cl-abnf

2015-06-08

ABNF DEFINITION OF ABNF

This Common Lisp librairie implements a parser generator for the ABNF grammar format as described in RFC2234.

The generated parser is a regular expression scanner provided by the cl-ppcre lib, which means that we can't parse recursive grammar definition. One such definition is the ABNF definition as given by the RFC. Fortunately, as you have this lib, you most probably don't need to generate another parser to handle that particular ABNF grammar.

Installation

The system has been made Quicklisp ready.

$ cd ~/quicklisp/local-projects/
$ git clone https://github.com/dimitri/cl-abnf.git
* (ql:quickload "abnf")

Currently the ABNF system is maintained as part of the pgloader tool as a central piece of its syslog message parser facility.

Usage

The parse-abnf-grammar function expects the grammar to be parsed as a string, and also needs the top level rule name of the grammar you're interested into, as a symbol or a string. You can also give a list of rule names that you want to capture, they will be capture in the order in which they are needed to expand the given top-level rule.

The parse-abnf-grammar function returns a cl-ppcre scanner.

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(defvar *timestamp-abnf*
  "   TIMESTAMP       = NILVALUE / FULL-DATE \"T\" FULL-TIME
      FULL-DATE       = DATE-FULLYEAR \"-\" DATE-MONTH \"-\" DATE-MDAY
      DATE-FULLYEAR   = 4DIGIT
      DATE-MONTH      = 2DIGIT  ; 01-12
      DATE-MDAY       = 2DIGIT  ; 01-28, 01-29, 01-30, 01-31 based on
                                ; month/year
      FULL-TIME       = PARTIAL-TIME TIME-OFFSET
      PARTIAL-TIME    = TIME-HOUR \":\" TIME-MINUTE \":\" TIME-SECOND
                        [TIME-SECFRAC]
      TIME-HOUR       = 2DIGIT  ; 00-23
      TIME-MINUTE     = 2DIGIT  ; 00-59
      TIME-SECOND     = 2DIGIT  ; 00-59
      TIME-SECFRAC    = \".\" 1*6DIGIT
      TIME-OFFSET     = \"Z\" / TIME-NUMOFFSET
      TIME-NUMOFFSET  = (\"+\" / \"-\") TIME-HOUR \":\" TIME-MINUTE

      NILVALUE        = \"-\" "
  "A timestamp ABNF grammar.")

(let ((scanner (abnf:parse-abnf-grammar *timestamp-abnf*
                    :timestamp
                    :registering-rules '(:full-date))))
  (cl-ppcre:register-groups-bind (date)
      (scanner "2013-09-08T00:02:03.123456Z+02:00")
    date))

In the previous usage example the let block returns "2013-09-08".

ABNF grammar

This library supports the ABNF grammar as given in RFC 2234, with additional support for plain regular expressions.

Parsed grammar

Here's the RFC syntax:

    rulelist       =  1*( rule / (*c-wsp c-nl) )

    rule           =  rulename defined-as elements c-nl
                           ; continues if next line starts
                           ;  with white space

    rulename       =  ALPHA *(ALPHA / DIGIT / "-")

    defined-as     =  *c-wsp ("=" / "=/") *c-wsp
                           ; basic rules definition and
                           ;  incremental alternatives

    elements       =  alternation *c-wsp

    c-wsp          =  WSP / (c-nl WSP)

    c-nl           =  comment / CRLF
                           ; comment or newline

    comment        =  ";" *(WSP / VCHAR) CRLF

    alternation    =  concatenation
                      *(*c-wsp "/" *c-wsp concatenation)

    concatenation  =  repetition *(1*c-wsp repetition)

    repetition     =  [repeat] element

    repeat         =  1*DIGIT / (*DIGIT "*" *DIGIT)

    element        =  rulename / group / option /
                      char-val / num-val / prose-val / regex
                           ; regex is an addition of this lib, see above

    group          =  "(" *c-wsp alternation *c-wsp ")"

    option         =  "[" *c-wsp alternation *c-wsp "]"

    char-val       =  DQUOTE *(%x20-21 / %x23-7E) DQUOTE
                           ; quoted string of SP and VCHAR
                           ;   without DQUOTE

    num-val        =  "%" (bin-val / dec-val / hex-val)

    bin-val        =  "b" 1*BIT
                      [ 1*("." 1*BIT) / ("-" 1*BIT) ]
                           ; series of concatenated bit values
                           ; or single ONEOF range

    dec-val        =  "d" 1*DIGIT
                      [ 1*("." 1*DIGIT) / ("-" 1*DIGIT) ]

    hex-val        =  "x" 1*HEXDIG
                      [ 1*("." 1*HEXDIG) / ("-" 1*HEXDIG) ]

    prose-val      =  "<" *(%x20-3D / %x3F-7E) ">"
                           ; bracketed string of SP and VCHAR
                           ;   without angles
                           ; prose description, to be used as
                           ;   last resort

Core rules

Those parts of the grammar are always provided, they are the defaults rules of the ABNF definition.

    ALPHA          =  %x41-5A / %x61-7A   ; A-Z / a-z

    BIT            =  "0" / "1"

    CHAR           =  %x01-7F
                           ; any 7-bit US-ASCII character, excluding NUL

    CR             =  %x0D
                           ; carriage return

    CRLF           =  CR LF
                           ; Internet standard newline

    CTL            =  %x00-1F / %x7F
                           ; controls

    DIGIT          =  %x30-39
                           ; 0-9

    DQUOTE         =  %x22
                           ; " (Double Quote)

    HEXDIG         =  DIGIT / "A" / "B" / "C" / "D" / "E" / "F"

    HTAB           =  %x09
                           ; horizontal tab

    LF             =  %x0A
                           ; linefeed

    LWSP           =  *(WSP / CRLF WSP)
                           ; linear white space (past newline)

    OCTET          =  %x00-FF
                           ; 8 bits of data

    SP             =  %x20

Regex Support

We add support for plain regexp in the element rule. A regexp is expected to follow the form:

   regex           = "~" delimiter expression delimiter

The expression shouldn't contain the delimiter of course, and the allowed delimiters are ~//, ~[], ~{}, ~(), ~<>, ~"", ~'', ~|| and ~##. If you have to build a regexp with more than one of those delimiters in it, you can just concatenate multiple parts together like in this example:

 complex-regex  = ~/foo{bar}/ ~{baz/quux}

That will be used in exactly the same way as the following example:

 complex-regex  = ~<foo{bar}baz/quux>
Author
Dimitri Fontaine <dim@tapoueh.org>
License
WTFPL