GITPROTOCOL-COMMON(5)                                        Git Manual                                       GITPROTOCOL-COMMON(5)

NAME
       gitprotocol-common - Things common to various protocols

SYNOPSIS
       <over-the-wire-protocol>

DESCRIPTION
       This document sets 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

Git 2.39.2                                                   04/24/2023                                       GITPROTOCOL-COMMON(5)