Fix potential non-random UUIDs

Use ReadFull to fetch random bytes from crypto/rand instead of calling
Read directly as Read may read less bytes than asked.

Fix #73

generator.go

@@ -165,7 +165,7 @@ func (g *rfc4122Generator) NewV3(ns UUID, name string) UUID {
 // NewV4 returns random generated UUID.
 func (g *rfc4122Generator) NewV4() (UUID, error) {
 	u := UUID{}
-	if _, err := g.rand.Read(u[:]); err != nil {
+	if _, err := io.ReadFull(g.rand, u[:]); err != nil {
 		return Nil, err
 	}
 	u.SetVersion(V4)
@@ -188,7 +188,7 @@ func (g *rfc4122Generator) getClockSequence() (uint64, uint16, error) {
 	var err error
 	g.clockSequenceOnce.Do(func() {
 		buf := make([]byte, 2)
-		if _, err = g.rand.Read(buf); err != nil {
+		if _, err = io.ReadFull(g.rand, buf); err != nil {
 			return
 		}
 		g.clockSequence = binary.BigEndian.Uint16(buf)
@@ -222,7 +222,7 @@ func (g *rfc4122Generator) getHardwareAddr() ([]byte, error) {
 
 		// Initialize hardwareAddr randomly in case
 		// of real network interfaces absence.
-		if _, err = g.rand.Read(g.hardwareAddr[:]); err != nil {
+		if _, err = io.ReadFull(g.rand, g.hardwareAddr[:]); err != nil {
 			return
 		}
 		// Set multicast bit as recommended by RFC 4122

generator_test.go

@@ -22,9 +22,11 @@
 package uuid
 
 import (
+	"bytes"
 	"crypto/rand"
 	"fmt"
 	"net"
+	"testing/iotest"
 	"time"
 
 	. "gopkg.in/check.v1"
@@ -195,6 +197,20 @@ func (s *genTestSuite) TestNewV4FaultyRand(c *C) {
 	c.Assert(u1, Equals, Nil)
 }
 
+func (s *genTestSuite) TestNewV4PartialRead(c *C) {
+	g := &rfc4122Generator{
+		epochFunc:  time.Now,
+		hwAddrFunc: defaultHWAddrFunc,
+		rand:       iotest.OneByteReader(rand.Reader),
+	}
+	u1, err := g.NewV4()
+	zeros := bytes.Count(u1.Bytes(), []byte{0})
+	mostlyZeros := zeros >= 10
+
+	c.Assert(err, IsNil)
+	c.Assert(mostlyZeros, Equals, false)
+}
+
 func (s *genTestSuite) BenchmarkNewV4(c *C) {
 	for i := 0; i < c.N; i++ {
 		NewV4()