abnf

ABNF LL-parser by golang

How to use

Make Parser function

Make parser function that implement Rule interface. Functions that returns Basic Operator Rule are provided by this package.

For example,

• abnf.C(Rule...) function returns Rule that concatenate all argument Rules.
• abnf.V(rune) function returns Rule that match argument rune.
• abnf.ALPHA() function returns Rule that match any alphanumeric text.
• abnf.ETX() function returns Rule that match no more text is left.

Combile multiple Basic Operator by set each function to arguement. abnf.C(abnf.V('-'), abnf.ALPHANUM()) will make Rule that match aplhanumeric text taht start with -.

Parse Text by created Parser

Call abnf.ParseString(string, Rule) function with created Rule. The string will parsed and parsed item Tree is returned.

If text is not match with Rule, nil is returned.

Get parsed value from Tree

Tree contains parsed value with tag. tree.Child(tag).V returns value that correlated with specified tag.

Tag is defined while making parser function. There is special function abnf.K(Rule, tag) that make Special Rule that define tag.

Example

This sample parse FQDN.

Identity ::= label *("." label)
label    ::= ALPHANUM *ldhstr
ldhstr   ::= ALPHANUM / ("-" ALPHANUM)

const (
	idFQDN int = iota
)

type Identity string

func ParseIdentity(str string) (id Identity, e error) {
	t := abnf.ParseString(str, _identity())
	if t == nil {
		e = fmt.Errorf("Invalid id text")
	} else {
		id = Identity(t.Child(idFQDN).V)
	}
	return
}

func _identity() abnf.Rule {
	return abnf.C(_fqdn(), abnf.ETX())
}

func _fqdn() abnf.Rule {
	return abnf.K(abnf.C(_label(), abnf.R0(abnf.C(abnf.V('.'), _label()))), idFQDN)
}

func _label() abnf.Rule {
	return abnf.C(abnf.ALPHANUM(), abnf.R0(_ldhstr()))
}

func _ldhstr() abnf.Rule {
	return abnf.A(abnf.ALPHANUM(), abnf.C(abnf.V('-'), abnf.ALPHANUM()))
}

Notice

This parser is LL parser. You should modify somae of ABNF definition to apply them this package.

License

MIT