Showing with 41 additions and 40 deletions.
  1. +41 −40 rfc9204.md
81 rfc9204.md
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@@ -149,7 +149,7 @@ Absolute Index:

Base:

: A reference point for relative and post-base indices. Representations that
: A reference point for relative and post-Base indices. Representations that
reference dynamic table entries are relative to a Base.

Insert Count:
@@ -638,17 +638,18 @@ throughout. This string format includes optional Huffman encoding.

HPACK defines string literals to begin on a byte boundary. They begin with a
single bit flag, denoted as 'H' in this document (indicating whether the string
is Huffman encoded), followed by the Length encoded as a 7-bit prefix integer,
and finally Length bytes of data. When Huffman encoding is enabled, the Huffman
table from {{Section B of RFC7541}} is used without modification and Length
indicates the size of the string after encoding.
is Huffman encoded), followed by the string length encoded as a 7-bit prefix
integer, and finally the indicated number of bytes of data. When Huffman
encoding is enabled, the Huffman table from {{Section B of RFC7541}} is used
without modification and the indicated length is the size of the string after
encoding.

This document expands the definition of string literals by permitting them to
begin other than on a byte boundary. An "N-bit prefix string literal" begins
mid-byte, with the first (8-N) bits allocated to a previous field. The string
uses one bit for the Huffman flag, followed by the Length encoded as a
(N-1)-bit prefix integer. The prefix size, N, can have a value between 2 and 8,
inclusive. The remainder of the string literal is unmodified.
uses one bit for the Huffman flag, followed by the length of the encoded string
as a (N-1)-bit prefix integer. The prefix size, N, can have a value between 2
and 8, inclusive. The remainder of the string literal is unmodified.

A string literal without a prefix length noted is an 8-bit prefix string literal
and follows the definitions in {{RFC7541}} without modification.
@@ -880,7 +881,7 @@ protocol.

Each encoded field section is prefixed with two integers. The Required Insert
Count is encoded as an integer with an 8-bit prefix using the encoding described
in {{ric}}. The Base is encoded as a sign bit ('S') and a Delta Base value
in {{ric}}. The Base is encoded as a Sign bit ('S') and a Delta Base value
with a 7-bit prefix; see {{base}}.

~~~~~~~~~~ ascii-art
@@ -968,16 +969,16 @@ The Base is used to resolve references in the dynamic table as described in
{{relative-indexing}}.

To save space, the Base is encoded relative to the Required Insert Count using a
one-bit sign ('S') and the Delta Base value. A sign bit of 0 indicates that the
Base is greater than or equal to the value of the Required Insert Count; the
decoder adds the value of Delta Base to the Required Insert Count to determine
the value of the Base. A sign bit of 1 indicates that the Base is less than the
Required Insert Count; the decoder subtracts the value of Delta Base from the
Required Insert Count and also subtracts one to determine the value of the Base.
That is:
one-bit Sign ('S' in {{fig-base-index}}) and the Delta Base value. A Sign bit
of 0 indicates that the Base is greater than or equal to the value of the
Required Insert Count; the decoder adds the value of Delta Base to the Required
Insert Count to determine the value of the Base. A Sign bit of 1 indicates that
the Base is less than the Required Insert Count; the decoder subtracts the value
of Delta Base from the Required Insert Count and also subtracts one to determine
the value of the Base. That is:

~~~ pseudocode
if S == 0:
if Sign == 0:
Base = ReqInsertCount + DeltaBase
else:
Base = ReqInsertCount - DeltaBase - 1
@@ -986,31 +987,31 @@ That is:
A single-pass encoder determines the Base before encoding a field section. If
the encoder inserted entries in the dynamic table while encoding the field
section and is referencing them, Required Insert Count will be greater than the
Base, so the encoded difference is negative and the sign bit is set to 1. If
Base, so the encoded difference is negative and the Sign bit is set to 1. If
the field section was not encoded using representations that reference the most
recent entry in the table and did not insert any new entries, the Base will be
greater than the Required Insert Count, so the delta will be positive and the
sign bit is set to 0.
greater than the Required Insert Count, so the encoded difference will be
positive and the Sign bit is set to 0.

The value of Base MUST NOT be negative. Though the protocol might operate
correctly with a negative base using post-base indexing, it is unnecessary and
inefficient. An endpoint MUST treat a field block with an S bit of 1 as invalid
if the value of Required Insert Count is less than or equal to the value of
Delta Base.
correctly with a negative Base using post-Base indexing, it is unnecessary and
inefficient. An endpoint MUST treat a field block with a Sign bit of 1 as
invalid if the value of Required Insert Count is less than or equal to the value
of Delta Base.

An encoder that produces table updates before encoding a field section might set
Base to the value of Required Insert Count. In such a case, both the sign bit
Base to the value of Required Insert Count. In such a case, both the Sign bit
and the Delta Base will be set to zero.

A field section that was encoded without references to the dynamic table can use
any value for the Base; setting Delta Base to zero is one of the most efficient
encodings.

For example, with a Required Insert Count of 9, a decoder receives an S bit of 1
and a Delta Base of 2. This sets the Base to 6 and enables post-base indexing
for three entries. In this example, a relative index of 1 refers to the fifth
entry that was added to the table; a post-base index of 1 refers to the eighth
entry.
For example, with a Required Insert Count of 9, a decoder receives a Sign bit
of 1 and a Delta Base of 2. This sets the Base to 6 and enables post-Base
indexing for three entries. In this example, a relative index of 1 refers to
the fifth entry that was added to the table; a post-Base index of 1 refers to
the eighth entry.


### Indexed Field Line
@@ -1037,7 +1038,7 @@ dynamic table.

### Indexed Field Line with Post-Base Index

An indexed field line with post-base index representation identifies an entry
An indexed field line with post-Base index representation identifies an entry
in the dynamic table with an absolute index greater than or equal to the value
of the Base.

@@ -1050,7 +1051,7 @@ of the Base.
{: title="Indexed Field Line with Post-Base Index"}

This representation starts with the '0001' 4-bit pattern. This is followed
by the post-base index ({{post-base}}) of the matching field line, represented
by the post-Base index ({{post-base}}) of the matching field line, represented
as an integer with a 4-bit prefix; see {{prefixed-integers}}.


@@ -1095,7 +1096,7 @@ encoded as an 8-bit prefix string literal; see {{string-literals}}.

### Literal Field Line with Post-Base Name Reference

A literal field line with post-base name reference representation encodes a
A literal field line with post-Base name reference representation encodes a
field line where the field name matches the field name of a dynamic table entry
with an absolute index greater than or equal to the value of the Base.

@@ -1113,7 +1114,7 @@ with an absolute index greater than or equal to the value of the Base.

This representation starts with the '0000' 4-bit pattern. The fifth bit is
the 'N' bit as described in {{literal-name-reference}}. This is followed by a
post-base index of the dynamic table entry ({{post-base}}) encoded as an
post-Base index of the dynamic table entry ({{post-base}}) encoded as an
integer with a 3-bit prefix; see {{prefixed-integers}}.

Only the field name is taken from the dynamic table entry; the field value is
@@ -1764,9 +1765,9 @@ Stream: Encoder
Size=215
~~~

# Sample One Pass Encoding Algorithm
# Sample Single-Pass Encoding Algorithm

Pseudocode for single pass encoding, excluding handling of duplicates,
Pseudocode for single-pass encoding, excluding handling of duplicates,
non-blocking mode, available encoder stream flow control and reference tracking.

~~~ pseudocode
@@ -1782,13 +1783,13 @@ encodeInsert(buffer, staticNameIndex, dynamicNameIndex, fieldLine)
# Encode a static index reference
encodeStaticIndexReference(buffer, staticIndex)

# Encode a dynamic index reference relative to base
# Encode a dynamic index reference relative to Base
encodeDynamicIndexReference(buffer, dynamicIndex, base)

# Encode a literal with an optional static name index
encodeLiteral(buffer, staticNameIndex, fieldLine)

# Encode a literal with a dynamic name index relative to base
# Encode a literal with a dynamic name index relative to Base
encodeDynamicLiteral(buffer, dynamicNameIndex, base, fieldLine)

# Encoding Algorithm
@@ -1816,7 +1817,7 @@ for line in fieldLines:
if dynamicIndex is None:
# Could not index it, literal
if dynamicNameIndex is not None:
# Encode literal with dynamic name, possibly above base
# Encode literal with dynamic name, possibly above Base
encodeDynamicLiteral(streamBuffer, dynamicNameIndex,
base, line)
requiredInsertCount = max(requiredInsertCount,
@@ -1828,7 +1829,7 @@ for line in fieldLines:
# Dynamic index reference
assert(dynamicIndex is not None)
requiredInsertCount = max(requiredInsertCount, dynamicIndex)
# Encode dynamicIndex, possibly above base
# Encode dynamicIndex, possibly above Base
encodeDynamicIndexReference(streamBuffer, dynamicIndex, base)

# encode the prefix