Re: Straw Poll: Restore Header Table and Static Table Indices

[Roberto Peon <[e-mail]>]

While I prefer the indexing scheme of the previous draft, this proposal
would be better than what is currently drafted.

-=R

On Mon, Oct 20, 2014 at 4:29 PM, Mark Nottingham <[e-mail]> wrote:

> Thanks for that, Willy.
>
> At the risk of repeating myself -- making this kind of change (one that
> does not impact security or interoperability) at this stage in our process
> needs to have *strong* consensus.
>
> What do others think?
>
> Regards,
>
>
> > On 21 Oct 2014, at 3:53 am, Willy Tarreau <[e-mail]> wrote:
> >
> > Hi Mark,
> >
> > On Fri, Oct 17, 2014 at 10:23:35AM +1100, Mark Nottingham wrote:
> >> I think we need to see a proposal here if we?re going to take this
> seriously
> >> ? i.e., either fairly complete text or a pull request.
> >
> > Here's the change I'm proposing. It's a diff against the text version
> because
> > it was easier for me to produce this, and it's easily readable by
> everyone here.
> >
> > The diff looks like what's below, I think it addresses what was
> discussed in
> > a way that is pretty straightforward since there's no more the need to
> explain
> > the split between the two tables.
> >
> > I have not changed anything else eventhough I'm seeing room for
> improvement
> > (eg: swapping encoding prefix of "literal without indexing" with the one
> > for "dynamic table size update" and gain one bit of encoding per header).
> >
> > Anyone would please review and/or comment ?
> >
> > Thanks,
> > Willy
> >
> > ------------
> >
> > diff --git a/compression.txt b/compression.txt
> > index a4c8a40..56b2ea0 100644
> > --- a/compression.txt
> > +++ b/compression.txt
> > @@ -309,9 +309,6 @@ Internet-Draft                    HPACK
>        October 2014
> >    (see Section 2.3.2) is dynamic and can be used by the encoder to
> >    index header fields repeated in the encoded header lists.
> >
> > -   These two tables are combined into a single address space for
> > -   defining index values (see Section 2.3.3).
> > -
> > 2.3.1.  Static Table
> >
> >    The static table consists of a predefined static list of header
> > @@ -348,37 +345,21 @@ Internet-Draft                    HPACK
>          October 2014
> >
> > 2.3.3.  Index Address Space
> >
> > -   The static table and the dynamic table are combined into a single
> > -   index address space.
> > -
> > -   Indices between 1 and the length of the static table (inclusive)
> > -   refer to elements in the static table (see Section 2.3.1).
> > -
> > +   Both the static and the dynamic tables are indexed starting at 1.
> >    Indices strictly greater than the length of the static table refer to
> >    elements in the dynamic table (see Section 2.3.2).  The length of the
> >    static table is subtracted to find the index into the dynamic table.
> >
> > -   Indices strictly greater than the sum of the lengths of both tables
> > -   MUST be treated as a decoding error.
> > +   Static table indices strictly greater than the length of the table as
> > +   defined in Appendix A MUST be treated as a decoding error. Dynamic
> table
> > +   indices strictly greater than the length of the dynamic table MUST be
> > +   treated as a decoding error.
> >
> > -   For a static table size of s and a dynamic table size of k, the
> > -   following diagram shows the entire valid index address space.
> > -
> > -           <----------  Index Address Space ---------->
> > -           <-- Static  Table -->  <-- Dynamic Table -->
> > -           +---+-----------+---+  +---+-----------+---+
> > -           | 1 |    ...    | s |  |s+1|    ...    |s+k|
> > -           +---+-----------+---+  +---+-----------+---+
> > -                                  ^                   |
> > -                                  |                   V
> > -                           Insertion Point      Dropping Point
> > -
> > -                       Figure 1: Index Address Space
> >
> > 2.4.  Header Field Representation
> >
> >    An encoded header field can be represented either as a literal or as
> > -   an index.
> > +   an index in one of the tables.
> >
> >    A literal representation defines a header field by specifying its
> >    name and value.  The header field name can be represented literally
> > @@ -740,14 +721,15 @@ Internet-Draft                    HPACK
>          October 2014
> >
> >      0   1   2   3   4   5   6   7
> >    +---+---+---+---+---+---+---+---+
> > -   | 1 |        Index (7+)         |
> > -   +---+---------------------------+
> > +   | 1 | D |     Index (6+)        |
> > +   +---+---+---+---+---+---+---+---+
> >
> >                       Figure 5: Indexed Header Field
> >
> > -   An indexed header field starts with the '1' 1-bit pattern, followed
> > -   by the index of the matching pair, represented as an integer with a
> > -   7-bit prefix (see Section 5.1).
> > +   An indexed header field starts with the '1' 1-bit pattern, followed
> by
> > +   the D bit indicating if the index references the static table (0) or
> > +   the dynamic table (1), and the index of the matching pair,
> represented
> > +   as an integer with a 6-bit prefix (see Section 5.1).
> >
> >    The index value of 0 is not used.  It MUST be treated as a decoding
> >    error if found in an indexed header field representation.
> > @@ -788,8 +770,8 @@ Internet-Draft                    HPACK
>        October 2014
> >
> >      0   1   2   3   4   5   6   7
> >    +---+---+---+---+---+---+---+---+
> > -   | 0 | 1 |      Index (6+)       |
> > -   +---+---+-----------------------+
> > +   | 0 | 1 | D |  Index (5+)       |
> > +   +---+---+---+-------------------+
> >    | H |     Value Length (7+)     |
> >    +---+---------------------------+
> >    | Value String (Length octets)  |
> > @@ -800,8 +782,8 @@ Internet-Draft                    HPACK
>        October 2014
> >
> >      0   1   2   3   4   5   6   7
> >    +---+---+---+---+---+---+---+---+
> > -   | 0 | 1 |           0           |
> > -   +---+---+-----------------------+
> > +   | 0 | 1 | 0 |       0           |
> > +   +---+---+---+-------------------+
> >    | H |     Name Length (7+)      |
> >    +---+---------------------------+
> >    |  Name String (Length octets)  |
> > @@ -819,11 +801,13 @@ Internet-Draft                    HPACK
>          October 2014
> >    If the header field name matches the header field name of an entry
> >    stored in the static table or the dynamic table, the header field
> >    name can be represented using the index of that entry.  In this case,
> > -   the index of the entry is represented as an integer with a 6-bit
> > -   prefix (see Section 5.1).  This value is always non-zero.
> > +   the index of the entry is represented as the D bit indicating if the
> > +   index references the static table (0) or the dynamic table (1),
> > +   followed by an integer with a 5-bit prefix (see Section 5.1).  This
> > +   value is always non-zero.
> >
> >    Otherwise, the header field name is represented as a literal string
> > -   (see Section 5.2).  A value 0 is used in place of the 6-bit index,
> > +   (see Section 5.2).  A value 0 is used in place of the 5-bit index,
> >    followed by the header field name.
> >
> >    Either form of header field name representation is followed by the
> > @@ -844,8 +828,8 @@ Internet-Draft                    HPACK
>        October 2014
> >
> >      0   1   2   3   4   5   6   7
> >    +---+---+---+---+---+---+---+---+
> > -   | 0 | 0 | 0 | 0 |  Index (4+)   |
> > -   +---+---+-----------------------+
> > +   | 0 | 0 | 0 | 0 | D | Index (3+)|
> > +   +---+---+---+---+---+-----------+
> >    | H |     Value Length (7+)     |
> >    +---+---------------------------+
> >    | Value String (Length octets)  |
> > @@ -855,8 +839,8 @@ Internet-Draft                    HPACK
>        October 2014
> >
> >      0   1   2   3   4   5   6   7
> >    +---+---+---+---+---+---+---+---+
> > -   | 0 | 0 | 0 | 0 |       0       |
> > -   +---+---+-----------------------+
> > +   | 0 | 0 | 0 | 0 | 0 |     0     |
> > +   +---+---+---+---+---+-----------+
> >    | H |     Name Length (7+)      |
> >    +---+---------------------------+
> >    |  Name String (Length octets)  |
> > @@ -874,11 +858,13 @@ Internet-Draft                    HPACK
>          October 2014
> >    If the header field name matches the header field name of an entry
> >    stored in the static table or the dynamic table, the header field
> >    name can be represented using the index of that entry.  In this case,
> > -   the index of the entry is represented as an integer with a 4-bit
> > -   prefix (see Section 5.1).  This value is always non-zero.
> > +   the index of the entry is represented as the D bit indicating if the
> > +   index references the static table (0) or the dynamic table (1),
> > +   followed by as an integer with a 3-bit prefix (see Section 5.1).
> > +   This value is always non-zero.
> >
> >    Otherwise, the header field name is represented as a literal string
> > -   (see Section 5.2).  A value 0 is used in place of the 4-bit index,
> > +   (see Section 5.2).  A value 0 is used in place of the 3-bit index,
> >    followed by the header field name.
> >
> >    Either form of header field name representation is followed by the
> > @@ -900,8 +886,8 @@ Internet-Draft                    HPACK
>        October 2014
> >
> >      0   1   2   3   4   5   6   7
> >    +---+---+---+---+---+---+---+---+
> > -   | 0 | 0 | 0 | 1 |  Index (4+)   |
> > -   +---+---+-----------------------+
> > +   | 0 | 0 | 0 | 1 | D | Index (3+)|
> > +   +---+---+---+---+---+-----------+
> >    | H |     Value Length (7+)     |
> >    +---+---------------------------+
> >    | Value String (Length octets)  |
> > @@ -911,8 +897,8 @@ Internet-Draft                    HPACK
>        October 2014
> >
> >      0   1   2   3   4   5   6   7
> >    +---+---+---+---+---+---+---+---+
> > -   | 0 | 0 | 0 | 1 |       0       |
> > -   +---+---+-----------------------+
> > +   | 0 | 0 | 0 | 1 | 0 |     0     |
> > +   +---+---+---+---+---+-----------+
> >    | H |     Name Length (7+)      |
> >    +---+---------------------------+
> >    |  Name String (Length octets)  |
> > @@ -957,7 +943,7 @@ Internet-Draft                    HPACK
>        October 2014
> >      0   1   2   3   4   5   6   7
> >    +---+---+---+---+---+---+---+---+
> >    | 0 | 0 | 1 |   Max size (5+)   |
> > -   +---+---------------------------+
> > +   +---+---+---+-------------------+
> >
> >                Figure 12: Maximum Dynamic Table Size Change
> >
> > ------------
>
> --
> Mark Nottingham   https://www.mnot.net/
>
>
>