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

"Len Holgate" <len.holgate@gmail.com> Wed, 22 June 2011 08:19 UTC

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From: "Len Holgate" <len.holgate@gmail.com>
To: <hybi@ietf.org>
Date: Wed, 22 Jun 2011 09:19:24 +0100
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Subject: [hybi] Masking of Control Frames that have a zero length payload.
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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

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.