Documentation/technical/protocol-common.txt

   1 Documentation Common to Pack and Http Protocols
   2 ===============================================
   3
   4 ABNF Notation
   5 -------------
   6
   7 ABNF notation as described by RFC 5234 is used within the protocol documents,
   8 except the following replacement core rules are used:
   9 ----
  10   HEXDIG    =  DIGIT / "a" / "b" / "c" / "d" / "e" / "f"
  11 ----
  12
  13 We also define the following common rules:
  14 ----
  15   NUL       =  %x00
  16   zero-id   =  40*"0"
  17   obj-id    =  40*(HEXDIGIT)
  18
  19   refname  =  "HEAD"
  20   refname /=  "refs/" <see discussion below>
  21 ----
  22
  23 A refname is a hierarchical octet string beginning with "refs/" and
  24 not violating the 'git-check-ref-format' command's validation rules.
  25 More specifically, they:
  26
  27 . They can include slash `/` for hierarchical (directory)
  28   grouping, but no slash-separated component can begin with a
  29   dot `.`.
  30
  31 . They must contain at least one `/`. This enforces the presence of a
  32   category like `heads/`, `tags/` etc. but the actual names are not
  33   restricted.
  34
  35 . They cannot have two consecutive dots `..` anywhere.
  36
  37 . They cannot have ASCII control characters (i.e. bytes whose
  38   values are lower than \040, or \177 `DEL`), space, tilde `~`,
  39   caret `{caret}`, colon `:`, question-mark `?`, asterisk `*`,
  40   or open bracket `[` anywhere.
  41
  42 . They cannot end with a slash `/` nor a dot `.`.
  43
  44 . They cannot end with the sequence `.lock`.
  45
  46 . They cannot contain a sequence `@{`.
  47
  48 . They cannot contain a `\\`.
  49
  50
  51 pkt-line Format
  52 ---------------
  53
  54 Much (but not all) of the payload is described around pkt-lines.
  55
  56 A pkt-line is a variable length binary string.  The first four bytes
  57 of the line, the pkt-len, indicates the total length of the line,
  58 in hexadecimal.  The pkt-len includes the 4 bytes used to contain
  59 the length's hexadecimal representation.
  60
  61 A pkt-line MAY contain binary data, so implementors MUST ensure
  62 pkt-line parsing/formatting routines are 8-bit clean.
  63
  64 A non-binary line SHOULD BE terminated by an LF, which if present
  65 MUST be included in the total length.
  66
  67 The maximum length of a pkt-line's data component is 65520 bytes.
  68 Implementations MUST NOT send pkt-line whose length exceeds 65524
  69 (65520 bytes of payload + 4 bytes of length data).
  70
  71 Implementations SHOULD NOT send an empty pkt-line ("0004").
  72
  73 A pkt-line with a length field of 0 ("0000"), called a flush-pkt,
  74 is a special case and MUST be handled differently than an empty
  75 pkt-line ("0004").
  76
  77 ----
  78   pkt-line     =  data-pkt / flush-pkt
  79
  80   data-pkt     =  pkt-len pkt-payload
  81   pkt-len      =  4*(HEXDIG)
  82   pkt-payload  =  (pkt-len - 4)*(OCTET)
  83
  84   flush-pkt    = "0000"
  85 ----
  86
  87 Examples (as C-style strings):
  88
  89 ----
  90   pkt-line          actual value
  91   ---------------------------------
  92   "0006a\n"         "a\n"
  93   "0005a"           "a"
  94   "000bfoobar\n"    "foobar\n"
  95   "0004"            ""
  96 ----