NAME

       gitprotocol-common - Things common to various protocols

SYNOPSIS

       <over-the-wire-protocol>

DESCRIPTION

       This document defines things common to various over-the-wire protocols and file formats
       used in Git.

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:

        1. They can include slash / for hierarchical (directory) grouping, but no slash-separated
           component can begin with a dot ..

        2. They must contain at least one /. This enforces the presence of a category like
           heads/, tags/ etc. but the actual names are not restricted.

        3. They cannot have two consecutive dots ..  anywhere.

        4. 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.

        5. They cannot end with a slash / or a dot ..

        6. They cannot end with the sequence .lock.

        7. They cannot contain a sequence @{.

        8. 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 65516 bytes. Implementations MUST NOT
       send pkt-line whose length exceeds 65520 (65516 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"            ""

GIT

       Part of the git(1) suite