RTCP: Add util/GetPadding

Simple helper function to do 32bit padding calculation

Relates to #119

internal/util/util.go

@@ -15,3 +15,11 @@ func RandSeq(n int) string {
 	}
 	return string(b)
 }
+
+// GetPadding Returns the padding required to make the length a multiple of 4
+func GetPadding(len int) int {
+	if len%4 == 0 {
+		return 0
+	}
+	return 4 - (len % 4)
+}

internal/util/util_test.go

@@ -0,0 +1,40 @@
+package util
+
+import (
+	"regexp"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRandSeq(t *testing.T) {
+	if len(RandSeq(10)) != 10 {
+		t.Errorf("RandSeq return invalid length")
+	}
+
+	var isLetter = regexp.MustCompile(`^[a-zA-Z]+$`).MatchString
+	if !isLetter(RandSeq(10)) {
+		t.Errorf("RandSeq should be AlphaNumeric only")
+	}
+}
+
+func TestGetPadding(t *testing.T) {
+	assert := assert.New(t)
+	type testCase struct {
+		input  int
+		result int
+	}
+
+	cases := []testCase{
+		{input: 0, result: 0},
+		{input: 1, result: 3},
+		{input: 2, result: 2},
+		{input: 3, result: 1},
+		{input: 4, result: 0},
+		{input: 100, result: 0},
+		{input: 500, result: 0},
+	}
+	for _, testCase := range cases {
+		assert.Equalf(GetPadding(testCase.input), testCase.result, "Test case returned wrong value for input %d", testCase.input)
+	}
+}

pkg/rtcp/goodbye.go

@@ -2,6 +2,8 @@ package rtcp
 
 import (
 	"encoding/binary"
+
+	"github.com/pions/webrtc/internal/util"
 )
 
 // The Goodbye packet indicates that one or more sources are no longer active.
@@ -49,10 +51,7 @@ func (g Goodbye) Marshal() ([]byte, error) {
 		rawPacket = append(rawPacket, reason...)
 
 		// align to 32-bit boundary
-		if len(rawPacket)%4 != 0 {
-			padCount := 4 - len(rawPacket)%4
-			rawPacket = append(rawPacket, make([]byte, padCount)...)
-		}
+		rawPacket = append(rawPacket, make([]byte, util.GetPadding(len(rawPacket)))...)
 	}
 
 	h := Header{
@@ -96,7 +95,7 @@ func (g *Goodbye) Unmarshal(rawPacket []byte) error {
 		return errWrongType
 	}
 
-	if len(rawPacket)%4 != 0 {
+	if util.GetPadding(len(rawPacket)) != 0 {
 		return errPacketTooShort
 	}
 

pkg/rtcp/source_description.go

@@ -2,6 +2,8 @@ package rtcp
 
 import (
 	"encoding/binary"
+
+	"github.com/pions/webrtc/internal/util"
 )
 
 // SDESType is the item type used in the RTCP SDES control packet.
@@ -187,10 +189,7 @@ func (s SourceDescriptionChunk) Marshal() ([]byte, error) {
 	rawPacket = append(rawPacket, uint8(SDESEnd))
 
 	// additional null octets MUST be included if needed to pad until the next 32-bit boundary
-	if size := len(rawPacket); size%4 != 0 {
-		padding := make([]byte, 4-size%4)
-		rawPacket = append(rawPacket, padding...)
-	}
+	rawPacket = append(rawPacket, make([]byte, util.GetPadding(len(rawPacket)))...)
 
 	return rawPacket, nil
 }
@@ -236,9 +235,7 @@ func (s SourceDescriptionChunk) len() int {
 	len += sdesTypeLen // for terminating null octet
 
 	// align to 32-bit boundary
-	if len%4 != 0 {
-		len += 4 - (len % 4)
-	}
+	len += util.GetPadding(len)
 
 	return len
 }