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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. - 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.