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git/Documentation/technical/protocol-common.txt
Jeff King 1c9b659d98 pack-protocol: clarify LF-handling in PKT-LINE()
The spec is very inconsistent about which PKT-LINE() parts
of the grammar include a LF. On top of that, the code is not
consistent, either (e.g., send-pack does not put newlines
into the ref-update commands it sends).

Let's make explicit the long-standing expectation that we
generally expect pkt-lines to end in a newline, but that
receivers should be lenient. This makes the spec consistent,
and matches what git already does (though it does not always
fulfill the SHOULD).

We do make an exception for the push-cert, where the
receiving code is currently a bit pickier. This is a
reasonable way to be, as the data needs to be byte-for-byte
compatible with what was signed. We _could_ make up some
rules about signing a canonicalized version including
newlines, but that would require a code change, and is out
of scope for this patch.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2015-09-03 15:18:12 -07:00

99 lines
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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 `^`, colon `:`, question-mark `?`, asterisk `*`,
or open bracket `[` anywhere.
. They cannot end with a slash `/` or 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. Receivers MUST treat pkt-lines
with non-binary data the same whether or not they contain the trailing
LF (stripping the LF if present, and not complaining when it is
missing).
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" ""
----