Source: rand.go in package google.golang.org/protobuf/internal/detrand

Source File
	rand.go

Belonging Package
	google.golang.org/protobuf/internal/detrand

Package detrand provides deterministically random functionality. The pseudo-randomness of these functions is seeded by the program binary itself and guarantees that the output does not change within a program, while ensuring that the output is unstable across different builds.

package detrand

import (
	"encoding/binary"
	"hash/fnv"
	"os"
)

Disable disables detrand such that all functions returns the zero value. This function is not concurrent-safe and must be called during program init.

func Disable() {
	randSeed = 0
}

Bool returns a deterministically random boolean.

func Bool() bool {
	return randSeed%2 == 1
}

randSeed is a best-effort at an approximate hash of the Go binary.

var randSeed = binaryHash()

Open the Go binary.

	s, err := os.Executable()
	if err != nil {
		return 0
	}
	f, err := os.Open(s)
	if err != nil {
		return 0
	}
	defer f.Close()

Hash the size and several samples of the Go binary.

	const numSamples = 8
	var buf [64]byte
	h := fnv.New64()
	fi, err := f.Stat()
	if err != nil {
		return 0
	}
	binary.LittleEndian.PutUint64(buf[:8], uint64(fi.Size()))
	h.Write(buf[:8])
	for i := int64(0); i < numSamples; i++ {
		if _, err := f.ReadAt(buf[:], i*fi.Size()/numSamples); err != nil {
			return 0
		}
		h.Write(buf[:])
	}
	return h.Sum64()


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