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git/Documentation/gitformat-bundle.txt
Ævar Arnfjörð Bjarmason 844739ba27 git docs: add a category for file formats, protocols and interfaces
Create a new "File formats, protocols and other developer interfaces"
section in the main "git help git" manual page and start moving the
documentation that now lives in "Documentation/technical/*.git" over
to it. This complements the newly added and adjacent "Repository,
command and file interfaces" section.

This makes the technical documentation more accessible and
discoverable. Before this we wouldn't install it by default, and had
no ability to build man page versions of them. The links to them from
our existing documentation link to the generated HTML version of these
docs.

So let's start moving those over, starting with just the
"bundle-format.txt" documentation added in 7378ec90e1c (doc: describe
Git bundle format, 2020-02-07). We'll now have a new
gitformat-bundle(5) man page. Subsequent commits will move more git
internal format documentation over.

Unfortunately the syntax of the current Documentation/technical/*.txt
is not the same (when it comes to section headings etc.) as our
Documentation/*.txt documentation, so change the relevant bits of
syntax as we're moving this over.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2022-08-04 14:12:23 -07:00

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gitformat-bundle(5)
===================
NAME
----
gitformat-bundle - The bundle file format
SYNOPSIS
--------
[verse]
*.bundle
*.bdl
DESCRIPTION
-----------
The Git bundle format is a format that represents both refs and Git
objects. A bundle is a header in a format similar to
linkgit:git-show-ref[1] followed by a pack in *.pack format.
The format is created and read by the linkgit:git-bundle[1] command,
and supported by e.g. linkgit:git-fetch[1] and linkgit:git-clone[1].
FORMAT
------
We will use ABNF notation to define the Git bundle format. See
link:technical/protocol-common.html for the details.
A v2 bundle looks like this:
----
bundle = signature *prerequisite *reference LF pack
signature = "# v2 git bundle" LF
prerequisite = "-" obj-id SP comment LF
comment = *CHAR
reference = obj-id SP refname LF
pack = ... ; packfile
----
A v3 bundle looks like this:
----
bundle = signature *capability *prerequisite *reference LF pack
signature = "# v3 git bundle" LF
capability = "@" key ["=" value] LF
prerequisite = "-" obj-id SP comment LF
comment = *CHAR
reference = obj-id SP refname LF
key = 1*(ALPHA / DIGIT / "-")
value = *(%01-09 / %0b-FF)
pack = ... ; packfile
----
SEMANTICS
---------
A Git bundle consists of several parts.
* "Capabilities", which are only in the v3 format, indicate functionality that
the bundle requires to be read properly.
* "Prerequisites" lists the objects that are NOT included in the bundle and the
reader of the bundle MUST already have, in order to use the data in the
bundle. The objects stored in the bundle may refer to prerequisite objects and
anything reachable from them (e.g. a tree object in the bundle can reference
a blob that is reachable from a prerequisite) and/or expressed as a delta
against prerequisite objects.
* "References" record the tips of the history graph, iow, what the reader of the
bundle CAN "git fetch" from it.
* "Pack" is the pack data stream "git fetch" would send, if you fetch from a
repository that has the references recorded in the "References" above into a
repository that has references pointing at the objects listed in
"Prerequisites" above.
In the bundle format, there can be a comment following a prerequisite obj-id.
This is a comment and it has no specific meaning. The writer of the bundle MAY
put any string here. The reader of the bundle MUST ignore the comment.
Note on the shallow clone and a Git bundle
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Note that the prerequisites does not represent a shallow-clone boundary. The
semantics of the prerequisites and the shallow-clone boundaries are different,
and the Git bundle v2 format cannot represent a shallow clone repository.
CAPABILITIES
------------
Because there is no opportunity for negotiation, unknown capabilities cause 'git
bundle' to abort.
* `object-format` specifies the hash algorithm in use, and can take the same
values as the `extensions.objectFormat` configuration value.
* `filter` specifies an object filter as in the `--filter` option in
linkgit:git-rev-list[1]. The resulting pack-file must be marked as a
`.promisor` pack-file after it is unbundled.
GIT
---
Part of the linkgit:git[1] suite