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1 gitprotocol-common(5)
2 =====================
3
4 NAME
5 ----
6 gitprotocol-common - Things common to various protocols
7
8 SYNOPSIS
9 --------
10 [verse]
11 <over-the-wire-protocol>
12
13 DESCRIPTION
14 -----------
15
16 This document sets defines things common to various over-the-wire
17 protocols and file formats used in Git.
18
19 ABNF Notation
20 -------------
21
22 ABNF notation as described by RFC 5234 is used within the protocol documents,
23 except the following replacement core rules are used:
24 ----
25 HEXDIG = DIGIT / "a" / "b" / "c" / "d" / "e" / "f"
26 ----
27
28 We also define the following common rules:
29 ----
30 NUL = %x00
31 zero-id = 40*"0"
32 obj-id = 40*(HEXDIGIT)
33
34 refname = "HEAD"
35 refname /= "refs/" <see discussion below>
36 ----
37
38 A refname is a hierarchical octet string beginning with "refs/" and
39 not violating the 'git-check-ref-format' command's validation rules.
40 More specifically, they:
41
42 . They can include slash `/` for hierarchical (directory)
43 grouping, but no slash-separated component can begin with a
44 dot `.`.
45
46 . They must contain at least one `/`. This enforces the presence of a
47 category like `heads/`, `tags/` etc. but the actual names are not
48 restricted.
49
50 . They cannot have two consecutive dots `..` anywhere.
51
52 . They cannot have ASCII control characters (i.e. bytes whose
53 values are lower than \040, or \177 `DEL`), space, tilde `~`,
54 caret `^`, colon `:`, question-mark `?`, asterisk `*`,
55 or open bracket `[` anywhere.
56
57 . They cannot end with a slash `/` or a dot `.`.
58
59 . They cannot end with the sequence `.lock`.
60
61 . They cannot contain a sequence `@{`.
62
63 . They cannot contain a `\\`.
64
65
66 pkt-line Format
67 ---------------
68
69 Much (but not all) of the payload is described around pkt-lines.
70
71 A pkt-line is a variable length binary string. The first four bytes
72 of the line, the pkt-len, indicates the total length of the line,
73 in hexadecimal. The pkt-len includes the 4 bytes used to contain
74 the length's hexadecimal representation.
75
76 A pkt-line MAY contain binary data, so implementors MUST ensure
77 pkt-line parsing/formatting routines are 8-bit clean.
78
79 A non-binary line SHOULD BE terminated by an LF, which if present
80 MUST be included in the total length. Receivers MUST treat pkt-lines
81 with non-binary data the same whether or not they contain the trailing
82 LF (stripping the LF if present, and not complaining when it is
83 missing).
84
85 The maximum length of a pkt-line's data component is 65516 bytes.
86 Implementations MUST NOT send pkt-line whose length exceeds 65520
87 (65516 bytes of payload + 4 bytes of length data).
88
89 Implementations SHOULD NOT send an empty pkt-line ("0004").
90
91 A pkt-line with a length field of 0 ("0000"), called a flush-pkt,
92 is a special case and MUST be handled differently than an empty
93 pkt-line ("0004").
94
95 ----
96 pkt-line = data-pkt / flush-pkt
97
98 data-pkt = pkt-len pkt-payload
99 pkt-len = 4*(HEXDIG)
100 pkt-payload = (pkt-len - 4)*(OCTET)
101
102 flush-pkt = "0000"
103 ----
104
105 Examples (as C-style strings):
106
107 ----
108 pkt-line actual value
109 ---------------------------------
110 "0006a\n" "a\n"
111 "0005a" "a"
112 "000bfoobar\n" "foobar\n"
113 "0004" ""
114 ----
115
116 GIT
117 ---
118 Part of the linkgit:git[1] suite