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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" ""
----
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