sgml/node-re2

node.js bindings for RE2: fast, safe alternative to backtracking regular expression engines.

node-re2

This project provides bindings for RE2: fast, safe alternative to backtracking regular expression engines written by Russ Cox. To learn more about RE2, start with an overview Regular Expression Matching in the Wild. More resources can be found at his Implementing Regular Expressions page.

RE2's regular expression language is almost a superset of what is provided by RegExp (see Syntax), but it lacks one feature: backreferences. See below for more details.

RE2 object emulates standard RegExp making it a practical drop-in replacement in most cases. RE2 is extended to provide String-based regular expression methods as well. To help converting RegExp objects to RE2 its constructor can take RegExp directly honoring all properties.

It can work with node.js buffers directly reducing overhead on recoding and copying characters, and making processing/parsing long files fast.

Standard features

RE2 object can be created just like RegExp:

• new RE2(pattern[, flags])

Supported properties:

• re2.lastIndex
• re2.global
• re2.ignoreCase
• re2.multiline
• re2.source

Supported methods:

• re2.exec(str)
• re2.test(str)
• re2.toString()

Extensions

Shortcut construction

RE2 object can be created from a regular expression:

var re1 = new RE2(/ab*/ig); // from a RegExp object
var re2 = new RE2(re1);     // from another RE2 object

String methods

Standard String defines four more methods that can use regular expressions. RE2 provides them as methods exchanging positions of a string, and a regular expression:

• re2.match(str)
  • See str.match(regexp)
• re2.replace(str, newSubStr|function)
  • See str.replace(regexp, newSubStr|function)
• re2.search(str)
  • See str.search(regexp)
• re2.split(str[, limit])
  • See str.split(regexp[, limit])

Buffer support

In order to support Buffer directly, most methods can accept buffers instead of strings. It speeds up all operations. Following signatures are supported:

• re2.exec(buf)
• re2.test(buf)
• re2.match(buf)
• re2.search(buf)
• re2.split(buf[, limit])
• re2.replace(buf, replacer)

Differences with their string-based versions:

• All buffers are assumed to be encoded as UTF-8 (ASCII is a proper subset of UTF-8).
• Instead of strings they return Buffer objects, even in composite objects. A buffer can be converted to a string with buf.toString().
• All offsets and lengths are in bytes, rather than characters (each UTF-8 character can occupy from 1 to 4 bytes). This way users can properly slice buffers without costly recalculations from characters to bytes.

When re2.replace() is used with a replacer function, the replacer can return a buffer, or a string. But all arguments (except for an input object) will be strings, and an offset will be in characters. If you prefer to deal with buffers and byte offsets in a replacer function, set a property useBuffers to true on the function:

function strReplacer(match, offset, input) {
	// typeof match == "string"
	return "<= " + offset + " characters|";
}

RE2("б").replace("абв", strReplacer);
// "а<= 1 characters|в"

function bufReplacer(match, offset, input) {
	// typeof match == "string"
	return "<= " + offset + " bytes|";
}
bufReplacer.useBuffers = true;

RE2("б").replace("абв", bufReplacer);
// "а<= 2 bytes|в"

This feature works for string and buffer inputs. If a buffer was used as an input, its output will be returned as a buffer too, otherwise a string will be returned.

Calculate length

Two functions to calculate string sizes between UTF-8 and UTF-16 are exposed on RE2:

• RE2.getUtf8Length(str) — calculates a buffer size in bytes to encode a UTF-16 string as a UTF-8 buffer.
• RE2.getUtf16Length(buf) — calculates a string size in characters to encode a UTF-8 buffer as a UTF-16 string.

JavaScript supports UCS-2 strings with 16-bit characters, while node.js 0.11 supports full UTF-16 as a default string.

How to install

Installation:

npm install re2

How to use

It is used just like a RegExp object.

var RE2 = require("re2");

// with default flags
var re = new RE2("a(b*)");
var result = re.exec("abbc");
console.log(result[0]); // "abb"
console.log(result[1]); // "bb"

result = re.exec("aBbC");
console.log(result[0]); // "a"
console.log(result[1]); // ""

// with explicit flags
re = new RE2("a(b*)", "i");
result = re.exec("aBbC");
console.log(result[0]); // "aBb"
console.log(result[1]); // "Bb"

// from regular expression object
var regexp = new RegExp("a(b*)", "i");
re = new RE2(regexp);
result = re.exec("aBbC");
console.log(result[0]); // "aBb"
console.log(result[1]); // "Bb"

// from regular expression literal
re = new RE2(/a(b*)/i);
result = re.exec("aBbC");
console.log(result[0]); // "aBb"
console.log(result[1]); // "Bb"

// from another RE2 object
var rex = new RE2(re);
result = rex.exec("aBbC");
console.log(result[0]); // "aBb"
console.log(result[1]); // "Bb"

// shortcut
result = new RE2("ab*").exec("abba");

// factory
result = RE2("ab*").exec("abba");

Backreferences

Unlike RegExp, RE2 doesn't support backreferences, which are numbered references to previously matched groups, like so: \1, \2, and so on. Example of backrefrences:

/(cat|dog)\1/.test("catcat"); // true
/(cat|dog)\1/.test("dogdog"); // true
/(cat|dog)\1/.test("catdog"); // false
/(cat|dog)\1/.test("dogcat"); // false

If your application uses this kind of matching, you should continue to use RegExp.

Release history

• 1.3.3 Refreshed dependencies.
• 1.3.2 Updated references in README (re2 was moved to github).
• 1.3.1 Refreshed dependencies, new Travis-CI config.
• 1.3.0 Upgraded NAN to 1.6.3, now we support node.js 0.10.36, 0.12.0, and io.js 1.3.0. Thx @reid!
• 1.2.0 Documented getUtfXLength() functions. Added support for \c and \u commands.
• 1.1.1 Minor corrections in README.
• 1.1.0 Buffer-based API is public. Unicode is fully supported.
• 1.0.0 Implemented all RegExp methods, and all relevant String methods.
• 0.9.0 The initial public release.

License

BSD