curl/docs/libcurl/curl_easy_setopt.3

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.TH curl_easy_setopt 3 "27 Oct 2005" "libcurl 7.14.2" "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 \fBlong\fP, a \fBfunction pointer\fP,
an \fBobject pointer\fP or a \fBcurl_off_t\fP, 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. You can optionally reset all
options back to internal default with \fIcurl_easy_reset(3)\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.

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.

This function may be called with zero bytes data if the transfered file is
empty.

Set this option to NULL to get the internal default function. The internal
default function will write the data to the FILE * given with
\fICURLOPT_WRITEDATA\fP.

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

The callback function will be passed as much data as possible in all invokes,
but you cannot possibly make any assumptions. It may be one byte, it may be
thousands. The maximum amount of data that can be passed to the write callback
is defined in the curl.h header file: CURL_MAX_WRITE_SIZE.
.IP CURLOPT_WRITEDATA
Data pointer to pass to the file write function. If you use the
\fICURLOPT_WRITEFUNCTION\fP option, this is the pointer you'll get as
input. If you don't use a callback, you must pass a 'FILE *' as libcurl will
pass this to fwrite() when writing data.

The internal \fICURLOPT_WRITEFUNCTION\fP will write the data to the FILE *
given with this option, or to stdout if this option hasn't been set.

If you're using libcurl as a win32 DLL, you \fBMUST\fP 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.

The read callback may return \fICURL_READFUNC_ABORT\fP to stop the current
operation immediately, resulting in a \fICURLE_ABORTED_BY_CALLBACK\fP error
code from the transfer (Added in 7.12.1)

If you set the callback pointer to NULL, or doesn't set it at all, the default
internal read function will be used. It is simply doing an fread() on the FILE
* stream set with \fICURLOPT_READDATA\fP.
.IP CURLOPT_READDATA
Data pointer to pass to the file read function. If you use the
\fICURLOPT_READFUNCTION\fP option, this is the pointer you'll get as input. If
you don't specify a read callback but instead rely on the default internal
read function, this data must be a valid readable FILE *.

If you're using libcurl as a win32 DLL, you MUST use a
\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_IOCTLFUNCTION
Function pointer that should match the \fIcurl_ioctl_callback\fP prototype
found in \fI<curl/curl.h>\fP. This function gets called by libcurl when
something special I/O-related needs to be done that the library can't do by
itself. For now, rewinding the read data stream is the only action it can
request. The rewinding of the read data stream may be necessary when doing a
HTTP PUT or POST with a multi-pass authentication method.  (Opion added in
7.12.3)
.IP CURLOPT_IOCTLDATA
Pass a pointer that will be untouched by libcurl and passed as the 3rd
argument in the ioctl callback set with \fICURLOPT_IOCTLFUNCTION\fP.  (Option
added in 7.12.3)
.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 (roughly
once per second).  Unknown/unused argument values pass to the callback will be
set to zero (like if you only download data, the upload size will remain
0). Returning a non-zero value from this callback will cause libcurl to abort
the transfer and return \fICURLE_ABORTED_BY_CALLBACK\fP.

If you transfer data with the multi interface, this function will not be
called during periods of idleness unless you call the appropriate libcurl
function that performs transfers. Usage of the \fBCURLOPT_PROGRESSFUNCTION\fP
callback is not recommended when using the multi interface.

\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 it has received header data. The
header callback will be called once for each header and only complete header
lines are passed on to the callback. Parsing headers should be easy enough
using this. The size of the data pointed to by \fIptr\fP is \fIsize\fP
multiplied with \fInmemb\fP. Do not assume that the header line is zero
terminated! The pointer named \fIstream\fP is the one you set with the
\fICURLOPT_WRITEHEADER\fP option. The callback function must return the number
of bytes actually taken care of, or return -1 to signal error to the library
(it will cause it to abort the transfer with a \fICURLE_WRITE_ERROR\fP return
code).

Since 7.14.1: When a server sends a chunked encoded transfer, it may contain a
trailer. That trailer is identical to a HTTP header and if such a trailer is
received it is passed to the application using this callback as well. There
are several ways to detect it being a trailer and not an ordinary header: 1)
it comes after the response-body. 2) it comes after the final header line (CR
LF) 3) a Trailer: header among the response-headers mention what header to
expect in the trailer.
.IP CURLOPT_WRITEHEADER
(This option is also known as \fBCURLOPT_HEADERDATA\fP) 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.

This function will get called on all new connections made to a server, during
the SSL negotiation. The SSL_CTX pointer will be a new one every time.

To use this properly, a non-trivial amount of knowledge of the openssl
libraries is necessary. 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
\fIcurl_easy_perform\fP. 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.

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 400. 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.

\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.

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.

libcurl respects the environment variables \fBhttp_proxy\fP, \fBftp_proxy\fP,
\fBall_proxy\fP etc, if any of those is set. The \fICURLOPT_PROXY\fP option
does however override any possibly set environment variables.

Starting with 7.14.1, the proxy host string can be specified the exact same
way as the proxy environment variables, include protocol prefix (http://) and
embedded user + password.
.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. 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 (in bytes) for the receive buffer
in libcurl.  The main point of this would be that the write callback gets
called more often and with smaller chunks. This is just treated as a request,
not an order. You cannot be guaranteed to actually get the given size. (Added
in 7.10)

This size is by default set as big as possible (CURL_MAX_WRITE_SIZE), so it
only makse sense to use this option if you want it smaller.
.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.

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).

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 NTLM, you can set domain by prepending it to the user name and
separating the domain and name with a forward (/) or backward slash (\\). Like
this: "domain/user:password" or "domain\\user:password". Some HTTP servers (on
Windows) support this style even for Basic authentication.

When using HTTP and \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. 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.

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.

You need to build libcurl with OpenSSL support for this option to work, or
build libcurl on Windows.
.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. 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, Digest 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.

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. This
option 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. Added in 7.15.1:
Setting the limit to 0 will make libcurl refuse any redirect. Set it to -1 for
an infinite number of redirects (which is the default)
.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 will
also make the library use the a "Content-Type:
application/x-www-form-urlencoded" header. (This is by far the most commonly
used POST method).

Use the \fICURLOPT_POSTFIELDS\fP option to specify what data to post and
\fICURLOPT_POSTFIELDSIZE\fP to set the data size.

Optionally, you can provide data to POST using the \fICURLOPT_READFUNCTION\fP
and \fICURLOPT_READDATA\fP options but then you must make sure to not set
\fICURLOPT_POSTFIELDS\fP to anything but NULL. When providing data with a
callback, you must transmit it using chunked transfer-encoding or you must set
the size of the data with the \fICURLOPT_POSTFIELDSIZE\fP option.

You can override the default POST Content-Type: header by setting your own
with \fICURLOPT_HTTPHEADER\fP.

Using POST with HTTP 1.1 implies the use of a "Expect: 100-continue" header.
You can disable this header with \fICURLOPT_HTTPHEADER\fP as usual.

If you use POST to a HTTP 1.1 server, you can send data without knowing the
size before starting the POST if you use chunked encoding. You enable this by
adding a header like "Transfer-Encoding: chunked" with
\fICURLOPT_HTTPHEADER\fP. With HTTP 1.0 or without chunked transfer, you must
specify the size in the request.

When setting \fICURLOPT_POST\fP to a non-zero value, it will automatically set
\fICURLOPT_NOBODY\fP to 0 (since 7.14.1).

If you issue a POST request and then want to make a HEAD or GET using the same
re-used handle, you must explictly set the new request type using
\fICURLOPT_NOBODY\fP or \fICURLOPT_HTTPGET\fP or similar.
.IP CURLOPT_POSTFIELDS
Pass a char * as parameter, which should be the full data to post in an HTTP
POST operation. You must make sure that the data is formatted the way you want
the server to receive it. libcurl will not convert or encode it for you. Most
web servers will assume this data to be url-encoded. Take note.

This POST is a normal application/x-www-form-urlencoded kind (and libcurl will
set that 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.

Using POST with HTTP 1.1 implies the use of a "Expect: 100-continue" header.
You can disable this header with \fICURLOPT_HTTPHEADER\fP as usual.

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 -1, 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 curl_httppost structs as parameter. . The easiest way to create such a
list, 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.

Using POST with HTTP 1.1 implies the use of a "Expect: 100-continue" header.
You can disable this header with \fICURLOPT_HTTPHEADER\fP as usual.

When setting \fICURLOPT_HTTPPOST\fP, it will automatically set
\fICURLOPT_NOBODY\fP to 0 (since 7.14.1).
.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.

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.

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 or by passing the empty string (""), this
option will enable cookies for this curl handle, making it understand and
parse received cookies and then use matching cookies in future request.

If you use this option multiple times, you just add more files to read.
Subsequent files will add more cookies.
.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.

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_COOKIELIST
Pass a char * to a cookie string. Cookie can be either in Netscape / Mozilla
format or just regular HTTP-style header (Set-Cookie: ...) format. If cURL
cookie engine was not enabled it will enable its cookie engine.  Passing a
magic string \&"ALL" will erase all cookies known by cURL. (Added in 7.14.1)
.IP CURLOPT_HTTPGET
Pass a long. If the long is non-zero, this forces the HTTP request to get back
to GET. usable if a POST, HEAD, PUT or a custom request have been used
previously using the same curl handle.

When setting \fICURLOPT_HTTPGET\fP to a non-zero value, it will automatically
set \fICURLOPT_NOBODY\fP to 0 (since 7.14.1).
.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.
.IP CURLOPT_IGNORE_CONTENT_LENGTH
Ignore the Content-Length header. This is useful for Apache 1.x (and similar
servers) which will report incorrect content length for files over 2
gigabytes. If this option is used, curl will not be able to accurately report
progress, and will simply stop the download when the server ends the
connection. (added in 7.14.1)
.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)

If the server is an IPv6 host, this option will have no effect as of 7.12.3.
.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.

If the server is an IPv6 host, this option will have no effect as of 7.12.3.
.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.  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_SKIP_PASV_IP
Pass a long. If set to a non-zero value, it instructs libcurl to not use the
IP address the server suggests in its 227-response to libcurl's PASV command
when libcurl connects the data connection. Instead libcurl will re-use the
same IP address it already uses for the control connection. But it will use
the port number from the 227-response. (Added in 7.14.2)

This option has no effect if PORT, EPRT or EPSV is used instead of PASV.
.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
.IP CURLOPT_FTPSSLAUTH
Pass a long using one of the values from below, to alter how libcurl issues
\&"AUTH TLS" or "AUTH SSL" when FTP over SSL is activated (see
\fICURLOPT_FTP_SSL\fP). (Added in 7.12.2)
.RS
.IP CURLFTPAUTH_DEFAULT
Allow libcurl to decide
.IP CURLFTPAUTH_SSL
Try "AUTH SSL" first, and only if that fails try "AUTH TLS"
.IP CURLFTPAUTH_TLS
Try "AUTH TLS" first, and only if that fails try "AUTH SSL"
.RE
.IP CURLOPT_SOURCE_URL
When set, it enables a FTP third party transfer, using the set URL as source,
while \fICURLOPT_URL\fP is the target.
.IP CURLOPT_SOURCE_USERPWD
Set "username:password" to use for the source connection when doing FTP third
party transfers.
.IP CURLOPT_SOURCE_QUOTE
Exactly like \fICURLOPT_QUOTE\fP, but for the source host.
.IP CURLOPT_SOURCE_PREQUOTE
Exactly like \fICURLOPT_PREQUOTE\fP, but for the source host.
.IP CURLOPT_SOURCE_POSTQUOTE
Exactly like \fICURLOPT_POSTQUOTE\fP, but for the source host.
.IP CURLOPT_FTP_ACCOUNT
Pass a pointer to a zero-terminated string (or NULL to disable). When an FTP
server asks for "account data" after user name and password has been provided,
this data is sent off using the ACCT command. (Added in 7.13.0)
.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 win32 systems it does not set the
stdout to binary mode. This option can be usable when transferring text data
between systems with different views on certain characters, such as newlines
or similar.

libcurl does not do a complete ASCII conversion when doing ASCII transfers
over FTP. This is a known limitation/flaw that nobody has rectified. libcurl
simply sets the mode to ascii and performs a standard transfer.
.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 a curl_off_t as parameter. It contains the offset in number of bytes that
you want the transfer to start from. (Added in 7.11.0)
.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.

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.

To change request to GET, you should use \fICURLOPT_HTTPGET\fP. Change request
to POST with \fICURLOPT_POST\fP etc.
.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_INFILESIZEE\fP or
\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.

Using PUT with HTTP 1.1 implies the use of a "Expect: 100-continue" header.
You can disable this header with \fICURLOPT_HTTPHEADER\fP as usual.

If you use PUT to a HTTP 1.1 server, you can upload data without knowing the
size before starting the transfer if you use chunked encoding. You enable this
by adding a header like "Transfer-Encoding: chunked" with
\fICURLOPT_HTTPHEADER\fP. With HTTP 1.0 or without chunked transfer, you must
specify the size.
.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.

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)

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.

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.

In unix-like systems, this might cause signals to be used unless
\fICURLOPT_NOSIGNAL\fP 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.

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.

In unix-like systems, this might cause signals to be used unless
\fICURLOPT_NOSIGNAL\fP 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".

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.

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.

If the crypto device cannot be set, \fICURLE_SSL_ENGINE_SETFAILED\fP is
returned.
.IP CURLOPT_SSLVERSION
Pass a long as parameter to control what version of SSL/TLS to attempt to use.
The available options are:
.RS
.IP CURL_SSLVERSION_DEFAULT
The default action. When libcurl built with OpenSSL, this will attempt to
figure out the remote SSL protocol version. Unfortunately there are a lot of
ancient and broken servers in use which cannot handle this technique and will
fail to connect. When libcurl is built with GnuTLS, this will mean SSLv3.
.IP CURL_SSLVERSION_TLSv1
Force TLSv1
.IP CURL_SSLVERSION_SSLv2
Force SSLv2
.IP CURL_SSLVERSION_SSLv3
Force SSLv3
.RE
.IP CURLOPT_SSL_VERIFYPEER
Pass a long as parameter.

This option determines whether curl verifies the authenticity of the
peer's certificate.  A nonzero value means curl verifies; zero means it
doesn't.  The default is nonzero, but before 7.10, it was zero.

When negotiating an SSL connection, the server sends a certificate
indicating its identity.  Curl verifies whether the certificate is
authentic, i.e. that you can trust that the server is who the
certificate says it is.  This trust is based on a chain of digital
signatures, rooted in certification authority (CA) certificates you
supply.  As of 7.10, curl installs a default bundle of CA certificates
and you can specify alternate certificates with the
\fICURLOPT_CAINFO\fP option or the \fICURLOPT_CAPATH\fP option.

When \fICURLOPT_SSL_VERIFYPEER\fP is nonzero, and the verification
fails to prove that the certificate is authentic, the connection
fails.  When the option is zero, the connection succeeds regardless.

Authenticating the certificate is not by itself very useful.  You
typically want to ensure that the server, as authentically identified
by its certificate, is the server you mean to be talking to.  Use
\fICURLOPT_SSL_VERIFYHOST\fP to control that.
.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 makes sense only when used in
combination with the \fICURLOPT_SSL_VERIFYPEER\fP option.  If
\fICURLOPT_SSL_VERIFYPEER\fP is zero, \fICURLOPT_CAINFO\fP need not
even indicate an accessible file.
.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
makes sense only when used in combination with the
\fICURLOPT_SSL_VERIFYPEER\fP option.  If \fICURLOPT_SSL_VERIFYPEER\fP
is zero, \fICURLOPT_CAPATH\fP need not even indicate an accessible
path.  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 as parameter.

This option determines whether libcurl verifies that the server cert is for
the server it is known as.

When negotiating an SSL connection, the server sends a certificate indicating
its identity.

When \fICURLOPT_SSL_VERIFYHOST\fP is 2, that certificate must indicate that
the server is the server to which you meant to connect, or the connection
fails.

Curl considers the server the intended one when the Common Name field or a
Subject Alternate Name field in the certificate matches the host name in the
URL to which you told Curl to connect.

When the value is 1, the certificate must contain a Common Name field, but it
doesn't matter what name it says.  (This is not ordinarily a useful setting).

When the value is 0, the connection succeeds regardless of the names in the
certificate.

The default, since 7.10, is 2.

The checking this option controls is of the identity that the server
\fIclaims\fP.  The server could be lying.  To control lying, see
\fICURLOPT_SSL_VERIFYPEER\fP.
.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), " curl_easy_reset "(3), "