Obtaining the hash of a file using the stream capa

问题:

The crypto module of node.js (at the time of this writing at least) is not still deemed stable and so the API may change. In fact, the methods that everyone in the internet use to get the hash (md5, sha1, ...) of a file are considered legacy (from the documentation of Hash class) (note: emphasis mine):

Class: Hash

The class for creating hash digests of data.

It is a stream that is both readable and writable. The written data is used to compute the hash. Once the writable side of the stream is ended, use the read() method to get the computed hash digest. The legacy update and digest methods are also supported.

Returned by crypto.createHash.

Despite hash.update and hash.digest being considered legacy, the example shown just above the quoted snippet is using them.

What's the correct way of obtaining hashes without using those legacy methods?

回答1:

From the quoted snippet in the question:

[the Hash class] It is a stream that is both readable and writable. The written data is used to compute the hash. Once the writable side of the stream is ended, use the read() method to get the computed hash digest.

So what you need to hash some text is:

var crypto = require('crypto');

// change to 'md5' if you want an MD5 hash
var hash = crypto.createHash('sha1');

// change to 'binary' if you want a binary hash.
hash.setEncoding('hex');

// the text that you want to hash
hash.write('hello world');

// very important! You cannot read from the stream until you have called end()
hash.end();

// and now you get the resulting hash
var sha1sum = hash.read();

If you want to get the hash of a file, the best way is create a ReadStream from the file and pipe it into the hash:

var fs = require('fs');
var crypto = require('crypto');

// the file you want to get the hash    
var fd = fs.createReadStream('/some/file/name.txt');
var hash = crypto.createHash('sha1');
hash.setEncoding('hex');

fd.on('end', function() {
    hash.end();
    console.log(hash.read()); // the desired sha1sum
});

// read all file and pipe it (write it) to the hash object
fd.pipe(hash);

回答2:

Short version of Carlos' answer:

var fs = require('fs')
var crypto = require('crypto')

fs.createReadStream('/some/file/name.txt').
  pipe(crypto.createHash('sha1').setEncoding('hex')).
  on('finish', function () {
    console.log(this.read()) //the hash
  })

回答3:

An ES6 version returning a Promise for the hash digest:

function checksumFile(hashName, path) {
  return new Promise((resolve, reject) => {
    let hash = crypto.createHash(hashName);
    let stream = fs.createReadStream(path);
    stream.on('error', err => reject(err));
    stream.on('data', chunk => hash.update(chunk));
    stream.on('end', () => resolve(hash.digest('hex')));
  });
}

回答4:

Further polish, ECMAScript 2015

function checksumFile(algorithm, path) {
  return new Promise((resolve, reject) =>
    fs.createReadStream(path)
      .on('error', reject)
      .pipe(crypto.createHash(algorithm)
        .setEncoding('hex'))
      .once('finish', function () {
        resolve(this.read())
      })
  )
}

回答5:

var fs = require('fs');
var crypto = require('crypto');
var fd = fs.createReadStream('data.txt');
var hash = crypto.createHash('md5');
hash.setEncoding('hex');
fd.pipe(hash);
hash.on('data', function (data) {
    console.log('# ',data);
});