Check if a file is binary or ASCII with Node.js?

Question

I\'m wondering what would be the best way to check if a file is binary or ASCII with Node.js?

There appears to be two ways not specific to node.js:

Answer 1

ASCII defines characters 0-127, so if a file's entire contents are byte values in that range then it can be considered an ASCII file.

function fileIsAscii(filename, callback) {
  // Read the file with no encoding for raw buffer access.
  require('fs').readFile(filename, function(err, buf) {
    if (err) throw err;
    var isAscii = true;
    for (var i=0, len=buf.length; i<len; i++) {
      if (buf[i] > 127) { isAscii=false; break; }
    }
    callback(isAscii); // true iff all octets are in [0, 127].
  });
}
fileIsAscii('/usr/share/dict/words', function(x){/* x === true */});
fileIsAscii('/bin/ls', function(x){/* x === false */});

If performance is critical then consider writing a custom C++ function per your linked answer.

Answer 2

I came here from google but as I couldn't find a satisfactory answer, I took another approach which works for me:

const string_to_test = "I am just a piece of text";
//const binary_to_test = "��˰!1�H��1�1����!H�=u�!�";
if(/\ufffd/.test(string_to_test) === true){
    console.log("I'm 'binary'");
}else{
    console.log("I'm proper text");
}

How does it works? If you try to open binary data in a normal way (without using a hex editor), it will encounter some rendering problems which translate to you as a succession of this weird character � called "Replacement character".

Answer 3

Thanks to the comments on this question by David Schwartz, I created istextorbinary to solve this problem.