mirror of
https://github.com/moparisthebest/curl
synced 2024-11-17 23:15:08 -05:00
8a49b291cb
The productname from Microsoft is "Schannel", but in infof/failf reporting we use "schannel". This removes different versions. Closes #3243 Reviewed-by: Daniel Stenberg <daniel@haxx.se>
128 lines
4.8 KiB
Markdown
128 lines
4.8 KiB
Markdown
HTTP/2 with curl
|
|
================
|
|
|
|
[HTTP/2 Spec](https://www.rfc-editor.org/rfc/rfc7540.txt)
|
|
[http2 explained](https://daniel.haxx.se/http2/)
|
|
|
|
Build prerequisites
|
|
-------------------
|
|
- nghttp2
|
|
- OpenSSL, libressl, BoringSSL, NSS, GnutTLS, mbedTLS, wolfSSL or Schannel
|
|
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.
|
|
|
|
`CURL_HTTP_VERSION_2TLS` was added in 7.47.0 as a way to ask libcurl to prefer
|
|
HTTP/2 for HTTPS but stick to 1.1 by default for plain old HTTP connections.
|
|
|
|
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.
|
|
|
|
`CURLOPT_SSL_ENABLE_ALPN` and `CURLOPT_SSL_ENABLE_NPN` are offered to allow
|
|
applications to explicitly disable ALPN or NPN.
|
|
|
|
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
|
|
- libressl: ALPN and NPN
|
|
- BoringSSL: ALPN and NPN
|
|
- NSS: ALPN and NPN
|
|
- GnuTLS: ALPN
|
|
- mbedTLS: ALPN
|
|
- Schannel: ALPN
|
|
- wolfSSL: ALPN
|
|
- Secure Transport: 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.
|
|
|
|
curl offers the `--http2-prior-knowledge` command line option to enable use of
|
|
HTTP/2 without HTTP/1.1 Upgrade.
|
|
|
|
Since 7.47.0, the curl tool enables HTTP/2 by default for HTTPS connections.
|
|
|
|
curl tool limitations
|
|
---------------------
|
|
|
|
The command line tool won't do any HTTP/2 multiplexing even though libcurl
|
|
supports it, simply because the curl tool is not written to take advantage of
|
|
the libcurl API that's necessary for this (the multi interface). We have an
|
|
outstanding TODO item for this and **you** can help us make it happen.
|
|
|
|
The command line tool also doesn't support HTTP/2 server push for the same
|
|
reason it doesn't do multiplexing: it needs to use the multi interface for
|
|
that so that multiplexing is supported.
|
|
|
|
HTTP Alternative Services
|
|
-------------------------
|
|
|
|
Alt-Svc is an 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 application and/or let a
|
|
subsequent request use the alternate route automatically.
|
|
|
|
[Detailed in RFC 7838](https://tools.ietf.org/html/rfc7838)
|