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52 lines
2.2 KiB
Plaintext
52 lines
2.2 KiB
Plaintext
HTTP Pipelining with libcurl
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============================
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Background
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Since pipelining implies that one or more requests are sent to a server before
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the previous response(s) have been received, we only support it for multi
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interface use.
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Considerations
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When using the multi interface, you create one easy handle for each transfer.
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Bascially any number of handles can be created, added and used with the multi
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interface - simultaneously. It is an interface designed to allow many
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simultaneous transfers while still using a single thread. Pipelining does not
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change any of these details.
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API
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We've added a new option to curl_multi_setopt() called CURLMOPT_PIPELINING
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that enables "attempted pipelining" and then all easy handles used on that
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handle will attempt to use an existing pipeline.
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Details
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- A pipeline is only created if a previous connection exists to the same IP
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address that the new request is being made to use.
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- Pipelines are only supported for HTTP(S) as no other currently supported
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protocol has features resemembling this, but we still name this feature
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plain 'pipelining' to possibly one day support it for other protocols as
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well.
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- HTTP Pipelining is for GET and HEAD requests only.
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- When a pipeline is in use, we must take precautions so that when used easy
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handles (i.e those who still wait for a response) are removed from the multi
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handle, we must deal with the outstanding response nicely.
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- Explicitly asking for pipelining handle X and handle Y won't be supported.
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It isn't easy for an app to do this association. The lib should probably
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still resolve the second one properly to make sure that they actually _can_
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be considered for pipelining. Also, asking for explicit pipelining on handle
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X may be tricky when handle X get a closed connection.
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- We need options to control max pipeline length, and probably how to behave
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if we reach that limit. As was discussed on the list, it can probably be
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made very complicated, so perhaps we can think of a way to pass all
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variables involved to a callback and let the application decide how to act
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in specific situations. Either way, these fancy options are only interesting
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to work on when everything is working and we have working apps to test with.
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