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bundle: add new version for use with SHA-256

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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>
This commit is contained in:
brian m. carlson
2020-07-29 23:14:20 +00:00
committed by Junio C Hamano
parent e74b606d47
commit c5aecfc866
7 changed files with 147 additions and 31 deletions
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30
Documentation/technical/bundle-format.txt
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@ -7,6 +7,8 @@ The Git bundle format is a format that represents both refs and Git objects.
We will use ABNF notation to define the Git bundle format. See
protocol-common.txt for the details.
A v2 bundle looks like this:
----
bundle = signature *prerequisite *reference LF pack
signature = "# v2 git bundle" LF
@ -18,9 +20,28 @@ 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 three parts.
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
@ -46,3 +67,10 @@ put any string here. The reader of the bundle MUST ignore the comment.
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. The only known capability is `object-format`, which specifies
the hash algorithm in use, and can take the same values as the
`extensions.objectFormat` configuration value.