mirror of
https://github.com/moparisthebest/curl
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88 lines
3.0 KiB
Plaintext
88 lines
3.0 KiB
Plaintext
HTTP2 with libcurl
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Spec: http://tools.ietf.org/html/draft-ietf-httpbis-http2
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Document explaining it: http://daniel.haxx.se/http2/
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Build prerequisites
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- nghttp2
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- OpenSSL, NSS, GnutTLS or PolarSSL with a new enough version
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nghttp2 (https://github.com/tatsuhiro-t/nghttp2)
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libcurl uses this 3rd party library for the low level protocol handling
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parts. The reason for this is that HTTP/2 is much more complex at that layer
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than HTTP/1.1 (which we implement on our own) and that nghttp2 is an already
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existing and well functional library.
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Right now, nghttp2 implements http2 draft-14
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We require at least version 0.6.0
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Over an http:// URL
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If CURLOPT_HTTP_VERSION is set to CURL_HTTP_VERSION_2_0, libcurl will
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include an upgrade header in the initial request to the host to allow
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upgrading to http2.
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Possibly we can later introduce an option that will cause libcurl to fail if
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not possible to upgrade. Possibly we introduce an option that makes libcurl
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use http2 at once over http://
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Over an https:// URL
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If CURLOPT_HTTP_VERSION is set to CURL_HTTP_VERSION_2_0, libcurl will use
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ALPN (or NPN) to negotiate which protocol to continue with. Possibly
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introduce an option that will cause libcurl to fail if not possible to use
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http2. Consider options to explicitly disable ALPN and/or NPN.
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ALPN is the TLS extension that http2 is expected to use. The NPN extension
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is for a similar purpose, was made prior to ALPN and is used for SPDY so
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early http2 servers are implemented using NPN before ALPN support is
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widespread.
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SSL libs
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The challenge is the ALPN and NPN support and all our different SSL
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backends. You may need a fairly updated SSL library version for it to
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provide the necessary TLS features. Right now we support:
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OpenSSL: ALPN and NPN
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NSS: ALPN and NPN
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GnuTLS: ALPN
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PolarSSL: ALPN
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HTTP Alternative Services
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Alt-Svc is a suggested extension with a corresponding frame (ALTSVC) in
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http2 that tells the client about an alternative "route" to the same content
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for the same origin server that you get the response from. A browser or
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long-living client can use that hint to create a new connection
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asynchronously. For libcurl, we may introduce a way to bring such clues to
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the applicaton and/or let a subsequent request use the alternate route
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automatically. Spec:
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http://tools.ietf.org/html/draft-ietf-httpbis-alt-svc-05
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Applications
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We hide http2's binary nature and convert received http2 traffic to headers
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in HTTP 1.1 style. This allows applications to work unmodified.
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curl tool
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curl offers the --http2 command line option to enable use of http2
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TODO:
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- Implement multiplexing
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- How to tell libcurl when using the multi interface that all or some of the
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handles are allowed to re-use the same physical connection. Can we just
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re-use existing pipelining logic?
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- Provide API to set priorities / dependencies of individual streams
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- Implement "prior-knowledge" HTTP/2 connecitons over clear text so that
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curl can connect with HTTP/2 at once without 1.1+Upgrade.
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