为什么文件流功能没有结束

Question

I wrote the following code to create a hash of a file:

function hashFile(filePath){
  try{
    // Setup hash
    var hash = crypto.createHash('sha256');
    hash.setEncoding('hex');

    // Setup filestream
    var fileStream = fs.createReadStream(filePath);
    fileStream.pipe(hash, { end: false });

    fileStream.on('end', function () {
      // Get the hash
      hash.end();
      var thisHash = String(hash.read());
    });
  }catch (err) {
    console.log( "Error thrown : " + err );
    return;
  }
}

This worked just fine until I threw some smaller files at it. When I did this the function would just hang. The filestream.on('end') callback would never happen.

I rewrote it to not use createReadStream:

function hashFile(filePath){
  try{
    fs.readFile(filePath, function (err, data) {

      // Make the hash
      var thisHash = crypto
        .createHash('sha256')
        .update(data, 'utf8')
        .digest( 'hex');

        console.log(thisHash);
    });
  }catch (err) {
    console.log( "Error: " + err );
    return;
  }
}

This code works just fine, except it's incredibly slow on files that are a few MB or larger.

My question is why doesn't the first function work on small files?

Answer 1

So after searching for the answer all evening, I figured it out 15 min after writing this post. The 'end' callback needs to configured before calling pipe:

var fileStream = fs.createReadStream(filePath);

var hash = crypto.createHash('sha256');
hash.setEncoding('hex');

fileStream.on('end', function () {
  hash.end();
  console.log(hash.read());
});

fileStream.pipe(hash);