[PATCH] doc: describe Git bundle format

[Masaya Suzuki <masayasuzuki@google.com>]

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>
---
 Documentation/technical/bundle-format.txt | 40 +++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100644 Documentation/technical/bundle-format.txt

diff --git a/Documentation/technical/bundle-format.txt b/Documentation/technical/bundle-format.txt
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+= 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    = signature references pack
+signature = "# v2 git bundle" LF
+
+references   = *(prerequisite / ref) LF
+prerequisite = "-" obj-id SP comment LF
+comment      = *CHAR
+ref          = obj-id SP refname LF
+
+pack         = ... ; packfile
+----
+
+== Semantics
+
+A Git bundle consists of three parts.
+
+*   Prerequisites: Optional list of objects that are not included in the bundle
+    file. A bundle can reference these prerequisite objects (or it can reference
+    the objects reachable from the prerequisite objects). The bundle itself
+    might not contain those objects.
+*   References: Mapping of ref names to objects.
+*   Git objects: Commit, tree, blob, and tags. These are included in the pack
+    format.
+
+If a bundle contains prerequisites, it means the bundle has a thin pack and the
+bundle alone is not enough for resolving all objects. When you read such
+bundles, you should have those missing objects beforehand.
+
+In the bundle format, there can be a comment following a prerequisite obj-id.
+This is a comment and it has no specific meaning. When you write a bundle, you
+can put any string here. When you read a bundle, you can ignore this part.
-- 
2.25.0.341.g760bfbb309-goog