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/" andnot 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 bytesof the line, the pkt-len, indicates the total length of the line,in hexadecimal.  The pkt-len includes the 4 bytes used to containthe length's hexadecimal representation. A pkt-line MAY contain binary data, so implementors MUST ensurepkt-line parsing/formatting routines are 8-bit clean. A non-binary line SHOULD BE terminated by an LF, which if presentMUST be included in the total length. Receivers MUST treat pkt-lineswith non-binary data the same whether or not they contain the trailingLF (stripping the LF if present, and not complaining when it ismissing). 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 emptypkt-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"            ""----