Re: [hybi] method of allocation of reserved bits to extensions

On Apr 27, 2011 11:12 PM, "Greg Wilkins" <gregw@intalio.com> wrote:
>
> Brodie,
>
> this is good. But I think we also need to say the same for op-codes.

It might be instructive to look at X Protocol opcodes for core and
extensions and how that played out over time.
>
> I think each extension needs to say how many bits, data op-codes and
> control op-codes it needs and then these should all be allocated in
> order.
>
> This will mean a minor inconvenience to developers of extensions, as
> they need to not have constant op-codes, but it is not a difficult
> thing we ask and it will give us interoperability of extensions.
>
> cheers
>
>
>
>
>
> On 28 April 2011 12:57, Brodie Thiesfield <brodie@jellycan.com> wrote:
> > If we accept Greg's suggestion, then the following text can be a base:
> >
> >
> >
> > 8.2 Allocating Reserved Bits
> >
> > An extension may require the use of a reserved bit in the framing for
> > proper operation. Because both the server and client must know all
> > extension requirements before negotiating their use, requirements for
> > use of reserved frame bit are known.
> >
> > The server and client will allocate reserved frame bits in a
> > predefined order. The order for the reserved bits is defined as the
> > number of the reserved bit as defined in section 4.2, i.e. RSV1 ->
> > RSV2 -> RSV3. The order of the extensions is defined by the order of
> > the extensions in the the Sec-WebSockets-Extensions response header.
> >
> > Example;
> >
> > The client requests the following 3 extensions:
> > Sec-WebSocket-Extensions: deflate-frame, sign-frame, mux-o-magic
> >
> > The server supports all extensions and sends the response header:
> > Sec-WebSocket-Extensions: deflate-frame, sign-frame, mux-o-magic
> >
> > If the deflate-frame extension requires 1 reserved bit and the
> > mux-o-magic extension requires 2 reserved bits, then the bits are
> > allocated as:
> >
> > deflate-frame: RSV1
> > mux-o-magic: RSV2, RSV3
> >
> > If the server response used a different ordering of extensions, the
> > allocated bits will be different according to the response extension
> > ordering.
> >
> > For example, given the following server response header:
> > Sec-WebSocket-Extensions: mux-o-magic, deflate-frame, sign-frame
> >
> > The reserved bits would be allocated as:
> > mux-o-magic: RSV1, RSV2
> > deflate-frame: RSV3
> >
> > If there are no available reserved bits to be allocated to an
> > extension the server MUST NOT agree to use the extension.
> >
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