The OT Fuzzer

This directory contains The Fuzzer (Bug finding hound, destroyer of confidence).

If you make an OT type and you haven't run the fuzzer on your type, you will almost certainly find bugs with your implementation. It is obnoxious the number of bugs this little bundle of joy has found over the years.

Use it like this:

var fuzzer = require('ot-fuzzer');
var mytype = require('./mytype');

var generateRandomOp = function(snapshot) {
  // ...
  return [op, newSnapshot];
};

fuzzer(mytype, generateRandomOp);

API

You need to write a random op generator function for your type:

generateRandomOp(snapshot) -> [op, newSnapshot]: generateRandomOp generates a random operation that is valid for the given snapshot. It returns the operation along with the expected result of applying the operation. You should not use type.apply to generate the expected snapshot - that would make it very hard to find bugs in the apply function itself.

The fuzzer will start with an empty document (type.create()) and then iteratively generate operations with generateRandomOp and apply them. If your generateRandomOp function only makes operations which increase the size of the document, the randomizer will eat all your RAM and get really slow. You should strike a balance in your generateRandomOp function between growing and shrinking the document.

Arguably this is a bug in the fuzzer - feel free to submit a pull request.

Once you've written generateRandomOp, you can run the fuzzer:

fuzzer(type, generateRandomOp, [iterations]): Runs the fuzzer. The randomizer generates a few new operations from the initial document snapshot and tests that the various OT functions do what they're supposed to.

If unspecified, the fuzzer defaults to 2000 iterations. When debugging your OT type, you should increase this so you can run the fuzzer overnight.

Random data functions

The fuzzer library also comes with a mersenne prime random number generator and some helper functions. These functions make the fuzzer repeatable, so each identical instantiation of the fuzzer will trigger the same bugs. This is extremely convenient when you're debugging your library, and as such its highly recommended that you use these functions instead of Math.random().

The seed changes every 6 hours. If you want to do more testing, don't change the seed - instead increase the iteration count or add more cases to your generator.

• randomReal(): Generate a random float less than 1. This function is a direct replacement for Math.random(), except it uses a seed.
• randomInt(n): Generate a random int in the range [0,n). (Ie, a non-negative integer less than n).
• randomWord(): Select and return a random word. The word is chosen from the jabberwocky.

These functions are exposed on the fuzzer function. Eg:

var fuzzer = require('ot-fuzzer');

console.log("I have " + fuzzer.randomInt(100) + " " + fuzzer.randomWord() + " in my basket");
// -> I have 69 mimsy in my basket

Commentary

This library is several years old now. I (Joseph) wrote it when I first started writing the original prototype of ShareJS. It then lived for awhile in the share/ottypes library, and its now been separated out.

The randomizer has also helped debug my C implementation of the text type. I wired the randomizer to output what it was testing into a few hundred megs of JSON files, and then read the data back in from my C program. It worked great.

The code is in coffeescript for purely historical reasons. I'd love to move it to javascript - I'm just strapped for time. I'd welcome a pull request if anyone is keen to help. (Please start with the coffeescript compiled output if so).

There's also no unit tests - and there really should be. This code is routinely tested by actually running it against things. But it could use some simple tests of its own to make sure it actually catches obvious bugs in a dummy OT type.

License

All code contributed to this repository is licensed under the standard MIT license:

Copyright 2011-2014 ottypes library contributors

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following condition:

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.