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| HTTP2 with libcurl |
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| Spec: http://tools.ietf.org/html/draft-ietf-httpbis-http2 |
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| Build prerequisites |
| - nghttp2 |
| - 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 |
| parts. The reason for this is that HTTP2 is much more complex at that layer |
| than HTTP1.1 (which we implement on our own) and that nghttp2 is an already |
| 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, libcurl will include |
| an upgrade header in the initial request to the host to allow upgrading to |
| http2. |
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| 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:// |
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| Over an https:// URL |
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| If CURLOPT_HTTP_VERSION is set to CURL_HTTP_VERSION_2, 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. |
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| 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. |
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| SSL libs |
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| 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: |
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| OpenSSL: ALPN and NPN |
| NSS: ALPN and NPN |
| GnuTLS: ALPN |
| PolarSSL: ALPN |
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| Alt-Svc |
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| Alt-Svc is a suggested new header 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. |
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| Applications |
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| We hide http2's binary nature and convert received http2 traffic to headers |
| 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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| To consider: |
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| - 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? |
