How to compare Buffer objects in NodeJS?

Question

I am new to Node and start to play some node code. The problem I met is how to compare Buffer objects in NodeJS directly? Here "directly" means without using buffer.toString() method or iterate the whole buffer.

Here is an example:

var buf1 = new Buffer("abc");
var buf2 = new Buffer("abc");
console.log(buf1===buf2); //result is false
Buffer.compare(buf1,buf2);//lengthy error message

Thanks Derek

Update: I am using version "v0.10.38", here is the message if I use buf1.compare(buf2):

>buf1.compare(buf2)
TypeError: Object abc has no method 'compare'
at repl:1:7
at REPLServer.self.eval (repl.js:110:21)
at Interface.<anonymous> (repl.js:239:12)
at Interface.emit (events.js:95:17)
at Interface._onLine (readline.js:203:10)
at Interface._line (readline.js:532:8)
at Interface._ttyWrite (readline.js:761:14)
at ReadStream.onkeypress (readline.js:100:10)
at ReadStream.emit (events.js:98:17)
at emitKey (readline.js:1096:12)

Answer 1

Per the nodejs change log, it looks like .compare() and .equals() were added in node v0.11.13.

I don't have explicit v0.10 doc that I can find, so maybe you'd have to write a byte by byte comparison yourself.

Here's a quick and dirty comparison function:

function areBuffersEqual(bufA, bufB) {
    var len = bufA.length;
    if (len !== bufB.length) {
        return false;
    }
    for (var i = 0; i < len; i++) {
        if (bufA.readUInt8(i) !== bufB.readUInt8(i)) {
            return false;
        }
    }
    return true;
}

FYI, in looking at the nodejs source code, the built-in .compare() or .equals() in the newer nodejs version will be a lot faster because they go to C and do memcmp() directly on the buffer which is going to be a lot faster than two method calls for every item in the buffer.

---

You can use any of these in node v0.12.2:

var buf1 = new Buffer("abc");
var buf2 = new Buffer("abc");
buf1.equals(buf2);            // returns true
buf1.compare(buf2).           // returns 0
Buffer.compare(buf1, buf2);   // returns 0

---

Here's more detail on each option:

var buf1 = new Buffer("abc");
var buf2 = new Buffer("abc");
console.log(buf1.compare(buf2));   // 0 means buffers are the same

The result will be 0 when the two buffers are identical non-zero if not.

---

You can also use:

var buf1 = new Buffer("abc");
var buf2 = new Buffer("abc");
console.log(buf1.equals(buf2));   // true means buffers are the same

To get a boolean back for whether the two buffers contain the same bytes.

---

FYI, your original code of:

var buf1 = new Buffer("abc");
var buf2 = new Buffer("abc");
Buffer.compare(buf1,buf2);

Works just fine for me. It returns 0 just like buf1.compare(buf2).

---

In Javascript the === operator for two objects compares to see if the two variables point to the exact same object, not whether the separate objects contain the same content. So, buf1 === buf1, but buf1 !== buf2.