Calculate a file hash and save the file - node.js

Question

Users upload files into my express app. I need to calc hash of the uploaded file and then write file to disk using calculated hash as a filename. I try to do it using the following code:
function storeFileStream(file, next) {
createFileHash(file, function(err, hash) {
if (err) {
return next(err);
}
var fileName = path.join(config.storagePath, hash),
stream = fs.createWriteStream(fileName);
stream.on('error', function(err) {
return next(err);
});
stream.on('finish', function() {
return next();
});
file.pipe(stream);
});
}
function createFileHash(file, next) {
var hash = crypto.createHash('sha1');
hash.setEncoding('hex');
file.on('error', function(err) {
return next(err);
});
file.on('end', function(data) {
hash.end();
return next(null, hash.read());
});
file.pipe(hash);
}
The problem is that after I calc file hash the writed file size is 0. What is the best way do solve this task?
Update
According #poke suggestion I try to duplicate my stream. Now my code is:
function storeFileStream(file, next) {
var s1 = new pass;
var s2 = new pass;
file.pipe(s1);
file.pipe(s2);
createFileHash(s1, function(err, hash) {
if (err) {
return next(err);
}
var fileName = path.join(config.storagePath, hash),
stream = fs.createWriteStream(fileName);
stream.on('error', function(err) {
return next(err);
});
stream.on('finish', function() {
return next();
});
s2.pipe(stream);
});
}
function createFileHash(file, next) {
var hash = crypto.createHash('sha1');
hash.setEncoding('hex');
file.on('error', function(err) {
return next(err);
});
file.on('end', function(data) {
hash.end();
return next(null, hash.read());
});
file.pipe(hash);
}
The problem of this code is that events end and finish are not emited. If I comment file.pipe(s2); events are emited, but I again get my origin problem.

Answer 1

This code fix the problem:
var s1 = new passThrough,
s2 = new passThrough;
file.on('data', function(data) {
s1.write(data);
s2.write(data);
});
file.on('end', function() {
s1.end();
s2.end();
});

Answer 2

The correct and simple way should be as follow:
we should resume the passthroughed stream
function storeFileStream(file, directory, version, reject, resolve) {
const fileHashSource = new PassThrough();
const writeSource = new PassThrough();
file.pipe(fileHashSource);
file.pipe(writeSource);
// this is the key point, see https://nodejs.org/api/stream.html#stream_three_states
fileHashSource.resume();
writeSource.resume();
createFileHash(fileHashSource, function(err, hash) {
if (err) {
return reject(err);
}
const fileName = path.join(directory, version + '_' + hash.slice(0, 8) + '.zip');
const writeStream = fs.createWriteStream(fileName);
writeStream.on('error', function(err) {
return reject(err);
});
writeStream.on('finish', function() {
return resolve();
});
writeSource.pipe(writeStream);
});
}
function createFileHash(readStream, next) {
const hash = crypto.createHash('sha1');
hash.setEncoding('hex');
hash.on('error', function(err) {
return next(err);
});
hash.on('finish', function(data) {
return next(null, hash.read());
});
readStream.pipe(hash);
}

Answer 3

You could use the async module (not tested but should work):
async.waterfall([
function(done) {
var hash = crypto.createHash('sha1');
hash.setEncoding('hex');
file.on('error', function(err) {
done(err);
});
file.on('end', function(data) {
done(null, hash.read);
});
file.pipe(hash);
},
function(hash, done) {
var fileName = path.join(config.storagePath, hash),
stream = fs.createWriteStream(fileName);
stream.on('error', function(err) {
done(err);
});
stream.on('finish', function() {
done(null);
});
file.pipe(stream);
}
], function (err) {
console.log("Everything is done!");
});