console: seed random number generator

[bas-vk]

The otto VM uses math/rand as source for Math.random(). The math/rand package uses by default a constant seed which generates the exact same sequence of (pseudo) random floats each time the console starts. This is unexpected behavior and brittle in the context of the console. If somewhere in the code base (e.g. one of the dependencies) resets the seed for math/rand the otto vm will produce predictable pseudo random numbers.

This PR will inject a pseudo random generator into the otto vm that is only used by the otto vm and is initialized with a new seed each time the console starts.

It required an upgrade of the otto vm package.

Fix: #2181

[robotally]

Vote	Count	Reviewers
👍	1	@fjl
👎	0

Updated: Fri Feb 19 12:08:56 UTC 2016

[codecov-io]

Current coverage is 48.17%

Merging #2227 into develop will increase coverage by +0.05% as of 48f5ddd

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[karalabe]

@bas-vk Please update your godep and repeat the dependency update. The new godep doesn't pull in test files of dependencies any more as they are really not needed.

[bas-vk]

@karalabe, check, thx.

[karalabe]

Ah, much better, thanks :D

[karalabe]

I don't think this si correct here, buy maybe I misunderstand.

src.Int63() should return an 63 bit random integer. That is, between 0 and 2^64 - 1. If you divide by 1 << 64 it should produce the intended results [0, 1). Whereas dividing by 1 << 63 actually produces quite a lot of values over 1.

[fjl]

Please don't build the logic to make random floats yourself.
You can setup a rand.Rand in runEventLoop, then just set r.Float64 as the source on the otto VM.

seed := make([]byte, 8)
crand.Read(seed)
r := rand.New(rand.NewSource(binary.BigEndian.Int64(seed)))
...
vm.SetRandomSource(r.Float64)

@karalabe It cannot be used concurrently.

[fjl]

I think we overlapped a bit with me editing the comment and you seeing it.
func () float64 { return r.Float64() } is equivalent to r.Float64, it's just more code.

[fjl]

👍

[bas-vk]

@fjl, we did just pushed the change as you suggested. Far cleaner solution.

[karalabe]

LGTM 👍