Cleartext HTTP/2 lands, and an HTTP/2 security fix.
Cleartext HTTP/2 (h2c)
http2_cleartext accepts prior-knowledge, upgrade, both or off (the
default). Prior knowledge serves a connection that opens with the HTTP/2
preface; upgrade honours an HTTP/1.1 Upgrade: h2c request. Both work on the
gthread, gevent and asgi workers.
This is for deployments where TLS is terminated by a proxy that speaks HTTP/2
upstream, so the hop into gunicorn no longer drops to HTTP/1.1. Only peers in
forwarded_allow_ips are considered; everyone else is served HTTP/1.x exactly
as if the setting were off. Each mechanism is enabled separately, so turning one
on does not turn the other on.
Do not expose a cleartext HTTP/2 port to the internet.
Security
HTTP2Request built its headers straight from the stream, so nothing the HTTP/1
path enforces applied over HTTP/2: the underscore and header_map policy,
duplicate Host and Content-Type, control characters in values, and the
forwarded_allow_ips trust gate. An untrusted client could set SCRIPT_NAME
and forge HTTP_* entries in the WSGI environ, and decide wsgi.url_scheme
through :scheme. Both request classes now share one policy mixin, and the
scheme comes from the transport.
If you serve HTTP/2, this is the reason to upgrade.
Other HTTP/2 fixes
WSGI responses were buffered whole before anything was sent; they stream now.
HEAD, 204 and 304 no longer carry a body. Events read while blocked on a
flow-control window were discarded, losing requests and body data outright.
sendfile() is refused on HTTP/2 responses rather than bypassing framing.
Request bodies dropped on Upgrade requests
On the ASGI worker with the fast parser, any request carrying an Upgrade
header reached the application with an empty body, whatever the header's value
and with HTTP/2 switched off entirely. Fixed in gunicorn_h1c 0.6.9, which the
fast extra now requires.
Full changelog: https://gunicorn.org/news/