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56 lines
2.5 KiB
Plaintext
56 lines
2.5 KiB
Plaintext
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Doing 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, it cannot be implemented easily
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into libcurl's easy interface due to its synchronous nature. We therefore only
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aim on adding it for multi 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.
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Pipelining however, will force us to allow apps to somehow "connect" two (or
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more) easy handles that are added to a multi handle. The first one sends a
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request and receives a response, just as normal, while the second (and
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subsequent) ones need to be attached to the first handle so that it can send
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its request on the same connection and then sit and wait until its response
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comes.
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To ponder about:
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- Explicitly ask for pipelining handle X and handle Y ? It isn't always that
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easy for an app to do this association. The lib should probably still resolve
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the second one properly to make sure that they actually _can_ be considered
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for pipelining. Also, asking for explicit pipelining on handle X may be
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tricky when handle X get a closed connection.
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- Have an option like "attempt pipelining" and then it _may_ use that if an
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existing connection is already present against our target HTTP server? May
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cause funny effects if the first transfer is a slow big file and the second
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is a very small one... Also probably requires some kind of notification
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support so that the app can get to know that the handle is put "in line" for
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pipelining.
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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.
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- When a pipeline is in use, we must take precautions so that we either don't
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allow the used handles (i.e those who still wait for a response) to be
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removed, or we allow removal but still deal with the outstanding response
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somehow.
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- Currently (before pipelining) we do not have any code or concept that lets
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multiple handles share the same physical connection. We need a lock concept
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and carefully make sure that each handle knows exactly what they can do and
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when, on the shared connection.
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- We need to keep a linked list of each handle that is part of a single pipe
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so that if it breaks, we know which handles that need to resend their
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requests.
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