From 8f3840d9724865c2a1ca1602512b04d365564fc7 Mon Sep 17 00:00:00 2001
From: Joe Wreschnig <joe.wreschnig@gmail.com>
Date: Sat, 31 Jul 2021 20:18:18 +0200
Subject: [PATCH] Add `ReadRandom` and reimplement `NewRandomFromReader` using
 it

Combined with e.g. `bufio.Reader` this provides fast zero-allocation
UUID generation if you do not consider heap memory particularly
sensitive, without a global state or lock.
---
 uuid_test.go | 14 ++++++++++++++
 version4.go  | 16 +++++++++++++---
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/uuid_test.go b/uuid_test.go
index e98d0fe..c47e827 100644
--- a/uuid_test.go
+++ b/uuid_test.go
@@ -5,6 +5,7 @@
 package uuid
 
 import (
+	"bufio"
 	"bytes"
 	"fmt"
 	"os"
@@ -700,3 +701,16 @@ func BenchmarkUUID_NewPooled(b *testing.B) {
 		}
 	})
 }
+
+func BenchmarkUUID_BufioReadRandom(b *testing.B) {
+	b.RunParallel(func(pb *testing.PB) {
+		r := bufio.NewReaderSize(rander, randPoolSize)
+		var uuid UUID
+		for pb.Next() {
+			err := ReadRandom(r, &uuid)
+			if err != nil {
+				b.Fatal(err)
+			}
+		}
+	})
+}
diff --git a/version4.go b/version4.go
index 7697802..36bc72f 100644
--- a/version4.go
+++ b/version4.go
@@ -38,7 +38,8 @@ func NewString() string {
 //  year and having one duplicate.
 func NewRandom() (UUID, error) {
 	if !poolEnabled {
-		return NewRandomFromReader(rander)
+		var uuid UUID
+		return uuid, ReadRandom(rander, &uuid)
 	}
 	return newRandomFromPool()
 }
@@ -46,13 +47,22 @@ func NewRandom() (UUID, error) {
 // NewRandomFromReader returns a UUID based on bytes read from a given io.Reader.
 func NewRandomFromReader(r io.Reader) (UUID, error) {
 	var uuid UUID
+	return uuid, ReadRandom(r, &uuid)
+}
+
+// ReadRandom fills a random (version 4) UUID based on bytes read from a
+// given io.Reader. When combined with e.g. a bufio.Reader, this is an
+// efficient way to generate many UUIDs quickly.
+//
+// If an error was returned, the UUID may still be modified.
+func ReadRandom(r io.Reader, uuid *UUID) error {
 	_, err := io.ReadFull(r, uuid[:])
 	if err != nil {
-		return Nil, err
+		return err
 	}
 	uuid[6] = (uuid[6] & 0x0f) | 0x40 // Version 4
 	uuid[8] = (uuid[8] & 0x3f) | 0x80 // Variant is 10
-	return uuid, nil
+	return nil
 }
 
 func newRandomFromPool() (UUID, error) {