mirror of
https://github.com/moparisthebest/curl
synced 2024-11-13 21:15:08 -05:00
108 lines
3.9 KiB
Markdown
108 lines
3.9 KiB
Markdown
HTTP/2 with curl
|
|
================
|
|
|
|
[HTTP/2 Spec](https://www.rfc-editor.org/rfc/rfc7540.txt)
|
|
[http2 explained](http://daniel.haxx.se/http2/)
|
|
|
|
Build prerequisites
|
|
-------------------
|
|
- nghttp2
|
|
- OpenSSL, NSS, GnutTLS or PolarSSL with a new enough version
|
|
|
|
[nghttp2](https://nghttp2.org/)
|
|
-------------------------------
|
|
|
|
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.
|
|
|
|
We require at least version 1.0.0.
|
|
|
|
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 HTTP/2.
|
|
|
|
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 HTTP/2 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 HTTP/2.
|
|
Consider options to explicitly disable ALPN and/or NPN.
|
|
|
|
ALPN is the TLS extension that HTTP/2 is expected to use. The NPN extension is
|
|
for a similar purpose, was made prior to ALPN and is used for SPDY so early
|
|
HTTP/2 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
|
|
|
|
Multiplexing
|
|
------------
|
|
|
|
Starting in 7.43.0, libcurl fully supports HTTP/2 multiplexing, which is the
|
|
term for doing multiple independent transfers over the same physical TCP
|
|
connection.
|
|
|
|
To take advantage of multiplexing, you need to use the multi interface and set
|
|
`CURLMOPT_PIPELINING` to `CURLPIPE_MULTIPLEX`. With that bit set, libcurl will
|
|
attempt to re-use existing HTTP/2 connections and just add a new stream over
|
|
that when doing subsequent parallel requests.
|
|
|
|
While libcurl sets up a connection to a HTTP server there is a period during
|
|
which it doesn't know if it can pipeline or do multiplexing and if you add new
|
|
transfers in that period, libcurl will default to start new connections for
|
|
those transfers. With the new option `CURLOPT_PIPEWAIT` (added in 7.43.0), you
|
|
can ask that a transfer should rather wait and see in case there's a
|
|
connection for the same host in progress that might end up being possible to
|
|
multiplex on. It favours keeping the number of connections low to the cost of
|
|
slightly longer time to first byte transferred.
|
|
|
|
Applications
|
|
------------
|
|
|
|
We hide HTTP/2's binary nature and convert received HTTP/2 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 HTTP/2
|
|
|
|
HTTP Alternative Services
|
|
-------------------------
|
|
|
|
Alt-Svc is a suggested extension with a corresponding frame (ALTSVC) in HTTP/2
|
|
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](https://tools.ietf.org/html/draft-ietf-httpbis-alt-svc-05)
|
|
|
|
TODO
|
|
----
|
|
|
|
- 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.
|
|
|