Diff for "BundleFormat2"

Differences between revisions 1 and 3 (spanning 2 versions)

This page describes the second iteration of the bundle format, tentatively called HG19 (since we hope to include it with Mercurial 1.9).

Bundles consist of the following sections:

A bundle header, describing the version and features present in the data.
A changegroups section containing the changelog, the manifest and each relevant filelog.
Optionally, a footer containing an index for more efficient random access?

Contents

Sections
1. Header
2. Changegroups section
Changegroups

Sections

For each section, the offsets are given relative to the beginning of the section. Fields with unknown length are assigned constants a, b, c etc.

The bundle header has the following format:

Offset	Size	Type	Description
0	4	string	Bundle format version. Always contains "HG19".
4	2	string	Compression type. Either "BZ", "GZ" or "UN".
6	4	uint	Length of feature string, in bytes.
10	a	string	Bundle features (or requirements). A list of newline separated strings describing features present in the bundle (unterminated).

Changegroups section

The changegroups section has the following format:

Offset	Size	Type	Description
0	4	uint	Number of changelog entries.
4	b	group	Changegroup containing changelog entries.
b + 4	4	uint	Number of manifest entries.
b + 8	c	group	Changegroup containing manifest entries.
b + c + 8	4	uint	Number of filelog changegroups (note: not the number of entries).

Then, for each filelog, the following:

Offset	Size	Type	Description
0	4	uint	Number of filelog entries.
4	4	uint	Length of filename, in bytes.
8	d	string	Filename (unterminated).
d + 8	e	group	Changroup containing filelog entries.

The changegroup format is described below.

Changegroups

A changegroup consists of a number of chunks describing revisions. Each chunk has the following format:

Offset	Size	Type	Description
0	4	uint	Total length of the chunk, including the 104 bytes header described here.
4	20	sha-1 hash	Node of this revision.
24	20	sha-1 hash	First parent of this revision.
44	20	sha-1 hash	Second parent of this revision (or 0-bytes).
64	20	sha-1 hash	Link pointer back to the changelog.
84	20	sha-1 hash	Parent for the delta (or 0-bytes for a snapshot).
104	f	data	Delta or full version snapshot.

So in the above table, we always have chunk length = f + 104.

-  ⇤ ← Revision 1 as of 2011-05-11 12:24:36 → 
  Size: 2108
  Editor: cyanite
  Comment: initial version
+   ← Revision 3 as of 2011-05-11 12:48:25 → ⇥
  Size: 3257
  Editor: cyanite
  Comment: wrote about changegroups
-Deletions are marked like this.
+Additions are marked like this.
 Line 5:
- * Changegroup sections for the changelog, the manifest and each relevant filelog.
+ * A changegroups section containing the changelog, the manifest and each relevant filelog.
 Line 11:
+For each section, the offsets are given relative to the beginning of the section. Fields with unknown length are assigned constants a, b, c etc.
-Line 17:
+Line 19:
-||<)> 6         ||<)> a        || string     || Bundle features (or requirements). A list of comma separated words (lowercase ASCII) describing features present in the bundle. The string is terminated by a newline character. ||
+||<)> 6         ||<)> 4        || uint       || Length of feature string, in bytes. ||
||<)> 10        ||<)> a        || string     || Bundle features (or requirements). A list of newline separated strings describing features present in the bundle (unterminated). ||
-Line 19:
+Line 22:
-=== Changegroup sections ===
The changegroup sections has the following format:
+=== Changegroups section ===
The changegroups section has the following format:
-Line 33:
+Line 36:
-||<)> 4         ||<)> 4        || uint       || Length of filename. ||
+||<)> 4         ||<)> 4        || uint       || Length of filename, in bytes. ||
-Line 37:
+Line 40:
+The changegroup format is described below.
-Line 38:
+Line 43:
-...
+A changegroup consists of a number of chunks describing revisions. Each chunk has the following format:

|| '''Offset''' || '''Size'''  || '''Type''' || '''Description''' ||
||<)> 0         ||<)> 4        || uint       || Total length of the chunk, including the 104 bytes header described here. ||
||<)> 4         ||<)> 20       || sha-1 hash || Node of this revision. ||
||<)> 24        ||<)> 20       || sha-1 hash || First parent of this revision. ||
||<)> 44        ||<)> 20       || sha-1 hash || Second parent of this revision (or 0-bytes). ||
||<)> 64        ||<)> 20       || sha-1 hash || Link pointer back to the changelog. ||
||<)> 84        ||<)> 20       || sha-1 hash || Parent for the delta (or 0-bytes for a snapshot). ||
||<)> 104       ||<)> f        || data       || Delta or full version snapshot. ||

So in the above table, we always have ''chunk length = f + 104.''

Diff for "BundleFormat2"

Sections

Header

Changegroups section

Changegroups