reused version4 NewRandom() and added better testing

uuid_source.go

@@ -5,17 +5,31 @@ import (
 	"crypto/rand"
 )
 
+// A UuidSource holds a random number generator and generates UUIDs using it as its source.
+//
+// It is useful when a process need its own random number generator, 
+// e.g. when running some processes concurrently.
 type UuidSource struct {
 	rander io.Reader
 }
 
+// Creates a new UuidSource which holds its own random number generator.
+//
+// Calling NewSource with nil sets the random number generator to a default
+// generator.
 func NewSource(r io.Reader) UuidSource {
 	var uuidSource UuidSource
 	uuidSource.SetRand(r)
 	return uuidSource
 
 }
 
+// SetRand sets the random number generator of the UuidSource to r, which implements io.Reader.
+// If r.Read returns an error when the package requests random data then
+// a panic will be issued.
+//
+// Calling SetRand with nil sets the random number generator to a default
+// generator.
 func (uuidSource *UuidSource) SetRand(r io.Reader) {
 	if r == nil {
 		uuidSource.rander = rand.Reader
@@ -24,17 +38,17 @@ func (uuidSource *UuidSource) SetRand(r io.Reader) {
 	uuidSource.rander = r
 }
 
+// NewRandom returns a Random (Version 4) UUID based on the random number generator in the UuidSource.
+//
+// See more detailed explanation here: https://godoc.org/github.com/google/uuid#NewRandom
 func (uuidSource UuidSource) NewRandom() (UUID, error) {
-	var uuid UUID
-	_, err := io.ReadFull(uuidSource.rander, uuid[:])
-	if err != nil {
-		return Nil, err
-	}
-	uuid[6] = (uuid[6] & 0x0f) | 0x40 // Version 4
-	uuid[8] = (uuid[8] & 0x3f) | 0x80 // Variant is 10
-	return uuid, nil
+	return newRandom(uuidSource.rander)
 }
 
+// New creates a new random UUID  based on the random number generator in the UuidSource or panics.  New is equivalent to
+// the expression
+//
+//    uuid.Must(uuid.NewRandom())
 func (uuidSource UuidSource) New() UUID {
 	return Must(uuidSource.NewRandom())
 }

uuid_source_test.go

@@ -7,23 +7,53 @@ import (
 )
 
 func TestUuidSources(t *testing.T) {
+
+	// Two identical sources, should give same sequence
 	currentTime := time.Now().UnixNano()
 	uuidSourceA := NewSource(rand.New(rand.NewSource(currentTime)))
 	uuidSourceB := NewSource(rand.New(rand.NewSource(currentTime)))
 
 	for i := 0; i < 10; i++ {
-		if uuidSourceA.New().String() != uuidSourceB.New().String() {
-			t.Error("Uuid values are not reproducaible!")
+		uuid1 := uuidSourceA.New()
+		uuid2 := uuidSourceB.New()
+		if uuid1 != uuid2 {
+			t.Errorf("expected duplicates, got %q and %q", uuid1, uuid2)
 		}
 	}
 
-	uuidSourceA = NewSource(rand.New(rand.NewSource(123)))
-	uuidSourceB = NewSource(rand.New(rand.NewSource(456)))
+	// Set rander with nil, each source will be random
+	uuidSourceA.SetRand(nil)
+	uuidSourceB.SetRand(nil)
+
+	for i := 0; i < 10; i++ {
+		uuid1 := uuidSourceA.New()
+		uuid2 := uuidSourceB.New()
+		if uuid1 == uuid2 {
+		t.Errorf("unexpected duplicates, got %q", uuid1)
+		}
+	}
 
+	// Set rander to rand source with same seed, should give same sequence
+	uuidSourceA.SetRand(rand.New(rand.NewSource(123)))
+	uuidSourceB.SetRand(rand.New(rand.NewSource(123)))
+
+	for i := 0; i < 10; i++ {
+		uuid1 := uuidSourceA.New()
+		uuid2 := uuidSourceB.New()
+		if uuid1 != uuid2 {
+			t.Errorf("expected duplicates, got %q and %q", uuid1, uuid2)
+		}
+	}
+
+	// Set rander to rand source with different seeds, should not give same sequence
+	uuidSourceA.SetRand(rand.New(rand.NewSource(456)))
+	uuidSourceB.SetRand(rand.New(rand.NewSource(789)))
 
 	for i := 0; i < 10; i++ {
-		if uuidSourceA.New().String() == uuidSourceB.New().String() {
-			t.Error("Uuid values should not match!")
+		uuid1 := uuidSourceA.New()
+		uuid2 := uuidSourceB.New()
+		if uuid1 == uuid2 {
+		t.Errorf("unexpected duplicates, got %q", uuid1)
 		}
 	}
 

uuid_test.go

@@ -13,6 +13,8 @@ import (
 	"testing"
 	"time"
 	"unsafe"
+
+	"math/rand"
 )
 
 type test struct {
@@ -479,6 +481,25 @@ func TestBadRand(t *testing.T) {
 	}
 }
 
+func TestSetRand(t *testing.T) {
+	SetRand(rand.New(rand.NewSource(456)))
+	uuid1 := New()
+	uuid2 := New()
+
+	SetRand(rand.New(rand.NewSource(456)))
+	uuid3 := New()
+	uuid4 := New()
+
+	if uuid1 != uuid3 {
+		t.Errorf("expected duplicates, got %q and %q", uuid1, uuid3)
+	}
+	if uuid2 != uuid4 {
+		t.Errorf("expected duplicates, got %q and %q", uuid2, uuid4)
+	}
+
+
+}
+
 var asString = "f47ac10b-58cc-0372-8567-0e02b2c3d479"
 var asBytes = []byte(asString)
 

version4.go

@@ -27,12 +27,17 @@ func New() UUID {
 //  equivalent to the odds of creating a few tens of trillions of UUIDs in a
 //  year and having one duplicate.
 func NewRandom() (UUID, error) {
+	return newRandom(rander)
+}
+
+func newRandom(r io.Reader) (UUID, error) {
 	var uuid UUID
-	_, err := io.ReadFull(rander, uuid[:])
+	_, err := io.ReadFull(r, uuid[:])
 	if err != nil {
 		return Nil, err
 	}
 	uuid[6] = (uuid[6] & 0x0f) | 0x40 // Version 4
 	uuid[8] = (uuid[8] & 0x3f) | 0x80 // Variant is 10
 	return uuid, nil
 }
+