Re: [hybi] Masking of Control Frames that have a zero length payload.

John Tamplin <jat@google.com> Wed, 22 June 2011 08:27 UTC

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From: John Tamplin <jat@google.com>
Date: Wed, 22 Jun 2011 04:27:05 -0400
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To: Len Holgate <len.holgate@gmail.com>
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Subject: Re: [hybi] Masking of Control Frames that have a zero length payload.
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On Wed, Jun 22, 2011 at 4:19 AM, Len Holgate <len.holgate@gmail.com> wrote:

> I haven't been able to find a previous discussion on this list about this
> point, forgive me if it's already been covered.
>
> 4.3 Client-to-Server Masking
>
> States that "The client MUST mask all frames sent to the server."
>
> 4.5 Control Frames
>
> States that "All control frames MUST have a payload length of 125 bytes or
> less..."
>
> 4.5.1 Close
>
> States that "The Close frame MAY contain a body (the "application data"
> portion of the frame)
>
> Which implies to me that control frames with a zero length payload may
> exist
> but if these are sent from client to server then these MUST still be
> masked,
> which results in the inclusion of a masking key which is not used for
> anything and simply increases the length of the frame for no reason.
>
> Perhaps the inclusion of the rationale behind client to server masking
> would
> clear this up - including the masking key when no data needs to be masked
> makes the control frame unique and unpredictable and perhaps this is the
> reason, but at present it's unclear as to why the above is desirable.
>

IMHO, the utility of a zero-length frame seems low enough that it doesn't
warrant adding a special case to leave off the mask if the payload length is
zero.

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