Re: [hybi] Comments about draft-13

[John Tamplin <[e-mail]>]

On Wed, Sep 7, 2011 at 9:52 PM, Greg Wilkins <[e-mail]> wrote:

> If the application layer accepts a connection with "foo" and "bar"
> then obviously it is saying that it has a way to tell the difference
> between "foo" and "bar" messages, because it is the application layer
> that does the protocol handling.
>
> If the application can't handle multiple protocols, or a particular
> mix of protocols, then it just doesn't accept the connection, or
> accepts with only 1 protocol.
>

Then it is your application that is the subprotocol and provides a way to
distinguish them.  A server component that understands the "foo" protocol
should be able to speak it without knowing it needs to add some
disambiguation about which subprotocol a particular message belongs to.

It seems to me that your example should be "my-layered-protocol", which has
some identifier for the next-layer protocol, then the payload of that next
layer protocol.

As a practical example, let's say that the client ask for the "foo" and
"bar" subprotocols.  The server can speak either of them.  How does it
decide between answering "foo", "bar", or "foo, bar"?  Does it have to keep
a table of which subprotocols are mutually distinguishable so they can be
accepted together?  Do you rely on heuristics, or do all subprotocols have
to have a "magic value" at the beginning of each message so they can be
distinguished?

-- 
John A. Tamplin
Software Engineer (GWT), Google