
together with the CURLOPT_PROXYUSERPWD option.
In order to specify the password to be used in conjunction with the user name use
the CURLOPT_PROXYPASSWORD option. (Added in 7.19.1)
CURLOPT_PROXYPASSWORD
Pass a char * as parameter, which should be pointing to the zero terminated pass-
word to use for the transfer while connecting to Proxy.
The CURLOPT_PROXYPASSWORD option should be used in conjunction with the CUR-
LOPT_PROXYUSERNAME option. (Added in 7.19.1)
CURLOPT_HTTPAUTH
Pass a long as parameter, which is set to a bitmask, to tell libcurl which authen-
tication method(s) you want it to use. The available bits are listed below. If more
than one bit is set, libcurl will first query the site to see which authentication
methods it supports and then pick the best one you allow it to use. For some meth-
ods, this will induce an extra network round-trip. Set the actual name and password
with the CURLOPT_USERPWD option or with the CURLOPT_USERNAME and the CURLOPT_PASS-
WORD options. (Added in 7.10.6)
CURLAUTH_BASIC
HTTP Basic authentication. This is the default choice, and the only method
that is in wide-spread use and supported virtually everywhere. This sends
the user name and password over the network in plain text, easily captured
by others.
CURLAUTH_DIGEST
HTTP Digest authentication. Digest authentication is defined in RFC2617 and
is a more secure way to do authentication over public networks than the reg-
ular old-fashioned Basic method.
CURLAUTH_DIGEST_IE
HTTP Digest authentication with an IE flavor. Digest authentication is
defined in RFC2617 and is a more secure way to do authentication over public
networks than the regular old-fashioned Basic method. The IE flavor is sim-
ply that libcurl will use a special "quirk" that IE is known to have used
before version 7 and that some servers require the client to use. (This
define was added in 7.19.3)
CURLAUTH_GSSNEGOTIATE
HTTP GSS-Negotiate authentication. The GSS-Negotiate (also known as plain
"Negotiate") method was designed by Microsoft and is used in their web
applications. It is primarily meant as a support for Kerberos5 authentica-
tion but may also be used along with other authentication methods. For more
information see IETF draft draft-brezak-spnego-http-04.txt.
You need to build libcurl with a suitable GSS-API library for this to work.
CURLAUTH_NTLM
HTTP NTLM authentication. A proprietary protocol invented and used by Micro-
soft. It uses a challenge-response and hash concept similar to Digest, to
prevent the password from being eavesdropped.
You need to build libcurl with either OpenSSL, GnuTLS or NSS support for
this option to work, or build libcurl on Windows.
CURLAUTH_NTLM_WB
NTLM delegating to winbind helper. Authentication is performed by a separate
binary application that is executed when needed. The name of the application
is specified at compile time but is typically /usr/bin/ntlm_auth (Added in
7.22.0)
Note that libcurl will fork when necessary to run the winbind application
and kill it when complete, calling waitpid() to await its exit when done. On
POSIX operating systems, killing the process will cause a SIGCHLD signal to
be raised (regardless of whether CURLOPT_NOSIGNAL is set), which must be
handled intelligently by the application. In particular, the application
must not unconditionally call wait() in its SIGCHLD signal handler to avoid
being subject to a race condition. This behavior is subject to change in
future versions of libcurl.
CURLAUTH_ANY
This is a convenience macro that sets all bits and thus makes libcurl pick
any it finds suitable. libcurl will automatically select the one it finds
most secure.
CURLAUTH_ANYSAFE
This is a convenience macro that sets all bits except Basic and thus makes
libcurl pick any it finds suitable. libcurl will automatically select the
one it finds most secure.
CURLAUTH_ONLY
This is a meta symbol. Or this value together with a single specific auth
value to force libcurl to probe for un-restricted auth and if not, only that
single auth algorithm is acceptable. (Added in 7.21.3)
CURLOPT_TLSAUTH_TYPE
Pass a long as parameter, which is set to a bitmask, to tell libcurl which authen-
tication method(s) you want it to use for TLS authentication.
CURLOPT_TLSAUTH_SRP
TLS-SRP authentication. Secure Remote Password authentication for TLS is
defined in RFC5054 and provides mutual authentication if both sides have a
shared secret. To use TLS-SRP, you must also set the CURLOPT_TLSAUTH_USER-
NAME and CURLOPT_TLSAUTH_PASSWORD options.
You need to build libcurl with GnuTLS or OpenSSL with TLS-SRP support for
this to work. (Added in 7.21.4)
CURLOPT_TLSAUTH_USERNAME
Pass a char * as parameter, which should point to the zero terminated username to
use for the TLS authentication method specified with the CURLOPT_TLSAUTH_TYPE
option. Requires that the CURLOPT_TLS_PASSWORD option also be set. (Added in
7.21.4)
CURLOPT_TLSAUTH_PASSWORD
Pass a char * as parameter, which should point to the zero terminated password to
use for the TLS authentication method specified with the CURLOPT_TLSAUTH_TYPE
option. Requires that the CURLOPT_TLS_USERNAME option also be set. (Added in
7.21.4)
CURLOPT_PROXYAUTH
Pass a long as parameter, which is set to a bitmask, to tell libcurl which authen-
tication method(s) you want it to use for your proxy authentication. If more than
one bit is set, libcurl will first query the site to see what authentication meth-
ods it supports and then pick the best one you allow it to use. For some methods,
this will induce an extra network round-trip. Set the actual name and password with
the CURLOPT_PROXYUSERPWD option. The bitmask can be constructed by or'ing together
the bits listed above for the CURLOPT_HTTPAUTH option. As of this writing, only
Basic, Digest and NTLM work. (Added in 7.10.7)
HTTP OPTIONS
CURLOPT_AUTOREFERER
Pass a parameter set to 1 to enable this. When enabled, libcurl will automatically
set the Referer: field in requests where it follows a Location: redirect.
CURLOPT_ACCEPT_ENCODING
Sets the contents of the Accept-Encoding: header sent in a HTTP request, and
enables decoding of a response when a Content-Encoding: header is received. Three
encodings are supported: identity, which does nothing, deflate which requests the
server to compress its response using the zlib algorithm, and gzip which requests
the gzip algorithm. If a zero-length string is set, then an Accept-Encoding:
header containing all supported encodings is sent.
This is a request, not an order; the server may or may not do it. This option must
be set (to any non-NULL value) or else any unsolicited encoding done by the server
is ignored. See the special file lib/README.encoding for details.
(This option was called CURLOPT_ENCODING before 7.21.6)
CURLOPT_TRANSFER_ENCODING
Adds a request for compressed Transfer Encoding in the outgoing HTTP request. If
the server supports this and so desires, it can respond with the HTTP response sent
using a compressed Transfer-Encoding that will be automatically uncompressed by
libcurl on reception.
Transfer-Encoding differs slightly from the Content-Encoding you ask for with CUR-
LOPT_ACCEPT_ENCODING in that a Transfer-Encoding is strictly meant to be for the
transfer and thus MUST be decoded before the data arrives in the client. Tradition-
ally, Transfer-Encoding has been much less used and supported by both HTTP clients
and HTTP servers.
(Added in 7.21.6)
CURLOPT_FOLLOWLOCATION
A parameter set to 1 tells the library to follow any Location: header that the
server sends as part of a HTTP header.
This means that the library will re-send the same request on the new location and
follow new Location: headers all the way until no more such headers are returned.
CURLOPT_MAXREDIRS can be used to limit the number of redirects libcurl will follow.
Since 7.19.4, libcurl can limit what protocols it will automatically follow. The
accepted protocols are set with CURLOPT_REDIR_PROTOCOLS and it excludes the FILE
protocol by default.
CURLOPT_UNRESTRICTED_AUTH
A parameter set to 1 tells the library it can continue to send authentication
(user+password) when following locations, even when hostname changed. This option
is meaningful only when setting CURLOPT_FOLLOWLOCATION.
CURLOPT_MAXREDIRS
Pass a long. The set number will be the redirection limit. If that many redirec-
tions have been followed, the next redirect will cause an error
(CURLE_TOO_MANY_REDIRECTS). This option only makes sense if the CURLOPT_FOLLOWLOCA-
TION is used at the same time. Added in 7.15.1: Setting the limit to 0 will make
libcurl refuse any redirect. Set it to -1 for an infinite number of redirects
(which is the default)
CURLOPT_POSTREDIR
Pass a bitmask to control how libcurl acts on redirects after POSTs that get a 301,
302 or 303 response back. A parameter with bit 0 set (value CURL_REDIR_POST_301)
tells the library to respect RFC2616/10.3.2 and not convert POST requests into GET
requests when following a 301 redirection. Setting bit 1 (value
CURL_REDIR_POST_302) makes libcurl maintain the request method after a 302 redirect
whilst setting bit 2 (value CURL_REDIR_POST_303) makes libcurl maintain the request
method after a 303 redirect. The value CURL_REDIR_POST_ALL is a convenience define
that sets all three bits.
The non-RFC behaviour is ubiquitous in web browsers, so the library does the con-
version by default to maintain consistency. However, a server may require a POST to
remain a POST after such a redirection. This option is meaningful only when setting
CURLOPT_FOLLOWLOCATION. (Added in 7.17.1) (This option was known as CUR-
LOPT_POST301 up to 7.19.0 as it only supported the 301 then)
CURLOPT_PUT
A parameter set to 1 tells the library to use HTTP PUT to transfer data. The data
should be set with CURLOPT_READDATA and CURLOPT_INFILESIZE.
This option is deprecated and starting with version 7.12.1 you should instead use
CURLOPT_UPLOAD.
CURLOPT_POST
A parameter set to 1 tells the library to do a regular HTTP post. This will also
make the library use a "Content-Type: application/x-www-form-urlencoded" header.
(This is by far the most commonly used POST method).
Use one of CURLOPT_POSTFIELDS or CURLOPT_COPYPOSTFIELDS options to specify what
data to post and CURLOPT_POSTFIELDSIZE or CURLOPT_POSTFIELDSIZE_LARGE to set the
data size.
Optionally, you can provide data to POST using the CURLOPT_READFUNCTION and CUR-
LOPT_READDATA options but then you must make sure to not set CURLOPT_POSTFIELDS to
anything but NULL. When providing data with a callback, you must transmit it using
chunked transfer-encoding or you must set the size of the data with the CUR-
LOPT_POSTFIELDSIZE or CURLOPT_POSTFIELDSIZE_LARGE option. To enable chunked encod-
ing, you simply pass in the appropriate Transfer-Encoding header, see the post-
callback.c example.
You can override the default POST Content-Type: header by setting your own with
CURLOPT_HTTPHEADER.
Using POST with HTTP 1.1 implies the use of a "Expect: 100-continue" header. You
can disable this header with CURLOPT_HTTPHEADER as usual.
If you use POST to a HTTP 1.1 server, you can send data without knowing the size
before starting the POST if you use chunked encoding. You enable this by adding a
header like "Transfer-Encoding: chunked" with CURLOPT_HTTPHEADER. With HTTP 1.0 or
without chunked transfer, you must specify the size in the request.
When setting CURLOPT_POST to 1, it will automatically set CURLOPT_NOBODY to 0
(since 7.14.1).
If you issue a POST request and then want to make a HEAD or GET using the same re-
used handle, you must explicitly set the new request type using CURLOPT_NOBODY or
CURLOPT_HTTPGET or similar.
CURLOPT_POSTFIELDS
Pass a void * as parameter, which should be the full data to post in a HTTP POST
operation. You must make sure that the data is formatted the way you want the
server to receive it. libcurl will not convert or encode it for you. Most web
servers will assume this data to be url-encoded.
The pointed data are NOT copied by the library: as a consequence, they must be pre-
served by the calling application until the transfer finishes.
This POST is a normal application/x-www-form-urlencoded kind (and libcurl will set
that Content-Type by default when this option is used), which is the most commonly
used one by HTML forms. See also the CURLOPT_POST. Using CURLOPT_POSTFIELDS implies
CURLOPT_POST.
If you want to do a zero-byte POST, you need to set CURLOPT_POSTFIELDSIZE explic-
itly to zero, as simply setting CURLOPT_POSTFIELDS to NULL or "" just effectively
disables the sending of the specified string. libcurl will instead assume that
you'll send the POST data using the read callback!
Using POST with HTTP 1.1 implies the use of a "Expect: 100-continue" header. You
can disable this header with CURLOPT_HTTPHEADER as usual.
To make multipart/formdata posts (aka RFC2388-posts), check out the CURLOPT_HTTP-
POST option.
CURLOPT_POSTFIELDSIZE
If you want to post data to the server without letting libcurl do a strlen() to
measure the data size, this option must be used. When this option is used you can
post fully binary data, which otherwise is likely to fail. If this size is set to
-1, the library will use strlen() to get the size.
CURLOPT_POSTFIELDSIZE_LARGE
Pass a curl_off_t as parameter. Use this to set the size of the CURLOPT_POSTFIELDS
data to prevent libcurl from doing strlen() on the data to figure out the size.
This is the large file version of the CURLOPT_POSTFIELDSIZE option. (Added in
7.11.1)
CURLOPT_COPYPOSTFIELDS
Pass a char * as parameter, which should be the full data to post in a HTTP POST
operation. It behaves as the CURLOPT_POSTFIELDS option, but the original data are
copied by the library, allowing the application to overwrite the original data
after setting this option.
Because data are copied, care must be taken when using this option in conjunction
with CURLOPT_POSTFIELDSIZE or CURLOPT_POSTFIELDSIZE_LARGE: If the size has not been
set prior to CURLOPT_COPYPOSTFIELDS, the data are assumed to be a NUL-terminated
string; else the stored size informs the library about the data byte count to copy.
In any case, the size must not be changed after CURLOPT_COPYPOSTFIELDS, unless
another CURLOPT_POSTFIELDS or CURLOPT_COPYPOSTFIELDS option is issued. (Added in
7.17.1)
CURLOPT_HTTPPOST
Tells libcurl you want a multipart/formdata HTTP POST to be made and you instruct
what data to pass on to the server. Pass a pointer to a linked list of curl_http-
post structs as parameter. The easiest way to create such a list, is to use
curl_formadd(3) as documented. The data in this list must remain intact until you
close this curl handle again with curl_easy_cleanup(3).
Using POST with HTTP 1.1 implies the use of a "Expect: 100-continue" header. You
can disable this header with CURLOPT_HTTPHEADER as usual.
When setting CURLOPT_HTTPPOST, it will automatically set CURLOPT_NOBODY to 0 (since
7.14.1).
CURLOPT_REFERER
Pass a pointer to a zero terminated string as parameter. It will be used to set the
Referer: header in the http request sent to the remote server. This can be used to
fool servers or scripts. You can also set any custom header with CURLOPT_HTTP-
HEADER.
CURLOPT_USERAGENT
Pass a pointer to a zero terminated string as parameter. It will be used to set the
User-Agent: header in the http request sent to the remote server. This can be used
to fool servers or scripts. You can also set any custom header with CURLOPT_HTTP-
HEADER.
CURLOPT_HTTPHEADER
Pass a pointer to a linked list of HTTP headers to pass to the server in your HTTP
request. The linked list should be a fully valid list of struct curl_slist structs
properly filled in. Use curl_slist_append(3) to create the list and
curl_slist_free_all(3) to clean up an entire list. If you add a header that is oth-
erwise generated and used by libcurl internally, your added one will be used
instead. If you add a header with no content as in 'Accept:' (no data on the right
side of the colon), the internally used header will get disabled. Thus, using this
option you can add new headers, replace internal headers and remove internal head-
ers. To add a header with no content, make the content be two quotes: "". The head-
ers included in the linked list must not be CRLF-terminated, because curl adds CRLF
after each header item. Failure to comply with this will result in strange bugs
because the server will most likely ignore part of the headers you specified.
The first line in a request (containing the method, usually a GET or POST) is not a
header and cannot be replaced using this option. Only the lines following the
request-line are headers. Adding this method line in this list of headers will only
cause your request to send an invalid header.
Pass a NULL to this to reset back to no custom headers.
The most commonly replaced headers have "shortcuts" in the options CURLOPT_COOKIE,
CURLOPT_USERAGENT and CURLOPT_REFERER.
CURLOPT_HTTP200ALIASES
Pass a pointer to a linked list of aliases to be treated as valid HTTP 200
responses. Some servers respond with a custom header response line. For example,
IceCast servers respond with "ICY 200 OK". By including this string in your list
of aliases, the response will be treated as a valid HTTP header line such as
"HTTP/1.0 200 OK". (Added in 7.10.3)
The linked list should be a fully valid list of struct curl_slist structs, and be
properly filled in. Use curl_slist_append(3) to create the list and
curl_slist_free_all(3) to clean up an entire list.
The alias itself is not parsed for any version strings. Before libcurl 7.16.3,
Libcurl used the value set by option CURLOPT_HTTP_VERSION, but starting with 7.16.3
the protocol is assumed to match HTTP 1.0 when an alias matched.
CURLOPT_COOKIE
Pass a pointer to a zero terminated string as parameter. It will be used to set a
cookie in the http request. The format of the string should be NAME=CONTENTS, where
NAME is the cookie name and CONTENTS is what the cookie should contain.
If you need to set multiple cookies, you need to set them all using a single option
and thus you need to concatenate them all in one single string. Set multiple cook-
ies in one string like this: "name1=content1; name2=content2;" etc.
This option sets the cookie header explicitly in the outgoing request(s). If multi-
ple requests are done due to authentication, followed redirections or similar, they
will all get this cookie passed on.
Using this option multiple times will only make the latest string override the pre-
vious ones.
CURLOPT_COOKIEFILE
Pass a pointer to a zero terminated string as parameter. It should contain the name
of your file holding cookie data to read. The cookie data may be in Netscape /
Mozilla cookie data format or just regular HTTP-style headers dumped to a file.
Given an empty or non-existing file or by passing the empty string (""), this
option will enable cookies for this curl handle, making it understand and parse
received cookies and then use matching cookies in future requests.
If you use this option multiple times, you just add more files to read. Subsequent
files will add more cookies.
CURLOPT_COOKIEJAR
Pass a file name as char *, zero terminated. This will make libcurl write all
internally known cookies to the specified file when curl_easy_cleanup(3) is called.
If no cookies are known, no file will be created. Specify "-" to instead have the
cookies written to stdout. Using this option also enables cookies for this session,
so if you for example follow a location it will make matching cookies get sent
accordingly.
If the cookie jar file can't be created or written to (when the
curl_easy_cleanup(3) is called), libcurl will not and cannot report an error for
this. Using CURLOPT_VERBOSE or CURLOPT_DEBUGFUNCTION will get a warning to display,
but that is the only visible feedback you get about this possibly lethal situation.
CURLOPT_COOKIESESSION
Pass a long set to 1 to mark this as a new cookie "session". It will force libcurl
to ignore all cookies it is about to load that are "session cookies" from the pre-
vious session. By default, libcurl always stores and loads all cookies, independent
if they are session cookies or not. Session cookies are cookies without expiry date
and they are meant to be alive and existing for this "session" only.
CURLOPT_COOKIELIST
Pass a char * to a cookie string. Cookie can be either in Netscape / Mozilla format
or just regular HTTP-style header (Set-Cookie: ...) format. If cURL cookie engine
was not enabled it will enable its cookie engine. Passing a magic string "ALL"
will erase all cookies known by cURL. (Added in 7.14.1) Passing the special string
"SESS" will only erase all session cookies known by cURL. (Added in 7.15.4) Passing
the special string "FLUSH" will write all cookies known by cURL to the file speci-
fied by CURLOPT_COOKIEJAR. (Added in 7.17.1)
CURLOPT_HTTPGET
Pass a long. If the long is 1, this forces the HTTP request to get back to GET.
Usable if a POST, HEAD, PUT, or a custom request has been used previously using the
same curl handle.
When setting CURLOPT_HTTPGET to 1, it will automatically set CURLOPT_NOBODY to 0
(since 7.14.1).
CURLOPT_HTTP_VERSION
Pass a long, set to one of the values described below. They force libcurl to use
the specific HTTP versions. This is not sensible to do unless you have a good rea-
son.
CURL_HTTP_VERSION_NONE
We don't care about what version the library uses. libcurl will use whatever
it thinks fit.
CURL_HTTP_VERSION_1_0
Enforce HTTP 1.0 requests.
CURL_HTTP_VERSION_1_1
Enforce HTTP 1.1 requests.
CURLOPT_IGNORE_CONTENT_LENGTH
Ignore the Content-Length header. This is useful for Apache 1.x (and similar
servers) which will report incorrect content length for files over 2 gigabytes. If
this option is used, curl will not be able to accurately report progress, and will
simply stop the download when the server ends the connection. (added in 7.14.1)
CURLOPT_HTTP_CONTENT_DECODING
Pass a long to tell libcurl how to act on content decoding. If set to zero, content
decoding will be disabled. If set to 1 it is enabled. Libcurl has no default con-
tent decoding but requires you to use CURLOPT_ENCODING for that. (added in 7.16.2)
CURLOPT_HTTP_TRANSFER_DECODING
Pass a long to tell libcurl how to act on transfer decoding. If set to zero, trans-
fer decoding will be disabled, if set to 1 it is enabled (default). libcurl does
chunked transfer decoding by default unless this option is set to zero. (added in
7.16.2)
SMTP OPTIONS
CURLOPT_MAIL_FROM
Pass a pointer to a zero terminated string as parameter. This should be used to
specify the sender's email address when sending SMTP mail with libcurl.
An originator email address should be specified with angled brackets (<>) around
it, which if not specified, will be added by libcurl from version 7.21.4 onwards.
Failing to provide such brackets may cause the server to reject the email.
If this parameter is not specified then an empty address will be sent to the mail
server which may or may not cause the email to be rejected.
(Added in 7.20.0)
CURLOPT_MAIL_RCPT
Pass a pointer to a linked list of recipients to pass to the server in your SMTP
mail request. The linked list should be a fully valid list of struct curl_slist
structs properly filled in. Use curl_slist_append(3) to create the list and
curl_slist_free_all(3) to clean up an entire list.
Each recipient should be specified within a pair of angled brackets (<>), however,
should you not use an angled bracket as the first character libcurl will assume you
provided a single email address and enclose that address within brackets for you.
(Added in 7.20.0)
CURLOPT_MAIL_AUTH
Pass a pointer to a zero terminated string as parameter. This will be used to spec-
ify the authentication address (identity) of a submitted message that is being
relayed to another server.
This optional parameter allows co-operating agents in a trusted environment to com-
municate the authentication of individual messages and should only be used by the
application program, using libcurl, if the application is itself a mail server act-
ing in such an environment. If the application is operating as such and the AUTH
address is not known or is invalid, then an empty string should be used for this
parameter.
Unlike CURLOPT_MAIL_FROM and CURLOPT_MAIL_RCPT, the address should not be specified
within a pair of angled brackets (<>). However, if an empty string is used then a
pair of brackets will be sent by libcurl as required by RFC2554.
(Added in 7.25.0)
TFTP OPTIONS
CURLOPT_TFTP_BLKSIZE
Specify block size to use for TFTP data transmission. Valid range as per RFC2348 is
8-65464 bytes. The default of 512 bytes will be used if this option is not speci-
fied. The specified block size will only be used pending support by the remote
server. If the server does not return an option acknowledgement or returns an
option acknowledgement with no blksize, the default of 512 bytes will be used.
(added in 7.19.4)
FTP OPTIONS
CURLOPT_FTPPORT
Pass a pointer to a zero terminated string as parameter. It will be used to get the
IP address to use for the FTP PORT instruction. The PORT instruction tells the
remote server to connect to our specified IP address. The string may be a plain IP
address, a host name, a network interface name (under Unix) or just a '-' symbol to
let the library use your system's default IP address. Default FTP operations are
passive, and thus won't use PORT.
The address can be followed by a ':' to specify a port, optionally followed by a
'-' to specify a port range. If the port specified is 0, the operating system will
pick a free port. If a range is provided and all ports in the range are not avail-
able, libcurl will report CURLE_FTP_PORT_FAILED for the handle. Invalid port/range
settings are ignored. IPv6 addresses followed by a port or portrange have to be in
brackets. IPv6 addresses without port/range specifier can be in brackets. (added
in 7.19.5)
Examples with specified ports:
eth0:0
192.168.1.2:32000-33000
curl.se:32123
[::1]:1234-4567
You disable PORT again and go back to using the passive version by setting this
option to NULL.
CURLOPT_QUOTE
Pass a pointer to a linked list of FTP or SFTP commands to pass to the server prior
to your FTP request. This will be done before any other commands are issued (even
before the CWD command for FTP). The linked list should be a fully valid list of
'struct curl_slist' structs properly filled in with text strings. Use
curl_slist_append(3) to append strings (commands) to the list, and clear the entire
list afterwards with curl_slist_free_all(3). Disable this operation again by set-
ting a NULL to this option. When speaking to a FTP (or SFTP since 7.24.0) server,
prefix the command with an asterisk (*) to make libcurl continue even if the com-
mand fails as by default libcurl will stop at first failure.
The set of valid FTP commands depends on the server (see RFC959 for a list of
mandatory commands).
The valid SFTP commands are: chgrp, chmod, chown, ln, mkdir, pwd, rename, rm,
rmdir, symlink (see curl(1)) (SFTP support added in 7.16.3)
CURLOPT_POSTQUOTE
Pass a pointer to a linked list of FTP or SFTP commands to pass to the server after
your FTP transfer request. The commands will only be run if no error occurred. The
linked list should be a fully valid list of struct curl_slist structs properly
filled in as described for CURLOPT_QUOTE. Disable this operation again by setting a
NULL to this option.
CURLOPT_PREQUOTE
Pass a pointer to a linked list of FTP commands to pass to the server after the
transfer type is set. The linked list should be a fully valid list of struct
curl_slist structs properly filled in as described for CURLOPT_QUOTE. Disable this
operation again by setting a NULL to this option. Before version 7.16.0, if you
also set CURLOPT_NOBODY to 1, this option didn't work.
CURLOPT_DIRLISTONLY
A parameter set to 1 tells the library to just list the names of files in a direc-
tory, instead of doing a full directory listing that would include file sizes,
dates etc. This works for FTP and SFTP URLs.
This causes an FTP NLST command to be sent on an FTP server. Beware that some FTP
servers list only files in their response to NLST; they might not include subdirec-
tories and symbolic links.
Setting this option to 1 also implies a directory listing even if the URL doesn't
end with a slash, which otherwise is necessary.
Do NOT use this option if you also use CURLOPT_WILDCARDMATCH as it will effectively
break that feature then.
(This option was known as CURLOPT_FTPLISTONLY up to 7.16.4)
CURLOPT_APPEND
A parameter set to 1 tells the library to append to the remote file instead of
overwrite it. This is only useful when uploading to an FTP site.
(This option was known as CURLOPT_FTPAPPEND up to 7.16.4)
CURLOPT_FTP_USE_EPRT
Pass a long. If the value is 1, it tells curl to use the EPRT (and LPRT) command
when doing active FTP downloads (which is enabled by CURLOPT_FTPPORT). Using EPRT
means that it will first attempt to use EPRT and then LPRT before using PORT, but
if you pass zero to this option, it will not try using EPRT or LPRT, only plain
PORT. (Added in 7.10.5)
If the server is an IPv6 host, this option will have no effect as of 7.12.3.
CURLOPT_FTP_USE_EPSV
Pass a long. If the value is 1, it tells curl to use the EPSV command when doing
passive FTP downloads (which it always does by default). Using EPSV means that it
will first attempt to use EPSV before using PASV, but if you pass zero to this
option, it will not try using EPSV, only plain PASV.
If the server is an IPv6 host, this option will have no effect as of 7.12.3.
CURLOPT_FTP_USE_PRET
Pass a long. If the value is 1, it tells curl to send a PRET command before PASV
(and EPSV). Certain FTP servers, mainly drftpd, require this non-standard command
for directory listings as well as up and downloads in PASV mode. Has no effect when
using the active FTP transfers mode. (Added in 7.20.0)
CURLOPT_FTP_CREATE_MISSING_DIRS
Pass a long. If the value is 1, curl will attempt to create any remote directory
that it fails to CWD into. CWD is the command that changes working directory.
(Added in 7.10.7)
This setting also applies to SFTP-connections. curl will attempt to create the
remote directory if it can't obtain a handle to the target-location. The creation
will fail if a file of the same name as the directory to create already exists or
lack of permissions prevents creation. (Added in 7.16.3)
Starting with 7.19.4, you can also set this value to 2, which will make libcurl
retry the CWD command again if the subsequent MKD command fails. This is especially
useful if you're doing many simultaneous connections against the same server and
they all have this option enabled, as then CWD may first fail but then another con-
nection does MKD before this connection and thus MKD fails but trying CWD works!
7.19.4 also introduced the CURLFTP_CREATE_DIR and CURLFTP_CREATE_DIR_RETRY enum
names for these arguments.
Before version 7.19.4, libcurl will simply ignore arguments set to 2 and act as if
1 was selected.
CURLOPT_FTP_RESPONSE_TIMEOUT
Pass a long. Causes curl to set a timeout period (in seconds) on the amount of
time that the server is allowed to take in order to generate a response message for
a command before the session is considered hung. While curl is waiting for a
response, this value overrides CURLOPT_TIMEOUT. It is recommended that if used in
conjunction with CURLOPT_TIMEOUT, you set CURLOPT_FTP_RESPONSE_TIMEOUT to a value
smaller than CURLOPT_TIMEOUT. (Added in 7.10.8)
CURLOPT_FTP_ALTERNATIVE_TO_USER
Pass a char * as parameter, pointing to a string which will be used to authenticate
if the usual FTP "USER user" and "PASS password" negotiation fails. This is cur-
rently only known to be required when connecting to Tumbleweed's Secure Transport
FTPS server using client certificates for authentication. (Added in 7.15.5)
CURLOPT_FTP_SKIP_PASV_IP
Pass a long. If set to 1, it instructs libcurl to not use the IP address the server
suggests in its 227-response to libcurl's PASV command when libcurl connects the
data connection. Instead libcurl will re-use the same IP address it already uses
for the control connection. But it will use the port number from the 227-response.
(Added in 7.14.2)
This option has no effect if PORT, EPRT or EPSV is used instead of PASV.
CURLOPT_FTPSSLAUTH
Pass a long using one of the values from below, to alter how libcurl issues "AUTH
TLS" or "AUTH SSL" when FTP over SSL is activated (see CURLOPT_USE_SSL). (Added in
7.12.2)
CURLFTPAUTH_DEFAULT
Allow libcurl to decide.
CURLFTPAUTH_SSL
Try "AUTH SSL" first, and only if that fails try "AUTH TLS".
CURLFTPAUTH_TLS
Try "AUTH TLS" first, and only if that fails try "AUTH SSL".
CURLOPT_FTP_SSL_CCC
If enabled, this option makes libcurl use CCC (Clear Command Channel). It shuts
down the SSL/TLS layer after authenticating. The rest of the control channel commu-
nication will be unencrypted. This allows NAT routers to follow the FTP transac-
tion. Pass a long using one of the values below. (Added in 7.16.1)
CURLFTPSSL_CCC_NONE
Don't attempt to use CCC.
CURLFTPSSL_CCC_PASSIVE
Do not initiate the shutdown, but wait for the server to do it. Do not send
a reply.
CURLFTPSSL_CCC_ACTIVE
Initiate the shutdown and wait for a reply.
CURLOPT_FTP_ACCOUNT
Pass a pointer to a zero terminated string (or NULL to disable). When an FTP server
asks for "account data" after user name and password has been provided, this data
is sent off using the ACCT command. (Added in 7.13.0)
CURLOPT_FTP_FILEMETHOD
Pass a long that should have one of the following values. This option controls what
method libcurl should use to reach a file on a FTP(S) server. The argument should
be one of the following alternatives:
CURLFTPMETHOD_MULTICWD
libcurl does a single CWD operation for each path part in the given URL. For
deep hierarchies this means many commands. This is how RFC1738 says it
should be done. This is the default but the slowest behavior.
CURLFTPMETHOD_NOCWD
libcurl does no CWD at all. libcurl will do SIZE, RETR, STOR etc and give a
full path to the server for all these commands. This is the fastest behav-
ior.
CURLFTPMETHOD_SINGLECWD
libcurl does one CWD with the full target directory and then operates on the
file "normally" (like in the multicwd case). This is somewhat more standards
compliant than 'nocwd' but without the full penalty of 'multicwd'.
(Added in 7.15.1)
RTSP OPTIONS
CURLOPT_RTSP_REQUEST
Tell libcurl what kind of RTSP request to make. Pass one of the following RTSP enum
values. Unless noted otherwise, commands require the Session ID to be initialized.
(Added in 7.20.0)
CURL_RTSPREQ_OPTIONS
Used to retrieve the available methods of the server. The application is
responsible for parsing and obeying the response. (The session ID is not
needed for this method.) (Added in 7.20.0)
CURL_RTSPREQ_DESCRIBE
Used to get the low level description of a stream. The application should
note what formats it understands in the 'Accept:' header. Unless set manu-
ally, libcurl will automatically fill in 'Accept: application/sdp'. Time-
condition headers will be added to Describe requests if the CURLOPT_TIMECON-
DITION option is active. (The session ID is not needed for this method)
(Added in 7.20.0)
CURL_RTSPREQ_ANNOUNCE
When sent by a client, this method changes the description of the session.
For example, if a client is using the server to record a meeting, the client
can use Announce to inform the server of all the meta-information about the
session. ANNOUNCE acts like a HTTP PUT or POST just like
CURL_RTSPREQ_SET_PARAMETER (Added in 7.20.0)
CURL_RTSPREQ_SETUP
Setup is used to initialize the transport layer for the session. The appli-
cation must set the desired Transport options for a session by using the
CURLOPT_RTSP_TRANSPORT option prior to calling setup. If no session ID is
currently set with CURLOPT_RTSP_SESSION_ID, libcurl will extract and use the
session ID in the response to this request. (The session ID is not needed
for this method). (Added in 7.20.0)
CURL_RTSPREQ_PLAY
Send a Play command to the server. Use the CURLOPT_RANGE option to modify
the playback time (e.g. 'npt=10-15'). (Added in 7.20.0)
CURL_RTSPREQ_PAUSE
Send a Pause command to the server. Use the CURLOPT_RANGE option with a sin-
gle value to indicate when the stream should be halted. (e.g. npt='25')
(Added in 7.20.0)
CURL_RTSPREQ_TEARDOWN
This command terminates an RTSP session. Simply closing a connection does
not terminate the RTSP session since it is valid to control an RTSP session
over different connections. (Added in 7.20.0)
CURL_RTSPREQ_GET_PARAMETER
Retrieve a parameter from the server. By default, libcurl will automatically
include a Content-Type: text/parameters header on all non-empty requests
unless a custom one is set. GET_PARAMETER acts just like a HTTP PUT or POST
(see CURL_RTSPREQ_SET_PARAMETER). Applications wishing to send a heartbeat
message (e.g. in the presence of a server-specified timeout) should send use
an empty GET_PARAMETER request. (Added in 7.20.0)
CURL_RTSPREQ_SET_PARAMETER
Set a parameter on the server. By default, libcurl will automatically
include a Content-Type: text/parameters header unless a custom one is set.
The interaction with SET_PARAMTER is much like a HTTP PUT or POST. An appli-
cation may either use CURLOPT_UPLOAD with CURLOPT_READDATA like a HTTP PUT,
or it may use CURLOPT_POSTFIELDS like a HTTP POST. No chunked transfers are
allowed, so the application must set the CURLOPT_INFILESIZE in the former
and CURLOPT_POSTFIELDSIZE in the latter. Also, there is no use of multi-part
POSTs within RTSP. (Added in 7.20.0)
CURL_RTSPREQ_RECORD
Used to tell the server to record a session. Use the CURLOPT_RANGE option to
modify the record time. (Added in 7.20.0)
CURL_RTSPREQ_RECEIVE
This is a special request because it does not send any data to the server.
The application may call this function in order to receive interleaved RTP
data. It will return after processing one read buffer of data in order to
give the application a chance to run. (Added in 7.20.0)
CURLOPT_RTSP_SESSION_ID
Pass a char * as a parameter to set the value of the current RTSP Session ID for
the handle. Useful for resuming an in-progress session. Once this value is set to
any non-NULL value, libcurl will return CURLE_RTSP_SESSION_ERROR if ID received
from the server does not match. If unset (or set to NULL), libcurl will automati-
cally set the ID the first time the server sets it in a response. (Added in 7.20.0)
CURLOPT_RTSP_STREAM_URI
Set the stream URI to operate on by passing a char * . For example, a single ses-
sion may be controlling rtsp://foo/twister/audio and rtsp://foo/twister/video and
the application can switch to the appropriate stream using this option. If unset,
libcurl will default to operating on generic server options by passing '*' in the
place of the RTSP Stream URI. This option is distinct from CURLOPT_URL. When work-
ing with RTSP, the CURLOPT_STREAM_URI indicates what URL to send to the server in
the request header while the CURLOPT_URL indicates where to make the connection to.
(e.g. the CURLOPT_URL for the above examples might be set to rtsp://foo/twister
(Added in 7.20.0)
CURLOPT_RTSP_TRANSPORT
Pass a char * to tell libcurl what to pass for the Transport: header for this RTSP
session. This is mainly a convenience method to avoid needing to set a custom
Transport: header for every SETUP request. The application must set a Transport:
header before issuing a SETUP request. (Added in 7.20.0)
CURLOPT_RTSP_HEADER
This option is simply an alias for CURLOPT_HTTP_HEADER. Use this to replace the
standard headers that RTSP and HTTP share. It is also valid to use the shortcuts
such as CURLOPT_USERAGENT. (Added in 7.20.0)
CURLOPT_RTSP_CLIENT_CSEQ
Manually set the the CSEQ number to issue for the next RTSP request. Useful if the
application is resuming a previously broken connection. The CSEQ will increment
from this new number henceforth. (Added in 7.20.0)
CURLOPT_RTSP_SERVER_CSEQ
Manually set the CSEQ number to expect for the next RTSP Server->Client request.
At the moment, this feature (listening for Server requests) is unimplemented.
(Added in 7.20.0)
PROTOCOL OPTIONS
CURLOPT_TRANSFERTEXT
A parameter set to 1 tells the library to use ASCII mode for FTP transfers, instead
of the default binary transfer. For win32 systems it does not set the stdout to
binary mode. This option can be usable when transferring text data between systems
with different views on certain characters, such as newlines or similar.
libcurl does not do a complete ASCII conversion when doing ASCII transfers over
FTP. This is a known limitation/flaw that nobody has rectified. libcurl simply sets
the mode to ASCII and performs a standard transfer.
CURLOPT_PROXY_TRANSFER_MODE
Pass a long. If the value is set to 1 (one), it tells libcurl to set the transfer
mode (binary or ASCII) for FTP transfers done via a HTTP proxy, by appending
;type=a or ;type=i to the URL. Without this setting, or it being set to 0 (zero,
the default), CURLOPT_TRANSFERTEXT has no effect when doing FTP via a proxy. Beware
that not all proxies support this feature. (Added in 7.18.0)
CURLOPT_CRLF
Pass a long. If the value is set to 1 (one), libcurl converts Unix newlines to CRLF
newlines on transfers. Disable this option again by setting the value to 0 (zero).
CURLOPT_RANGE
Pass a char * as parameter, which should contain the specified range you want. It
should be in the format "X-Y", where X or Y may be left out. HTTP transfers also
support several intervals, separated with commas as in "X-Y,N-M". Using this kind
of multiple intervals will cause the HTTP server to send the response document in
pieces (using standard MIME separation techniques). For RTSP, the formatting of a
range should follow RFC2326 Section 12.29. For RTSP, byte ranges are not permitted.
Instead, ranges should be given in npt, utc, or smpte formats.
Pass a NULL to this option to disable the use of ranges.
Ranges work on HTTP, FTP, FILE (since 7.18.0), and RTSP (since 7.20.0) transfers
only.
CURLOPT_RESUME_FROM
Pass a long as parameter. It contains the offset in number of bytes that you want
the transfer to start from. Set this option to 0 to make the transfer start from
the beginning (effectively disabling resume). For FTP, set this option to -1 to
make the transfer start from the end of the target file (useful to continue an
interrupted upload).
When doing uploads with FTP, the resume position is where in the local/source file
libcurl should try to resume the upload from and it will then append the source
file to the remote target file.
CURLOPT_RESUME_FROM_LARGE
Pass a curl_off_t as parameter. It contains the offset in number of bytes that you
want the transfer to start from. (Added in 7.11.0)
CURLOPT_CUSTOMREQUEST
Pass a pointer to a zero terminated string as parameter. It can be used to specify
the request instead of GET or HEAD when performing HTTP based requests, instead of
LIST and NLST when performing FTP directory listings and instead of LIST and RETR
when issuing POP3 based commands. This is particularly useful, for example, for
performing a HTTP DELETE request or a POP3 DELE command.
Please don't perform this at will, on HTTP based requests, by making sure your
server supports the command you are sending first.
When you change the request method by setting CURLOPT_CUSTOMREQUEST to something,
you don't actually change how libcurl behaves or acts in regards to the particular
request method, it will only change the actual string sent in the request.
For example:
With the HTTP protocol when you tell libcurl to do a HEAD request, but then specify
a GET though a custom request libcurl will still act as if it sent a HEAD. To
switch to a proper HEAD use CURLOPT_NOBODY, to switch to a proper POST use CUR-
LOPT_POST or CURLOPT_POSTFIELDS and to switch to a proper GET use CURLOPT_HTTPGET.
With the POP3 protocol when you tell libcurl to use a custom request it will behave
like a LIST or RETR command was sent where it expects data to be returned by the
server. As such CURLOPT_NOBODY should be used when specifying commands such as DELE
and NOOP for example.
Restore to the internal default by setting this to NULL.
Many people have wrongly used this option to replace the entire request with their
own, including multiple headers and POST contents. While that might work in many
cases, it will cause libcurl to send invalid requests and it could possibly confuse
the remote server badly. Use CURLOPT_POST and CURLOPT_POSTFIELDS to set POST data.
Use CURLOPT_HTTPHEADER to replace or extend the set of headers sent by libcurl. Use
CURLOPT_HTTP_VERSION to change HTTP version.
(Support for POP3 added in 7.26.0)
CURLOPT_FILETIME
Pass a long. If it is 1, libcurl will attempt to get the modification date of the
remote document in this operation. This requires that the remote server sends the
time or replies to a time querying command. The curl_easy_getinfo(3) function with
the CURLINFO_FILETIME argument can be used after a transfer to extract the received
time (if any).
CURLOPT_NOBODY
A parameter set to 1 tells the library to not include the body-part in the output.
This is only relevant for protocols that have separate header and body parts. On
HTTP(S) servers, this will make libcurl do a HEAD request.
To change request to GET, you should use CURLOPT_HTTPGET. Change request to POST
with CURLOPT_POST etc.
CURLOPT_INFILESIZE
When uploading a file to a remote site, this option should be used to tell libcurl
what the expected size of the infile is. This value should be passed as a long. See
also CURLOPT_INFILESIZE_LARGE.
For uploading using SCP, this option or CURLOPT_INFILESIZE_LARGE is mandatory.
When sending emails using SMTP, this command can be used to specify the optional
SIZE parameter for the MAIL FROM command. (Added in 7.23.0)
This option does not limit how much data libcurl will actually send, as that is
controlled entirely by what the read callback returns.
CURLOPT_INFILESIZE_LARGE
When uploading a file to a remote site, this option should be used to tell libcurl
what the expected size of the infile is. This value should be passed as a
curl_off_t. (Added in 7.11.0)
For uploading using SCP, this option or CURLOPT_INFILESIZE is mandatory.
This option does not limit how much data libcurl will actually send, as that is
controlled entirely by what the read callback returns.
CURLOPT_UPLOAD
A parameter set to 1 tells the library to prepare for an upload. The CURLOPT_READ-
DATA and CURLOPT_INFILESIZE or CURLOPT_INFILESIZE_LARGE options are also interest-
ing for uploads. If the protocol is HTTP, uploading means using the PUT request
unless you tell libcurl otherwise.
Using PUT with HTTP 1.1 implies the use of a "Expect: 100-continue" header. You
can disable this header with CURLOPT_HTTPHEADER as usual.
If you use PUT to a HTTP 1.1 server, you can upload data without knowing the size
before starting the transfer if you use chunked encoding. You enable this by adding
a header like "Transfer-Encoding: chunked" with CURLOPT_HTTPHEADER. With HTTP 1.0
or without chunked transfer, you must specify the size.
CURLOPT_MAXFILESIZE
Pass a long as parameter. This allows you to specify the maximum size (in bytes) of
a file to download. If the file requested is larger than this value, the transfer
will not start and CURLE_FILESIZE_EXCEEDED will be returned.
The file size is not always known prior to download, and for such files this option
has no effect even if the file transfer ends up being larger than this given limit.
This concerns both FTP and HTTP transfers.
CURLOPT_MAXFILESIZE_LARGE
Pass a curl_off_t as parameter. This allows you to specify the maximum size (in
bytes) of a file to download. If the file requested is larger than this value, the
transfer will not start and CURLE_FILESIZE_EXCEEDED will be returned. (Added in
7.11.0)
The file size is not always known prior to download, and for such files this option
has no effect even if the file transfer ends up being larger than this given limit.
This concerns both FTP and HTTP transfers.
CURLOPT_TIMECONDITION
Pass a long as parameter. This defines how the CURLOPT_TIMEVALUE time value is
treated. You can set this parameter to CURL_TIMECOND_IFMODSINCE or CURL_TIME-
COND_IFUNMODSINCE. This feature applies to HTTP, FTP, RTSP, and FILE.
The last modification time of a file is not always known and in such instances this
feature will have no effect even if the given time condition would not have been
met. curl_easy_getinfo(3) with the CURLINFO_CONDITION_UNMET option can be used
after a transfer to learn if a zero-byte successful "transfer" was due to this con-
dition not matching.
CURLOPT_TIMEVALUE
Pass a long as parameter. This should be the time in seconds since 1 Jan 1970, and
the time will be used in a condition as specified with CURLOPT_TIMECONDITION.
CONNECTION OPTIONS
CURLOPT_TIMEOUT
Pass a long as parameter containing the maximum time in seconds that you allow the
libcurl transfer operation to take. Normally, name lookups can take a considerable
time and limiting operations to less than a few minutes risk aborting perfectly
normal operations. This option will cause curl to use the SIGALRM to enable time-
outing system calls.
In unix-like systems, this might cause signals to be used unless CURLOPT_NOSIGNAL
is set.
Default timeout is 0 (zero) which means it never times out.
CURLOPT_TIMEOUT_MS
Like CURLOPT_TIMEOUT but takes number of milliseconds instead. If libcurl is built
to use the standard system name resolver, that portion of the transfer will still
use full-second resolution for timeouts with a minimum timeout allowed of one sec-
ond. (Added in 7.16.2)
CURLOPT_LOW_SPEED_LIMIT
Pass a long as parameter. It contains the transfer speed in bytes per second that
the transfer should be below during CURLOPT_LOW_SPEED_TIME seconds for the library
to consider it too slow and abort.
CURLOPT_LOW_SPEED_TIME
Pass a long as parameter. It contains the time in seconds that the transfer should
be below the CURLOPT_LOW_SPEED_LIMIT for the library to consider it too slow and
abort.
CURLOPT_MAX_SEND_SPEED_LARGE
Pass a curl_off_t as parameter. If an upload exceeds this speed (counted in bytes
per second) on cumulative average during the transfer, the transfer will pause to
keep the average rate less than or equal to the parameter value. Defaults to
unlimited speed.
This option doesn't affect transfer speeds done with FILE:// URLs. (Added in
7.15.5)
CURLOPT_MAX_RECV_SPEED_LARGE
Pass a curl_off_t as parameter. If a download exceeds this speed (counted in bytes
per second) on cumulative average during the transfer, the transfer will pause to
keep the average rate less than or equal to the parameter value. Defaults to unlim-
ited speed.
This option doesn't affect transfer speeds done with FILE:// URLs. (Added in
7.15.5)
CURLOPT_MAXCONNECTS
Pass a long. The set number will be the persistent connection cache size. The set
amount will be the maximum amount of simultaneously open connections that libcurl
may cache in this easy handle. Default is 5, and there isn't much point in changing
this value unless you are perfectly aware of how this works and changes libcurl's
behaviour. This concerns connections using any of the protocols that support per-
sistent connections.
When reaching the maximum limit, curl closes the oldest one in the cache to prevent
increasing the number of open connections.
If you already have performed transfers with this curl handle, setting a smaller
MAXCONNECTS than before may cause open connections to get closed unnecessarily.
If you add this easy handle to a multi handle, this setting is not acknowledged,
and you must instead use curl_multi_setopt(3) and the CURLMOPT_MAXCONNECTS option.
CURLOPT_CLOSEPOLICY
(Obsolete) This option does nothing.
CURLOPT_FRESH_CONNECT
Pass a long. Set to 1 to make the next transfer use a new (fresh) connection by
force. If the connection cache is full before this connection, one of the existing
connections will be closed as according to the selected or default policy. This
option should be used with caution and only if you understand what it does. Set
this to 0 to have libcurl attempt re-using an existing connection (default behav-
ior).
CURLOPT_FORBID_REUSE
Pass a long. Set to 1 to make the next transfer explicitly close the connection
when done. Normally, libcurl keeps all connections alive when done with one trans-
fer in case a succeeding one follows that can re-use them. This option should be
used with caution and only if you understand what it does. Set to 0 to have libcurl
keep the connection open for possible later re-use (default behavior).
CURLOPT_CONNECTTIMEOUT
Pass a long. It should contain the maximum time in seconds that you allow the con-
nection to the server to take. This only limits the connection phase, once it has
connected, this option is of no more use. Set to zero to switch to the default
built-in connection timeout - 300 seconds. See also the CURLOPT_TIMEOUT option.
In unix-like systems, this might cause signals to be used unless CURLOPT_NOSIGNAL
is set.
CURLOPT_CONNECTTIMEOUT_MS
Like CURLOPT_CONNECTTIMEOUT but takes the number of milliseconds instead. If
libcurl is built to use the standard system name resolver, that portion of the con-
nect will still use full-second resolution for timeouts with a minimum timeout
allowed of one second. (Added in 7.16.2)
CURLOPT_IPRESOLVE
Allows an application to select what kind of IP addresses to use when resolving
host names. This is only interesting when using host names that resolve addresses
using more than one version of IP. The allowed values are:
CURL_IPRESOLVE_WHATEVER
Default, resolves addresses to all IP versions that your system allows.
CURL_IPRESOLVE_V4
Resolve to IPv4 addresses.
CURL_IPRESOLVE_V6
Resolve to IPv6 addresses.
CURLOPT_CONNECT_ONLY
Pass a long. If the parameter equals 1, it tells the library to perform all the
required proxy authentication and connection setup, but no data transfer. This
option is implemented for HTTP, SMTP and POP3.
The option can be used to simply test a connection to a server, but is more useful
when used with the CURLINFO_LASTSOCKET option to curl_easy_getinfo(3) as the
library can set up the connection and then the application can obtain the most
recently used socket for special data transfers. (Added in 7.15.2)
CURLOPT_USE_SSL
Pass a long using one of the values from below, to make libcurl use your desired
level of SSL for the transfer. (Added in 7.11.0)
This is for enabling SSL/TLS when you use FTP, SMTP, POP3, IMAP etc.
(This option was known as CURLOPT_FTP_SSL up to 7.16.4, and the constants were
known as CURLFTPSSL_*)
CURLUSESSL_NONE
Don't attempt to use SSL.
CURLUSESSL_TRY
Try using SSL, proceed as normal otherwise.
CURLUSESSL_CONTROL
Require SSL for the control connection or fail with CURLE_USE_SSL_FAILED.
CURLUSESSL_ALL
Require SSL for all communication or fail with CURLE_USE_SSL_FAILED.
CURLOPT_RESOLVE
Pass a pointer to a linked list of strings with host name resolve information to
use for requests with this handle. The linked list should be a fully valid list of
struct curl_slist structs properly filled in. Use curl_slist_append(3) to create
the list and curl_slist_free_all(3) to clean up an entire list.
Each single name resolve string should be written using the format
HOST:PORT:ADDRESS where HOST is the name libcurl will try to resolve, PORT is the
port number of the service where libcurl wants to connect to the HOST and ADDRESS
is the numerical IP address. If libcurl is built to support IPv6, ADDRESS can of
course be either IPv4 or IPv6 style addressing.
This option effectively pre-populates the DNS cache with entries for the host+port
pair so redirects and everything that operations against the HOST+PORT will instead
use your provided ADDRESS.
You can remove names from the DNS cache again, to stop providing these fake
resolves, by including a string in the linked list that uses the format
"-HOST:PORT". The host name must be prefixed with a dash, and the host name and
port number must exactly match what was already added previously.
(Added in 7.21.3)
CURLOPT_DNS_SERVERS
Set the list of DNS servers to be used instead of the system default. The format
of the dns servers option is:
host[:port][,host[:port]]...
For example:
192.168.1.100,192.168.1.101,3.4.5.6
This option requires that libcurl was built with a resolver backend that supports
this operation. The c-ares backend is the only such one.
(Added in 7.24.0)
CURLOPT_ACCEPTTIMEOUT_MS
Pass a long telling libcurl the maximum number of milliseconds to wait for a server
to connect back to libcurl when an active FTP connection is used. If no timeout is
set, the internal default of 60000 will be used. (Added in 7.24.0)
SSL and SECURITY OPTIONS
CURLOPT_SSLCERT
Pass a pointer to a zero terminated string as parameter. The string should be the
file name of your certificate. The default format is "PEM" and can be changed with
CURLOPT_SSLCERTTYPE.
With NSS this can also be the nickname of the certificate you wish to authenticate
with. If you want to use a file from the current directory, please precede it with
"./" prefix, in order to avoid confusion with a nickname.
CURLOPT_SSLCERTTYPE
Pass a pointer to a zero terminated string as parameter. The string should be the
format of your certificate. Supported formats are "PEM" and "DER". (Added in
7.9.3)
CURLOPT_SSLKEY
Pass a pointer to a zero terminated string as parameter. The string should be the
file name of your private key. The default format is "PEM" and can be changed with
CURLOPT_SSLKEYTYPE.
CURLOPT_SSLKEYTYPE
Pass a pointer to a zero terminated string as parameter. The string should be the
format of your private key. Supported formats are "PEM", "DER" and "ENG".
The format "ENG" enables you to load the private key from a crypto engine. In this
case CURLOPT_SSLKEY is used as an identifier passed to the engine. You have to set
the crypto engine with CURLOPT_SSLENGINE. "DER" format key file currently does not
work because of a bug in OpenSSL.
CURLOPT_KEYPASSWD
Pass a pointer to a zero terminated string as parameter. It will be used as the
password required to use the CURLOPT_SSLKEY or CURLOPT_SSH_PRIVATE_KEYFILE private
key. You never needed a pass phrase to load a certificate but you need one to load
your private key.
(This option was known as CURLOPT_SSLKEYPASSWD up to 7.16.4 and CURLOPT_SSLCERT-
PASSWD up to 7.9.2)
CURLOPT_SSLENGINE
Pass a pointer to a zero terminated string as parameter. It will be used as the
identifier for the crypto engine you want to use for your private key.
If the crypto device cannot be loaded, CURLE_SSL_ENGINE_NOTFOUND is returned.
CURLOPT_SSLENGINE_DEFAULT
Sets the actual crypto engine as the default for (asymmetric) crypto operations.
If the crypto device cannot be set, CURLE_SSL_ENGINE_SETFAILED is returned.
Even though this option doesn't need any parameter, in some configurations
curl_easy_setopt might be defined as a macro taking exactly three arguments. There-
fore, it's recommended to pass 1 as parameter to this option.
CURLOPT_SSLVERSION
Pass a long as parameter to control what version of SSL/TLS to attempt to use.
(Added in 7.9.2)
The available options are:
CURL_SSLVERSION_DEFAULT
The default action. This will attempt to figure out the remote SSL protocol
version, i.e. either SSLv3 or TLSv1 (but not SSLv2, which became disabled by
default with 7.18.1).
CURL_SSLVERSION_TLSv1
Force TLSv1.x
CURL_SSLVERSION_SSLv2
Force SSLv2
CURL_SSLVERSION_SSLv3
Force SSLv3
CURL_SSLVERSION_TLSv1_0
Force TLSv1.0 (Added in 7.34.0)
CURL_SSLVERSION_TLSv1_1
Force TLSv1.1 (Added in 7.34.0)
CURL_SSLVERSION_TLSv1_2
Force TLSv1.2 (Added in 7.34.0)
CURL_SSLVERSION_TLSv1_3
Force TLSv1.3 (Added in 7.52.0)
CURL_SSLVERSION_MAX_DEFAULT
The flag defines maximum supported TLS version as TLSv1.2 or default value
from SSL library. (Added in 7.54.0)
CURL_SSLVERSION_MAX_TLSv1_0
The flag defines maximum supported TLS version as TLSv1.0. (Added in
7.54.0)
CURL_SSLVERSION_MAX_TLSv1_1
The flag defines maximum supported TLS version as TLSv1.1. (Added in
7.54.0)
CURL_SSLVERSION_MAX_TLSv1_2
The flag defines maximum supported TLS version as TLSv1.2. (Added in
7.54.0)
CURL_SSLVERSION_MAX_TLSv1_3
The flag defines maximum supported TLS version as TLSv1.3. (Added in
7.54.0)
CURLOPT_SSL_VERIFYPEER
Pass a long as parameter. By default, curl assumes a value of 1.
This option determines whether curl verifies the authenticity of the peer's cer-
tificate. A value of 1 means curl verifies; 0 (zero) means it doesn't.
When negotiating a SSL connection, the server sends a certificate indicating its
identity. Curl verifies whether the certificate is authentic, i.e. that you can
trust that the server is who the certificate says it is. This trust is based on a
chain of digital signatures, rooted in certification authority (CA) certificates
you supply. curl uses a default bundle of CA certificates (the path for that is
determined at build time) and you can specify alternate certificates with the CUR-
LOPT_CAINFO option or the CURLOPT_CAPATH option.
When CURLOPT_SSL_VERIFYPEER is nonzero, and the verification fails to prove that
the certificate is authentic, the connection fails. When the option is zero, the
peer certificate verification succeeds regardless.
Authenticating the certificate is not by itself very useful. You typically want to
ensure that the server, as authentically identified by its certificate, is the
server you mean to be talking to. Use CURLOPT_SSL_VERIFYHOST to control that. The
check that the host name in the certificate is valid for the host name you're con-
necting to is done independently of the CURLOPT_SSL_VERIFYPEER option.
CURLOPT_CAINFO
Pass a char * to a zero terminated string naming a file holding one or more cer-
tificates to verify the peer with. This makes sense only when used in combination
with the CURLOPT_SSL_VERIFYPEER option. If CURLOPT_SSL_VERIFYPEER is zero, CUR-
LOPT_CAINFO need not even indicate an accessible file.
This option is by default set to the system path where libcurl's cacert bundle is
assumed to be stored, as established at build time.
If curl is built against the NSS SSL library, the NSS PEM PKCS#11 module (lib-
nsspem.so) needs to be available for this option to work properly.
CURLOPT_ISSUERCERT
Pass a char * to a zero terminated string naming a file holding a CA certificate in
PEM format. If the option is set, an additional check against the peer certificate
is performed to verify the issuer is indeed the one associated with the certificate
provided by the option. This additional check is useful in multi-level PKI where
one needs to enforce that the peer certificate is from a specific branch of the
tree.
This option makes sense only when used in combination with the CURLOPT_SSL_VERI-
FYPEER option. Otherwise, the result of the check is not considered as failure.
A specific error code (CURLE_SSL_ISSUER_ERROR) is defined with the option, which is
returned if the setup of the SSL/TLS session has failed due to a mismatch with the
issuer of peer certificate (CURLOPT_SSL_VERIFYPEER has to be set too for the check
to fail). (Added in 7.19.0)
CURLOPT_CAPATH
Pass a char * to a zero terminated string naming a directory holding multiple CA
certificates to verify the peer with. If libcurl is built against OpenSSL, the cer-
tificate directory must be prepared using the openssl c_rehash utility. This makes
sense only when used in combination with the CURLOPT_SSL_VERIFYPEER option. If
CURLOPT_SSL_VERIFYPEER is zero, CURLOPT_CAPATH need not even indicate an accessible
path. The CURLOPT_CAPATH function apparently does not work in Windows due to some
limitation in openssl. This option is OpenSSL-specific and does nothing if libcurl
is built to use GnuTLS. NSS-powered libcurl provides the option only for backward
compatibility.
CURLOPT_CRLFILE
Pass a char * to a zero terminated string naming a file with the concatenation of
CRL (in PEM format) to use in the certificate validation that occurs during the SSL
exchange.
When curl is built to use NSS or GnuTLS, there is no way to influence the use of
CRL passed to help in the verification process. When libcurl is built with OpenSSL
support, X509_V_FLAG_CRL_CHECK and X509_V_FLAG_CRL_CHECK_ALL are both set, requir-
ing CRL check against all the elements of the certificate chain if a CRL file is
passed.
This option makes sense only when used in combination with the CURLOPT_SSL_VERI-
FYPEER option.
A specific error code (CURLE_SSL_CRL_BADFILE) is defined with the option. It is
returned when the SSL exchange fails because the CRL file cannot be loaded. A
failure in certificate verification due to a revocation information found in the
CRL does not trigger this specific error. (Added in 7.19.0)
CURLOPT_SSL_VERIFYHOST
Pass a long as parameter.
This option determines whether libcurl verifies that the server cert is for the
server it is known as.
When negotiating a SSL connection, the server sends a certificate indicating its
identity.
When CURLOPT_SSL_VERIFYHOST is 2, that certificate must indicate that the server is
the server to which you meant to connect, or the connection fails.
Curl considers the server the intended one when the Common Name field or a Subject
Alternate Name field in the certificate matches the host name in the URL to which
you told Curl to connect.
When the value is 1, libcurl will return a failure. It was previously (in 7.28.0
and earlier) a debug option of some sorts, but it is no longer supported due to
frequently leading to programmer mistakes.
When the value is 0, the connection succeeds regardless of the names in the cer-
tificate.
The default value for this option is 2.
This option controls checking the server's certificate's claimed identity. The
server could be lying. To control lying, see CURLOPT_SSL_VERIFYPEER. If libcurl
is built against NSS and CURLOPT_SSL_VERIFYPEER is zero, CURLOPT_SSL_VERIFYHOST is
ignored.
CURLOPT_CERTINFO
Pass a long set to 1 to enable libcurl's certificate chain info gatherer. With this
enabled, libcurl (if built with OpenSSL) will extract lots of information and data
about the certificates in the certificate chain used in the SSL connection. This
data is then possible to extract after a transfer using curl_easy_getinfo(3) and
its option CURLINFO_CERTINFO. (Added in 7.19.1)
CURLOPT_RANDOM_FILE
Pass a char * to a zero terminated file name. The file will be used to read from to
seed the random engine for SSL. The more random the specified file is, the more
secure the SSL connection will become.
CURLOPT_EGDSOCKET
Pass a char * to the zero terminated path name to the Entropy Gathering Daemon
socket. It will be used to seed the random engine for SSL.
CURLOPT_SSL_CIPHER_LIST
Pass a char *, pointing to a zero terminated string holding the list of ciphers to
use for the SSL connection. The list must be syntactically correct, it consists of
one or more cipher strings separated by colons. Commas or spaces are also accept-
able separators but colons are normally used, !, - and + can be used as operators.
For OpenSSL and GnuTLS valid examples of cipher lists include 'RC4-SHA',
'SHA1+DES', 'TLSv1' and 'DEFAULT'. The default list is normally set when you com-
pile OpenSSL.
You'll find more details about cipher lists on this URL:
http://www.openssl.org/docs/apps/ciphers.html
For NSS, valid examples of cipher lists include 'rsa_rc4_128_md5',
'rsa_aes_128_sha', etc. With NSS you don't add/remove ciphers. If one uses this
option then all known ciphers are disabled and only those passed in are enabled.
You'll find more details about the NSS cipher lists on this URL: http://git.fedora-
hosted.org/cgit/mod_nss.git/plain/docs/mod_nss.html#Directives
CURLOPT_SSL_SESSIONID_CACHE
Pass a long set to 0 to disable libcurl's use of SSL session-ID caching. Set this
to 1 to enable it. By default all transfers are done using the cache. While nothing
ever should get hurt by attempting to reuse SSL session-IDs, there seem to be bro-
ken SSL implementations in the wild that may require you to disable this in order
for you to succeed. (Added in 7.16.0)
CURLOPT_SSL_OPTIONS
Pass a long with a bitmask to tell libcurl about specific SSL behaviors.
CURLSSLOPT_ALLOW_BEAST is the only supported bit and by setting this the user will
tell libcurl to not attempt to use any workarounds for a security flaw in the SSL3
and TLS1.0 protocols. If this option isn't used or this bit is set to 0, the SSL
layer libcurl uses may use a work-around for this flaw although it might cause
interoperability problems with some (older) SSL implementations. WARNING: avoiding
this work-around loosens the security, and by setting this option to 1 you ask for
exactly that. (Added in 7.25.0)
CURLOPT_KRBLEVEL
Pass a char * as parameter. Set the kerberos security level for FTP; this also
enables kerberos awareness. This is a string, 'clear', 'safe', 'confidential' or
'private'. If the string is set but doesn't match one of these, 'private' will be
used. Set the string to NULL to disable kerberos support for FTP.
(This option was known as CURLOPT_KRB4LEVEL up to 7.16.3)
CURLOPT_GSSAPI_DELEGATION
Set the parameter to CURLGSSAPI_DELEGATION_FLAG to allow unconditional GSSAPI cre-
dential delegation. The delegation is disabled by default since 7.21.7. Set the
parameter to CURLGSSAPI_DELEGATION_POLICY_FLAG to delegate only if the OK-AS-DELE-
GATE flag is set in the service ticket in case this feature is supported by the
GSSAPI implementation and the definition of GSS_C_DELEG_POLICY_FLAG was available
at compile-time. (Added in 7.22.0)
SSH OPTIONS
CURLOPT_SSH_AUTH_TYPES
Pass a long set to a bitmask consisting of one or more of CURLSSH_AUTH_PUBLICKEY,
CURLSSH_AUTH_PASSWORD, CURLSSH_AUTH_HOST, CURLSSH_AUTH_KEYBOARD and
CURLSSH_AUTH_AGENT. Set CURLSSH_AUTH_ANY to let libcurl pick a suitable one. Cur-
rently CURLSSH_AUTH_HOST has no effect. (Added in 7.16.1) If CURLSSH_AUTH_AGENT is
used, libcurl attempts to connect to ssh-agent or pageant and let the agent attempt
the authentication. (Added in 7.28.0)
CURLOPT_SSH_HOST_PUBLIC_KEY_MD5
Pass a char * pointing to a string containing 32 hexadecimal digits. The string
should be the 128 bit MD5 checksum of the remote host's public key, and libcurl
will reject the connection to the host unless the md5sums match. This option is
only for SCP and SFTP transfers. (Added in 7.17.1)
CURLOPT_SSH_PUBLIC_KEYFILE
Pass a char * pointing to a file name for your public key. If not used, libcurl
defaults to $HOME/.ssh/id_dsa.pub if the HOME environment variable is set, and just
"id_dsa.pub" in the current directory if HOME is not set. (Added in 7.16.1) If
NULL (or an empty string) is passed, libcurl will pass no public key to libssh2,
which then tries to compute it from the private key. This is known to work with
libssh2 1.4.0+ linked against OpenSSL. (Added in 7.26.0)
CURLOPT_SSH_PRIVATE_KEYFILE
Pass a char * pointing to a file name for your private key. If not used, libcurl
defaults to $HOME/.ssh/id_dsa if the HOME environment variable is set, and just
"id_dsa" in the current directory if HOME is not set. If the file is password-pro-
tected, set the password with CURLOPT_KEYPASSWD. (Added in 7.16.1)
CURLOPT_SSH_KNOWNHOSTS
Pass a pointer to a zero terminated string holding the file name of the known_host
file to use. The known_hosts file should use the OpenSSH file format as supported
by libssh2. If this file is specified, libcurl will only accept connections with
hosts that are known and present in that file, with a matching public key. Use CUR-
LOPT_SSH_KEYFUNCTION to alter the default behavior on host and key (mis)matching.
(Added in 7.19.6)
CURLOPT_SSH_KEYFUNCTION
Pass a pointer to a curl_sshkeycallback function. It gets called when the
known_host matching has been done, to allow the application to act and decide for
libcurl how to proceed. The callback will only be called if CURLOPT_SSH_KNOWNHOSTS
is also set.
The curl_sshkeycallback function gets passed the CURL handle, the key from the
known_hosts file, the key from the remote site, info from libcurl on the matching
status and a custom pointer (set with CURLOPT_SSH_KEYDATA). It MUST return one of
the following return codes to tell libcurl how to act:
CURLKHSTAT_FINE_ADD_TO_FILE
The host+key is accepted and libcurl will append it to the known_hosts file
before continuing with the connection. This will also add the host+key combo
to the known_host pool kept in memory if it wasn't already present there.
The adding of data to the file is done by completely replacing the file with
a new copy, so the permissions of the file must allow this.
CURLKHSTAT_FINE
The host+key is accepted libcurl will continue with the connection. This
will also add the host+key combo to the known_host pool kept in memory if it
wasn't already present there.
CURLKHSTAT_REJECT
The host+key is rejected. libcurl will deny the connection to continue and
it will be closed.
CURLKHSTAT_DEFER
The host+key is rejected, but the SSH connection is asked to be kept alive.
This feature could be used when the app wants to somehow return back and act
on the host+key situation and then retry without needing the overhead of
setting it up from scratch again.
(Added in 7.19.6)
CURLOPT_SSH_KEYDATA
Pass a void * as parameter. This pointer will be passed along verbatim to the call-
back set with CURLOPT_SSH_KEYFUNCTION. (Added in 7.19.6)
OTHER OPTIONS
CURLOPT_PRIVATE
Pass a void * as parameter, pointing to data that should be associated with this
curl handle. The pointer can subsequently be retrieved using curl_easy_getinfo(3)
with the CURLINFO_PRIVATE option. libcurl itself does nothing with this data.
(Added in 7.10.3)
CURLOPT_SHARE
Pass a share handle as a parameter. The share handle must have been created by a
previous call to curl_share_init(3). Setting this option, will make this curl han-
dle use the data from the shared handle instead of keeping the data to itself. This
enables several curl handles to share data. If the curl handles are used simultane-
ously in multiple threads, you MUST use the locking methods in the share handle.
See curl_share_setopt(3) for details.
If you add a share that is set to share cookies, your easy handle will use that
cookie cache and get the cookie engine enabled. If you unshare an object that was
using cookies (or change to another object that doesn't share cookies), the easy
handle will get its cookie engine disabled.
Data that the share object is not set to share will be dealt with the usual way, as
if no share was used.
CURLOPT_NEW_FILE_PERMS
Pass a long as a parameter, containing the value of the permissions that will be
assigned to newly created files on the remote server. The default value is 0644,
but any valid value can be used. The only protocols that can use this are sftp://,
scp://, and file://. (Added in 7.16.4)
CURLOPT_NEW_DIRECTORY_PERMS
Pass a long as a parameter, containing the value of the permissions that will be
assigned to newly created directories on the remote server. The default value is
0755, but any valid value can be used. The only protocols that can use this are
sftp://, scp://, and file://. (Added in 7.16.4)
TELNET OPTIONS
CURLOPT_TELNETOPTIONS
Provide a pointer to a curl_slist with variables to pass to the telnet negotia-
tions. The variables should be in the format <option=value>. libcurl supports the
options 'TTYPE', 'XDISPLOC' and 'NEW_ENV'. See the TELNET standard for details.
RETURN VALUE
CURLE_OK (zero) means that the option was set properly, non-zero means an error occurred
as <curl/curl.h> defines. See the libcurl-errors(3) man page for the full list with
descriptions.
If you try to set an option that libcurl doesn't know about, perhaps because the library
is too old to support it or the option was removed in a recent version, this function will
return CURLE_FAILED_INIT.
SEE ALSO
curl_easy_init(3), curl_easy_cleanup(3), curl_easy_reset(3)
libcurl 7.20.0 1 Jan 2010 curl_easy_setopt(3)
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