Re: [quicwg/base-drafts] Use "Insert Count" rather than "Largest Reference" (#2111)

[Martin Thomson <[e-mail]>]

martinthomson commented on this pull request.

Thanks for the comments @bencebeky.

I think that this needs to change absolute indexing to 0-based to be consistent.  That makes everything else better.

> @@ -249,18 +250,19 @@ Because QUIC does not guarantee order between data on different streams, a
 header block might reference an entry in the dynamic table that has not yet been
 received.
 
-Each header block contains a Largest Reference ({{header-prefix}}) 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 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 the decoder encounters a header block where the actual largest reference is
-not equal to the Largest Reference declared in the prefix, it MAY treat this as
-a stream error of type HTTP_QPACK_DECOMPRESSION_FAILED.
+Each header block contains the total number of entries added to the dynamic

Thanks, that prompted me to restructure this (massive) paragraph.

> -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 the decoder encounters a header block where the actual largest reference is
-not equal to the Largest Reference declared in the prefix, it MAY treat this as
-a stream error of type HTTP_QPACK_DECOMPRESSION_FAILED.
+Each header block contains the total number of entries added to the dynamic
+table - the Required Insert Count - which identifies the table state necessary
+for decoding (see {{header-prefix}}). If the Required Insert Count is greater
+than the number of dynamic table entries received, the stream is considered
+"blocked."  While blocked, header field data SHOULD remain in the blocked
+stream's flow control window.  When the Required Insert Count is zero, the frame
+contains no references to the dynamic table and can always be processed
+immediately. A stream becomes unblocked when the number of entries inserted in
+the dynamic table becomes greater than or equal to the Required Insert Count for
+all header blocks the decoder has started reading from the stream.  If the
+decoder encounters a header block where the largest Absolute Index used not

I think that I'm OK with this as is.  Repeating the requirement is OK if that requirement is tricky.

>  
 n = count of entries inserted
 d = count of entries dropped
 ~~~~~
 {: title="Example Dynamic Table Indexing - Control Stream"}
 
 Because frames from request streams can be delivered out of order with
-instructions on the encoder stream, relative indices are relative to the Base
-Index at the beginning of the header block (see {{header-prefix}}). The Base
-Index is an absolute index. When interpreting the rest of the frame, the entry
-identified by Base Index has a relative index of zero.  The relative indices of
-entries do not change while interpreting headers on a request or push stream.
+instructions on the encoder stream, relative indices are relative to the Base at
+the beginning of the header block (see {{header-prefix}}). The Base is encoded

Thanks.  That's better.

> @@ -784,29 +798,29 @@ streams emit the headers for an HTTP request or response.
 
 ### Header Data Prefix {#header-prefix}
 
-Header data is prefixed with two integers, `Largest Reference` and `Base Index`.
+Header data is prefixed with two integers, `Required Insert Count` and `Base`.

Yeah, that is a good idea.  The prose here was a little light.

>  
 ~~~~~~~~~~  drawing
   0   1   2   3   4   5   6   7
 +---+---+---+---+---+---+---+---+
-|     Largest Reference (8+)    |
+|   Required Insert Count (8+)  |

I think that I'll stick with Required Insert Count at this level.

>  +---+---------------------------+
 |      Compressed Headers     ...
 +-------------------------------+
 ~~~~~~~~~~
 {:#fig-base-index title="Frame Payload"}
 
-#### Largest Reference
+#### Insert Count

Done.  Thanks.

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