curl_easy_setopt.3

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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_MAX_SEND_SPEED_LARGE
Pass a curl_off_t as parameter.  If an upload exceeds this speed on cumulative 
average during the transfer, the transfer will pause to keep the average rate 
less than or equal to the parameter value.  (default: 0, unlimited)
.IP CURLOPT_MAX_RECV_SPEED_LARGE
Pass a curl_off_t as parameter.  If an upload exceeds this speed on cumulative 
average during the transfer, the transfer will pause to keep the average rate 
less than or equal to the parameter value.  (default: 0, unlimited)
.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
.IP CURLOPT_CONNECT_ONLY
Pass a long. A non-zero parameter tells the library to perform any required
proxy authentication and connection setup, but no data transfer.

This option is useful with the \fICURLINFO_LASTSOCKET\fP option to
\fIcurl_easy_getinfo(3)\fP. The library can set up the connection and then the
application can obtain the most recently used socket for special data
transfers. (Added in 7.15.2)
.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.

Note that option is by default set to the system path where libcurl's cacert
bundle is assumed to be stored, as established at build time.
.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