How to generate a deterministic set of UUIDs in golang - go

Question

I'm doing some testing and it would be useful to have a known set of UUIDs that are getting used by our code. However, I'm having trouble figuring out how to create a deterministic set of UUIDs in golang.
I've tried a few approaches, but neither seemed to work:
type KnownReader struct {
store *Store
}
type Store struct {
val uint16
}
func (r KnownReader) Read(p []byte) (n int, err error) {
ret := r.store.val
r.store.val = ret + 1
fmt.Printf("\nStore: %v", r.store.val)
p = make([]byte, 4)
binary.LittleEndian.PutUint16(p, uint16(ret))
fmt.Printf("\nreader p: % x", p)
return binary.MaxVarintLen16, nil
}
func main() {
r := KnownReader{
store: &Store{val: 111},
}
uuid.SetRand(r)
u, _ := uuid.NewRandomFromReader(r)
fmt.Printf("\n%v",u)
u, _ = uuid.NewRandomFromReader(r)
fmt.Printf("\n%v",u)
}
---- OUTPUT ----
Store: 1
reader p: 00 00 00 00
Store: 2
reader p: 01 00 00 00
Store: 3
reader p: 02 00 00 00
Store: 4
reader p: 03 00 00 00
Store: 5
reader p: 04 00 00 00
Store: 6
reader p: 05 00 00 00
00000000-0000-4000-8000-000000000000
Store: 7
reader p: 06 00 00 00
Store: 8
reader p: 07 00 00 00
Store: 9
reader p: 08 00 00 00
Store: 10
reader p: 09 00 00 00
Store: 11
reader p: 0a 00 00 00
Store: 12
reader p: 0b 00 00 00
00000000-0000-4000-8000-000000000000
As you can see, the UUID, does not change between calls
I also tried using uuid.FromBytes, but that didn't seem to work either:
func getbytes(num uint16) []byte {
p := make([]byte, 4)
binary.LittleEndian.PutUint16(p, num)
fmt.Printf("\ngetbytes p: % x", p)
return p
}
func main() {
var i uint16 = 0
fmt.Printf("\nout getbytes: % x", getbytes(i))
u, _ := uuid.FromBytes(getbytes(i))
i = i + 1
fmt.Printf("\nUUID: %v", u)
fmt.Printf("\nout getbytes: % x", getbytes(i))
u, _ = uuid.FromBytes(getbytes(i))
fmt.Printf("\nUUID: %v", u)
}
---- OUTPUT ----
getbytes p: 00 00 00 00
out getbytes: 00 00 00 00
getbytes p: 00 00 00 00
UUID: 00000000-0000-0000-0000-000000000000
getbytes p: 01 00 00 00
out getbytes: 01 00 00 00
getbytes p: 01 00 00 00
UUID: 00000000-0000-0000-0000-000000000000
As you can see the UUIDs are still the same here as well.
So, is there something I'm missing? How can I get a consistent set of UUIDs?
Thanks

Answer 1

Thanks Adrian, I think I figured out the answer:
rnd := rand.New(rand.NewSource(1))
uuid.SetRand(rnd)
u, _ = uuid.NewRandomFromReader(rnd)
fmt.Printf("\n%v", u)
u, _ = uuid.NewRandomFromReader(rnd)
fmt.Printf("\n%v", u)
--- OUTPUT ---
52fdfc07-2182-454f-963f-5f0f9a621d72
9566c74d-1003-4c4d-bbbb-0407d1e2c649