BundleFormat2

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

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).

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.

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.