curl_easy_setopt
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 parame-
ter. That parameter can be a long, a function pointer or an object
pointer, all 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 dif-
ferent options, you must change them between the transfers.
NOTE: 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 differ-
ent 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
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 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 actu-
ally 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.
NOTE: 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 func-
tions 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
timeout options etc, without risking getting signals. (Added
in 7.10)
Consider building libcurl with ares support to enable asyn-
chronous 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 multiplied 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 func-
tion, it’ll signal an error to the library and it will abort
the transfer and return CURLE_WRITE_ERROR.
Set the stream argument with the CURLOPT_WRITEDATA option.
NOTE: you 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. Note that if
you specify the CURLOPT_WRITEFUNCTION, 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.
NOTE: If you’re using libcurl as a win32 DLL, you MUST use the
CURLOPT_WRITEFUNCTION if you set this option or you will expe-
rience 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 mem-
ory 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 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.
In libcurl 7.12.1 and later, the read callback may return
CURL_READFUNC_ABORT to stop the current operation at once, with
a CURLE_ABORTED_BY_CALLBACK error code from the transfer.
CURLOPT_READDATA
Data pointer to pass to the file read function. Note that if
you specify the CURLOPT_READFUNCTION, this is the pointer
you’ll get as input. If you don’t specify a read callback, this
must be a valid FILE *.
NOTE: 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_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 data transfer. Unknown/unused argument values
will be set to zero (like if you only download data, the upload
size will remain 0). Returning a non-zero value from this call-
back will cause libcurl to abort the transfer and return
CURLE_ABORTED_BY_CALLBACK.
Also note that 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 CUR-
LOPT_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
there is received header data that needs to be written down.
The headers are guaranteed to be written one-by-one and only
complete lines are written. Parsing headers should be easy
enough using this. The size of the data pointed to by ptr is
size multiplied with nmemb. The pointer named stream will be
the one you passed to libcurl with the CURLOPT_WRITEHEADER
option. Return the number of bytes actually written or return
-1 to signal error to the library (it will cause it to abort
the transfer with a CURLE_WRITE_ERROR return code).
CURLOPT_WRITEHEADER
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 CUR-
LOPT_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 mod-
ify 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 CUR-
LOPT_SSL_CTX_DATA option. This option was introduced in 7.11.0.
NOTE: 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, cer-
tificate 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)
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 the library. The buffer must be at least
CURL_ERROR_SIZE big.
Use CURLOPT_VERBOSE and CURLOPT_DEBUGFUNCTION to better
debug/trace why errors happen.
Note: 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 display-
ing 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 300. The default
action would be to return the page normally, ignoring that
code.
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_UNSUP-
PORTED_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.
NOTE: 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 accessibil-
ity.
CURLOPT_PROTOCOLS
Pass a long that holds a bitmask of CURLPROTO_* defines. If
used, this bitmask limits 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 transfers to
only be allowed to use a subset of them. By default libcurl
will accept all protocols it supports. See also CUR-
LOPT_REDIR_PROTOCOLS. (Added in 7.19.4)
CURLOPT_REDIR_PROTOCOLS
Pass a long that holds a bitmask of CURLPROTO_* defines. If
used, this bitmask limits what protocols libcurl may use in a
transfer that it follows to in a redirect when CURLOPT_FOL-
LOWLOCATION 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. 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 sepa-
rate option CURLOPT_PROXYPORT.
NOTE: when you tell the library to use an HTTP proxy, libcurl
will transparently convert operations to HTTP even if you spec-
ify an FTP URL etc. This may have an impact on what other fea-
tures 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_HTTP-
PROXYTUNNEL.
NOTE2: libcurl respects the environment variables http_proxy,
ftp_proxy, all_proxy etc, if any of those is set.
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. Avail-
able options for this are CURLPROXY_HTTP and CURLPROXY_SOCKS5,
with the HTTP one being 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. Note that 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_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 survive between easy handle cre-
ations 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 CUR-
LOPT_SHARE and curl_share_init(3).
CURLOPT_BUFFERSIZE
Pass a long specifying your preferred size 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)
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 net-
work).
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 conges-
tion 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.
Note: libcurl uses a user name (and supplied or prompted pass-
word) 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 informa-
tion in the URL is to be preferred. The file will be
scanned with the host and user name (to find the pass-
word only) or with the host only, to find the first user
name and password after that machine, which ever infor-
mation 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 infor-
mation 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 with the host only.
Only machine name, user name and password are taken into account (init
macros and similar things aren’t supported).
Note: 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 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]:[pass-
word] to use for the connection. Use CURLOPT_HTTPAUTH to decide
authentication method.
When using HTTP and CURLOPT_FOLLOWLOCATION, libcurl might per-
form 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]:[pass-
word] to use for the connection to the HTTP proxy. Use CUR-
LOPT_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. Note that for some methods, this will induce an extra net-
work round-trip. Set the actual name and password with the CUR-
LOPT_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 sup-
ported 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 authentica-
tion but may be also used along with another authentica-
tion methods. For more information see IETF draft draft-
brezak-spnego-http-04.txt.
NOTE that 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.
NOTE that you need to build libcurl with SSL support for
this option to work.
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. Note that for some methods, this will induce an extra net-
work round-trip. Set the actual name and password with the CUR-
LOPT_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 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 Con-
tent-Encoding: header is received. Three encodings are sup-
ported: 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.
NOTE: 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 fol-
low.
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. Note that this is meaningful only when
setting 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.
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.
NOTE: since 7.19.4, libcurl can limit to what protocols it will
automatically follow. The accepted protocols are set with CUR-
LOPT_REDIR_PROTOCOLS and it excludes the FILE protocol by
default.
This option is deprecated and starting with version 7.12.1 you
should instead use CURLOPT_UPLOAD.
CURLOPT_POST
A non-zero parameter tells the library to do a regular HTTP
post. This is a normal application/x-www-form-urlencoded kind,
which is the most commonly used one by HTML forms. See the CUR-
LOPT_POSTFIELDS option for how to specify the data to post and
CURLOPT_POSTFIELDSIZE in how to set the data size. Using the
CURLOPT_POSTFIELDS option implies this option.
CURLOPT_POSTFIELDS
Pass a char * as parameter, which should be the full data to
post in an HTTP post operation. You need to 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 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.
Note: 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 zero,
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 ver-
sion 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 HTTP post structs as parameter.
The linked list should be a fully valid list of ’struct Http-
Post’ structs properly filled in. The best and most elegant way
to do this, is to use curl_formadd(3) as documented. The data
in this list must remain intact until you close this curl han-
dle again with curl_easy_cleanup(3).
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 otherwise generated and used by libcurl inter-
nally, 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. 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 (usually containing a GET or POST)
is not a header and cannot be replaced using this option. Only
the lines following the request-line are headers.
Pass a NULL to this to reset back to no custom headers.
NOTE: The most commonly replaced headers have "shortcuts" in
the options CURLOPT_COOKIE, CURLOPT_USERAGENT and CURLOPT_REF-
ERER.
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.
NOTE: The alias itself is not parsed for any version strings.
So if your alias is "MYHTTP/9.9", Libcurl will not treat the
server as responding with HTTP version 9.9. Instead Libcurl
will use the value set by option CURLOPT_HTTP_VERSION.
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, this option will enable
cookies for this curl handle, making it understand and parse
received cookies and then use matching cookies in future
request.
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 cook-
ies for this session, so if you for example follow a location
it will make matching cookies get sent accordingly.
NOTE: 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 "ses-
sion". 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, inde-
pendent if they are session cookies are not. Session cookies
are cookies without expiry date and they are meant to be alive
and existing for this "session" only.
CURLOPT_HTTPGET
Pass a long. If the long is non-zero, this forces the HTTP
request to get back to GET. Only really usable if POST, PUT or
a custom request have been used previously using the same curl
handle.
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.
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 commands to pass to the
server prior to your ftp request. This will be done before any
other FTP commands are issued (even before the CWD command).
The linked list should be a fully valid list of to append
strings (commands) to the list, and clear the entire list
afterwards with curl_slist_free_all(3). Disable this operation
again by setting a NULL to this option.
CURLOPT_POSTQUOTE
Pass a pointer to a linked list of FTP 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 opera-
tion 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 opera-
tion again by setting a NULL to this option.
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 upload-
ing 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)
CURLOPT_FTP_USE_EPSV
Pass a long. If the value is non-zero, 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 FALSE (zero) to
this option, it will not try using EPSV, only plain PASV.
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)
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. Note that 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_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.
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 LDAP
transfers it gets the data in plain text instead of HTML and
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.
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 mul-
tiple intervals will cause the HTTP server to send the response
document in pieces (using standard MIME separation techniques).
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).
CURLOPT_RESUME_FROM_LARGE
Pass an curl_off_t as parameter. It contains the offset in num-
ber 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 listing.
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.
NOTE: 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 CUR-
LOPT_POSTFIELDS to set POST data. Use CURLOPT_HTTPHEADER to
replace or extend the set of headers sent by libcurl. Use CUR-
LOPT_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 opera-
tion. 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 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.
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_INFILE-
SIZE_LARGE.
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)
CURLOPT_UPLOAD
A non-zero parameter tells the library to prepare for an
upload. The CURLOPT_READDATA and CURLOPT_INFILESIZE_LARGE are
also interesting for uploads. If the protocol is HTTP, upload-
ing means using the PUT request unless you tell libcurl other-
wise.
CURLOPT_MAXFILESIZE
Pass a long as parameter. This allows you to specify the maxi-
mum 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.
NOTE: 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 con-
cerns 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)
NOTE: 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 con-
cerns both FTP and HTTP transfers.
CURLOPT_TIMECONDITION
Pass a long as parameter. This defines how the CUR-
LOPT_TIMEVALUE time value is treated. You can set this
parameter to CURL_TIMECOND_IFMODSINCE or CURL_TIMECOND_IFUN-
MODSINCE. This feature applies to HTTP and FTP.
NOTE: 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. Nor-
mally, 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.
NOTE: this is not recommended to use in unix multi-threaded
programs, as it uses signals unless CURLOPT_NOSIGNAL (see
above) is set.
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 CUR-
LOPT_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_MAXCONNECTS
Pass a long. The set number will be the persistent connection
cache size. The set amount will be the maximum amount of simul-
taneously open connections that libcurl may cache. Default is
5, and there isn’t much point in changing this value unless you
are perfectly 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 uses the CURLOPT_CLOSE-
POLICY to figure out which of the existing connections to close
to prevent the number of open connections to increase.
NOTE: if you already have performed transfers with this curl
handle, setting a smaller MAXCONNECTS than before may cause
open connections to get closed unnecessarily.
CURLOPT_CLOSEPOLICY
Pass a long. This option sets what policy libcurl should use
when the connection cache is filled and one of the open connec-
tions has to be closed to make room for a new connection. This
must be one of the CURLCLOSEPOLICY_* defines. Use CURLCLOSEPOL-
ICY_LEAST_RECENTLY_USED to make libcurl close the connection
that was least recently used, that connection is also least
likely to be capable of re-use. Use CURLCLOSEPOLICY_OLDEST to
make libcurl close the oldest connection, the one that was cre-
ated first among the ones in the connection cache. The other
close policies are not support yet.
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 caution and only if you under-
stand 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 explic-
itly 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 lim-
its 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.
NOTE: this is not recommended to use in unix multi-threaded
programs, as it uses signals unless CURLOPT_NOSIGNAL (see
above) is set.
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.
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.
CURLOPT_SSLCERTTYPE
Pass a pointer to a zero terminated string as parameter. The
string should be the format of your certificate. Supported for-
mats 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 CUR-
LOPT_SSLCERT certificate.
This option is replaced by CURLOPT_SSLKEYPASSWD and should only
be used for backward compatibility. You never needed a pass
phrase to load a certificate but you need one to load your pri-
vate 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 for-
mats are "PEM", "DER" and "ENG".
NOTE: 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_SSLKEYPASSWD
Pass a pointer to a zero terminated string as parameter. It
will be used as the password required to use the CURLOPT_SSLKEY
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.
NOTE: 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.
NOTE: If the crypto device cannot be set, CURLE_SSL_ENGINE_SET-
FAILED is returned.
CURLOPT_SSLVERSION
Pass a long as parameter. Set what version of SSL to attempt to
use, 2 or 3. By default, the SSL library will try to solve this
by itself although some servers make this difficult why you at
times may have to use this option.
CURLOPT_SSL_VERIFYPEER
Pass a long that is set to a zero value to stop curl from veri-
fying the peer’s certificate (7.10 starting setting this option
to non-zero by default). Alternate certificates to verify
against can be specified with the CURLOPT_CAINFO option or a
certificate directory can be specified with the CURLOPT_CAPATH
option. As of 7.10, curl installs a default bundle. CUR-
LOPT_SSL_VERIFYHOST may also need to be set to 1 or 0 if CUR-
LOPT_SSL_VERIFYPEER is disabled (it defaults to 2).
CURLOPT_CAINFO
Pass a char * to a zero terminated string naming a file holding
one or more certificates to verify the peer with. This only
makes sense when used in combination with the CURLOPT_SSL_VERI-
FYPEER option.
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 only makes sense when used in combina-
tion with the CURLOPT_SSL_VERIFYPEER option. The CURLOPT_CAPATH
function apparently does not work in Windows due to some limi-
tation in openssl. (Added in 7.9.8)
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. Set if we should verify the Common name from the
peer certificate in the SSL handshake, set 1 to check exis-
tence, 2 to ensure that it matches the provided hostname. This
is by default set to 2. (default changed in 7.10)
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. 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
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 kerberos4. The kerberos support only
works for FTP.
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_PRI-
VATE 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 variables should be in the format
<option=value>. libcurl supports the options ’TTYPE’, ’XDIS-
PLOC’ 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),
libcurl 7.11.1 12 Mar 2004 curl_easy_setopt(3)
