Data race in RandomString()

[vladimiroff]

When running tests which use this package with the race detector it finds out there are data races.
Trivial to reproduce example is with the following useless program:

package main

import "syreclabs.com/go/faker"

func main() {
	go faker.RandomString(10)
	go faker.RandomString(10)
}

When I run it with go run -race this is the output from go's race detector:

==================
WARNING: DATA RACE
Read at 0x00c42018afb8 by goroutine 7:
  math/rand.read()
      /usr/lib/go/src/math/rand/rand.go:265 +0x3c
  math/rand.(*Rand).Read()
      /usr/lib/go/src/math/rand/rand.go:261 +0x16d
  syreclabs.com/go/faker.RandomString()
      /home/kiril/go/src/syreclabs.com/go/faker/faker.go:90 +0xb2

Previous write at 0x00c42018afb8 by goroutine 6:
  math/rand.read()
      /usr/lib/go/src/math/rand/rand.go:276 +0xee
  math/rand.(*Rand).Read()
      /usr/lib/go/src/math/rand/rand.go:261 +0x16d
  syreclabs.com/go/faker.RandomString()
      /home/kiril/go/src/syreclabs.com/go/faker/faker.go:90 +0xb2

Goroutine 7 (running) created at:
  main.main()
      /tmp/fake.go:7 +0x6c

Goroutine 6 (finished) created at:
  main.main()
      /tmp/fake.go:6 +0x4b
==================
==================
WARNING: DATA RACE
Read at 0x00c42018afb0 by goroutine 7:
  math/rand.read()
      /usr/lib/go/src/math/rand/rand.go:266 +0x56
  math/rand.(*Rand).Read()
      /usr/lib/go/src/math/rand/rand.go:261 +0x16d
  syreclabs.com/go/faker.RandomString()
      /home/kiril/go/src/syreclabs.com/go/faker/faker.go:90 +0xb2

Previous write at 0x00c42018afb0 by goroutine 6:
  math/rand.read()
      /usr/lib/go/src/math/rand/rand.go:277 +0x108
  math/rand.(*Rand).Read()
      /usr/lib/go/src/math/rand/rand.go:261 +0x16d
  syreclabs.com/go/faker.RandomString()
      /home/kiril/go/src/syreclabs.com/go/faker/faker.go:90 +0xb2

Goroutine 7 (running) created at:
  main.main()
      /tmp/fake.go:7 +0x6c

Goroutine 6 (finished) created at:
  main.main()
      /tmp/fake.go:6 +0x4b
==================
Found 2 data race(s)
exit status 66

Now, this makes a lot of sense, since math/rand.Rand.Read is documented as not safe to be called concurrently. Which is okay for a method of type. RandomString in this package however is a global function and this issue could not be worked around as easily as with Rand.Read. For instance math/rand.Read (the global function) is safe to be called concurrently.

[dmgk]

Thanks!