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 applica-tion application
tion 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 han-dle. handle.
dle. 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, will not be copied by the library. Instead you
should keep them available until libcurl no longer needs them. Failing to do so will cause very odd
behavior or even crashes. libcurl will need them until you call curl_easy_cleanup(3) or you set the
same option again to use a different pointer.
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 non-zero to get the library to display a lot of verbose information about
its operations. Very useful for libcurl and/or protocol debugging and understanding. The ver-bose verbose
bose 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 CURLOPT_DEBUGFUNCTION.
CURLOPT_HEADER
A non-zero parameter 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).
CURLOPT_NOPROGRESS
A non-zero parameter tells the library to shut off the built-in progress meter completely.
Future versions of libcurl is likely to not have any built-in progress meter at all.
CURLOPT_NOSIGNAL
Pass a long. If it is non-zero, libcurl will not use any functions that install signal han-dlers handlers
dlers 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 timeout options etc, with-out without
out risking getting signals. (Added in 7.10)
Consider building libcurl with ares support to enable asynchronous DNS lookups. It enables
nice timeouts for name resolves without signals.
CALLBACK OPTIONS
CURLOPT_WRITEFUNCTION
Function pointer that should match the following prototype: size_t function( void *ptr, size_t
size, size_t nmemb, void *stream); 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 multi-plied multiplied
plied with nmemb, it will not be zero terminated. 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 and it will abort the transfer and return CURLE_WRITE_ERROR.
This function may be called with zero bytes data if the transfered 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 stream 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
data that can be passed to the write callback is defined in the curl.h header file:
CURL_MAX_WRITE_SIZE.
CURLOPT_WRITEDATA
Data pointer to pass to the file write function. If you use the CURLOPT_WRITEFUNCTION 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_WRITEDATA was
introduced in 7.9.7.
CURLOPT_READFUNCTION
Function pointer that should match the following prototype: size_t function( void *ptr, size_t
size, size_t nmemb, void *stream); 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 end-offile
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 told 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)
If you set the callback pointer to NULL, or doesn't set it at all, the default internal read
function will be used. It is simply doing an fread() on the FILE * stream set with CUR-LOPT_READDATA. CURLOPT_READDATA.
LOPT_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 callback 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 is also known with the older name CURLOPT_INFILE, the name CURLOPT_READDATA was
introduced in 7.9.7.
CURLOPT_IOCTLFUNCTION
Function pointer that should match the curl_ioctl_callback prototype found in <curl/curl.h>.
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)
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_SOCKOPTFUNCTION
Function pointer that should match the curl_sockopt_callback prototype found in <curl/curl.h>.
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, and
currently only one value is supported: CURLSOCKTYPE_IPCXN for the primary connection (meaning
the control connection in the FTP case). 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 discretion. A non-zero return code from the callback function will signal an unre-coverable unrecoverable
coverable error to the library and it will close the socket and return CURLE_COULDNT_CONNECT.
(Option added in 7.15.6.)
CURLOPT_SOCKOPTDATA
Pass a pointer that will be untouched by libcurl and passed as the first argument in the sock-opt sockopt
opt callback set with CURLOPT_SOCKOPTFUNCTION. (Option added in 7.15.6.)
CURLOPT_PROGRESSFUNCTION
Function pointer that should match the curl_progress_callback prototype found in
<curl/curl.h>. This function gets called by libcurl instead of its internal equivalent with a
frequent interval during operation (roughly once per second) no matter if data is being trans-fered transfered
fered 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. Usage of
the CURLOPT_PROGRESSFUNCTION callback is not recommended when using the multi interface.
CURLOPT_NOPROGRESS must be set to FALSE 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
Function pointer that should match the following prototype: size_t function( void *ptr, size_t
size, size_t nmemb, void *stream);. 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 com-plete complete
plete header lines are passed on to the callback. Parsing headers should be easy enough 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 stream is the one you set with the CUR-LOPT_WRITEHEADER CURLOPT_WRITEHEADER
LOPT_WRITEHEADER option. The callback function must return the number of bytes actually taken
care of, or return -1 to signal error to the library (it will cause it to abort the transfer
with a CURLE_WRITE_ERROR return code).
Since 7.14.1: 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 response-headers mention what header to
expect in the trailer.
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 your own callback to take care of the
writing, this must be a valid FILE *. See also the CURLOPT_HEADERFUNCTION option above on how
to set a custom get-all-headers callback.
CURLOPT_DEBUGFUNCTION
Function pointer that should match the following prototype: int curl_debug_callback (CURL *,
curl_infotype, char *, size_t, void *); CURLOPT_DEBUGFUNCTION replaces the standard debug
function used when CURLOPT_VERBOSE is in effect. This callback receives debug information, as
specified with the curl_infotype 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
Function pointer that should match the following prototype: CURLcode sslctxfun(CURL *curl,
void *sslctx, void *parm); This function gets called by libcurl just before the initialization
of an 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 function. 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 negotia-tion. negotiation.
tion. 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.
Using this function allows for example to use openssl callbacks to add additional validation
code for certificates, and even to change the actual URI of an 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 CURLOPT_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
Function pointers that should match the following prototype: CURLcode function(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_ver-sion_info(3) curl_version_info(3)
sion_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 encoding. 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 follows:
#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.
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.
Use CURLOPT_VERBOSE and CURLOPT_DEBUGFUNCTION to better debug/trace why errors happen.
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 non-zero parameter 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 normally, 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 for
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
The actual URL to deal with. The parameter should be a char * to a zero terminated string. The
string must remain present until curl no longer needs it, as it doesn't copy the string.
If the given URL lacks the protocol part ("http://" or "ftp://" etc), it will attempt to guess
which protocol to use based on the given host name. If the given protocol of the set URL is
not supported, libcurl will return on error (CURLE_UNSUPPORTED_PROTOCOL) when you call
curl_easy_perform(3) or curl_multi_perform(3). Use curl_version_info(3) for detailed info on
which protocols that are supported.
The string given to CURLOPT_URL must be url-encoded and following the RFC 2396
(http://curl.haxx.se/rfc/rfc2396.txt)
CURLOPT_URL is the only option that must be set before curl_easy_perform(3) is called.
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 CURLOPT_PROXYPORT.
When you tell the library to use an 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 tunneling is activated with CURLOPT_HTTPPROXY-
TUNNEL.
libcurl respects the environment variables http_proxy, ftp_proxy, all_proxy etc, if any of
those is 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.
CURLOPT_PROXYPORT
Pass a long with this option to set the proxy port to connect to unless it is specified 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 CURL-
PROXY_HTTP, CURLPROXY_SOCKS4 (added in 7.15.2) CURLPROXY_SOCKS5. The HTTP type is default.
(Added in 7.10)
CURLOPT_HTTPPROXYTUNNEL
Set the parameter to non-zero to get the library to 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_INTERFACE
Pass a char * as parameter. This set the interface name to use as outgoing network interface.
The name can be an interface name, an IP address or a host name.
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_LOCALPOR-
TRANGE as well when this is set. Note that port numbers are only valid 1 - 65535. (Added in
7.15.2)
CURLOPT_LOCALPORTRANGE
Pass a long. This is the number of attempts libcurl should do 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 value to 1 or below will make libcurl do only one try for exact port number. Note
that port numbers by nature is a scarce resource 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 (0) to completely disable caching, or set to -1 to make the
cached entries remain forever. By default, libcurl caches this info for 60 seconds.
CURLOPT_DNS_USE_GLOBAL_CACHE
Pass a long. If the value is non-zero, it tells curl to use a global DNS cache that will sur-
vive 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. This is just treated as a request, not an order. You cannot be guaranteed to actually
get the given size. (Added in 7.10)
This size is by default set as big as possible (CURL_MAX_WRITE_SIZE), so it only makes sense
to use this option if you want it smaller.
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 should 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 algorithm 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.
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 CURLOPT_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 pre-
ferred. The file will be scanned with the host and user name (to find the password
only) or with 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 informa-
tion in the URL, and to search the file with 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 CUR-
LOPT_NETRC is set, libcurl will attempt to find the 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 authentication method.
When using NTLM, you can set domain by prepending it to the user name and separating 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 information 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 authentication method.
CURLOPT_HTTPAUTH
Pass a long as parameter, which is set to a bitmask, to tell libcurl what authentication
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 what authentication methods 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_USERPWD option. (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 is sending 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 regular old-fashioned
Basic method.
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 authentication but may be also used along with another
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 Microsoft. It
uses a challenge-response and hash concept similar to Digest, to prevent the password
from being eavesdropped.
You need to build libcurl with OpenSSL support for this option to work, or build
libcurl on Windows.
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.
CURLOPT_PROXYAUTH
Pass a long as parameter, which is set to a bitmask, to tell libcurl what authentication
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 methods 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 non-zero parameter to enable this. When enabled, libcurl will automatically set the
Referer: field in requests where it follows a Location: redirect.
CURLOPT_ENCODING
Sets the contents of the Accept-Encoding: header sent in an 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.
CURLOPT_FOLLOWLOCATION
A non-zero parameter tells the library to follow any Location: header that the server sends as
part of an 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.
CURLOPT_UNRESTRICTED_AUTH
A non-zero parameter tells the library it can continue to send authentication (user+password)
when following locations, even when hostname changed. This option is meaningful only when set-
ting CURLOPT_FOLLOWLOCATION.
CURLOPT_MAXREDIRS
Pass a long. The set number will be the redirection limit. If that many redirections have been
followed, the next redirect will cause an error (CURLE_TOO_MANY_REDIRECTS). This option only
makes sense if the CURLOPT_FOLLOWLOCATION 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_PUT
A non-zero parameter 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 CUR-
LOPT_UPLOAD.
CURLOPT_POST
A non-zero parameter tells the library to do a regular HTTP post. This will also make the
library use the a "Content-Type: application/x-www-form-urlencoded" header. (This is by far
the most commonly used POST method).
Use the CURLOPT_POSTFIELDS option to specify what data to post and CURLOPT_POSTFIELDSIZE to
set the data size.
Optionally, you can provide data to POST using the CURLOPT_READFUNCTION and CURLOPT_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 CURLOPT_POSTFIELDSIZE option.
You can override the default POST Content-Type: header by setting your own with CURLOPT_HTTP-
HEADER.
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 start-
ing 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 a non-zero value, 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 simi-
lar.
CURLOPT_POSTFIELDS
Pass a char * as parameter, which should be the full data to post in an 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. Take note.
This POST is a normal application/x-www-form-urlencoded kind (and libcurl will set that Con-
tent-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.
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 rfc1867-posts), check out the CURLOPT_HTTPPOST 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_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_httppost 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_HTTPHEADER.
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_HTTPHEADER.
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 otherwise generated and used by libcurl internally, your
added one will be used instead. If you add a header with no contents 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 headers. To
add a header with no contents, make the contents be two quotes: "". The headers 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, CUR-
LOPT_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 cookies in one string like
this: "name1=content1; name2=content2;" etc.
Using this option multiple times will only make the latest string override the previously
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 request.
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 CUR-
LOPT_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 non-zero 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 previous session.
By default, libcurl always stores and loads all cookies, independent if they are session cook-
ies are 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)
CURLOPT_HTTPGET
Pass a long. If the long is non-zero, this forces the HTTP request to get back to GET. usable
if a POST, HEAD, PUT or a custom request have been used previously using the same curl handle.
When setting CURLOPT_HTTPGET to a non-zero value, 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 reason.
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. Note however that libcurl has no
default content 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, transfer
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)
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, an network
interface name (under Unix) or just a '-' letter to let the library use your systems default
IP address. Default FTP operations are passive, and thus won't use PORT.
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 com-
mand 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 oper-
ation again by setting a NULL to this option.
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 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 7.15.6, if you also set CURLOPT_NOBODY non-zero, this option
didn't work.
CURLOPT_FTPLISTONLY
A non-zero parameter tells the library to just list the names of an ftp directory, instead of
doing a full directory listing that would include file sizes, dates etc.
This causes an FTP NLST command to be sent. Beware that some FTP servers list only files in
their response to NLST; they might not include subdirectories and symbolic links.
CURLOPT_FTPAPPEND
A non-zero parameter tells the library to append to the remote file instead of overwrite it.
This is only useful when uploading to an ftp site.
CURLOPT_FTP_USE_EPRT
Pass a long. If the value is non-zero, 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 FALSE (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 non-zero, it tells curl to use the EPSV command when doing pas-
sive 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 FALSE (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_CREATE_MISSING_DIRS
Pass a long. If the value is non-zero, 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 direc-
tory 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 cre-
ation. (Added in 7.16.3)
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 CUR-
LOPT_TIMEOUT. It is recommended that if used in conjunction with CURLOPT_TIMEOUT, you set CUR-
LOPT_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 currently only known to
be required when connecting to Tumbleweed's Secure Transport FTPS server using client certifi-
cates for authentication. (Added in 7.15.5)
CURLOPT_FTP_SKIP_PASV_IP
Pass a long. If set to a non-zero value, 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_FTP_SSL
Pass a long using one of the values from below, to make libcurl use your desired level of SSL
for the ftp transfer. (Added in 7.11.0)
CURLFTPSSL_NONE
Don't attempt to use SSL.
CURLFTPSSL_TRY
Try using SSL, proceed as normal otherwise.
CURLFTPSSL_CONTROL
Require SSL for the control connection or fail with CURLE_FTP_SSL_FAILED.
CURLFTPSSL_ALL
Require SSL for all communication or fail with CURLE_FTP_SSL_FAILED.
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_FTP_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 communication will be
unencrypted. This allows NAT routers to follow the FTP transaction. 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 fol-
lowing alternatives:
CURLFTPMETHOD_MULTICWD
libcurl does a single CWD operation for each path part in the given URL. For deep hier-
archies this means very 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 behavior.
CURLFTPMETHOD_SINGLECWD
libcurl does one CWD with the full target directory and then operates on the file "nor-
mally" (like in the multicwd case). This is somewhat more standards compliant than
'nocwd' but without the full penalty of 'multicwd'.
PROTOCOL OPTIONS
CURLOPT_TRANSFERTEXT
A non-zero parameter 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 cer-
tain 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_CRLF
Convert Unix newlines to CRLF newlines on transfers.
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 tech-
niques). Pass a NULL to this option to disable the use of ranges.
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).
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 will be user instead of GET or
HEAD when doing an HTTP request, or instead of LIST or NLST when doing an ftp directory list-
ing. This is useful for doing DELETE or other more or less obscure HTTP requests. Don't do
this at will, make sure your server supports the command first.
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.
CURLOPT_FILETIME
Pass a long. If it is a non-zero value, 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_FILE-
TIME argument can be used after a transfer to extract the received time (if any).
CURLOPT_NOBODY
A non-zero parameter 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 CUR-
LOPT_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 CUR-
LOPT_INFILESIZE_LARGE.
For uploading using SCP, this option or CURLOPT_INFILESIZE_LARGE is mandatory.
Note that this option does not limit how much data libcurl will actually send, as that is con-
trolled 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.
Note that this option does not limit how much data libcurl will actually send, as that is con-
trolled entirely by what the read callback returns.
CURLOPT_UPLOAD
A non-zero parameter tells the library to prepare for an upload. The CURLOPT_READDATA and CUR-
LOPT_INFILESIZE or CURLOPT_INFILESIZE_LARGE options are also interesting 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 trans-
fer, 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_TIMECOND_IFUNMODSINCE. This feature
applies to HTTP and FTP.
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 have not been met.
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.
CURLOPT_TIMEOUT_MS
Like CURLOPT_TIMEOUT but takes number of milliseconds instead. If libcurl is built to use the
standard system name resolver, that part will still use full-second resolution for timeouts.
(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 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. (Added in 7.15.5)
CURLOPT_MAX_RECV_SPEED_LARGE
Pass a curl_off_t as parameter. If a download exceeds this speed 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. (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 per-
fectly aware of how this work and changes libcurl's behaviour. This concerns connection using
any of the protocols that support persistent connections.
When reaching the maximum limit, curl closes the oldest one in the cache to prevent the number
of open connections to increase.
If you already have performed transfers with this curl handle, setting a smaller MAXCONNECTS
than before may cause open connections to get closed unnecessarily.
Note that if you add this easy handle to a multi handle, this setting is not being acknowl-
edged, but 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 non-zero 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 cau-
tion and only if you understand what it does. Set this to 0 to have libcurl attempt re-using
an existing connection (default behavior).
CURLOPT_FORBID_REUSE
Pass a long. Set to non-zero to make the next transfer explicitly close the connection when
done. Normally, libcurl keep all connections alive when done with one transfer in case there
comes a succeeding one 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 possibly
later re-use (default behavior).
CURLOPT_CONNECTTIMEOUT
Pass a long. It should contain the maximum time in seconds that you allow the connection 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 disable connection timeout (it will then only timeout on the
system's internal timeouts). 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 number of milliseconds instead. If libcurl is built to
use the standard system name resolver, that part will still use full-second resolution for
timeouts. (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 ver-
sion 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. A non-zero parameter tells the library to perform any required proxy authentica-
tion and connection setup, but no data transfer.
This option is useful with the CURLINFO_LASTSOCKET option to curl_easy_getinfo(3). 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)
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 is the nickname of the certificate you wish to authenticate with.
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_SSLCERTPASSWD
Pass a pointer to a zero terminated string as parameter. It will be used as the password
required to use the CURLOPT_SSLCERT certificate.
This option is replaced by CURLOPT_SSLKEYPASSWD and should only be used for backward compati-
bility. You never needed a pass phrase to load a certificate but you need one to load your
private key.
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 CUR-
LOPT_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_SSLKEYPASSWD
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.
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.
CURLOPT_SSLVERSION
Pass a long as parameter to control what version of SSL/TLS to attempt to use. The available
options are:
CURL_SSLVERSION_DEFAULT
The default action. When libcurl built with OpenSSL or NSS, this will attempt to figure
out the remote SSL protocol version. Unfortunately there are a lot of ancient and bro-
ken servers in use which cannot handle this technique and will fail to connect. When
libcurl is built with GnuTLS, this will mean SSLv3.
CURL_SSLVERSION_TLSv1
Force TLSv1
CURL_SSLVERSION_SSLv2
Force SSLv2
CURL_SSLVERSION_SSLv3
Force SSLv3
CURLOPT_SSL_VERIFYPEER
Pass a long as parameter.
This option determines whether curl verifies the authenticity of the peer's certificate. A
nonzero value means curl verifies; zero means it doesn't. The default is nonzero, but before
7.10, it was zero.
When negotiating an 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. As of 7.10, curl installs a default
bundle of CA certificates and you can specify alternate certificates with the CURLOPT_CAINFO
option or the CURLOPT_CAPATH option.
When CURLOPT_SSL_VERIFYPEER is nonzero, and the verification fails to prove that the certifi-
cate is authentic, the connection fails. When the option is zero, the connection 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.
CURLOPT_CAINFO
Pass a char * to a zero terminated string naming a file holding one or more certificates to
verify the peer with. This makes sense only when used in combination with the CUR-
LOPT_SSL_VERIFYPEER option. If CURLOPT_SSL_VERIFYPEER is zero, CURLOPT_CAINFO need not even
indicate an accessible file.
Note that option is by default set to the system path where libcurl's cacert bundle is assumed
to be stored, as established at build time.
When built against NSS this is the directory that the NSS certificate database resides in.
CURLOPT_CAPATH
Pass a char * to a zero terminated string naming a directory holding multiple CA certificates
to verify the peer with. The certificate 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 accessi-
ble path. The CURLOPT_CAPATH function apparently does not work in Windows due to some limita-
tion in openssl. This option is OpenSSL-specific and does nothing if libcurl is built to use
GnuTLS.
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 connec-
tion 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_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 an 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 con-
nect.
When the value is 1, the certificate must contain a Common Name field, but it doesn't matter
what name it says. (This is not ordinarily a useful setting).
When the value is 0, the connection succeeds regardless of the names in the certificate.
The default, since 7.10, is 2.
The checking this option controls is of the identity that the server claims. The server could
be lying. To control lying, see CURLOPT_SSL_VERIFYPEER.
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 acceptable 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 compile 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://directory.fedora.red-
hat.com/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. Note that while nothing ever
should get hurt by attempting to reuse SSL session-IDs, there seem to be broken SSL implemen-
tations in the wild that may require you to disable this in order for you to succeed. (Added
in 7.16.0)
CURLOPT_KRB4LEVEL
Pass a char * as parameter. Set the krb4 security level, this also enables krb4 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 Ker-
beros4. The Kerberos support only works for FTP.
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. Set CURLSSH_AUTH_ANY to let
libcurl pick one.
CURLOPT_SSH_PUBLIC_KEYFILE
Pass a char * pointing to a file name for your public key. If not used, libcurl defaults to
using ~/.ssh/id_dsa.pub.
CURLOPT_SSH_PRIVATE_KEYFILE
Pass a char * pointing to a file name for your private key. If not used, libcurl defaults to
using ~/.ssh/id_dsa. If the file is password-protected, set the password with CURLOPT_SSLKEY-
PASSWD.
OTHER OPTIONS
CURLOPT_PRIVATE
Pass a char * 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 handle 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 simultaneously, you MUST use the locking methods in
the share handle. See curl_share_setopt(3) for details.
TELNET OPTIONS
CURLOPT_TELNETOPTIONS
Provide a pointer to a curl_slist with variables to pass to the telnet negotiations. The vari-
ables 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 7.16.2 22 Feb 2007 curl_easy_setopt(3)
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