mirror/git
1
0
Fork 0
mirror of https://github.com/git/git.git synced 2024-11-16 00:53:09 +01:00
Code
d976c5100f
git/Documentation/technical/bundle-format.txt

82 lines
2.7 KiB
Plaintext
Raw Normal View History

doc: describe Git bundle format The bundle format was not documented. Describe the format with ABNF and explain the meaning of each part. Signed-off-by: Masaya Suzuki <masayasuzuki@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-02-07 21:42:25 +01:00
= Git bundle v2 format
The Git bundle format is a format that represents both refs and Git objects.
== Format
We will use ABNF notation to define the Git bundle format. See
protocol-common.txt for the details.
bundle: add new version for use with SHA-256 Currently we detect the hash algorithm in use by the length of the object ID. This is inelegant and prevents us from using a different hash algorithm that is also 256 bits in length. Since we cannot extend the v2 format in a backward-compatible way, let's add a v3 format, which is identical, except for the addition of capabilities, which are prefixed by an at sign. We add "object-format" as the only capability and reject unknown capabilities, since we do not have a network connection and therefore cannot negotiate with the other side. For compatibility, default to the v2 format for SHA-1 and require v3 for SHA-256. In t5510, always use format v3 so we can be sure we produce consistent results across hash algorithms. Since head -n N lists the top N lines instead of the Nth line, let's run our output through sed to normalize it and compare it against a fixed value, which will make sure we get exactly what we're expecting. Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net> Reviewed-by: Eric Sunshine <sunshine@sunshineco.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-07-30 01:14:20 +02:00
A v2 bundle looks like this:
doc: describe Git bundle format The bundle format was not documented. Describe the format with ABNF and explain the meaning of each part. Signed-off-by: Masaya Suzuki <masayasuzuki@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-02-07 21:42:25 +01:00
----
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
----
bundle: add new version for use with SHA-256 Currently we detect the hash algorithm in use by the length of the object ID. This is inelegant and prevents us from using a different hash algorithm that is also 256 bits in length. Since we cannot extend the v2 format in a backward-compatible way, let's add a v3 format, which is identical, except for the addition of capabilities, which are prefixed by an at sign. We add "object-format" as the only capability and reject unknown capabilities, since we do not have a network connection and therefore cannot negotiate with the other side. For compatibility, default to the v2 format for SHA-1 and require v3 for SHA-256. In t5510, always use format v3 so we can be sure we produce consistent results across hash algorithms. Since head -n N lists the top N lines instead of the Nth line, let's run our output through sed to normalize it and compare it against a fixed value, which will make sure we get exactly what we're expecting. Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net> Reviewed-by: Eric Sunshine <sunshine@sunshineco.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-07-30 01:14:20 +02:00
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
----
doc: describe Git bundle format The bundle format was not documented. Describe the format with ABNF and explain the meaning of each part. Signed-off-by: Masaya Suzuki <masayasuzuki@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-02-07 21:42:25 +01:00
== Semantics
bundle: add new version for use with SHA-256 Currently we detect the hash algorithm in use by the length of the object ID. This is inelegant and prevents us from using a different hash algorithm that is also 256 bits in length. Since we cannot extend the v2 format in a backward-compatible way, let's add a v3 format, which is identical, except for the addition of capabilities, which are prefixed by an at sign. We add "object-format" as the only capability and reject unknown capabilities, since we do not have a network connection and therefore cannot negotiate with the other side. For compatibility, default to the v2 format for SHA-1 and require v3 for SHA-256. In t5510, always use format v3 so we can be sure we produce consistent results across hash algorithms. Since head -n N lists the top N lines instead of the Nth line, let's run our output through sed to normalize it and compare it against a fixed value, which will make sure we get exactly what we're expecting. Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net> Reviewed-by: Eric Sunshine <sunshine@sunshineco.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-07-30 01:14:20 +02:00
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.
doc: describe Git bundle format The bundle format was not documented. Describe the format with ABNF and explain the meaning of each part. Signed-off-by: Masaya Suzuki <masayasuzuki@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-02-07 21:42:25 +01:00
* "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.
bundle: add new version for use with SHA-256 Currently we detect the hash algorithm in use by the length of the object ID. This is inelegant and prevents us from using a different hash algorithm that is also 256 bits in length. Since we cannot extend the v2 format in a backward-compatible way, let's add a v3 format, which is identical, except for the addition of capabilities, which are prefixed by an at sign. We add "object-format" as the only capability and reject unknown capabilities, since we do not have a network connection and therefore cannot negotiate with the other side. For compatibility, default to the v2 format for SHA-1 and require v3 for SHA-256. In t5510, always use format v3 so we can be sure we produce consistent results across hash algorithms. Since head -n N lists the top N lines instead of the Nth line, let's run our output through sed to normalize it and compare it against a fixed value, which will make sure we get exactly what we're expecting. Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net> Reviewed-by: Eric Sunshine <sunshine@sunshineco.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2020-07-30 01:14:20 +02:00
== Capabilities
Because there is no opportunity for negotiation, unknown capabilities cause 'git
bundle: parse filter capability The v3 bundle format has capabilities, allowing newer versions of Git to create bundles with newer features. Older versions that do not understand these new capabilities will fail with a helpful warning. Create a new capability allowing Git to understand that the contained pack-file is filtered according to some object filter. Typically, this filter will be "blob:none" for a blobless partial clone. This change teaches Git to parse this capability, place its value in the bundle header, and demonstrate this understanding by adding a message to 'git bundle verify'. Since we will use gently_parse_list_objects_filter() outside of list-objects-filter-options.c, make it an external method and move its API documentation to before its declaration. Signed-off-by: Derrick Stolee <derrickstolee@github.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2022-03-09 17:01:39 +01:00
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.
Copy Permalink