Section: curl_multi_setopt options (3)
Updated: November 04, 2020
CURLMOPT_PIPELINING - enable HTTP pipelining and multiplexing
CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_PIPELINING, long bitmask);
Pass in the bitmask
parameter to instruct libcurl to enable HTTP
pipelining and/or HTTP/2 multiplexing for this multi handle.
When enabled, libcurl will attempt to use those protocol features when doing
parallel requests to the same hosts.
For pipelining, this means that if you add a second request that can use an
already existing connection, the second request will be "piped" on the same
connection rather than being executed in parallel.
For multiplexing, this means that follow-up requests can re-use an existing
connection and send the new request multiplexed over that at the same time as
other transfers are already using that single connection.
There are several other related options that are interesting to tweak and
adjust to alter how libcurl spreads out requests on different connections or
Before 7.43.0, this option was set to 1 and 0 to enable and disable HTTP/1.1
Starting in 7.43.0, bitmask's second bit also has a meaning, and you can
ask for pipelining and multiplexing independently of each other by toggling
the correct bits.
Default, which means doing no attempts at pipelining or multiplexing.
If this bit is set, libcurl will try to pipeline HTTP/1.1 requests on
connections that are already established and in use to hosts.
This bit is deprecated and has no effect since version 7.62.0.
If this bit is set, libcurl will try to multiplex the new transfer over an
existing connection if possible. This requires HTTP/2.
Since 7.62.0, CURLPIPE_MULTIPLEX
is enabled by default.
Before that, default was CURLPIPE_NOTHING.
CURLM *m = curl_multi_init();
/* try HTTP/2 multiplexing */
curl_multi_setopt(m, CURLMOPT_PIPELINING, CURLPIPE_MULTIPLEX);
Added in 7.16.0. Multiplex support bit added in 7.43.0. HTTP/1 Pipelining
support was disabled in 7.62.0.
Returns CURLM_OK if the option is supported, and CURLM_UNKNOWN_OPTION if not.