HTTP/2.0 Implementation Notes - 2013-11-07
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OVERVIEW

    HTTP/2.0 allows clients to send multiple, simultaneous requests over a
    single connection, as well as supporting server-side push delivery of
    content.  In the context of IPP, this would allow a single connection to
    support simultaneous job submission and monitoring.

    This will require changes to the HTTP API used in CUPS, and to cupsd and
    other CUPS-based servers.  This branch tracks that development.


DESIGN

    http_t will be updated to be accessible from multiple threads and track the
    HTTP state in a thread ID to stream ID/state table.  Applications can
    discover whether a Printer supports HTTP/2.0 with a new httpSupportsVersion
    API and upgrade to HTTP/2.0 with httpUpgradeToVersion.

    Calling httpPost in HTTP/1.1 mode will serialize requests between threads.
    Calling httpPost in HTTP/2.0 mode will create a new stream ID and issue
    requests in parallel.

    Q: How to handle incoming 2.0 requests? New httpServerRunLoop with
    callback that creates a new thread for all incoming requests and associates
    the thread with the stream ID.  httpWriteResponse is then tied to the stream
    ID.  For 1.1 mode the callback gets called on the current thread (no new
    threads created).

    Q: How to handle PUSH_PROMISE? New httpPushPromise API that creates a new
    thread and stream ID?


REFERENCES

    HTTPbis WG web site: http://tools.ietf.org/wg/httpbis

    Main spec: http://tools.ietf.org/html/draft-ietf-httpbis-http2

    Header compression spec:
        http://tools.ietf.org/html/draft-ietf-httpbis-header-compression