curl_easy_setopt(3) libcurl Manual curl_easy_setopt(3)NAMEcurl_easy_setopt - set options for a curl easy handle
SYNOPSIS
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLoption option, parameter);
DESCRIPTIONcurl_easy_setopt() is used to tell libcurl how to behave. By using the
appropriate options to curl_easy_setopt, you can change libcurl's
behavior. All options are set with the option followed by a parameter.
That parameter can be a long, a function pointer, an object pointer or
a curl_off_t, 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 applica‐
tion uses many curl_easy_setopt() calls in the setup phase.
Options set with this function call are valid for all forthcoming
transfers performed using this handle. The options are not in any way
reset between transfers, so if you want subsequent transfers with dif‐
ferent options, you must change them between the transfers. You can
optionally reset all options back to internal default with
curl_easy_reset(3).
Strings passed to libcurl as 'char *' arguments, are copied by the
library; thus the string storage associated to the pointer argument may
be overwritten after curl_easy_setopt() returns. Exceptions to this
rule are described in the option details below.
NOTE: before 7.17.0 strings were not copied. Instead the user was
forced keep them available until libcurl no longer needed them.
The handle is the return code from a curl_easy_init(3) or
curl_easy_duphandle(3) call.
BEHAVIOR OPTIONS
CURLOPT_VERBOSE
Set the parameter to 1 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 CUR‐
LOPT_STDERR.
You hardly ever want this set in production use, you will almost
always want this when you debug/report problems. Another neat
option for debugging is the CURLOPT_DEBUGFUNCTION.
CURLOPT_HEADER
A parameter set to 1 tells the library to include the header in
the body output. This is only relevant for protocols that actu‐
ally have headers preceding the data (like HTTP).
CURLOPT_NOPROGRESS
A parameter set to 1 tells the library to shut off the built-in
progress meter completely.
Future versions of libcurl are likely to not have any built-in
progress meter at all.
CURLOPT_NOSIGNAL
Pass a long. If it is 1, 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)
If this option is set and libcurl has been built with the stan‐
dard name resolver, timeouts will not occur while the name
resolve takes place. Consider building libcurl with c-ares sup‐
port to enable asynchronous DNS lookups, which enables nice
timeouts for name resolves without signals.
CALLBACK OPTIONS
CURLOPT_WRITEFUNCTION
Function pointer that should match the following prototype:
size_t function( void *ptr, size_t size, size_t nmemb, void
*stream); This function gets called by libcurl as soon as there
is data received that needs to be saved. The size of the data
pointed to by ptr is size multiplied with nmemb, it will not be
zero terminated. Return the number of bytes actually taken care
of. If that amount differs from the amount passed to your func‐
tion, it'll signal an error to the library and it will abort the
transfer and return CURLE_WRITE_ERROR.
From 7.18.0, the function can return CURL_WRITEFUNC_PAUSE which
then will cause writing to this connection to become paused. See
curl_easy_pause(3) for further details.
This function may be called with zero bytes data if the trans‐
ferred 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 CURLOPT_WRITEDATA.
Set the stream argument with the CURLOPT_WRITEDATA 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.
CURLOPT_WRITEDATA
Data pointer to pass to the file write function. If you use the
CURLOPT_WRITEFUNCTION 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 CURLOPT_WRITEFUNCTION 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 MUST use the CUR‐
LOPT_WRITEFUNCTION if you set this option or you will experience
crashes.
This option is also known with the older name CURLOPT_FILE, the
name CURLOPT_WRITEDATA was introduced in 7.9.7.
CURLOPT_READFUNCTION
Function pointer that should match the following prototype:
size_t function( void *ptr, size_t size, size_t nmemb, void
*stream); This function gets called by libcurl as soon as it
needs to read data in order to send it to the peer. The data
area pointed at by the pointer ptr may be filled with at most
size multiplied with nmemb number of bytes. Your function must
return the actual number of bytes that you stored in that 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 said 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 CURL_READFUNC_ABORT to stop the
current operation immediately, resulting in a
CURLE_ABORTED_BY_CALLBACK error code from the transfer (Added in
7.12.1)
From 7.18.0, the function can return CURL_READFUNC_PAUSE which
then will cause reading from this connection to become paused.
See curl_easy_pause(3) for further details.
If you set the callback pointer to NULL, or don'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 CURLOPT_READDATA.
CURLOPT_READDATA
Data pointer to pass to the file read function. If you use the
CURLOPT_READFUNCTION 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 CUR‐
LOPT_READFUNCTION if you set this option.
This option was also known by the older name CURLOPT_INFILE, the
name CURLOPT_READDATA was introduced in 7.9.7.
CURLOPT_IOCTLFUNCTION
Function pointer that should match the curl_ioctl_callback pro‐
totype found in <curl/curl.h>. 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. (Option added in
7.12.3).
Use CURLOPT_SEEKFUNCTION instead to provide seeking!
CURLOPT_IOCTLDATA
Pass a pointer that will be untouched by libcurl and passed as
the 3rd argument in the ioctl callback set with CURLOPT_IOCTL‐
FUNCTION. (Option added in 7.12.3)
CURLOPT_SEEKFUNCTION
Function pointer that should match the following prototype: int
function(void *instream, curl_off_t offset, int origin); This
function gets called by libcurl to seek to a certain position in
the input stream and can be used to fast forward a file in a
resumed upload (instead of reading all uploaded bytes with the
normal read function/callback). It is also called to rewind a
stream when doing a HTTP PUT or POST with a multi-pass authenti‐
cation method. The function shall work like "fseek" or "lseek"
and accepted SEEK_SET, SEEK_CUR and SEEK_END as argument for
origin, although (in 7.18.0) libcurl only passes SEEK_SET. The
callback must return 0 (CURL_SEEKFUNC_OK) on success, 1
(CURL_SEEKFUNC_FAIL) to cause the upload operation to fail or 2
(CURL_SEEKFUNC_CANTSEEK) to indicate that while the seek failed,
libcurl is free to work around the problem if possible. The lat‐
ter can sometimes be done by instead reading from the input or
similar.
If you forward the input arguments directly to "fseek" or
"lseek", note that the data type for offset is not the same as
defined for curl_off_t on many systems! (Option added in 7.18.0)
CURLOPT_SEEKDATA
Data pointer to pass to the file read function. If you use the
CURLOPT_SEEKFUNCTION option, this is the pointer you'll get as
input. If you don't specify a seek callback, NULL is passed.
(Option added in 7.18.0)
CURLOPT_SOCKOPTFUNCTION
Function pointer that should match the curl_sockopt_callback
prototype found in <curl/curl.h>. This function gets called by
libcurl after the socket() call but before the connect() call.
The callback's purpose argument identifies the exact purpose for
this particular socket, and currently only one value is sup‐
ported: CURLSOCKTYPE_IPCXN for the primary connection (meaning
the control connection in the FTP case). Future versions of
libcurl may support more purposes. It passes the newly created
socket descriptor so additional setsockopt() calls can be done
at the user's discretion. Return 0 (zero) from the callback on
success. Return 1 from the callback function to signal an unre‐
coverable error to the library and it will close the socket and
return CURLE_COULDNT_CONNECT. (Option added in 7.15.6.)
CURLOPT_SOCKOPTDATA
Pass a pointer that will be untouched by libcurl and passed as
the first argument in the sockopt callback set with CUR‐
LOPT_SOCKOPTFUNCTION. (Option added in 7.15.6.)
CURLOPT_OPENSOCKETFUNCTION
Function pointer that should match the curl_opensocket_callback
prototype found in <curl/curl.h>. This function gets called by
libcurl instead of the socket(2) call. The callback's purpose
argument identifies the exact purpose for this particular
socket, and currently only one value is supported: CURLSOCK‐
TYPE_IPCXN for the primary connection (meaning the control con‐
nection in the FTP case). Future versions of libcurl may support
more purposes. It passes the resolved peer address as a address
argument so the callback can modify the address or refuse to
connect at all. The callback function should return the socket
or CURL_SOCKET_BAD in case no connection should be established
or any error detected. Any additional setsockopt(2) calls can be
done on the socket at the user's discretion. CURL_SOCKET_BAD
return value from the callback function will signal an unrecov‐
erable error to the library and it will return
CURLE_COULDNT_CONNECT. This return code can be used for IP
address blacklisting. The default behavior is:
return socket(addr->family, addr->socktype, addr->protocol);
(Option added in 7.17.1.)
CURLOPT_OPENSOCKETDATA
Pass a pointer that will be untouched by libcurl and passed as
the first argument in the opensocket callback set with CUR‐
LOPT_OPENSOCKETFUNCTION. (Option added in 7.17.1.)
CURLOPT_PROGRESSFUNCTION
Function pointer that should match the curl_progress_callback
prototype found in <curl/curl.h>. This function gets called by
libcurl instead of its internal equivalent with a frequent
interval during operation (roughly once per second) no matter if
data is being transferred or not. Unknown/unused argument val‐
ues passed 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 CURLE_ABORTED_BY_CALLBACK.
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.
CURLOPT_NOPROGRESS must be set to 0 to make this function actu‐
ally get called.
CURLOPT_PROGRESSDATA
Pass a pointer that will be untouched by libcurl and passed as
the first argument in the progress callback set with CUR‐
LOPT_PROGRESSFUNCTION.
CURLOPT_HEADERFUNCTION
Function pointer that should match the following prototype:
size_t function( void *ptr, size_t size, size_t nmemb, void
*stream);. This function gets called by libcurl as soon as 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 ptr is size multiplied
with nmemb. Do not assume that the header line is zero termi‐
nated! The pointer named stream is the one you set with the CUR‐
LOPT_WRITEHEADER 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 CURLE_WRITE_ERROR return code).
If this option is not set, or if it is set to NULL, but CUR‐
LOPT_HEADERDATA (CURLOPT_WRITEHEADER) is set to anything but
NULL, the function used to accept response data will be used
instead. That is, it will be the function specified with CUR‐
LOPT_WRITEFUNCTION, or if it is not specified or NULL - the
default, stream-writing function.
It's important to note that the callback will be invoked for the
headers of all responses received after initiating a request and
not just the final response. This includes all responses which
occur during authentication negotiation. If you need to operate
on only the headers from the final response, you will need to
collect headers in the callback yourself and use HTTP status
lines, for example, to delimit response boundaries.
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.
CURLOPT_WRITEHEADER
(This option is also known as CURLOPT_HEADERDATA) Pass a pointer
to be used to write the header part of the received data to. If
you don't use your own callback to take care of the writing,
this must be a valid FILE *. See also the CURLOPT_HEADERFUNCTION
option above on how to set a custom get-all-headers callback.
CURLOPT_DEBUGFUNCTION
Function pointer that should match the following prototype: int
curl_debug_callback (CURL *, curl_infotype, char *, size_t, void
*); CURLOPT_DEBUGFUNCTION replaces the standard debug function
used when CURLOPT_VERBOSE is in effect. This callback receives
debug information, as specified with the curl_infotype argument.
This function must return 0. The data pointed to by the char *
passed to this function WILL NOT be zero terminated, but will be
exactly of the size as told by the size_t argument.
Available curl_infotype values:
CURLINFO_TEXT
The data is informational text.
CURLINFO_HEADER_IN
The data is header (or header-like) data received from
the peer.
CURLINFO_HEADER_OUT
The data is header (or header-like) data sent to the
peer.
CURLINFO_DATA_IN
The data is protocol data received from the peer.
CURLINFO_DATA_OUT
The data is protocol data sent to the peer.
CURLOPT_DEBUGDATA
Pass a pointer to whatever you want passed in to your CUR‐
LOPT_DEBUGFUNCTION in the last void * argument. This pointer is
not used by libcurl, it is only passed to the callback.
CURLOPT_SSL_CTX_FUNCTION
This option does only function for libcurl powered by OpenSSL.
If libcurl was built against another SSL library, this function‐
ality is absent.
Function pointer that should match the following prototype:
CURLcode sslctxfun(CURL *curl, void *sslctx, void *parm); This
function gets called by libcurl just before the initialization
of an SSL connection after having processed all other SSL
related options to give a last chance to an application to mod‐
ify the behaviour of openssl's ssl initialization. The sslctx
parameter is actually a pointer to an openssl SSL_CTX. If an
error is returned no attempt to establish a connection is made
and the perform operation will return the error code from this
callback function. Set the parm argument with the CUR‐
LOPT_SSL_CTX_DATA option. This option was introduced in 7.11.0.
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. For example, using this function
allows you 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.
CURLOPT_SSL_CTX_DATA
Data pointer to pass to the ssl context callback set by the
option CURLOPT_SSL_CTX_FUNCTION, this is the pointer you'll get
as third parameter, otherwise NULL. (Added in 7.11.0)
CURLOPT_CONV_TO_NETWORK_FUNCTION
CURLOPT_CONV_FROM_NETWORK_FUNCTION
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 CURL_DOES_CONVERSIONS was defined when libcurl
was built. When this is the case, curl_version_info(3) 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.
CURLOPT_CONV_TO_NETWORK_FUNCTION and CURLOPT_CONV_FROM_NET‐
WORK_FUNCTION convert between the host encoding and the network
encoding. They are used when commands or ASCII data are
sent/received over the network.
CURLOPT_CONV_FROM_UTF8_FUNCTION 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 call‐
back 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 differ‐
ent on your system.
ERROR OPTIONS
CURLOPT_ERRORBUFFER
Pass a char * to a buffer that the libcurl may store human read‐
able error messages in. This may be more helpful than just the
return code from curl_easy_perform. 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 behav‐
ior or even crashes. libcurl will need it until you call
curl_easy_cleanup(3) or you set the same option again to use a
different pointer.
Use CURLOPT_VERBOSE and CURLOPT_DEBUGFUNCTION 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.
CURLOPT_STDERR
Pass a FILE * as parameter. Tell libcurl to use this stream
instead of stderr when showing the progress meter and displaying
CURLOPT_VERBOSE data.
CURLOPT_FAILONERROR
A parameter set to 1 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 when a "100-continue" is received as
a response to a POST/PUT and a 401 or 407 is received immedi‐
ately afterwards.
NETWORK OPTIONS
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 (CURLE_UNSUPPORTED_PRO‐
TOCOL) when you call curl_easy_perform(3) or curl_multi_per‐
form(3). Use curl_version_info(3) for detailed info on which
protocols are supported.
The string given to CURLOPT_URL must be url-encoded and follow
RFC 2396 (http://curl.haxx.se/rfc/rfc2396.txt).
CURLOPT_URL is the only option that must be set before
curl_easy_perform(3) is called.
CURLOPT_PROTOCOLS can be used to limit what protocols libcurl
will use for this transfer, independent of what libcurl has been
compiled to support. That may be useful if you accept the URL
from an external source and want to limit the accessibility.
CURLOPT_PROTOCOLS
Pass a long that holds a bitmask of CURLPROTO_* defines. If
used, this bitmask limits what protocols libcurl may use in the
transfer. This allows you to have a libcurl built to support a
wide range of protocols but still limit specific transfers to
only be allowed to use a subset of them. By default libcurl will
accept all protocols it supports. See also CURLOPT_REDIR_PROTO‐
COLS. (Added in 7.19.4)
CURLOPT_REDIR_PROTOCOLS
Pass a long that holds a bitmask of CURLPROTO_* defines. If
used, this bitmask limits what protocols libcurl may use in a
transfer that it follows to in a redirect when CURLOPT_FOLLOWLO‐
CATION is enabled. This allows you to limit specific transfers
to only be allowed to use a subset of protocols in redirections.
By default libcurl will allow all protocols except for FILE and
SCP. This is a difference compared to pre-7.19.4 versions which
unconditionally would follow to all protocols supported. (Added
in 7.19.4)
CURLOPT_PROXY
Set HTTP proxy to use. The parameter should be a char * to a
zero terminated string holding the host name or dotted IP
address. To specify port number in this string, append :[port]
to the end of the host name. The proxy string may be prefixed
with [protocol]:// since any such prefix will be ignored. The
proxy's port number may optionally be specified with the sepa‐
rate option. If not specified, libcurl will default to using
port 1080 for proxies. CURLOPT_PROXYPORT.
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 CURLOPT_QUOTE and similar FTP
specifics that don't work unless you tunnel through the HTTP
proxy. Such tunneling is activated with CURLOPT_HTTPPROXYTUNNEL.
libcurl respects the environment variables http_proxy,
ftp_proxy, all_proxy etc, if any of those are set. The CUR‐
LOPT_PROXY option does however override any possibly set envi‐
ronment 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 vari‐
ables can be specified the exact same way as the proxy can be
set with CURLOPT_PROXY, include protocol prefix (http://) and
embedded user + password.
CURLOPT_PROXYPORT
Pass a long with this option to set the proxy port to connect to
unless it is specified in the proxy string CURLOPT_PROXY.
CURLOPT_PROXYTYPE
Pass a long with this option to set type of the proxy. Available
options for this are CURLPROXY_HTTP, CURLPROXY_HTTP_1_0 (added
in 7.19.4), CURLPROXY_SOCKS4 (added in 7.15.2), CURL‐
PROXY_SOCKS5, CURLPROXY_SOCKS4A (added in 7.18.0) and CURL‐
PROXY_SOCKS5_HOSTNAME (added in 7.18.0). The HTTP type is
default. (Added in 7.10)
CURLOPT_NOPROXY
Pass a pointer to a zero terminated string. The should be a
comma- separated list of hosts which do not use a proxy, if one
is specified. The only wildcard is a single * character, which
matches all hosts, and effectively disables the proxy. Each name
in this list is matched as either a domain which contains the
hostname, or the hostname itself. For example, local.com would
match local.com, local.com:80, and www.local.com, but not
www.notlocal.com. (Added in 7.19.4)
CURLOPT_HTTPPROXYTUNNEL
Set the parameter to 1 to make the library 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.
CURLOPT_SOCKS5_GSSAPI_SERVICE
Pass a char * as parameter to a string holding the name of the
service. The default service name for a SOCKS5 server is
rcmd/server-fqdn. This option allows you to change it. (Added in
7.19.4)
CURLOPT_SOCKS5_GSSAPI_NEC
Pass a long set to 1 to enable or 0 to disable. As part of the
gssapi negotiation a protection mode is negotiated. The rfc1961
says in section 4.3/4.4 it should be protected, but the NEC ref‐
erence implementation does not. If enabled, this option allows
the unprotected exchange of the protection mode negotiation.
(Added in 7.19.4).
CURLOPT_INTERFACE
Pass a char * as parameter. This sets the interface name to use
as outgoing network interface. The name can be an interface
name, an IP address, or a host name.
CURLOPT_LOCALPORT
Pass a long. This sets the local port number of the socket used
for connection. This can be used in combination with CUR‐
LOPT_INTERFACE and you are recommended to use CURLOPT_LOCALPOR‐
TRANGE as well when this is set. Note that the only valid port
numbers are 1 - 65535. (Added in 7.15.2)
CURLOPT_LOCALPORTRANGE
Pass a long. This is the number of attempts libcurl should make
to find a working local port number. It starts with the given
CURLOPT_LOCALPORT and adds one to the number for each retry.
Setting this to 1 or below will make libcurl do only one try for
the exact port number. Note that port numbers by nature are
scarce resources 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)
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
to completely disable caching, or set to -1 to make the cached
entries remain forever. By default, libcurl caches this info for
60 seconds.
NOTE: the name resolve functions of various libc implementations
don't re-read name server information unless explicitly told so
(for example, by calling res_init(3)). This may cause libcurl to
keep using the older server even if DHCP has updated the server
info, and this may look like a DNS cache issue to the casual
libcurl-app user.
CURLOPT_DNS_USE_GLOBAL_CACHE
Pass a long. If the value is 1, 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.
WARNING: this option is considered obsolete. Stop using it.
Switch over to using the share interface instead! See CUR‐
LOPT_SHARE and curl_share_init(3).
CURLOPT_BUFFERSIZE
Pass a long specifying your preferred size (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.
CURLOPT_PORT
Pass a long specifying what remote port number to connect to,
instead of the one specified in the URL or the default port for
the used protocol.
CURLOPT_TCP_NODELAY
Pass a long specifying whether the TCP_NODELAY option should be
set or cleared (1 = set, 0 = clear). The option is cleared by
default. This will have no effect after the connection has been
established.
Setting this option will disable TCP's Nagle algorithm. The pur‐
pose 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 conges‐
tion on the network if overdone.
CURLOPT_ADDRESS_SCOPE
Pass a long specifying the scope_id value to use when connecting
to IPv6 link-local or site-local addresses. (Added in 7.19.0)
NAMES and PASSWORDS OPTIONS (Authentication)
CURLOPT_NETRC
This parameter controls the preference of libcurl between using
user names and passwords from your ~/.netrc file, relative to
user names and passwords in the URL supplied with CURLOPT_URL.
libcurl uses a user name (and supplied or prompted password)
supplied with CURLOPT_USERPWD in preference to any of the
options controlled by this parameter.
Pass a long, set to one of the values described below.
CURL_NETRC_OPTIONAL
The use of your ~/.netrc file is optional, and informa‐
tion in the URL is to be preferred. The file will be
scanned for the host and user name (to find the password
only) or for the host only, to find the first user name
and password after that machine, which ever information
is not specified in the URL.
Undefined values of the option will have this effect.
CURL_NETRC_IGNORED
The library will ignore the file and use only the infor‐
mation in the URL.
This is the default.
CURL_NETRC_REQUIRED
This value tells the library that use of the file is
required, to ignore the information in the URL, and to
search the file for the host only.
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.
CURLOPT_NETRC_FILE
Pass a char * as parameter, pointing to a zero terminated string
containing the full path name to the file you want libcurl to
use as .netrc file. If this option is omitted, and CURLOPT_NETRC
is set, libcurl will attempt to find a .netrc file in the cur‐
rent user's home directory. (Added in 7.10.9)
CURLOPT_USERPWD
Pass a char * as parameter, which should be [user name]:[pass‐
word] to use for the connection. Use CURLOPT_HTTPAUTH to decide
the authentication method.
When using NTLM, you can set the 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 CURLOPT_FOLLOWLOCATION, libcurl might per‐
form several requests to possibly different hosts. libcurl will
only send this user and password information to hosts using the
initial host name (unless CURLOPT_UNRESTRICTED_AUTH is set), so
if libcurl follows locations to other hosts it will not send the
user and password to those. This is enforced to prevent acciden‐
tal information leakage.
CURLOPT_PROXYUSERPWD
Pass a char * as parameter, which should be [user name]:[pass‐
word] to use for the connection to the HTTP proxy. Use CUR‐
LOPT_PROXYAUTH to decide the authentication method.
CURLOPT_USERNAME
Pass a char * as parameter, which should be pointing to the zero
terminated user name to use for the transfer.
CURLOPT_USERNAME sets the user name to be used in protocol
authentication. You should not use this option together with the
(older) CURLOPT_USERPWD option.
In order to specify the password to be used in conjunction with
the user name use the CURLOPT_PASSWORD option. (Added in
7.19.1)
CURLOPT_PASSWORD
Pass a char * as parameter, which should be pointing to the zero
terminated password to use for the transfer.
The CURLOPT_PASSWORD option should be used in conjunction with
the CURLOPT_USERNAME option. (Added in 7.19.1)
CURLOPT_PROXYUSERNAME
Pass a char * as parameter, which should be pointing to the zero
terminated user name to use for the transfer while connecting to
Proxy.
The CURLOPT_PROXYUSERNAME option should be used in same way as
the CURLOPT_PROXYUSERPWD is used. In comparison to CUR‐
LOPT_PROXYUSERPWD the CURLOPT_PROXYUSERNAME allows the username
to contain a colon, like in the following example:
"sip:user@example.com". Note the CURLOPT_PROXYUSERNAME option
is an alternative way to set the user name while connecting to
Proxy. There is no meaning to use it together with the CUR‐
LOPT_PROXYUSERPWD option.
In order to specify the password to be used in conjunction with
the user name use the CURLOPT_PROXYPASSWORD option. (Added in
7.19.1)
CURLOPT_PROXYPASSWORD
Pass a char * as parameter, which should be pointing to the zero
terminated password to use for the transfer while connecting to
Proxy.
The CURLOPT_PROXYPASSWORD option should be used in conjunction
with the CURLOPT_PROXYUSERNAME option. (Added in 7.19.1)
CURLOPT_HTTPAUTH
Pass a long as parameter, which is set to a bitmask, to tell
libcurl which 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 which 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 CURLOPT_USERPWD
option or with the CURLOPT_USERNAME and the CURLOPT_USERPASSWORD
options. (Added in 7.10.6)
CURLAUTH_BASIC
HTTP Basic authentication. This is the default choice,
and the only method that is in wide-spread use and sup‐
ported virtually everywhere. This sends the user name and
password over the network in plain text, easily captured
by others.
CURLAUTH_DIGEST
HTTP Digest authentication. Digest authentication is
defined in RFC2617 and is a more secure way to do authen‐
tication over public networks than the regular old-fash‐
ioned Basic method.
CURLAUTH_DIGEST_IE
HTTP Digest authentication with an IE flavor. 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. The IE flavor is sim‐
ply that libcurl will use a special "quirk" that IE is
known to have used before version 7 and that some servers
require the client to use. (This define was added in
7.19.3)
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 also be used along with other 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.
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.
CURLAUTH_ANY
This is a convenience macro that sets all bits and thus
makes libcurl pick any it finds suitable. libcurl will
automatically select the one it finds most secure.
CURLAUTH_ANYSAFE
This is a convenience macro that sets all bits except
Basic and thus makes libcurl pick any it finds suitable.
libcurl will automatically select the one it finds most
secure.
CURLOPT_PROXYAUTH
Pass a long as parameter, which is set to a bitmask, to tell
libcurl which 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 CURLOPT_PROXYUSERPWD
option. The bitmask can be constructed by or'ing together the
bits listed above for the CURLOPT_HTTPAUTH option. As of this
writing, only Basic, Digest and NTLM work. (Added in 7.10.7)
HTTP OPTIONS
CURLOPT_AUTOREFERER
Pass a parameter set to 1 to enable this. When enabled, libcurl
will automatically set the Referer: field in requests where it
follows a Location: redirect.
CURLOPT_ENCODING
Sets the contents of the Accept-Encoding: header sent in an HTTP
request, and enables decoding of a response when a Content-
Encoding: header is received. Three encodings are supported:
identity, which does nothing, deflate which requests the server
to compress its response using the zlib algorithm, and gzip
which requests the gzip algorithm. If a zero-length string is
set, then an Accept-Encoding: header containing all supported
encodings is sent.
This is a request, not an order; the server may or may not do
it. This option must be set (to any non-NULL value) or else any
unsolicited encoding done by the server is ignored. See the spe‐
cial file lib/README.encoding for details.
CURLOPT_FOLLOWLOCATION
A parameter set to 1 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. CURLOPT_MAXREDIRS can be used
to limit the number of redirects libcurl will follow.
NOTE: since 7.19.4, libcurl can limit to what protocols it will
automatically follow. The accepted protocols are set with CUR‐
LOPT_REDIR_PROTOCOLS and it excludes the FILE protocol by
default.
CURLOPT_UNRESTRICTED_AUTH
A parameter set to 1 tells the library it can continue to send
authentication (user+password) when following locations, even
when hostname changed. This option is meaningful only when set‐
ting CURLOPT_FOLLOWLOCATION.
CURLOPT_MAXREDIRS
Pass a long. The set number will be the redirection limit. If
that many redirections have been followed, the next redirect
will cause an error (CURLE_TOO_MANY_REDIRECTS). This option only
makes sense if the CURLOPT_FOLLOWLOCATION is used at the same
time. 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)
CURLOPT_POSTREDIR
Pass a bitmask to control how libcurl acts on redirects after
POSTs that get a 301 or 302 response back. A parameter with bit
0 set (value CURL_REDIR_POST_301) tells the library to respect
RFC 2616/10.3.2 and not convert POST requests into GET requests
when following a 301 redirection. Setting bit 1 (value
CURL_REDIR_POST_302) makes libcurl maintain the request method
after a 302 redirect. CURL_REDIR_POST_ALL is a convenience
define that sets both bits.
The non-RFC behaviour is ubiquitous in web browsers, so the
library does the conversion by default to maintain consistency.
However, a server may require a POST to remain a POST after such
a redirection. This option is meaningful only when setting CUR‐
LOPT_FOLLOWLOCATION. (Added in 7.17.1) (This option was known
as CURLOPT_POST301 up to 7.19.0 as it only supported the 301 way
before then)
CURLOPT_PUT
A parameter set to 1 tells the library to use HTTP PUT to trans‐
fer data. The data should be set with CURLOPT_READDATA and CUR‐
LOPT_INFILESIZE.
This option is deprecated and starting with version 7.12.1 you
should instead use CURLOPT_UPLOAD.
CURLOPT_POST
A parameter set to 1 tells the library to do a regular HTTP
post. This will also make the library use a "Content-Type:
application/x-www-form-urlencoded" header. (This is by far the
most commonly used POST method).
Use one of CURLOPT_POSTFIELDS or CURLOPT_COPYPOSTFIELDS options
to specify what data to post and CURLOPT_POSTFIELDSIZE or CUR‐
LOPT_POSTFIELDSIZE_LARGE to set the data size.
Optionally, you can provide data to POST using the CURLOPT_READ‐
FUNCTION and CURLOPT_READDATA options but then you must make
sure to not set CURLOPT_POSTFIELDS to anything but NULL. When
providing data with a callback, you must transmit it using chun‐
ked transfer-encoding or you must set the size of the data with
the CURLOPT_POSTFIELDSIZE or CURLOPT_POSTFIELDSIZE_LARGE option.
To enable chunked encoding, you simply pass in the appropriate
Transfer-Encoding header, see the post-callback.c example.
You can override the default POST Content-Type: header by set‐
ting your own with CURLOPT_HTTPHEADER.
Using POST with HTTP 1.1 implies the use of a "Expect: 100-con‐
tinue" header. You can disable this header with CURLOPT_HTTP‐
HEADER 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 CURLOPT_HTTPHEADER. With HTTP 1.0 or
without chunked transfer, you must specify the size in the
request.
When setting CURLOPT_POST to 1, it will automatically set CUR‐
LOPT_NOBODY 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 explicitly set the new
request type using CURLOPT_NOBODY or CURLOPT_HTTPGET or similar.
CURLOPT_POSTFIELDS
Pass a void * 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.
The pointed data are NOT copied by the library: as a conse‐
quence, they must be preserved by the calling application until
the transfer finishes.
This POST is a normal application/x-www-form-urlencoded kind
(and libcurl will set that Content-Type by default when this
option is used), which is the most commonly used one by HTML
forms. See also the CURLOPT_POST. Using CURLOPT_POSTFIELDS
implies CURLOPT_POST.
If you want to do a zero-byte POST, you need to set CUR‐
LOPT_POSTFIELDSIZE explicitly to zero, as simply setting CUR‐
LOPT_POSTFIELDS to NULL or "" just effectively disables the
sending of the specified string. libcurl will instead assume
that you'll send the POST data using the read callback!
Using POST with HTTP 1.1 implies the use of a "Expect: 100-con‐
tinue" header. You can disable this header with CURLOPT_HTTP‐
HEADER as usual.
To make multipart/formdata posts (aka RFC2388-posts), check out
the CURLOPT_HTTPPOST option.
CURLOPT_POSTFIELDSIZE
If you want to post data to the server without letting libcurl
do a strlen() to measure the data size, this option must be
used. When this option is used you can post fully binary data,
which otherwise is likely to fail. If this size is set to -1,
the library will use strlen() to get the size.
CURLOPT_POSTFIELDSIZE_LARGE
Pass a curl_off_t as parameter. Use this to set the size of the
CURLOPT_POSTFIELDS data to prevent libcurl from doing strlen()
on the data to figure out the size. This is the large file ver‐
sion of the CURLOPT_POSTFIELDSIZE option. (Added in 7.11.1)
CURLOPT_COPYPOSTFIELDS
Pass a char * as parameter, which should be the full data to
post in an HTTP POST operation. It behaves as the CURLOPT_POST‐
FIELDS option, but the original data are copied by the library,
allowing the application to overwrite the original data after
setting this option.
Because data are copied, care must be taken when using this
option in conjunction with CURLOPT_POSTFIELDSIZE or CUR‐
LOPT_POSTFIELDSIZE_LARGE: If the size has not been set prior to
CURLOPT_COPYPOSTFIELDS, the data are assumed to be a NUL-termi‐
nated string; else the stored size informs the library about the
data byte count to copy. In any case, the size must not be
changed after CURLOPT_COPYPOSTFIELDS, unless another CUR‐
LOPT_POSTFIELDS or CURLOPT_COPYPOSTFIELDS option is issued.
(Added in 7.17.1)
CURLOPT_HTTPPOST
Tells libcurl you want a multipart/formdata HTTP POST to be made
and you instruct what data to pass on to the server. Pass a
pointer to a linked list of curl_httppost structs as parameter.
The easiest way to create such a list, is to use curl_formadd(3)
as documented. The data in this list must remain intact until
you close this curl handle again with curl_easy_cleanup(3).
Using POST with HTTP 1.1 implies the use of a "Expect: 100-con‐
tinue" header. You can disable this header with CURLOPT_HTTP‐
HEADER as usual.
When setting CURLOPT_HTTPPOST, it will automatically set CUR‐
LOPT_NOBODY to 0 (since 7.14.1).
CURLOPT_REFERER
Pass a pointer to a zero terminated string as parameter. It will
be used to set the Referer: header in the http request sent to
the remote server. This can be used to fool servers or scripts.
You can also set any custom header with CURLOPT_HTTPHEADER.
CURLOPT_USERAGENT
Pass a pointer to a zero terminated string as parameter. It will
be used to set the User-Agent: header in the http request sent
to the remote server. This can be used to fool servers or
scripts. You can also set any custom header with CURLOPT_HTTP‐
HEADER.
CURLOPT_HTTPHEADER
Pass a pointer to a linked list of HTTP headers to pass to the
server in your HTTP request. The linked list should be a fully
valid list of struct curl_slist structs properly filled in. Use
curl_slist_append(3) to create the list and
curl_slist_free_all(3) to clean up an entire list. If you add a
header that is otherwise generated and used by libcurl inter‐
nally, your added one will be used instead. If you add a header
with no content 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. To add a header with no
content, make the content be two quotes: "". 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 (containing the method, usually a
GET or POST) is not a header and cannot be replaced using this
option. Only the lines following the request-line are headers.
Adding this method line in this list of headers will only cause
your request to send an invalid header.
Pass a NULL to this to reset back to no custom headers.
The most commonly replaced headers have "shortcuts" in the
options CURLOPT_COOKIE, CURLOPT_USERAGENT and CURLOPT_REFERER.
CURLOPT_HTTP200ALIASES
Pass a pointer to a linked list of aliases to be treated as
valid HTTP 200 responses. Some servers respond with a custom
header response line. For example, IceCast servers respond with
"ICY 200 OK". By including this string in your list of aliases,
the response will be treated as a valid HTTP header line such as
"HTTP/1.0 200 OK". (Added in 7.10.3)
The linked list should be a fully valid list of struct
curl_slist structs, and be properly filled in. Use
curl_slist_append(3) to create the list and
curl_slist_free_all(3) to clean up an entire list.
The alias itself is not parsed for any version strings. Before
libcurl 7.16.3, Libcurl used the value set by option CUR‐
LOPT_HTTP_VERSION, but starting with 7.16.3 the protocol is
assumed to match HTTP 1.0 when an alias matched.
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.
Note that this option sets the cookie header explicitly in the
outgoing request(s). If multiple requests are done due to
authentication, followed redirections or similar, they will all
get this cookie passed on.
Using this option multiple times will only make the latest
string override the previous ones.
CURLOPT_COOKIEFILE
Pass a pointer to a zero terminated string as parameter. It
should contain the name of your file holding cookie data to
read. The cookie data may be in Netscape / Mozilla cookie data
format or just regular HTTP-style headers dumped to a file.
Given an empty or non-existing file or by passing the empty
string (""), this option will enable cookies for this curl han‐
dle, making it understand and parse received cookies and then
use matching cookies in future requests.
If you use this option multiple times, you just add more files
to read. Subsequent files will add more cookies.
CURLOPT_COOKIEJAR
Pass a file name as char *, zero terminated. This will make
libcurl write all internally known cookies to the specified file
when curl_easy_cleanup(3) is called. If no cookies are known, no
file will be created. Specify "-" to instead have the cookies
written to stdout. Using this option also enables 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
curl_easy_cleanup(3) is called), libcurl will not and cannot
report an error for this. Using CURLOPT_VERBOSE or CUR‐
LOPT_DEBUGFUNCTION will get a warning to display, but that is
the only visible feedback you get about this possibly lethal
situation.
CURLOPT_COOKIESESSION
Pass a long set to 1 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, indepen‐
dent if they are session cookies or not. Session cookies are
cookies without expiry date and they are meant to be alive and
existing for this "session" only.
CURLOPT_COOKIELIST
Pass a char * to a cookie string. Cookie can be either in Net‐
scape / 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) Passing
the special string "SESS" will only erase all session cookies
known by cURL. (Added in 7.15.4) Passing the special string
"FLUSH" will write all cookies known by cURL to the file speci‐
fied by CURLOPT_COOKIEJAR. (Added in 7.17.1)
CURLOPT_HTTPGET
Pass a long. If the long is 1, this forces the HTTP request to
get back to GET. Usable if a POST, HEAD, PUT, or a custom
request has been used previously using the same curl handle.
When setting CURLOPT_HTTPGET to 1, it will automatically set
CURLOPT_NOBODY to 0 (since 7.14.1).
CURLOPT_HTTP_VERSION
Pass a long, set to one of the values described below. They
force libcurl to use the specific HTTP versions. This is not
sensible to do unless you have a good reason.
CURL_HTTP_VERSION_NONE
We don't care about what version the library uses.
libcurl will use whatever it thinks fit.
CURL_HTTP_VERSION_1_0
Enforce HTTP 1.0 requests.
CURL_HTTP_VERSION_1_1
Enforce HTTP 1.1 requests.
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)
CURLOPT_HTTP_CONTENT_DECODING
Pass a long to tell libcurl how to act on content decoding. If
set to zero, content decoding will be disabled. If set to 1 it
is enabled. Note however that libcurl has no default content
decoding but requires you to use CURLOPT_ENCODING for that.
(added in 7.16.2)
CURLOPT_HTTP_TRANSFER_DECODING
Pass a long to tell libcurl how to act on transfer decoding. If
set to zero, transfer decoding will be disabled, if set to 1 it
is enabled (default). libcurl does chunked transfer decoding by
default unless this option is set to zero. (added in 7.16.2)
TFTP OPTIONS
CURLOPT_TFTPBLKSIZE
Specify block size to use for TFTP data transmission. Valid
range as per RFC 2348 is 8-65464 bytes. The default of 512 bytes
will be used if this option is not specified. The specified
block size will only be used pending support by the remote
server. If the server does not return an option acknowledgment
or returns an option acknowledgment with no blksize, the default
of 512 bytes will be used. (added in 7.19.4)
FTP OPTIONS
CURLOPT_FTPPORT
Pass a pointer to a zero terminated string as parameter. It will
be used to get the IP address to use for the FTP PORT instruc‐
tion. 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, a network interface name (under Unix) or just a '-'
symbol to let the library use your system's default IP address.
Default FTP operations are passive, and thus won't use PORT.
The address can be followed by a ':' to specify a port, option‐
ally followed by a '-' to specify a port range. If the port
specified is 0, the operating system will pick a free port. If
a range is provided and all ports in the range are not avail‐
able, libcurl will report CURLE_FTP_PORT_FAILED for the handle.
Invalid port/range settings are ignored. IPv6 addresses fol‐
lowed by a port or portrange have to be in brackets. IPv6
addresses without port/range specifier can be in brackets.
(added in 7.19.5)
Examples with specified ports:
eth0:0
192.168.1.2:32000-33000
curl.se:32123
[::1]:1234-4567
You disable PORT again and go back to using the passive version
by setting this option to NULL.
CURLOPT_QUOTE
Pass a pointer to a linked list of FTP or SFTP commands to pass
to the server prior to your FTP request. This will be done
before any other commands are issued (even before the CWD com‐
mand for FTP). The linked list should be a fully valid list of
'struct curl_slist' structs properly filled in with text
strings. Use curl_slist_append(3) to append strings (commands)
to the list, and clear the entire list afterwards with
curl_slist_free_all(3). Disable this operation again by setting
a NULL to this option. The set of valid FTP commands depends on
the server (see RFC959 for a list of mandatory commands). The
valid SFTP commands are: chgrp, chmod, chown, ln, mkdir, pwd,
rename, rm, rmdir, symlink (see curl(1)) (SFTP support added in
7.16.3)
CURLOPT_POSTQUOTE
Pass a pointer to a linked list of FTP or SFTP commands to pass
to the server after your FTP transfer request. The commands will
only be run if no error occurred. The linked list should be a
fully valid list of struct curl_slist structs properly filled in
as described for CURLOPT_QUOTE. Disable this operation again by
setting a NULL to this option.
CURLOPT_PREQUOTE
Pass a pointer to a linked list of FTP commands to pass to the
server after the transfer type is set. The linked list should be
a fully valid list of struct curl_slist structs properly filled
in as described for CURLOPT_QUOTE. Disable this operation again
by setting a NULL to this option. Before version 7.15.6, if you
also set CURLOPT_NOBODY to 1, this option didn't work.
CURLOPT_DIRLISTONLY
A parameter set to 1 tells the library to just list the names of
files in a directory, instead of doing a full directory listing
that would include file sizes, dates etc. This works for FTP and
SFTP URLs.
This causes an FTP NLST command to be sent on an FTP server.
Beware that some FTP servers list only files in their response
to NLST; they might not include subdirectories and symbolic
links.
(This option was known as CURLOPT_FTPLISTONLY up to 7.16.4)
CURLOPT_APPEND
A parameter set to 1 tells the library to append to the remote
file instead of overwrite it. This is only useful when uploading
to an FTP site.
(This option was known as CURLOPT_FTPAPPEND up to 7.16.4)
CURLOPT_FTP_USE_EPRT
Pass a long. If the value is 1, it tells curl to use the EPRT
(and LPRT) command when doing active FTP downloads (which is
enabled by CURLOPT_FTPPORT). Using EPRT means that it will first
attempt to use EPRT and then LPRT before using PORT, but if you
pass 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.
CURLOPT_FTP_USE_EPSV
Pass a long. If the value is 1, 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 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.
CURLOPT_FTP_CREATE_MISSING_DIRS
Pass a long. If the value is 1, 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)
This setting also applies to SFTP-connections. curl will attempt
to create the remote directory if it can't obtain a handle to
the target-location. The creation will fail if a file of the
same name as the directory to create already exists or lack of
permissions prevents creation. (Added in 7.16.3)
Starting with 7.19.4, you can also set this value to 2, which
will make libcurl retry the CWD command again if the subsequent
MKD command fails. This is especially useful if you're doing
many simultaneous connections against the same server and they
all have this option enabled, as then CWD may first fail but
then another connection does MKD before this connection and thus
MKD fails but trying CWD works! 7.19.4 also introduced the
CURLFTP_CREATE_DIR and CURLFTP_CREATE_DIR_RETRY enum names for
these arguments.
Before version 7.19.4, libcurl will simply ignore arguments set
to 2 and act as if 1 was selected.
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 CURLOPT_TIMEOUT. It is recom‐
mended that if used in conjunction with CURLOPT_TIMEOUT, you set
CURLOPT_FTP_RESPONSE_TIMEOUT to a value smaller than CUR‐
LOPT_TIMEOUT. (Added in 7.10.8)
CURLOPT_FTP_ALTERNATIVE_TO_USER
Pass a char * as parameter, pointing to a string which will be
used to authenticate if the usual FTP "USER user" and "PASS
password" negotiation fails. This is currently only known to be
required when connecting to Tumbleweed's Secure Transport FTPS
server using client certificates for authentication. (Added in
7.15.5)
CURLOPT_FTP_SKIP_PASV_IP
Pass a long. If set to 1, 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.
CURLOPT_USE_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)
(This option was known as CURLOPT_FTP_SSL up to 7.16.4, and the
constants were known as CURLFTPSSL_*)
CURLUSESSL_NONE
Don't attempt to use SSL.
CURLUSESSL_TRY
Try using SSL, proceed as normal otherwise.
CURLUSESSL_CONTROL
Require SSL for the control connection or fail with
CURLE_USE_SSL_FAILED.
CURLUSESSL_ALL
Require SSL for all communication or fail with
CURLE_USE_SSL_FAILED.
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 CURLOPT_USE_SSL). (Added in 7.12.2)
CURLFTPAUTH_DEFAULT
Allow libcurl to decide.
CURLFTPAUTH_SSL
Try "AUTH SSL" first, and only if that fails try "AUTH
TLS".
CURLFTPAUTH_TLS
Try "AUTH TLS" first, and only if that fails try "AUTH
SSL".
CURLOPT_FTP_SSL_CCC
If enabled, this option makes libcurl use CCC (Clear Command
Channel). It shuts down the SSL/TLS layer after authenticating.
The rest of the control channel communication will be unen‐
crypted. This allows NAT routers to follow the FTP transaction.
Pass a long using one of the values below. (Added in 7.16.1)
CURLFTPSSL_CCC_NONE
Don't attempt to use CCC.
CURLFTPSSL_CCC_PASSIVE
Do not initiate the shutdown, but wait for the server to
do it. Do not send a reply.
CURLFTPSSL_CCC_ACTIVE
Initiate the shutdown and wait for a reply.
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)
CURLOPT_FTP_FILEMETHOD
Pass a long that should have one of the following values. This
option controls what method libcurl should use to reach a file
on a FTP(S) server. The argument should be one of the following
alternatives:
CURLFTPMETHOD_MULTICWD
libcurl does a single CWD operation for each path part in
the given URL. For deep hierarchies this means many com‐
mands. This is how RFC1738 says it should be done. This
is the default but the slowest behavior.
CURLFTPMETHOD_NOCWD
libcurl does no CWD at all. libcurl will do SIZE, RETR,
STOR etc and give a full path to the server for all these
commands. This is the fastest behavior.
CURLFTPMETHOD_SINGLECWD
libcurl does one CWD with the full target directory and
then operates on the file "normally" (like in the multi‐
cwd case). This is somewhat more standards compliant than
'nocwd' but without the full penalty of 'multicwd'.
(Added in 7.15.1)
PROTOCOL OPTIONS
CURLOPT_TRANSFERTEXT
A parameter set to 1 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 simi‐
lar.
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 per‐
forms a standard transfer.
CURLOPT_PROXY_TRANSFER_MODE
Pass a long. If the value is set to 1 (one), it tells libcurl to
set the transfer mode (binary or ASCII) for FTP transfers done
via an HTTP proxy, by appending ;type=a or ;type=i to the URL.
Without this setting, or it being set to 0 (zero, the default),
CURLOPT_TRANSFERTEXT has no effect when doing FTP via a proxy.
Beware that not all proxies support this feature. (Added in
7.18.0)
CURLOPT_CRLF
Convert Unix newlines to CRLF newlines on transfers.
CURLOPT_RANGE
Pass a char * as parameter, which should contain the specified
range you want. It should be in the format "X-Y", where X or Y
may be left out. HTTP transfers also support several intervals,
separated with commas as in "X-Y,N-M". Using this kind of multi‐
ple 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.
Ranges work on HTTP, FTP and FILE (since 7.18.0) transfers only.
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). For FTP, set this option to -1 to make the
transfer start from the end of the target file (useful to con‐
tinue an interrupted upload).
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)
CURLOPT_CUSTOMREQUEST
Pass a pointer to a zero terminated string as parameter. It will
be used instead of GET or HEAD when doing an HTTP request, or
instead of LIST or NLST when doing a 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.
When you change the request method by setting CURLOPT_CUSTOMRE‐
QUEST to something, you don't actually change how libcurl
behaves or acts in regards to the particular request method, it
will only change the actual string sent in the request.
For example: if you tell libcurl to do a HEAD request, but then
change the request to a "GET" with CURLOPT_CUSTOMREQUEST you'll
still see libcurl act as if it sent a HEAD even when it does
send a GET.
To switch to a proper HEAD, use CURLOPT_NOBODY, to switch to a
proper POST, use CURLOPT_POST or CURLOPT_POSTFIELDS and so on.
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 con‐
tents. While that might work in many cases, it will cause
libcurl to send invalid requests and it could possibly confuse
the remote server badly. Use CURLOPT_POST and CURLOPT_POSTFIELDS
to set POST data. Use CURLOPT_HTTPHEADER to replace or extend
the set of headers sent by libcurl. Use CURLOPT_HTTP_VERSION to
change HTTP version.
CURLOPT_FILETIME
Pass a long. If it is 1, libcurl will attempt to get the modifi‐
cation 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 curl_easy_getinfo(3) function with
the CURLINFO_FILETIME argument can be used after a transfer to
extract the received time (if any).
CURLOPT_NOBODY
A parameter set to 1 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 CURLOPT_HTTPGET. Change
request to POST with CURLOPT_POST etc.
CURLOPT_INFILESIZE
When uploading a file to a remote site, this option should be
used to tell libcurl what the expected size of the infile is.
This value should be passed as a long. See also CURLOPT_INFILE‐
SIZE_LARGE.
For uploading using SCP, this option or CURLOPT_INFILESIZE_LARGE
is mandatory.
Note that this option does not limit how much data libcurl will
actually send, as that is controlled entirely by what the read
callback returns.
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)
For uploading using SCP, this option or CURLOPT_INFILESIZE is
mandatory.
Note that this option does not limit how much data libcurl will
actually send, as that is controlled entirely by what the read
callback returns.
CURLOPT_UPLOAD
A parameter set to 1 tells the library to prepare for an upload.
The CURLOPT_READDATA and CURLOPT_INFILESIZE or CURLOPT_INFILE‐
SIZE_LARGE options are also interesting for uploads. If the pro‐
tocol 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-con‐
tinue" header. You can disable this header with CURLOPT_HTTP‐
HEADER 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 CURLOPT_HTTPHEADER. With HTTP 1.0 or
without chunked transfer, you must specify the size.
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.
CURLOPT_MAXFILESIZE_LARGE
Pass a curl_off_t as parameter. This allows you to specify the
maximum size (in bytes) of a file to download. If the file
requested is larger than this value, the transfer will not start
and CURLE_FILESIZE_EXCEEDED will be returned. (Added in 7.11.0)
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.
CURLOPT_TIMECONDITION
Pass a long as parameter. This defines how the CURLOPT_TIMEVALUE
time value is treated. You can set this parameter to CURL_TIME‐
COND_IFMODSINCE or CURL_TIMECOND_IFUNMODSINCE. 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 not have been met. curl_easy_get‐
info(3) with the CURLINFO_CONDITION_UNMET option can be used
after a transfer to learn if a zero-byte successful "transfer"
was due to this condition not matching.
CURLOPT_TIMEVALUE
Pass a long as parameter. This should be the time in seconds
since 1 Jan 1970, and the time will be used in a condition as
specified with CURLOPT_TIMECONDITION.
CONNECTION OPTIONS
CURLOPT_TIMEOUT
Pass a long as parameter containing the maximum time in seconds
that you allow the libcurl transfer operation to take. Normally,
name lookups can take a considerable time and limiting opera‐
tions 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
CURLOPT_NOSIGNAL is set.
CURLOPT_TIMEOUT_MS
Like CURLOPT_TIMEOUT but takes number of milliseconds instead.
If libcurl is built to use the standard system name resolver,
that portion of the transfer will still use full-second resolu‐
tion for timeouts with a minimum timeout allowed of one second.
(Added in 7.16.2)
CURLOPT_LOW_SPEED_LIMIT
Pass a long as parameter. It contains the transfer speed in
bytes per second that the transfer should be below during CUR‐
LOPT_LOW_SPEED_TIME seconds for the library to consider it too
slow and abort.
CURLOPT_LOW_SPEED_TIME
Pass a long as parameter. It contains the time in seconds that
the transfer should be below the CURLOPT_LOW_SPEED_LIMIT for the
library to consider it too slow and abort.
CURLOPT_MAX_SEND_SPEED_LARGE
Pass a curl_off_t as parameter. If an upload exceeds this speed
(counted in bytes per second) on cumulative average during the
transfer, the transfer will pause to keep the average rate less
than or equal to the parameter value. Defaults to unlimited
speed. (Added in 7.15.5)
CURLOPT_MAX_RECV_SPEED_LARGE
Pass a curl_off_t as parameter. If a download exceeds this
speed (counted in bytes per second) on cumulative average during
the transfer, the transfer will pause to keep the average rate
less than or equal to the parameter value. Defaults to unlimited
speed. (Added in 7.15.5)
CURLOPT_MAXCONNECTS
Pass a long. The set number will be the persistent connection
cache size. The set amount will be the maximum amount of simul‐
taneously open connections that libcurl may cache in this easy
handle. Default is 5, and there isn't much point in changing
this value unless you are perfectly aware of how this works and
changes libcurl's behaviour. This concerns connections using any
of the protocols that support persistent connections.
When reaching the maximum limit, curl closes the oldest one in
the cache to prevent increasing the number of open connections.
If you already have performed transfers with this curl handle,
setting a smaller MAXCONNECTS than before may cause open connec‐
tions to get closed unnecessarily.
Note that if you add this easy handle to a multi handle, this
setting is not acknowledged, and you must instead use
curl_multi_setopt(3) and the CURLMOPT_MAXCONNECTS option.
CURLOPT_CLOSEPOLICY
(Obsolete) This option does nothing.
CURLOPT_FRESH_CONNECT
Pass a long. Set to 1 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).
CURLOPT_FORBID_REUSE
Pass a long. Set to 1 to make the next transfer explicitly close
the connection when done. Normally, libcurl keeps all connec‐
tions alive when done with one transfer in case a succeeding one
follows 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 possible later re-use
(default behavior).
CURLOPT_CONNECTTIMEOUT
Pass a long. It should contain the maximum time in seconds that
you allow the connection to the server to take. This only lim‐
its the connection phase, once it has connected, this option is
of no more use. Set to zero to disable connection timeout (it
will then only timeout on the system's internal timeouts). See
also the CURLOPT_TIMEOUT option.
In unix-like systems, this might cause signals to be used unless
CURLOPT_NOSIGNAL is set.
CURLOPT_CONNECTTIMEOUT_MS
Like CURLOPT_CONNECTTIMEOUT but takes the number of milliseconds
instead. If libcurl is built to use the standard system name
resolver, that portion of the connect will still use full-second
resolution for timeouts with a minimum timeout allowed of one
second. (Added in 7.16.2)
CURLOPT_IPRESOLVE
Allows an application to select what kind of IP addresses to use
when resolving host names. This is only interesting when using
host names that resolve addresses using more than one version of
IP. The allowed values are:
CURL_IPRESOLVE_WHATEVER
Default, resolves addresses to all IP versions that your
system allows.
CURL_IPRESOLVE_V4
Resolve to IPv4 addresses.
CURL_IPRESOLVE_V6
Resolve to IPv6 addresses.
CURLOPT_CONNECT_ONLY
Pass a long. If the parameter equals 1, it tells the library to
perform all the required proxy authentication and connection
setup, but no data transfer. This option is useful only on HTTP
URLs.
This option is useful with the CURLINFO_LASTSOCKET option to
curl_easy_getinfo(3). 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)
SSL and SECURITY OPTIONS
CURLOPT_SSLCERT
Pass a pointer to a zero terminated string as parameter. The
string should be the file name of your certificate. The default
format is "PEM" and can be changed with CURLOPT_SSLCERTTYPE.
With NSS this can also be the nickname of the certificate you
wish to authenticate with. If you want to use a file from the
current directory, please precede it with "./" prefix, in order
to avoid confusion with a nickname.
CURLOPT_SSLCERTTYPE
Pass a pointer to a zero terminated string as parameter. The
string should be the format of your certificate. Supported for‐
mats are "PEM" and "DER". (Added in 7.9.3)
CURLOPT_SSLKEY
Pass a pointer to a zero terminated string as parameter. The
string should be the file name of your private key. The default
format is "PEM" and can be changed with CURLOPT_SSLKEYTYPE.
CURLOPT_SSLKEYTYPE
Pass a pointer to a zero terminated string as parameter. The
string should be the format of your private key. Supported for‐
mats are "PEM", "DER" and "ENG".
The format "ENG" enables you to load the private key from a
crypto engine. In this case CURLOPT_SSLKEY is used as an identi‐
fier passed to the engine. You have to set the crypto engine
with CURLOPT_SSLENGINE. "DER" format key file currently does
not work because of a bug in OpenSSL.
CURLOPT_KEYPASSWD
Pass a pointer to a zero terminated string as parameter. It will
be used as the password required to use the CURLOPT_SSLKEY or
CURLOPT_SSH_PRIVATE_KEYFILE private key. You never needed a
pass phrase to load a certificate but you need one to load your
private key.
(This option was known as CURLOPT_SSLKEYPASSWD up to 7.16.4 and
CURLOPT_SSLCERTPASSWD up to 7.9.2)
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, CURLE_SSL_ENGINE_NOTFOUND
is returned.
CURLOPT_SSLENGINE_DEFAULT
Sets the actual crypto engine as the default for (asymmetric)
crypto operations.
If the crypto device cannot be set, CURLE_SSL_ENGINE_SETFAILED
is returned.
Note that even though this option doesn't need any parameter, in
some configurations curl_easy_setopt might be defined as a macro
taking exactly three arguments. Therefore, it's recommended to
pass 1 as parameter to this option.
CURLOPT_SSLVERSION
Pass a long as parameter to control what version of SSL/TLS to
attempt to use. The available options are:
CURL_SSLVERSION_DEFAULT
The default action. This will attempt to figure out the
remote SSL protocol version, i.e. either SSLv3 or TLSv1
(but not SSLv2, which became disabled by default with
7.18.1).
CURL_SSLVERSION_TLSv1
Force TLSv1
CURL_SSLVERSION_SSLv2
Force SSLv2
CURL_SSLVERSION_SSLv3
Force SSLv3
CURLOPT_SSL_VERIFYPEER
Pass a long as parameter.
This option determines whether curl verifies the authenticity of
the peer's certificate. A value of 1 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 certifi‐
cate indicating its identity. Curl verifies whether the cer‐
tificate 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 CURLOPT_CAINFO option or the CURLOPT_CAP‐
ATH option.
When CURLOPT_SSL_VERIFYPEER is nonzero, and the verification
fails to prove that the certificate is authentic, the connection
fails. When the option is zero, the connection succeeds regard‐
less.
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 CURLOPT_SSL_VERIFYHOST to control that.
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 CURLOPT_SSL_VERI‐
FYPEER option. If CURLOPT_SSL_VERIFYPEER is zero, CUR‐
LOPT_CAINFO 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.
If curl is built against the NSS SSL library, the NSS PEM
PKCS#11 module (libnsspem.so) needs to be available for this
option to work properly.
CURLOPT_ISSUERCERT
Pass a char * to a zero terminated string naming a file holding
a CA certificate in PEM format. If the option is set, an addi‐
tional check against the peer certificate is performed to verify
the issuer is indeed the one associated with the certificate
provided by the option. This additional check is useful in
multi-level PKI where one needs to enforce that the peer cer‐
tificate is from a specific branch of the tree.
This option makes sense only when used in combination with the
CURLOPT_SSL_VERIFYPEER option. Otherwise, the result of the
check is not considered as failure.
A specific error code (CURLE_SSL_ISSUER_ERROR) is defined with
the option, which is returned if the setup of the SSL/TLS ses‐
sion has failed due to a mismatch with the issuer of peer cer‐
tificate (CURLOPT_SSL_VERIFYPEER has to be set too for the check
to fail). (Added in 7.19.0)
CURLOPT_CAPATH
Pass a char * to a zero terminated string naming a directory
holding multiple CA certificates to verify the peer with. This
makes sense only when used in combination with the CUR‐
LOPT_SSL_VERIFYPEER option. If CURLOPT_SSL_VERIFYPEER is zero,
CURLOPT_CAPATH need not even indicate an accessible path. The
CURLOPT_CAPATH function apparently does not work in Windows due
to some limitation in openssl. This option is OpenSSL-specific
and does nothing if libcurl is built to use GnuTLS.
CURLOPT_CRLFILE
Pass a char * to a zero terminated string naming a file with the
concatenation of CRL (in PEM format) to use in the certificate
validation that occurs during the SSL exchange.
When curl is built to use NSS or GnuTLS, there is no way to
influence the use of CRL passed to help in the verification
process. When libcurl is built with OpenSSL support,
X509_V_FLAG_CRL_CHECK and X509_V_FLAG_CRL_CHECK_ALL are both
set, requiring CRL check against all the elements of the cer‐
tificate chain if a CRL file is passed.
This option makes sense only when used in combination with the
CURLOPT_SSL_VERIFYPEER option.
A specific error code (CURLE_SSL_CRL_BADFILE) is defined with
the option. It is returned when the SSL exchange fails because
the CRL file cannot be loaded. Note that a failure in certifi‐
cate verification due to a revocation information found in the
CRL does not trigger this specific error. (Added in 7.19.0)
CURLOPT_CERTINFO
Pass a long set to 1 to enable libcurl's certificate chain info
gatherer. With this enabled, libcurl (if built with OpenSSL)
will extract lots of information and data about the certificates
in the certificate chain used in the SSL connection. This data
is then possible to extract after a transfer using
curl_easy_getinfo(3) and its option CURLINFO_CERTINFO. (Added in
7.19.1)
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.
CURLOPT_EGDSOCKET
Pass a char * to the zero terminated path name to the Entropy
Gathering Daemon socket. It will be used to seed the random
engine for SSL.
CURLOPT_SSL_VERIFYHOST
Pass a long as parameter.
This option determines whether libcurl verifies that the server
cert is for the server it is known as.
When negotiating a SSL connection, the server sends a certifi‐
cate indicating its identity.
When CURLOPT_SSL_VERIFYHOST 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 con‐
nect.
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.
This makes sense only when used in combination with the CUR‐
LOPT_SSL_VERIFYPEER option. If CURLOPT_SSL_VERIFYPEER is zero,
CURLOPT_SSL_VERIFYHOST is ignored.
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 sepa‐
rators but colons are normally used, !, - and + can be used as
operators.
For OpenSSL and GnuTLS valid examples of cipher lists include
'RC4-SHA', ´SHA1+DES´, 'TLSv1' and 'DEFAULT'. The default list
is normally set when you compile OpenSSL.
You'll find more details about cipher lists on this URL:
http://www.openssl.org/docs/apps/ciphers.html
For NSS, valid examples of cipher lists include
'rsa_rc4_128_md5', ´rsa_aes_128_sha´, etc. With NSS you don't
add/remove ciphers. If one uses this option then all known
ciphers are disabled and only those passed in are enabled.
You'll find more details about the NSS cipher lists on this URL:
http://directory.fedora.redhat.com/docs/mod_nss.html#Directives
CURLOPT_SSL_SESSIONID_CACHE
Pass a long set to 0 to disable libcurl's use of SSL session-ID
caching. Set this to 1 to enable it. By default all transfers
are done using the cache. Note that while nothing ever should
get hurt by attempting to reuse SSL session-IDs, there seem to
be broken SSL implementations in the wild that may require you
to disable this in order for you to succeed. (Added in 7.16.0)
CURLOPT_KRBLEVEL
Pass a char * as parameter. Set the kerberos security level for
FTP; this also enables kerberos 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 kerberos support for FTP.
(This option was known as CURLOPT_KRB4LEVEL up to 7.16.3)
CURLOPT_GSSAPI_DELEGATION
Set the parameter to CURLGSSAPI_DELEGATION_FLAG to allow uncon‐
ditional GSSAPI credential delegation. The delegation is dis‐
abled by default since 7.21.7. Set the parameter to CURLGSS‐
API_DELEGATION_POLICY_FLAG to delegate only if the OK-AS-DELE‐
GATE flag is set in the service ticket in case this feature is
supported by the GSSAPI implementation and the definition of
GSS_C_DELEG_POLICY_FLAG was available at compile-time. (Added
in 7.21.8)
SSH OPTIONS
CURLOPT_SSH_AUTH_TYPES
Pass a long set to a bitmask consisting of one or more of
CURLSSH_AUTH_PUBLICKEY, CURLSSH_AUTH_PASSWORD,
CURLSSH_AUTH_HOST, CURLSSH_AUTH_KEYBOARD. Set CURLSSH_AUTH_ANY
to let libcurl pick one. (Added in 7.16.1)
CURLOPT_SSH_HOST_PUBLIC_KEY_MD5
Pass a char * pointing to a string containing 32 hexadecimal
digits. The string should be the 128 bit MD5 checksum of the
remote host's public key, and libcurl will reject the connection
to the host unless the md5sums match. This option is only for
SCP and SFTP transfers. (Added in 7.17.1)
CURLOPT_SSH_PUBLIC_KEYFILE
Pass a char * pointing to a file name for your public key. If
not used, libcurl defaults to using ~/.ssh/id_dsa.pub. (Added
in 7.16.1)
CURLOPT_SSH_PRIVATE_KEYFILE
Pass a char * pointing to a file name for your private key. If
not used, libcurl defaults to using ~/.ssh/id_dsa. If the file
is password-protected, set the password with CURLOPT_KEYPASSWD.
(Added in 7.16.1)
CURLOPT_SSH_KNOWNHOSTS
Pass a pointer to a zero terminated string holding the file name
of the known_host file to use. The known_hosts file should use
the OpenSSH file format as supported by libssh2. If this file is
specified, libcurl will only accept connections with hosts that
are known and present in that file, with a matching public key.
Use CURLOPT_SSH_KEYFUNCTION to alter the default behavior on
host and key (mis)matching. (Added in 7.19.6)
CURLOPT_SSH_KEYFUNCTION
Pass a pointer to a curl_sshkeycallback function. It gets called
when the known_host matching has been done, to allow the appli‐
cation to act and decide for libcurl how to proceed. It gets
passed the CURL handle, the key from the known_hosts file, the
key from the remote site, info from libcurl on the matching sta‐
tus and a custom pointer (set with CURLOPT_SSH_KEYDATA). It MUST
return one of the following return codes to tell libcurl how to
act:
CURLKHSTAT_FINE_ADD_TO_FILE
The host+key is accepted and libcurl will append it to
the known_hosts file before continuing with the connec‐
tion. This will also add the host+key combo to the
known_host pool kept in memory if it wasn't already
present there. Note that the adding of data to the file
is done by completely replacing the file with a new copy,
so the permissions of the file must allow this.
CURLKHSTAT_FINE
The host+key is accepted libcurl will continue with the
connection. This will also add the host+key combo to the
known_host pool kept in memory if it wasn't already
present there.
CURLKHSTAT_REJECT
The host+key is rejected. libcurl will deny the connec‐
tion to continue and it will be closed.
CURLKHSTAT_DEFER
The host+key is rejected, but the SSH connection is asked
to be kept alive. This feature could be used when the
app wants to somehow return back and act on the host+key
situation and then retry without needing the overhead of
setting it up from scratch again.
(Added in 7.19.6)
CURLOPT_SSH_KEYDATA
Pass a void * as parameter. This pointer will be passed along
verbatim to the callback set with CURLOPT_SSH_KEYFUNCTION.
(Added in 7.19.6)
OTHER OPTIONS
CURLOPT_PRIVATE
Pass a void * as parameter, pointing to data that should be
associated with this curl handle. The pointer can subsequently
be retrieved using curl_easy_getinfo(3) with the CURLINFO_PRI‐
VATE option. libcurl itself does nothing with this data. (Added
in 7.10.3)
CURLOPT_SHARE
Pass a share handle as a parameter. The share handle must have
been created by a previous call to curl_share_init(3). Setting
this option, will make this curl handle use the data from the
shared handle instead of keeping the data to itself. This
enables several curl handles to share data. If the curl handles
are used simultaneously in multiple threads, you MUST use the
locking methods in the share handle. See curl_share_setopt(3)
for details.
If you add a share that is set to share cookies, your easy han‐
dle will use that cookie cache and get the cookie engine
enabled. If you unshare an object that was using cookies (or
change to another object that doesn't share cookies), the easy
handle will get its cookie engine disabled.
Data that the share object is not set to share will be dealt
with the usual way, as if no share was used.
CURLOPT_NEW_FILE_PERMS
Pass a long as a parameter, containing the value of the permis‐
sions that will be assigned to newly created files on the remote
server. The default value is 0644, but any valid value can be
used. The only protocols that can use this are sftp://, scp://,
and file://. (Added in 7.16.4)
CURLOPT_NEW_DIRECTORY_PERMS
Pass a long as a parameter, containing the value of the permis‐
sions that will be assigned to newly created directories on the
remote server. The default value is 0755, but any valid value
can be used. The only protocols that can use this are sftp://,
scp://, and file://. (Added in 7.16.4)
TELNET OPTIONS
CURLOPT_TELNETOPTIONS
Provide a pointer to a curl_slist with variables to pass to the
telnet negotiations. The variables should be in the format
<option=value>. libcurl supports the options 'TTYPE', 'XDISPLOC'
and 'NEW_ENV'. See the TELNET standard for details.
RETURN VALUE
CURLE_OK (zero) means that the option was set properly, non-zero means
an error occurred as <curl/curl.h> defines. See the libcurl-errors(3)
man page for the full list with descriptions.
If you try to set an option that libcurl doesn't know about, perhaps
because the library is too old to support it or the option was removed
in a recent version, this function will return CURLE_FAILED_INIT.
SEE ALSOcurl_easy_init(3), curl_easy_cleanup(3), curl_easy_reset(3)libcurl 7.19.3 11 Dec 2008 curl_easy_setopt(3)
