Re: [quicwg/base-drafts] Extension frames (#1473)

[ianswett <[e-mail]>]

ianswett approved this pull request.

Looking good.

> @@ -921,6 +924,30 @@ explained in more detail as they are referenced later in the document.
 All QUIC frames are idempotent.  That is, a valid frame does not cause
 undesirable side effects or errors when received more than once.
 
+The Frame Type field uses a variable length integer encoding (see
+{{integer-encoding}}) with one exception.  To ensure simple and efficient
+implementations of frame parsing, a frame type MUST use the shortest possible
+encoding.  Though a two-, four- or eight-octet encoding of the frame types
+defined in this document is possible, the Frame Type field for these frames are
+encoded on a single octet.  For instance, though 0x4007 is a legitimate
+two-octet encoding for a variable-length integer with a value of 7, PING frames
+are always encoded as a single octet with the value 0x07.

Agreed, I think we either need to say you MAY close the connection or this is a SHOULD not a MUST

> +implementations of frame parsing, a frame type MUST use the shortest possible
+encoding.  Though a two-, four- or eight-octet encoding of the frame types
+defined in this document is possible, the Frame Type field for these frames are
+encoded on a single octet.  For instance, though 0x4007 is a legitimate
+two-octet encoding for a variable-length integer with a value of 7, PING frames
+are always encoded as a single octet with the value 0x07.
+
+## Extension Frames
+
+QUIC frames do not use a self-describing encoding.  An endpoint therefore needs
+to understand the syntax of all frame before it can successfully process a
+packet.  This allows for efficient encoding of frames, but it means that an
+endpoint cannot send a frame of a type that is unknown to its peer.
+
+An extension to QUIC that wishes to use a new type of frame MUST first ensure
+that a peer is able to understand the frame.  An endpoint can use a transport

It would be nice to have an example here at some point, but since we don't have any extension frames, I guess that's for the future?

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