Annotation of embedaddon/curl/docs/HTTP2.md, revision 1.1.1.1
1.1 misho 1: HTTP/2 with curl
2: ================
3:
4: [HTTP/2 Spec](https://www.rfc-editor.org/rfc/rfc7540.txt)
5: [http2 explained](https://daniel.haxx.se/http2/)
6:
7: Build prerequisites
8: -------------------
9: - nghttp2
10: - OpenSSL, libressl, BoringSSL, NSS, GnutTLS, mbedTLS, wolfSSL or Schannel
11: with a new enough version.
12:
13: [nghttp2](https://nghttp2.org/)
14: -------------------------------
15:
16: libcurl uses this 3rd party library for the low level protocol handling
17: parts. The reason for this is that HTTP/2 is much more complex at that layer
18: than HTTP/1.1 (which we implement on our own) and that nghttp2 is an already
19: existing and well functional library.
20:
21: We require at least version 1.12.0.
22:
23: Over an http:// URL
24: -------------------
25:
26: If `CURLOPT_HTTP_VERSION` is set to `CURL_HTTP_VERSION_2_0`, libcurl will
27: include an upgrade header in the initial request to the host to allow
28: upgrading to HTTP/2.
29:
30: Possibly we can later introduce an option that will cause libcurl to fail if
31: not possible to upgrade. Possibly we introduce an option that makes libcurl
32: use HTTP/2 at once over http://
33:
34: Over an https:// URL
35: --------------------
36:
37: If `CURLOPT_HTTP_VERSION` is set to `CURL_HTTP_VERSION_2_0`, libcurl will use
38: ALPN (or NPN) to negotiate which protocol to continue with. Possibly introduce
39: an option that will cause libcurl to fail if not possible to use HTTP/2.
40:
41: `CURL_HTTP_VERSION_2TLS` was added in 7.47.0 as a way to ask libcurl to prefer
42: HTTP/2 for HTTPS but stick to 1.1 by default for plain old HTTP connections.
43:
44: ALPN is the TLS extension that HTTP/2 is expected to use. The NPN extension is
45: for a similar purpose, was made prior to ALPN and is used for SPDY so early
46: HTTP/2 servers are implemented using NPN before ALPN support is widespread.
47:
48: `CURLOPT_SSL_ENABLE_ALPN` and `CURLOPT_SSL_ENABLE_NPN` are offered to allow
49: applications to explicitly disable ALPN or NPN.
50:
51: SSL libs
52: --------
53:
54: The challenge is the ALPN and NPN support and all our different SSL
55: backends. You may need a fairly updated SSL library version for it to provide
56: the necessary TLS features. Right now we support:
57:
58: - OpenSSL: ALPN and NPN
59: - libressl: ALPN and NPN
60: - BoringSSL: ALPN and NPN
61: - NSS: ALPN and NPN
62: - GnuTLS: ALPN
63: - mbedTLS: ALPN
64: - Schannel: ALPN
65: - wolfSSL: ALPN
66: - Secure Transport: ALPN
67:
68: Multiplexing
69: ------------
70:
71: Starting in 7.43.0, libcurl fully supports HTTP/2 multiplexing, which is the
72: term for doing multiple independent transfers over the same physical TCP
73: connection.
74:
75: To take advantage of multiplexing, you need to use the multi interface and set
76: `CURLMOPT_PIPELINING` to `CURLPIPE_MULTIPLEX`. With that bit set, libcurl will
77: attempt to re-use existing HTTP/2 connections and just add a new stream over
78: that when doing subsequent parallel requests.
79:
80: While libcurl sets up a connection to a HTTP server there is a period during
81: which it doesn't know if it can pipeline or do multiplexing and if you add new
82: transfers in that period, libcurl will default to start new connections for
83: those transfers. With the new option `CURLOPT_PIPEWAIT` (added in 7.43.0), you
84: can ask that a transfer should rather wait and see in case there's a
85: connection for the same host in progress that might end up being possible to
86: multiplex on. It favours keeping the number of connections low to the cost of
87: slightly longer time to first byte transferred.
88:
89: Applications
90: ------------
91:
92: We hide HTTP/2's binary nature and convert received HTTP/2 traffic to headers
93: in HTTP 1.1 style. This allows applications to work unmodified.
94:
95: curl tool
96: ---------
97:
98: curl offers the `--http2` command line option to enable use of HTTP/2.
99:
100: curl offers the `--http2-prior-knowledge` command line option to enable use of
101: HTTP/2 without HTTP/1.1 Upgrade.
102:
103: Since 7.47.0, the curl tool enables HTTP/2 by default for HTTPS connections.
104:
105: curl tool limitations
106: ---------------------
107:
108: The command line tool won't do any HTTP/2 multiplexing even though libcurl
109: supports it, simply because the curl tool is not written to take advantage of
110: the libcurl API that's necessary for this (the multi interface). We have an
111: outstanding TODO item for this and **you** can help us make it happen.
112:
113: The command line tool also doesn't support HTTP/2 server push for the same
114: reason it doesn't do multiplexing: it needs to use the multi interface for
115: that so that multiplexing is supported.
116:
117: HTTP Alternative Services
118: -------------------------
119:
120: Alt-Svc is an extension with a corresponding frame (ALTSVC) in HTTP/2 that
121: tells the client about an alternative "route" to the same content for the same
122: origin server that you get the response from. A browser or long-living client
123: can use that hint to create a new connection asynchronously. For libcurl, we
124: may introduce a way to bring such clues to the application and/or let a
125: subsequent request use the alternate route automatically.
126:
127: [Detailed in RFC 7838](https://tools.ietf.org/html/rfc7838)
FreeBSD-CVSweb <freebsd-cvsweb@FreeBSD.org>
![[BACK]](/icons/cvsweb/back.gif){kind=icon}
Return to HTTP2.md CVS log ![[TXT]](/icons/cvsweb/text.gif){kind=icon}
![[DIR]](/icons/cvsweb/dir.gif){kind=icon}
Up to [ELWIX - Embedded LightWeight unIX -] / embedaddon / curl / docs