Hypercorn is based on the excellent hyper-h2 library.

TLS settings#

The recommendations in this documentation for the SSL/TLS ciphers and version are from RFC 7540. As required in the RFC ECDHE+AESGCM is the minimal cipher set HTTP/2 and TLSv2 the minimal TLS version servers should support. By default Hypercorn will use this as the cipher set.

ALPN Protocol#

The ALPN Protocols should be set to include h2 and http/1.1 as Hypercorn supports both. It is feasible to omit one to only serve the other. If these aren’t set most clients will assume Hypercorn is a HTTP/1.1 only server. By default Hypercorn will set h2 and http/1.1 as the ALPN protocols.


Most clients, including all the web browsers only support HTTP/2 over TLS. Hypercorn, however, supports the h2c HTTP/1.1 to HTTP/2 upgrade process. This allows a client to send a HTTP/1.1 request with a Upgrade: h2c header that results in the connection being upgraded to HTTP/2. To test this try

$ curl --http2 http://url:port/path

Note that in the absence of either the upgrade header or an ALPN protocol Hypercorn will assume and treat the connection as HTTP/1.1.

HTTP/2 features#

Hypercorn supports pipeling, flow control, server push, and prioritisation.