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