Buffer write* silently sets 0 instead of failing for wrong values

[unbornchikken]

Repro:

> var b = new Buffer(6);
undefined
> b.writeUInt32LE(10, 0);
4
> b.readUInt32LE(0)
10
> b.writeUInt32LE("5", 0);
4
> b.readUInt32LE(0)
5
> b.writeUInt32LE({}, 0);
4
> b.readUInt32LE(0)
0
> b.writeUInt32LE({}, 0, false);
4
> b.readUInt32LE(0)
0

According to this: https://iojs.org/api/buffer.html#buffer_buf_writeint32le_value_offset_noassert, the last three writes should be failed, because value is not a valid integer.

[mathiask88]

I think io.js should just check if the argument is a number instead of casting everything to number(or NaN for {}) (https://github.com/iojs/io.js/blob/v1.x/lib/buffer.js#L863) ?

[trevnorris]

Related: #2668

This is because we auto coerce the value like so:

Buffer.prototype.writeUInt32LE = function(value, offset, noAssert) {
  value = +value;

I did this to improve performance, but forgot about the passing of non-numeric values. Was only considering out of range numeric values.

So current functionality doesn't match documentation. The probable best solution is to put the assert checks above the value coercion. We'll work on this in the aforementioned issue.

[trevnorris]

On second thought I'm inclined to say that documentation should be updated. Would better read like so:

Note, value will be range checked then coerced to a valid signed 32 bit integer.

Basically, it should follow the same coercion rules as DataVew.