[hybi] Frame size

["Thomson, Martin" <[e-mail]>]

Responding to specific concerns on framing seems not especially productive.

Proposal:

 - Frame size is indicated up front.
 - Frames are binary.
 - Frame size be strictly limited (2 octets should suffice).
 - Sub-protocol needed if messages are larger than the max frame.

Justification:

Most use cases are for low latency bi-directional communications.  These don't need large messages.

HTTP is (much) better suited to file transfers in the server->client direction and despite some historical shortcomings in the other direction, still arguably superior (chunked encoding, etc...).

Limiting message size helps keep simple implementations simple; but isn't a burden on implementations that have more complex requirements.

Binary frames isolate user-space (the payload) from the framing layer.  We had this discussion in the meeting (c.f. Pete Resnick's comments).  Thus, 
 - binary frames are easier to process (intermediaries don't have to inspect every octet)
 - kinder on implementations (framing component does not depend on UTF-8 component)
 - isolates framing layer from the bugs of higher layers

Shortcomings:

Greg did have some use cases where larger messages were desired.  A trivial sub-protocol that consists of a continuation marker would solve this.

IF used for UTF-8 AND implementer counts characters instead of octets THEN framing doesn't work.  (One solution to this problem is to start a frame with a known sequence of octets, so that this can be detected.  Another "solution" is to not worry about it.)

--Martin