1HTTP Pipelining with libcurl 2============================ 3 4Background 5 6Since pipelining implies that one or more requests are sent to a server before 7the previous response(s) have been received, we only support it for multi 8interface use. 9 10Considerations 11 12When using the multi interface, you create one easy handle for each transfer. 13Bascially any number of handles can be created, added and used with the multi 14interface - simultaneously. It is an interface designed to allow many 15simultaneous transfers while still using a single thread. Pipelining does not 16change any of these details. 17 18API 19 20We've added a new option to curl_multi_setopt() called CURLMOPT_PIPELINING 21that enables "attempted pipelining" and then all easy handles used on that 22handle will attempt to use an existing pipeline. 23 24Details 25 26- A pipeline is only created if a previous connection exists to the same IP 27 address that the new request is being made to use. 28 29- Pipelines are only supported for HTTP(S) as no other currently supported 30 protocol has features resemembling this, but we still name this feature 31 plain 'pipelining' to possibly one day support it for other protocols as 32 well. 33 34- HTTP Pipelining is for GET and HEAD requests only. 35 36- When a pipeline is in use, we must take precautions so that when used easy 37 handles (i.e those who still wait for a response) are removed from the multi 38 handle, we must deal with the outstanding response nicely. 39 40- Explicitly asking for pipelining handle X and handle Y won't be supported. 41 It isn't easy for an app to do this association. The lib should probably 42 still resolve the second one properly to make sure that they actually _can_ 43 be considered for pipelining. Also, asking for explicit pipelining on handle 44 X may be tricky when handle X get a closed connection. 45 46- We need options to control max pipeline length, and probably how to behave 47 if we reach that limit. As was discussed on the list, it can probably be 48 made very complicated, so perhaps we can think of a way to pass all 49 variables involved to a callback and let the application decide how to act 50 in specific situations. Either way, these fancy options are only interesting 51 to work on when everything is working and we have working apps to test with. 52