The net effect of this bug as it appeared to users, would be that
libcurl would timeout in the connect phase.
When disabling IPv6 use but still using getaddrinfo, libcurl would
wrongly not init the "hints" struct field in init_thread_sync() which
would subsequently lead to a getaddrinfo() invoke with a zeroed hints
with ai_socktype set to 0 instead of SOCK_STREAM. This would lead to
different behaviors on different platforms but basically incorrect
output.
This code was introduced in 483ff1ca75cbea, released in curl 7.20.0.
This bug became a problem now due to the happy eyeballs code and how
libcurl now traverses the getaddrinfo() results differently.
Bug: http://curl.haxx.se/mail/lib-2014-01/0061.html
Reported-by: Fabian Frank
Debugged-by: Fabian Frank
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.
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