[hybi] Handling multiple compression method entries of the same extension

[Takeshi Yoshino <[e-mail]>]

Hi,

I'm going to clarify whether multiple method descriptions with the same
method name is allowed to be listed in the perframe-compress's method
parameter or not.

The benefit of allowing multiple entries is that the client can offer the
same extension with different parameter settings to try to use the best
parameter both endpoints can agree.

There's also a problem with this. The client cannot identify which of the
entries has been accepted by the remote endpoint.

Options we can take are:

----

1-a) disallow use of multiple entries

2-a) tag requested methods
Request:
perframe-compress: method="deflate; id=0; foo=200, deflate; id=1; foo=100,
deflate; id=2; foo=0"
Response:
perframe-compress: method="deflate; id=1; bar=3.14"

2-b) put "rejected" that means the method placed at the corresponding
position in the requested-method-list has been rejected.
Request:
perframe-compress: method="deflate; foo=200, deflate; foo=100, deflate;
foo=0"
Response:
perframe-compress: method="rejected, deflate; bar=3.14, rejected"

2-c) send back not a method description but the index of the description to
accept and server-side parameter
Request:
perframe-compress: method="deflate; foo=200, deflate; foo=100, deflate;
foo=0"
Response:
perframe-compress: accept=1; bar=3.14

2-d) ack the requested parameters by echoing them back to make the
accepted-method-desc self-contained (describing all negotiated parameters)
Request:
perframe-compress: method="deflate; foo=200, deflate; foo=100, deflate;
foo=0"
Response:
perframe-compress: method="deflate; foo=100; bar=3.14"

----

My preference is 2-d). I'll rename max_window_bits and no_context_takeover
by prefixing them.

What do you think?