curl/docs/libcurl/curl_easy_setopt.3

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.TH curl_easy_setopt 3 "12 Mar 2004" "libcurl 7.11.1" "libcurl Manual"
.SH NAME
curl_easy_setopt - set options for a curl easy handle
.SH SYNOPSIS
#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLoption option, parameter);
.SH DESCRIPTION
curl_easy_setopt() is used to tell libcurl how to behave. By using the
appropriate options to \fIcurl_easy_setopt\fP, you can change libcurl's
behavior.  All options are set with the \fIoption\fP followed by a
\fIparameter\fP. 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 \fIhandle\fP.  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.

\fBNOTE:\fP 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 \fIcurl_easy_cleanup(3)\fP or
you set the same option again to use a different pointer.

The \fIhandle\fP is the return code from a \fIcurl_easy_init(3)\fP or
\fIcurl_easy_duphandle(3)\fP call.
.SH BEHAVIOR OPTIONS
.IP 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 \fICURLOPT_STDERR\fP.

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
\fICURLOPT_DEBUGFUNCTION\fP.
.IP 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).
.IP CURLOPT_NOPROGRESS
A non-zero parameter tells the library to shut off the built-in progress meter
completely.

\fBNOTE:\fP future versions of libcurl is likely to not have any built-in
progress meter at all.
.IP CURLOPT_NOSIGNAL
Pass a long. If it is non-zero, libcurl will not use any functions that
install signal handlers or any functions that cause signals to be sent to the
process. This option is mainly here to allow multi-threaded unix applications
to still set/use all timeout options etc, without 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.
.PP
.SH CALLBACK OPTIONS
.IP CURLOPT_WRITEFUNCTION
Function pointer that should match the following prototype: \fBsize_t
function( void *ptr, size_t size, size_t nmemb, void *stream);\fP 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 \fIptr\fP is \fIsize\fP
multiplied with \fInmemb\fP, 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 \fICURLE_WRITE_ERROR\fP.

Set the \fIstream\fP argument with the \fICURLOPT_WRITEDATA\fP option.

\fBNOTE:\fP 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.
.IP CURLOPT_WRITEDATA
Data pointer to pass to the file write function. Note that if you specify the
\fICURLOPT_WRITEFUNCTION\fP, 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.

\fBNOTE:\fP If you're using libcurl as a win32 DLL, you MUST use the
\fICURLOPT_WRITEFUNCTION\fP if you set this option or you will experience
crashes.

This option is also known with the older name \fICURLOPT_FILE\fP, the name
\fICURLOPT_WRITEDATA\fP was introduced in 7.9.7.
.IP CURLOPT_READFUNCTION
Function pointer that should match the following prototype: \fBsize_t
function( void *ptr, size_t size, size_t nmemb, void *stream);\fP 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 \fIptr\fP may be
filled with at most \fIsize\fP multiplied with \fInmemb\fP number of
bytes. Your function must return the actual number of bytes that you stored in
that memory area. Returning 0 will signal end-of-file to the library and cause
it to stop the current transfer.

If you stop the current transfer by returning 0 "pre-maturely" (i.e before the
server expected it, like when you've 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
\fICURL_READFUNC_ABORT\fP to stop the current operation at once, with a
\fICURLE_ABORTED_BY_CALLBACK\fP error code from the transfer.
.IP CURLOPT_READDATA
Data pointer to pass to the file read function. Note that if you specify the
\fICURLOPT_READFUNCTION\fP, this is the pointer you'll get as input. If you
don't specify a read callback, this must be a valid FILE *.

\fBNOTE:\fP If you're using libcurl as a win32 DLL, you MUST use a
\fICURLOPT_READFUNCTION\fP if you set this option.

This option is also known with the older name \fICURLOPT_INFILE\fP, the name
\fICURLOPT_READDATA\fP was introduced in 7.9.7.
.IP CURLOPT_PROGRESSFUNCTION
Function pointer that should match the \fIcurl_progress_callback\fP prototype
found in \fI<curl/curl.h>\fP. 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
callback will cause libcurl to abort the transfer and return
\fICURLE_ABORTED_BY_CALLBACK\fP.

Also note that \fICURLOPT_NOPROGRESS\fP must be set to FALSE to make this
function actually get called.
.IP CURLOPT_PROGRESSDATA
Pass a pointer that will be untouched by libcurl and passed as the first
argument in the progress callback set with \fICURLOPT_PROGRESSFUNCTION\fP.
.IP CURLOPT_HEADERFUNCTION
Function pointer that should match the following prototype: \fIsize_t
function( void *ptr, size_t size, size_t nmemb, void *stream);\fP. 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 \fIptr\fP is \fIsize\fP
multiplied with \fInmemb\fP.  The pointer named \fIstream\fP will be the one
you passed to libcurl with the \fICURLOPT_WRITEHEADER\fP 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 \fICURLE_WRITE_ERROR\fP return
code).
.IP 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 \fICURLOPT_HEADERFUNCTION\fP option above on how to
set a custom get-all-headers callback.
.IP CURLOPT_DEBUGFUNCTION
Function pointer that should match the following prototype: \fIint
curl_debug_callback (CURL *, curl_infotype, char *, size_t, void *);\fP
\fICURLOPT_DEBUGFUNCTION\fP replaces the standard debug function used when
\fICURLOPT_VERBOSE \fP is in effect. This callback receives debug information,
as specified with the \fBcurl_infotype\fP 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:
.RS
.IP CURLINFO_TEXT
The data is informational text.
.IP CURLINFO_HEADER_IN
The data is header (or header-like) data received from the peer.
.IP CURLINFO_HEADER_OUT
The data is header (or header-like) data sent to the peer.
.IP CURLINFO_DATA_IN
The data is protocol data received from the peer.
.IP CURLINFO_DATA_OUT
The data is protocol data sent to the peer.
.RE
.IP CURLOPT_DEBUGDATA
Pass a pointer to whatever you want passed in to your
\fICURLOPT_DEBUGFUNCTION\fP in the last void * argument. This pointer is not
used by libcurl, it is only passed to the callback.
.IP CURLOPT_SSL_CTX_FUNCTION
Function pointer that should match the following prototype: \fBCURLcode
sslctxfun(CURL *curl, void *sslctx, void *parm);\fP 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
\fIsslctx\fP parameter is actually a pointer to an openssl \fISSL_CTX\fP. 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 \fIparm\fP argument with the \fICURLOPT_SSL_CTX_DATA\fP option. This
option was introduced in 7.11.0.

\fBNOTE:\fP 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.
.IP CURLOPT_SSL_CTX_DATA
Data pointer to pass to the ssl context callback set by the option
\fICURLOPT_SSL_CTX_FUNCTION\fP, this is the pointer you'll get as third
parameter, otherwise \fBNULL\fP. (Added in 7.11.0)
.SH ERROR OPTIONS
.IP 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 \fICURLOPT_VERBOSE\fP and \fICURLOPT_DEBUGFUNCTION\fP to better
debug/trace why errors happen.

\fBNote:\fP if the library does not return an error, the buffer may not have
been touched. Do not rely on the contents in those cases.
.IP CURLOPT_STDERR
Pass a FILE * as parameter. Tell libcurl to use this stream instead of stderr
when showing the progress meter and displaying \fICURLOPT_VERBOSE\fP data.
.IP 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.
.SH NETWORK OPTIONS
.IP 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
(\fICURLE_UNSUPPORTED_PROTOCOL\fP) when you call \fIcurl_easy_perform(3)\fP or
\fIcurl_multi_perform(3)\fP. Use \fIcurl_version_info(3)\fP for detailed info
on which protocols that are supported.

\fBNOTE:\fP \fICURLOPT_URL\fP is the only option that must be set before
\fIcurl_easy_perform(3)\fP is called.
.IP 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
\fICURLOPT_PROXYPORT\fP.

\fBNOTE:\fP 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 \fICURLOPT_QUOTE\fP and similar FTP specifics that don't work
unless you tunnel through the HTTP proxy. Such tunneling is activated with
\fICURLOPT_HTTPPROXYTUNNEL\fP.

\fBNOTE2:\fP libcurl respects the environment variables \fBhttp_proxy\fP,
\fBftp_proxy\fP, \fBall_proxy\fP etc, if any of those is set.
.IP CURLOPT_PROXYPORT
Pass a long with this option to set the proxy port to connect to unless it is
specified in the proxy string \fICURLOPT_PROXY\fP.
.IP CURLOPT_PROXYTYPE
Pass a long with this option to set type of the proxy. Available options for
this are \fICURLPROXY_HTTP\fP and \fICURLPROXY_SOCKS5\fP, with the HTTP one
being default. (Added in 7.10)
.IP 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.
.IP 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.
.IP 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.
.IP 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 creations and deletions. This is not
thread-safe and this will use a global variable.

\fBWARNING:\fP this option is considered obsolete. Stop using it. Switch over
to using the share interface instead! See \fICURLOPT_SHARE\fP and
\fIcurl_share_init(3)\fP.
.IP 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)
.IP 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.
.IP 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.
.SH NAMES and PASSWORDS OPTIONS (Authentication)
.IP CURLOPT_NETRC
This parameter controls the preference of libcurl between using user names and
passwords from your \fI~/.netrc\fP file, relative to user names and passwords
in the URL supplied with \fICURLOPT_URL\fP.

\fBNote:\fP libcurl uses a user name (and supplied or prompted password)
supplied with \fICURLOPT_USERPWD\fP in preference to any of the options
controlled by this parameter.

Pass a long, set to one of the values described below.
.RS
.IP CURL_NETRC_OPTIONAL
The use of your \fI~/.netrc\fP file is optional,
and information in the URL is to be preferred.  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 \fImachine\fP,
which ever information is not specified in the URL.

Undefined values of the option will have this effect.
.IP CURL_NETRC_IGNORED
The library will ignore the file and use only the information in the URL.

This is the default.
.IP 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.
.RE
Only machine name, user name and password are taken into account
(init macros and similar things aren't supported).

\fBNote:\fP 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.
.IP 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 \fICURLOPT_NETRC\fP is set, libcurl will attempt to
find the a .netrc file in the current user's home directory. (Added in 7.10.9)
.IP CURLOPT_USERPWD
Pass a char * as parameter, which should be [user name]:[password] to use for
the connection. Use \fICURLOPT_HTTPAUTH\fP to decide authentication method.

When using HTTP and \fICURLOPT_FOLLOWLOCATION\fP, 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
\fICURLOPT_UNRESTRICTED_AUTH\fP 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.
.IP CURLOPT_PROXYUSERPWD
Pass a char * as parameter, which should be [user name]:[password] to use for
the connection to the HTTP proxy.  Use \fICURLOPT_PROXYAUTH\fP to decide
authentication method.
.IP 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 network
round-trip. Set the actual name and password with the \fICURLOPT_USERPWD\fP
option. (Added in 7.10.6)
.RS
.IP 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.
.IP 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.
.IP 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.

\fBNOTE\fP that you need to build libcurl with a suitable GSS-API library for
this to work.
.IP 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.

\fBNOTE\fP that you need to build libcurl with SSL support for this option to
work.
.IP 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.
.IP 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.
.RE
.IP 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 network
round-trip. Set the actual name and password with the
\fICURLOPT_PROXYUSERPWD\fP option. The bitmask can be constructed by or'ing
together the bits listed above for the \fICURLOPT_HTTPAUTH\fP option. As of
this writing, only Basic and NTLM work. (Added in 7.10.7)
.SH HTTP OPTIONS
.IP 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.
.IP 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: \fIidentity\fP,
which does nothing, \fIdeflate\fP which requests the server to
compress its response using the zlib algorithm, and \fIgzip\fP 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.
.IP CURLOPT_FOLLOWLOCATION
A non-zero parameter tells the library to follow any Location: header that the
server sends as part of an HTTP header.

\fBNOTE:\fP 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. \fICURLOPT_MAXREDIRS\fP can be used to limit the number
of redirects libcurl will follow.
.IP 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 \fICURLOPT_FOLLOWLOCATION\fP.
.IP 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
(\fICURLE_TOO_MANY_REDIRECTS\fP). This option only makes sense if the
\fICURLOPT_FOLLOWLOCATION\fP is used at the same time.
.IP CURLOPT_PUT
A non-zero parameter tells the library to use HTTP PUT to transfer data. The
data should be set with \fICURLOPT_READDATA\fP and \fICURLOPT_INFILESIZE\fP.

This option is deprecated and starting with version 7.12.1 you should instead
use \fICURLOPT_UPLOAD\fP.
.IP 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 \fICURLOPT_POSTFIELDS\fP option for how to specify
the data to post and \fICURLOPT_POSTFIELDSIZE\fP in how to set the data
size. Using the \fICURLOPT_POSTFIELDS\fP option implies this option.
.IP 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 \fICURLOPT_POST\fP. Using
\fICURLOPT_POSTFIELDS\fP implies \fICURLOPT_POST\fP.

\fBNote:\fP to make multipart/formdata posts (aka rfc1867-posts), check out
the \fICURLOPT_HTTPPOST\fP option.
.IP 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.
.IP CURLOPT_POSTFIELDSIZE_LARGE
Pass a curl_off_t as parameter. Use this to set the size of the
\fICURLOPT_POSTFIELDS\fP data to prevent libcurl from doing strlen() on the
data to figure out the size. This is the large file version of the
\fICURLOPT_POSTFIELDSIZE\fP option. (Added in 7.11.1)
.IP 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 HttpPost' structs properly filled in. The best and most
elegant way to do this, is to use \fIcurl_formadd(3)\fP as documented. The
data in this list must remain intact until you close this curl handle again
with \fIcurl_easy_cleanup(3)\fP.
.IP 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 \fICURLOPT_HTTPHEADER\fP.
.IP 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 \fICURLOPT_HTTPHEADER\fP.
.IP 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 \fBstruct
curl_slist\fP structs properly filled in. Use \fIcurl_slist_append(3)\fP to
create the list and \fIcurl_slist_free_all(3)\fP 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. 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.

\fBNOTE:\fP The most commonly replaced headers have "shortcuts" in the options
\fICURLOPT_COOKIE\fP, \fICURLOPT_USERAGENT\fP and \fICURLOPT_REFERER\fP.
.IP 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 \fIcurl_slist_append(3)\fP to create the list and
\fIcurl_slist_free_all(3)\fP to clean up an entire list.

\fBNOTE:\fP 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
\fICURLOPT_HTTP_VERSION\fP.
.IP 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.
.IP 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.
.IP CURLOPT_COOKIEJAR
Pass a file name as char *, zero terminated. This will make libcurl write all
internally known cookies to the specified file when \fIcurl_easy_cleanup(3)\fP
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.

\fBNOTE:\fP If the cookie jar file can't be created or written to (when the
\fIcurl_easy_cleanup(3)\fP is called), libcurl will not and cannot report an
error for this. Using \fICURLOPT_VERBOSE\fP or \fICURLOPT_DEBUGFUNCTION\fP
will get a warning to display, but that is the only visible feedback you get
about this possibly lethal situation.
.IP 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 cookies are not. Session
cookies are cookies without expiry date and they are meant to be alive and
existing for this "session" only.
.IP 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.
.IP 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.
.RS
.IP CURL_HTTP_VERSION_NONE
We don't care about what version the library uses. libcurl will use whatever
it thinks fit.
.IP CURL_HTTP_VERSION_1_0
Enforce HTTP 1.0 requests.
.IP CURL_HTTP_VERSION_1_1
Enforce HTTP 1.1 requests.
.RE
.SH FTP OPTIONS
.IP 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.
.IP 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
'struct curl_slist' structs properly filled in. Use \fIcurl_slist_append(3)\fP
to append strings (commands) to the list, and clear the entire list afterwards
with \fIcurl_slist_free_all(3)\fP. Disable this operation again by setting a
NULL to this option.
.IP 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
\fICURLOPT_QUOTE\fP. Disable this operation again by setting a NULL to this
option.
.IP 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
\fICURLOPT_QUOTE\fP. Disable this operation again by setting a NULL to this
option.
.IP 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.
.IP 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.
.IP 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
\fICURLOPT_FTPPORT\fP). 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)
.IP 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.
.IP 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)
.IP 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 \fICURLOPT_TIMEOUT\fP. It
is recommended that if used in conjunction with \fICURLOPT_TIMEOUT\fP, you set
\fICURLOPT_FTP_RESPONSE_TIMEOUT\fP to a value smaller than
\fICURLOPT_TIMEOUT\fP.  (Added in 7.10.8)
.IP 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)
.RS
.IP CURLFTPSSL_NONE
Don't attempt to use SSL.
.IP CURLFTPSSL_TRY
Try using SSL, proceed as normal otherwise.
.IP CURLFTPSSL_CONTROL
Require SSL for the control connection or fail with \fICURLE_FTP_SSL_FAILED\fP.
.IP CURLFTPSSL_ALL
Require SSL for all communication or fail with \fICURLE_FTP_SSL_FAILED\fP.
.RE
.SH PROTOCOL OPTIONS
.IP 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.
.IP CURLOPT_CRLF
Convert Unix newlines to CRLF newlines on transfers.
.IP 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
\fI"X-Y,N-M"\fP. Using this kind of multiple 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.
.IP 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).
.IP CURLOPT_RESUME_FROM_LARGE
Pass an 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)
.IP 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.

\fBNOTE:\fP 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 \fICURLOPT_POST\fP
and \fICURLOPT_POSTFIELDS\fP to set POST data. Use \fICURLOPT_HTTPHEADER\fP to
replace or extend the set of headers sent by libcurl. Use
\fICURLOPT_HTTP_VERSION\fP to change HTTP version.
.IP 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
\fIcurl_easy_getinfo(3)\fP function with the \fICURLINFO_FILETIME\fP argument
can be used after a transfer to extract the received time (if any).
.IP 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.
.IP 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 \fICURLOPT_INFILESIZE_LARGE\fP.
.IP 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)
.IP CURLOPT_UPLOAD
A non-zero parameter tells the library to prepare for an upload. The
\fICURLOPT_READDATA\fP and \fICURLOPT_INFILESIZE_LARGE\fP are also interesting
for uploads. If the protocol is HTTP, uploading means using the PUT request
unless you tell libcurl otherwise.
.IP 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.

\fBNOTE:\fP 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.
.IP 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 \fICURLE_FILESIZE_EXCEEDED\fP will be
returned. (Added in 7.11.0)

\fBNOTE:\fP 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.
.IP CURLOPT_TIMECONDITION
Pass a long as parameter. This defines how the \fICURLOPT_TIMEVALUE\fP time
value is treated. You can set this parameter to \fICURL_TIMECOND_IFMODSINCE\fP
or \fICURL_TIMECOND_IFUNMODSINCE\fP. This feature applies to HTTP and FTP.

\fBNOTE:\fP 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.
.IP 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
\fICURLOPT_TIMECONDITION\fP.
.SH CONNECTION OPTIONS
.IP 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.

\fBNOTE:\fP this is not recommended to use in unix multi-threaded programs, as
it uses signals unless \fICURLOPT_NOSIGNAL\fP (see above) is set.
.IP 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 \fICURLOPT_LOW_SPEED_TIME\fP seconds
for the library to consider it too slow and abort.
.IP CURLOPT_LOW_SPEED_TIME
Pass a long as parameter. It contains the time in seconds that the transfer
should be below the \fICURLOPT_LOW_SPEED_LIMIT\fP for the library to consider
it too slow and abort.
.IP 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. 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 \fICURLOPT_CLOSEPOLICY\fP to
figure out which of the existing connections to close to prevent the number of
open connections to increase.

\fBNOTE:\fP if you already have performed transfers with this curl handle,
setting a smaller MAXCONNECTS than before may cause open connections to get
closed unnecessarily.
.IP CURLOPT_CLOSEPOLICY
Pass a long. This option sets what policy libcurl should use when the
connection cache is filled and one of the open connections has to be closed to
make room for a new connection. This must be one of the CURLCLOSEPOLICY_*
defines. Use \fICURLCLOSEPOLICY_LEAST_RECENTLY_USED\fP to make libcurl close
the connection that was least recently used, that connection is also least
likely to be capable of re-use. Use \fICURLCLOSEPOLICY_OLDEST\fP to make
libcurl close the oldest connection, the one that was created first among the
ones in the connection cache. The other close policies are not support
yet.
.IP 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
understand what it does. Set this to 0 to have libcurl attempt re-using an
existing connection (default behavior).
.IP 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).
.IP 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 \fICURLOPT_TIMEOUT\fP option.

\fBNOTE:\fP this is not recommended to use in unix multi-threaded programs, as
it uses signals unless \fICURLOPT_NOSIGNAL\fP (see above) is set.
.IP 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:
.RS
.IP CURL_IPRESOLVE_WHATEVER
Default, resolves addresses to all IP versions that your system allows.
.IP CURL_IPRESOLVE_V4
Resolve to ipv4 addresses.
.IP CURL_IPRESOLVE_V6
Resolve to ipv6 addresses.
.RE
.SH SSL and SECURITY OPTIONS
.IP 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 \fICURLOPT_SSLCERTTYPE\fP.
.IP 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)
.IP CURLOPT_SSLCERTPASSWD
Pass a pointer to a zero terminated string as parameter. It will be used as
the password required to use the \fICURLOPT_SSLCERT\fP certificate.

This option is replaced by \fICURLOPT_SSLKEYPASSWD\fP 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 private key.
.IP 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 \fICURLOPT_SSLKEYTYPE\fP.
.IP 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".

\fBNOTE:\fP The format "ENG" enables you to load the private key from a crypto
engine. In this case \fICURLOPT_SSLKEY\fP is used as an identifier passed to
the engine. You have to set the crypto engine with \fICURLOPT_SSLENGINE\fP.
\&"DER" format key file currently does not work because of a bug in OpenSSL.
.IP CURLOPT_SSLKEYPASSWD
Pass a pointer to a zero terminated string as parameter. It will be used as
the password required to use the \fICURLOPT_SSLKEY\fP private key.
.IP 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.

\fBNOTE:\fP If the crypto device cannot be loaded,
\fICURLE_SSL_ENGINE_NOTFOUND\fP is returned.
.IP CURLOPT_SSLENGINE_DEFAULT
Sets the actual crypto engine as the default for (asymmetric) crypto
operations.

\fBNOTE:\fP If the crypto device cannot be set,
\fICURLE_SSL_ENGINE_SETFAILED\fP is returned.
.IP 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.
.IP CURLOPT_SSL_VERIFYPEER
Pass a long that is set to a zero value to stop curl from verifying 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
\fICURLOPT_CAINFO\fP option or a certificate directory can be specified with
the \fICURLOPT_CAPATH\fP option.  As of 7.10, curl installs a default bundle.
\fICURLOPT_SSL_VERIFYHOST\fP may also need to be set to 1 or 0 if
\fICURLOPT_SSL_VERIFYPEER\fP is disabled (it defaults to 2).
.IP 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 \fICURLOPT_SSL_VERIFYPEER\fP option.
.IP 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 combination with the \fICURLOPT_SSL_VERIFYPEER\fP option. The
\fICURLOPT_CAPATH\fP function apparently does not work in Windows due to some
limitation in openssl. (Added in 7.9.8)
.IP CURLOPT_RANDOM_FILE
Pass a char * to a zero terminated file name. The file will be used to read
from to seed the random engine for SSL. The more random the specified file is,
the more secure the SSL connection will become.
.IP 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.
.IP 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 existence, 2 to ensure that it matches
the provided hostname. This is by default set to 2. (default changed in 7.10)
.IP 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. 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:
\fIhttp://www.openssl.org/docs/apps/ciphers.html\fP
.IP 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.
.SH OTHER OPTIONS
.IP 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
\fIcurl_easy_getinfo(3)\fP with the CURLINFO_PRIVATE option. libcurl itself
does nothing with this data. (Added in 7.10.3)
.IP CURLOPT_SHARE
Pass a share handle as a parameter. The share handle must have been created by
a previous call to \fIcurl_share_init(3)\fP. 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 \fBMUST\fP use the locking methods in the
share handle. See \fIcurl_share_setopt(3)\fP for details.
.SH TELNET OPTIONS
.IP 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', 'XDISPLOC' and 'NEW_ENV'. See the TELNET
standard for details.
.SH RETURN VALUE
CURLE_OK (zero) means that the option was set properly, non-zero means an
error occurred as \fI<curl/curl.h>\fP defines. See the \fIlibcurl-errors(3)\fP
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 \fICURLE_FAILED_INIT\fP.
.SH "SEE ALSO"
.BR curl_easy_init "(3), " curl_easy_cleanup "(3), "