curl_easy_setopt.3

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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)
.IP CURLOPT_CONV_TO_NETWORK_FUNCTION
.IP CURLOPT_CONV_FROM_NETWORK_FUNCTION
.IP CURLOPT_CONV_FROM_UTF8_FUNCTION
Function pointers that should match the following prototype: CURLcode
function(char *ptr, size_t length);

These three options apply to non-ASCII platforms only.  They are available
only if \fBCURL_DOES_CONVERSIONS\fP was defined when libcurl was built. When
this is the case, \fIcurl_version_info(3)\fP will return the CURL_VERSION_CONV
feature bit set.

The data to be converted is in a buffer pointed to by the ptr parameter.  The
amount of data to convert is indicated by the length parameter.  The converted
data overlays the input data in the buffer pointed to by the ptr parameter.
CURLE_OK should be returned upon successful conversion.  A CURLcode return
value defined by curl.h, such as CURLE_CONV_FAILED, should be returned if an
error was encountered.

\fBCURLOPT_CONV_TO_NETWORK_FUNCTION\fP and
\fBCURLOPT_CONV_FROM_NETWORK_FUNCTION\fP convert between the host encoding and
the network encoding.  They are used when commands or ASCII data are
sent/received over the network.

\fBCURLOPT_CONV_FROM_UTF8_FUNCTION\fP is called to convert from UTF8 into the
host encoding.  It is required only for SSL processing.

If you set a callback pointer to NULL, or don't set it at all, the built-in
libcurl iconv functions will be used.  If HAVE_ICONV was not defined when
libcurl was built, and no callback has been established, conversion will
return the CURLE_CONV_REQD error code.

If HAVE_ICONV is defined, CURL_ICONV_CODESET_OF_HOST must also be defined.
For example:

 \&#define CURL_ICONV_CODESET_OF_HOST "IBM-1047"

The iconv code in libcurl will default the network and UTF8 codeset names as
follows:

 \&#define CURL_ICONV_CODESET_OF_NETWORK "ISO8859-1"

 \&#define CURL_ICONV_CODESET_FOR_UTF8   "UTF-8"

You will need to override these definitions if they are different on your
system.
.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.
Although this argument is a 'char *', it does not describe an input string.
Therefore the (probably undefined) contents of the buffer is NOT copied
by the library. You should keep the associated storage available until
libcurl no longer needs it. Failing to do so will cause very odd behavior
or even crashes. libcurl will need it until you call \fIcurl_easy_cleanup(3)\fP
or you set the same option again to use a different pointer. 

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.

This method is not fail-safe and there are occasions where non-successful
response codes will slip through, especially when authentication is involved
(response codes 401 and 407).

You might get some amounts of headers transferred before this situation is
detected, like for when a "100-continue" is received as a response to a
POST/PUT and a 401 or 407 is received immediately afterwards.
.SH NETWORK OPTIONS
.IP CURLOPT_URL
The actual URL to deal with. The parameter should be a char * to a zero
terminated 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.

The string given to CURLOPT_URL must be url-encoded and following the RFC 2396
(http://curl.haxx.se/rfc/rfc2396.txt).

\fICURLOPT_URL\fP is the only option that \fBmust\fP 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.

Setting the proxy string to "" (an empty string) will explicitly disable the
use of a proxy, even if there is an environment variable set for it.

Since 7.14.1, the proxy host string given in environment variables can be
specified the exact same way as the proxy can be set with \fICURLOPT_PROXY\fP,
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, \fICURLPROXY_SOCKS4\fP (added in 7.15.2)
\fICURLPROXY_SOCKS5\fP. The HTTP type is 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_LOCALPORT
Pass a long. This sets the local port number of the socket used for
connection. This can be used in combination with \fICURLOPT_INTERFACE\fP and
you are recommended to use \fICURLOPT_LOCALPORTRANGE\fP as well when this is
set. Note that port numbers are only valid 1 - 65535. (Added in 7.15.2)
.IP CURLOPT_LOCALPORTRANGE
Pass a long. This is the number of attempts libcurl should do to find a
working local port number. It starts with the given \fICURLOPT_LOCALPORT\fP
and adds one to the number for each retry. Setting this value to 1 or below
will make libcurl do only one try for exact port number. Note that port
numbers by nature is a scarce resource that will be busy at times so setting
this value to something too low might cause unnecessary connection setup
failures. (Added in 7.15.2)
.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 makes 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)