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
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
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.