Bug: https://github.com/bagder/curl/pull/168
(trynextip)
- Don't try the "other" protocol family unless IPv6 is available. In an
IPv4-only build the other family can only be IPv6 which is unavailable.
This change essentially stops IPv4-only builds from attempting the
"happy eyeballs" secondary parallel connection that is supposed to be
used by the "other" address family.
Prior to this change in IPv4-only builds that secondary parallel
connection attempt could be erroneously used by the same family (IPv4)
which caused a bug where every address after the first for a host could
be tried twice, often in parallel. This change fixes that bug. An
example of the bug is shown below.
Assume MTEST resolves to 3 addresses 127.0.0.2, 127.0.0.3 and 127.0.0.4:
* STATE: INIT => CONNECT handle 0x64f4b0; line 1046 (connection #-5000)
* Rebuilt URL to: http://MTEST/
* Added connection 0. The cache now contains 1 members
* STATE: CONNECT => WAITRESOLVE handle 0x64f4b0; line 1083
(connection #0)
* Trying 127.0.0.2...
* STATE: WAITRESOLVE => WAITCONNECT handle 0x64f4b0; line 1163
(connection #0)
* Trying 127.0.0.3...
* connect to 127.0.0.2 port 80 failed: Connection refused
* Trying 127.0.0.3...
* connect to 127.0.0.3 port 80 failed: Connection refused
* Trying 127.0.0.4...
* connect to 127.0.0.3 port 80 failed: Connection refused
* Trying 127.0.0.4...
* connect to 127.0.0.4 port 80 failed: Connection refused
* connect to 127.0.0.4 port 80 failed: Connection refused
* Failed to connect to MTEST port 80: Connection refused
* Closing connection 0
* The cache now contains 0 members
* Expire cleared
curl: (7) Failed to connect to MTEST port 80: Connection refused
The bug was born in commit bagder/curl@2d435c7.
HTTP Pipelining with libcurl
============================
Background
Since pipelining implies that one or more requests are sent to a server before
the previous response(s) have been received, we only support it for multi
interface use.
Considerations
When using the multi interface, you create one easy handle for each transfer.
Bascially any number of handles can be created, added and used with the multi
interface - simultaneously. It is an interface designed to allow many
simultaneous transfers while still using a single thread. Pipelining does not
change any of these details.
API
We've added a new option to curl_multi_setopt() called CURLMOPT_PIPELINING
that enables "attempted pipelining" and then all easy handles used on that
handle will attempt to use an existing pipeline.
Details
- A pipeline is only created if a previous connection exists to the same IP
address that the new request is being made to use.
- Pipelines are only supported for HTTP(S) as no other currently supported
protocol has features resemembling this, but we still name this feature
plain 'pipelining' to possibly one day support it for other protocols as
well.
- HTTP Pipelining is for GET and HEAD requests only.
- When a pipeline is in use, we must take precautions so that when used easy
handles (i.e those who still wait for a response) are removed from the multi
handle, we must deal with the outstanding response nicely.
- Explicitly asking for pipelining handle X and handle Y won't be supported.
It isn't easy for an app to do this association. The lib should probably
still resolve the second one properly to make sure that they actually _can_
be considered for pipelining. Also, asking for explicit pipelining on handle
X may be tricky when handle X get a closed connection.
059b3a5770