mirror of
https://github.com/moparisthebest/curl
synced 2024-11-14 05:25:06 -05:00
72 lines
3.3 KiB
Plaintext
72 lines
3.3 KiB
Plaintext
Doing 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, it cannot be implemented easily
|
|
into libcurl's easy interface due to its synchronous nature. We therefore only
|
|
aim on adding 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 however, will force us to allow apps to somehow "connect" two (or
|
|
more) easy handles that are added to a multi handle. The first one sends a
|
|
request and receives a response, just as normal, while the second (and
|
|
subsequent) ones need to be attached to the first handle so that it can send
|
|
its request on the same connection and then sit and wait until its response
|
|
comes.
|
|
|
|
API
|
|
|
|
We add 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.
|
|
|
|
Decisions Already Made
|
|
|
|
- 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.
|
|
|
|
To Ponder About
|
|
|
|
- We need options to control max pipeline length, and probably how to behave
|
|
if we reach that limit. As was discussed on the list, it can probably be
|
|
made very complicated, so perhaps we can think of a way to pass all
|
|
variables involved to a callback and let the application decide how to act
|
|
in specific situations. Either way, these fancy options are only interesting
|
|
to work on when everything is working and we have working apps to test with.
|
|
|
|
- Currently (before pipelining) we do not have any code or concept that lets
|
|
multiple handles share the same physical connection. We need to carefully
|
|
make sure that each easy handle knows exactly what they can do and when, on
|
|
the shared connection.
|
|
|
|
- We need to keep a linked list of each handle that is part of a single pipe
|
|
so that if it breaks, we know which handles that need to resend their
|
|
requests. The pipe linked-lists could very well be "held" in the multi
|
|
handle struct so that they won't "belong" to a particular easy handle that
|
|
happens to be part of the pipeline during a certain period.
|