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authorScott Chacon <schacon@gmail.com>2009-11-04 05:58:23 (GMT)
committerJunio C Hamano <gitster@pobox.com>2009-11-13 20:07:21 (GMT)
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Update packfile transfer protocol documentation
The current technical documentation for the packfile protocol is both sparse and incorrect. This documents the fetch-pack/upload-pack and send-pack/ receive-pack protocols much more fully. Add documentation from Shawn's upcoming http-protocol docs that is shared by the packfile protocol. protocol-common.txt describes ABNF notation amendments, refname rules and the packet line format. Add documentation on the various capabilities supported by the upload-pack and receive-pack protocols. protocol-capabilities.txt describes multi-ack, thin-pack, side-band[-64k], shallow, no-progress, include-tag, ofs-delta, delete-refs and report-status. Signed-off-by: Scott Chacon <schacon@gmail.com> Signed-off-by: Nanako Shiraishi <nanako3@lavabit.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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+Documentation Common to Pack and Http Protocols
+===============================================
+
+ABNF Notation
+-------------
+
+ABNF notation as described by RFC 5234 is used within the protocol documents,
+except the following replacement core rules are used:
+----
+ HEXDIG = DIGIT / "a" / "b" / "c" / "d" / "e" / "f"
+----
+
+We also define the following common rules:
+----
+ NUL = %x00
+ zero-id = 40*"0"
+ obj-id = 40*(HEXDIGIT)
+
+ refname = "HEAD"
+ refname /= "refs/" <see discussion below>
+----
+
+A refname is a hierarchical octet string beginning with "refs/" and
+not violating the 'git-check-ref-format' command's validation rules.
+More specifically, they:
+
+. They can include slash `/` for hierarchical (directory)
+ grouping, but no slash-separated component can begin with a
+ dot `.`.
+
+. They must contain at least one `/`. This enforces the presence of a
+ category like `heads/`, `tags/` etc. but the actual names are not
+ restricted.
+
+. They cannot have two consecutive dots `..` anywhere.
+
+. They cannot have ASCII control characters (i.e. bytes whose
+ values are lower than \040, or \177 `DEL`), space, tilde `~`,
+ caret `{caret}`, colon `:`, question-mark `?`, asterisk `*`,
+ or open bracket `[` anywhere.
+
+. They cannot end with a slash `/` nor a dot `.`.
+
+. They cannot end with the sequence `.lock`.
+
+. They cannot contain a sequence `@{`.
+
+. They cannot contain a `\\`.
+
+
+pkt-line Format
+---------------
+
+Much (but not all) of the payload is described around pkt-lines.
+
+A pkt-line is a variable length binary string. The first four bytes
+of the line, the pkt-len, indicates the total length of the line,
+in hexadecimal. The pkt-len includes the 4 bytes used to contain
+the length's hexadecimal representation.
+
+A pkt-line MAY contain binary data, so implementors MUST ensure
+pkt-line parsing/formatting routines are 8-bit clean.
+
+A non-binary line SHOULD BE terminated by an LF, which if present
+MUST be included in the total length.
+
+The maximum length of a pkt-line's data component is 65520 bytes.
+Implementations MUST NOT send pkt-line whose length exceeds 65524
+(65520 bytes of payload + 4 bytes of length data).
+
+Implementations SHOULD NOT send an empty pkt-line ("0004").
+
+A pkt-line with a length field of 0 ("0000"), called a flush-pkt,
+is a special case and MUST be handled differently than an empty
+pkt-line ("0004").
+
+----
+ pkt-line = data-pkt / flush-pkt
+
+ data-pkt = pkt-len pkt-payload
+ pkt-len = 4*(HEXDIG)
+ pkt-payload = (pkt-len - 4)*(OCTET)
+
+ flush-pkt = "0000"
+----
+
+Examples (as C-style strings):
+
+----
+ pkt-line actual value
+ ---------------------------------
+ "0006a\n" "a\n"
+ "0005a" "a"
+ "000bfoobar\n" "foobar\n"
+ "0004" ""
+----