feat: restructure random value generation

device/awg/junk_creator.go

@@ -2,59 +2,42 @@ package awg
 
 import (
 	"bytes"
-	crand "crypto/rand"
 	"fmt"
-	v2 "math/rand/v2"
 )
 
 type junkCreator struct {
 	aSecCfg         aSecCfgType
-	cha8Rand *v2.ChaCha8
+	randomGenerator PRNG[int]
 }
 
 // TODO: refactor param to only pass the junk related params
-func NewJunkCreator(aSecCfg aSecCfgType) (junkCreator, error) {
-	buf := make([]byte, 32)
-	_, err := crand.Read(buf)
-	if err != nil {
-		return junkCreator{}, err
-	}
-	return junkCreator{aSecCfg: aSecCfg, cha8Rand: v2.NewChaCha8([32]byte(buf))}, nil
+func NewJunkCreator(aSecCfg aSecCfgType) junkCreator {
+	return junkCreator{aSecCfg: aSecCfg, randomGenerator: NewPRNG[int]()}
 }
 
 // Should be called with aSecMux RLocked
-func (jc *junkCreator) CreateJunkPackets(junks *[][]byte) error {
+func (jc *junkCreator) CreateJunkPackets(junks *[][]byte) {
 	if jc.aSecCfg.JunkPacketCount == 0 {
-		return nil
+		return
 	}
 
 	for range jc.aSecCfg.JunkPacketCount {
 		packetSize := jc.randomPacketSize()
-		junk, err := jc.randomJunkWithSize(packetSize)
-		if err != nil {
-			return fmt.Errorf("create junk packet: %v", err)
-		}
+		junk := jc.randomJunkWithSize(packetSize)
 		*junks = append(*junks, junk)
 	}
-	return nil
+	return
 }
 
 // Should be called with aSecMux RLocked
 func (jc *junkCreator) randomPacketSize() int {
-	return int(
-		jc.cha8Rand.Uint64()%uint64(
-			jc.aSecCfg.JunkPacketMaxSize-jc.aSecCfg.JunkPacketMinSize,
-		),
-	) + jc.aSecCfg.JunkPacketMinSize
+	return jc.randomGenerator.RandomSizeInRange(jc.aSecCfg.JunkPacketMinSize, jc.aSecCfg.JunkPacketMaxSize)
 }
 
 // Should be called with aSecMux RLocked
 func (jc *junkCreator) AppendJunk(writer *bytes.Buffer, size int) error {
-	headerJunk, err := jc.randomJunkWithSize(size)
-	if err != nil {
-		return fmt.Errorf("create header junk: %v", err)
-	}
-	_, err = writer.Write(headerJunk)
+	headerJunk := jc.randomJunkWithSize(size)
+	_, err := writer.Write(headerJunk)
 	if err != nil {
 		return fmt.Errorf("write header junk: %v", err)
 	}
@@ -62,9 +45,6 @@ func (jc *junkCreator) AppendJunk(writer *bytes.Buffer, size int) error {
 }
 
 // Should be called with aSecMux RLocked
-func (jc *junkCreator) randomJunkWithSize(size int) ([]byte, error) {
-	// TODO: use a memory pool to allocate
-	junk := make([]byte, size)
-	_, err := jc.cha8Rand.Read(junk)
-	return junk, err
+func (jc *junkCreator) randomJunkWithSize(size int) []byte {
+	return jc.randomGenerator.ReadSize(size)
 }

device/awg/junk_creator_test.go

@@ -6,43 +6,29 @@ import (
 	"testing"
 )
 
-func setUpJunkCreator(t *testing.T) (junkCreator, error) {
-	jc, err := NewJunkCreator(aSecCfgType{
+func setUpJunkCreator() junkCreator {
+	jc := NewJunkCreator(aSecCfgType{
 		IsSet:                  true,
 		JunkPacketCount:        5,
 		JunkPacketMinSize:      500,
 		JunkPacketMaxSize:      1000,
 		InitHeaderJunkSize:     30,
 		ResponseHeaderJunkSize: 40,
-		InitPacketMagicHeader:      123456,
-		ResponsePacketMagicHeader:  67543,
-		UnderloadPacketMagicHeader: 32345,
-		TransportPacketMagicHeader: 123123,
+		// TODO
+		// InitPacketMagicHeader:      123456,
+		// ResponsePacketMagicHeader:  67543,
+		// UnderloadPacketMagicHeader: 32345,
+		// TransportPacketMagicHeader: 123123,
 	})
 
-	if err != nil {
-		t.Errorf("failed to create junk creator %v", err)
-		return junkCreator{}, err
-	}
-
-	return jc, nil
+	return jc
 }
 
 func Test_junkCreator_createJunkPackets(t *testing.T) {
-	jc, err := setUpJunkCreator(t)
-	if err != nil {
-		return
-	}
+	jc := setUpJunkCreator()
 	t.Run("valid", func(t *testing.T) {
 		got := make([][]byte, 0, jc.aSecCfg.JunkPacketCount)
-		err := jc.CreateJunkPackets(&got)
-		if err != nil {
-			t.Errorf(
-				"junkCreator.createJunkPackets() = %v; failed",
-				err,
-			)
-			return
-		}
+		jc.CreateJunkPackets(&got)
 		seen := make(map[string]bool)
 		for _, junk := range got {
 			key := string(junk)
@@ -61,25 +47,19 @@ func Test_junkCreator_createJunkPackets(t *testing.T) {
 
 func Test_junkCreator_randomJunkWithSize(t *testing.T) {
 	t.Run("valid", func(t *testing.T) {
-		jc, err := setUpJunkCreator(t)
-		if err != nil {
-			return
-		}
-		r1, _ := jc.randomJunkWithSize(10)
-		r2, _ := jc.randomJunkWithSize(10)
+		jc := setUpJunkCreator()
+		r1 := jc.randomJunkWithSize(10)
+		r2 := jc.randomJunkWithSize(10)
 		fmt.Printf("%v\n%v\n", r1, r2)
 		if bytes.Equal(r1, r2) {
-			t.Errorf("same junks %v", err)
+			t.Errorf("same junks")
 			return
 		}
 	})
 }
 
 func Test_junkCreator_randomPacketSize(t *testing.T) {
-	jc, err := setUpJunkCreator(t)
-	if err != nil {
-		return
-	}
+	jc := setUpJunkCreator()
 	for range [30]struct{}{} {
 		t.Run("valid", func(t *testing.T) {
 			if got := jc.randomPacketSize(); jc.aSecCfg.JunkPacketMinSize > got ||
@@ -96,10 +76,7 @@ func Test_junkCreator_randomPacketSize(t *testing.T) {
 }
 
 func Test_junkCreator_appendJunk(t *testing.T) {
-	jc, err := setUpJunkCreator(t)
-	if err != nil {
-		return
-	}
+	jc := setUpJunkCreator()
 	t.Run("valid", func(t *testing.T) {
 		s := "apple"
 		buffer := bytes.NewBuffer([]byte(s))

device/awg/util.go

@@ -0,0 +1,44 @@
+package awg
+
+import (
+	crand "crypto/rand"
+	v2 "math/rand/v2"
+
+	"golang.org/x/exp/constraints"
+)
+
+type PRNG[T constraints.Integer] struct {
+	cha8Rand *v2.ChaCha8
+}
+
+func NewPRNG[T constraints.Integer]() PRNG[T] {
+	buf := make([]byte, 32)
+	_, _ = crand.Read(buf)
+
+	return PRNG[T]{
+		cha8Rand: v2.NewChaCha8([32]byte(buf)),
+	}
+}
+
+func (p PRNG[T]) RandomSizeInRange(min, max T) T {
+	if min >= max {
+		panic("min must be less than max")
+	}
+
+	if min == max {
+		return min
+	}
+
+	return T(p.Get()%uint64(max-min)) + min
+}
+
+func (p PRNG[T]) Get() uint64 {
+	return p.cha8Rand.Uint64()
+}
+
+func (p PRNG[T]) ReadSize(size int) []byte {
+	// TODO: use a memory pool to allocate
+	buf := make([]byte, size)
+	_, _ = p.cha8Rand.Read(buf)
+	return buf
+}