The motivation for having a separate struct that keep track of an easy
handle when using the multi handle was removed when we switched to
always using the multi interface internally. Now they were just two
separate struct that was always allocated for each easy handle.
This first step just moves the Curl_one_easy struct members into the
SessionHandle struct and hides this somehow (== keeps the source code
changes to a minimum) by defining Curl_one_easy to SessionHandle
The biggest changes in this commit are:
1 - the linked list of easy handles had to be changed somewhat due
to the new struct layout. This made the main linked list pointer
get renamed to 'easyp' and there's also a new pointer to the last
node, called easylp. It is no longer circular but ends with ->next
pointing to NULL. New nodes are still added last.
2 - easy->state is now called easy->mstate to avoid name collision
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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