node-rollsum: rollsum library for node.js

This library is a node.js wrapper of librsync's rollsum module.

see test/test.js for more info. You can run it with node test/test.js <filename>.

My email is [email protected] and any suggestions and discussions are welcomed.

Module

var Rollsum = require("node-rollsum")
var s = new Rollsum(ChunkSize, DigestSize);

Rollsum is a writable stream which you can write data into it. The constructor has two arguments:

• ChunkSize: The size of the data that calculate one digest.
• DigestSize: When the digest is rolling, it is not efficient to get notified in each byte. So I use a buffer to store calculated digests. The buffer's size is DigestSize. When the buffer is full (or the input stream ends), a "digest" event is fire.

Events

• on('digest', function(length){ }): when digest buffer is full filled or the stream ends, you will get notified by this event. The argument length represents the number of digests in the buffer. In most cases it should be equal to DigestSize. Only when the stream ends, the event will be fired with the number of remaining digests.
• on('end', function(){ }): Called after the stream ends and the last digest event is fired.
• Rollsum is a writable stream so other events of stream is also availiable.

Methods

• getLength(): Get length in bytes of the processed data.
• getDigest(index): When the event digest is fired, you can get digests in the event handler. The argument index should be non-negative and less than the callback argument length. This function will return a 32-bit non-negative integer as the digest.
• getDigestData(index): You should call it in the callback of event digest just as getDigest(index). Sometimes you want to know the actual data that calculates the digest. For example, in rsync algorithm, You should calculate a stronger digest of the content when the rolling digest matches the input. This function returns a Buffer which contains the desired data.