getSourceString is not uniquely decodable

[fitzn]

(Feel free to resolve this as Won't Fix based on the limited set of potential strings that can be keys in a Unit dictionary. This is merely proof-of-concept for something that struck me as weird.)

The object_hash module uses the getSourceString function to turn a Unit into a String before hashing the String to produce a content_hash (among other things). The getSourceString function produces the same output String for different inputs, which, in turn, produces an identical hash. This is because the object type is not tokenized, and this could theoretically cause an issue as it breaks the widespread assumption that different inputs of the same data type (e.g., Unit) will hash to different values.

This example input:

var objectOne = ['s', 'a'];
var sourceStringOne = getSourceString(objectOne);

var objectTwo = [{s: {s: 'a'}}];
var sourceStringTwo = getSourceString(objectTwo);

console.log("Object One: " + sourceStringOne);
console.log("Object Two: " + sourceStringTwo);
console.log("Strings match? " + (sourceStringOne === sourceStringTwo));

produces this output (including unprintable characters):

Object One: [�s�s�s�a�]
Object Two: [�s�s�s�a�]
Strings match? true

Again, this case is extremely unlikely (maybe impossible) in this code base since the Unit object's keys are fixed, but I figured I'd call it out.

[tonyofbyteball]

you're right that should have been avoided but the fixed structure of unit and other objects saves us.

[fitzn]

@tonyofbyteball Okay, resolving this for now then.