HTTP/2 support

HTTP/2 gives a number of optimizations, while keeping support for the
protocol.  HTTP/2 support was recently added to the Redfish
specification.  The largest performance increase in bmc usage is likely
header compression.  Almost all requests reuse the same header values,
so the hpack based compression scheme in HTTP/2 allows OpenBMC to be
more efficient as a transport, and has the potential to significantly
reduce the number of bytes we're sending on the wire.

This commit adds HTTP2 support to bmcweb through nghttp2 library.  When
static linked into bmcweb, this support adds 53.4KB to the bmcweb binary
size.  nghttp2 is available in meta-oe already.

Given the experimental nature of this option, it is added under the
meson option "experimental-http2" and disabled by default.  The hope is
to enable it at some point in the future.

To accomplish the above, there a new class, HTTP2Connection is created.
This is intended to isolate HTTP/2 connections code from HttpConnection
such that it is far less likely to cause bugs, although it does
duplicate about 20 lines of code (async_read_some, async_write_some,
buffers, etc).  This seems worth it for the moment.

In a similar way to Websockets, when an HTTP/2 connection is detected
through ALPN, the HTTP2Connection class will be instantiated, and the
socket object passed to it, thus allowing the Connection class to be
destroyed, and the HTTP2Connection to take over for the user.

Tested: Redfish service validator passes with option enabled
With option disabled
GET /redfish/v1 in curl shows ALPN non negotiation, and fallback to
http1.1

With the option enable
GET /redfish/v1 in curl shows ALPN negotiates to HTTP2

Change-Id: I7839e457e0ba918b0695e04babddd0925ed3383c
Signed-off-by: Ed Tanous <edtanous@google.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/meson_options.txt b/meson_options.txt
index dbfa00d0fe..017c16bd68 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -281,6 +281,15 @@ option(
     production environment, or where API stability is required.'''
 )
 
+option(
+    'experimental-http2',
+    type: 'feature',
+    value: 'disabled',
+    description: '''Enable HTTP/2 protocol support using nghttp2.  Do not rely
+                    on this option for any production systems.  It may have
+                    behavior changes or be removed at any time.'''
+)
+
 # Insecure options. Every option that starts with a `insecure` flag should
 # not be enabled by default for any platform, unless the author fully comprehends
 # the implications of doing so.In general, enabling these options will cause security