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Start indexing dynamic QPACK table beginning at zero #1650

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Start indexing dynamic QPACK table beginning at zero #1650

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14 changes: 10 additions & 4 deletions draft-ietf-quic-qpack.md
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Expand Up @@ -166,7 +166,7 @@ setting a maximum size of 0, which can subsequently be restored.

Each entry possesses both an absolute index which is fixed for the lifetime of
that entry and a relative index which changes over time based on the context of
the reference. The first entry inserted has an absolute index of "1"; indices
the reference. The first entry inserted has an absolute index of "0"; indices
increase sequentially with each insertion.

The relative index begins at zero and increases in the opposite direction from
Expand Down Expand Up @@ -255,8 +255,8 @@ Each header block contains a Largest Reference which identifies the table state
necessary for decoding. If the greatest absolute index in the dynamic table is
less than the value of the Largest Reference, the stream is considered
"blocked." While blocked, header field data should remain in the blocked
stream's flow control window. When the Largest Reference is zero, the frame
contains no references to the dynamic table and can always be processed
stream's flow control window. When the Largest Reference is not specified, the
frame contains no references to the dynamic table and can always be processed
immediately. A stream becomes unblocked when the greatest absolute index in the
dynamic table becomes greater than or equal to the Largest Reference for all
header blocks the decoder has started reading from the stream. If a decoder
Expand Down Expand Up @@ -573,7 +573,7 @@ before using it.

### Header Acknowledgement

After processing a header block whose declared Largest Reference is not zero,
After processing a header block whose declared Largest Reference is specified,
the decoder emits a Header Acknowledgement instruction on the decoder stream.
The instruction begins with the '1' one-bit pattern and includes the request
stream's stream ID, encoded as a 7-bit prefix integer. It is used by the
Expand Down Expand Up @@ -653,6 +653,12 @@ Header data is prefixed with two integers, `Largest Reference` and `Base Index`.
the block. Blocking decoders use the Largest Reference to determine when it is
safe to process the rest of the block.

Because zero is a valid absolute dynamic index value, the index of the
largest referenced entry is incremented by 1 before it is recorded in the
`Largest Reference` field. If the header block does not reference the
dynamic table, this field is set to zero: this indicates that the value
is not specified.

`Base Index` is used to resolve references in the dynamic table as described in
{{indexing}}.

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