cohttp-eio(client/server): Mitigate Against Attacks via Protocol Element Length

[bikallem]

cohttp-eio client/server should attempt to mitigate against some of the issues highlighted in the RFC advisory https://www.rfc-editor.org/rfc/rfc7230#section-9.3.

9.3. Attacks via Protocol Element Length

Because HTTP uses mostly textual, character-delimited fields, parsers
are often vulnerable to attacks based on sending very long (or very
slow) streams of data, particularly where an implementation is
expecting a protocol element with no predefined length.

This should be considered for both eio client and server.

This is a meta/parent issue to track specific action items below:

• Body length (cohttp-eio: Allow maximum content-length header to be configurable in client and server #928)
• resource path length

References:

1. https://www.rfc-editor.org/rfc/rfc6585#section-5
2. https://www.rfc-editor.org/rfc/rfc6585#section-7
3. https://www.rfc-editor.org/rfc/rfc7230#section-9.3