Merge pull request #5 from PreetamJinka/4-errors

Add decoding errors

Author: Preetam Jinka

decode_test.go

@@ -15,17 +15,29 @@ func TestMultilayerDecode(t *testing.T) {
 		10, 184, 73, 195, 65, 0, 0, 0, 0, 1, 3, 3, 7,
 	}
 
-	ethernetFrame := DecodeEthernet(b)
+	ethernetFrame, err := DecodeEthernet(b)
+	if err != nil {
+		t.Fatal(err)
+	}
+
 	if ethernetFrame.EtherType != 0x86dd {
 		t.Fatalf("expected to see EtherType %x, got %x", 0x86dd, ethernetFrame.EtherType)
 	}
 
-	ipv6Packet := DecodeIPv6(ethernetFrame.Payload)
+	ipv6Packet, err := DecodeIPv6(ethernetFrame.Payload)
+	if err != nil {
+		t.Fatal(err)
+	}
+
 	if ipv6Packet.NextHeader != 0x6 {
 		t.Fatalf("expected to see NextHeader %x, got %x", 0x6, ipv6Packet.NextHeader)
 	}
 
-	tcpPacket := DecodeTCP(ipv6Packet.Payload)
+	tcpPacket, err := DecodeTCP(ipv6Packet.Payload)
+	if err != nil {
+		t.Fatal(err)
+	}
+
 	if tcpPacket.DestinationPort != 80 {
 		t.Fatalf("expected to see destination port %v, got %v", 80, tcpPacket.DestinationPort)
 	}
@@ -51,8 +63,8 @@ func BenchmarkMultilayerDecode(b *testing.B) {
 	}
 
 	for i := 0; i < b.N; i++ {
-		ethernetFrame := DecodeEthernet(buf[:])
-		ipv6Packet := DecodeIPv6(ethernetFrame.Payload)
+		ethernetFrame, _ := DecodeEthernet(buf[:])
+		ipv6Packet, _ := DecodeIPv6(ethernetFrame.Payload)
 		DecodeTCP(ipv6Packet.Payload)
 	}
 }

errors.go

@@ -0,0 +1,9 @@
+package proto
+
+import (
+	"errors"
+)
+
+var (
+	ErrorNotEnoughBytes = errors.New("proto: not enough bytes available to decode")
+)

ethernet.go

@@ -12,35 +12,44 @@ type EthernetFrame struct {
 	Payload     []byte           `json:"payload"`
 }
 
-func DecodeEthernet(b []byte) EthernetFrame {
+const minEthernetFrameSize = 6 + 6 + 4 + 2
+
+// DecodeEthernet decodes an Ethernet frame.
+func DecodeEthernet(b []byte) (EthernetFrame, error) {
 	frame := EthernetFrame{}
 
-	i := 0 // just a helper for indexing
+	if len(b) < minEthernetFrameSize {
+		return frame, ErrorNotEnoughBytes
+	}
+
+	i := 0 // Just a helper for indexing.
 
+	// Decode MAC addresses.
 	frame.Destination = net.HardwareAddr(b[i : i+6])
 	i += 6
 	frame.Source = net.HardwareAddr(b[i : i+6])
 	i += 6
 
-	// Check for a VLAN tag
+	// Check for a VLAN tag.
 	if b[i] == 0x81 && b[i+1] == 0x00 {
 		i += 2
 		frame.VlanTag = uint32(0x81<<24) | uint32(0x00<<16) | uint32(b[i]<<8) | uint32(b[i+1])
 		i += 2
 	}
 
 	// Check the Ethernet type
-	if t := uint16(b[i])<<8 | uint16(b[i+1]); t >= 1536 { // if 1500 or less, then it's the payload length
+	if t := uint16(b[i])<<8 | uint16(b[i+1]); t >= 1536 { // If 1500 or less, it's the payload length.
 		frame.EtherType = t
 	}
 
 	i += 2
 
 	frame.Payload = b[i:]
 
-	return frame
+	return frame, nil
 }
 
+// Bytes returns an encoded Ethernet frame.
 func (f EthernetFrame) Bytes() []byte {
 	i := 0
 

ethernet_test.go

@@ -20,7 +20,11 @@ func TestEthernet(t *testing.T) {
 		1, 0, 0, 84, 7, 0, 4, 199, 58, 162, 130,
 	}
 
-	frame := DecodeEthernet(b)
+	frame, err := DecodeEthernet(b)
+	if err != nil {
+		t.Fatal(err)
+	}
+
 	if frame.Source.String() != "e8:de:27:bb:6b:aa" {
 		t.Error("Got the wrong source MAC:", frame.Source.String())
 	}
@@ -37,7 +41,10 @@ func TestEthernetEncode(t *testing.T) {
 
 	b := e.Bytes()
 
-	frame := DecodeEthernet(b)
+	frame, err := DecodeEthernet(b)
+	if err != nil {
+		t.Fatal(err)
+	}
 
 	if !reflect.DeepEqual(frame, e) {
 		t.Error("Encoded and decoded Ethernet frames not equal:", frame, e)

ipv4.go

@@ -22,9 +22,16 @@ type IPv4Packet struct {
 	Payload              []byte `json:"payload"`
 }
 
-func DecodeIPv4(b []byte) IPv4Packet {
+const minIPv4PacketSize = 1 + 1 + 1 + 1 + 2 + 2 + 1 + 2 + 1 + 1 + 2 + 4 + 4
+
+// DecodeIPv4 decodes an IPv4 packet.
+func DecodeIPv4(b []byte) (IPv4Packet, error) {
 	packet := IPv4Packet{}
 
+	if len(b) < minIPv4PacketSize {
+		return packet, ErrorNotEnoughBytes
+	}
+
 	i := 0
 
 	packet.Version = uint8(b[i] >> 4)
@@ -66,9 +73,10 @@ func DecodeIPv4(b []byte) IPv4Packet {
 
 	packet.Payload = b[i:]
 
-	return packet
+	return packet, nil
 }
 
+// Bytes returns an encoded IPv4 packet.
 func (p IPv4Packet) Bytes() []byte {
 	i := 0
 
@@ -125,6 +133,7 @@ func (p IPv4Packet) Bytes() []byte {
 	return b[:i]
 }
 
+// ComputeChecksum returns the checksum for the IPv4 packet.
 func (p IPv4Packet) ComputeChecksum() uint16 {
 	sum := ((uint32(p.Version)<<4|uint32(p.InternetHeaderLength))<<8 |
 		(uint32(p.DSCP)<<2 | uint32(p.ECN))) +

ipv4_test.go

@@ -19,7 +19,11 @@ func TestIPv4(t *testing.T) {
 		58, 32, 42, 47, 42, 13, 10, 13, 10,
 	}
 
-	packet := DecodeIPv4(b)
+	packet, err := DecodeIPv4(b)
+	if err != nil {
+		t.Fatal(err)
+	}
+
 	if packet.Source.String() != "192.168.0.103" {
 		t.Errorf("expected source IPv4 address %v, got %v", "192.168.0.103", packet.Source)
 	}
@@ -63,7 +67,10 @@ func TestIPv4Encode(t *testing.T) {
 
 	packet.HeaderChecksum = packet.ComputeChecksum()
 
-	decoded := DecodeIPv4(packet.Bytes())
+	decoded, err := DecodeIPv4(packet.Bytes())
+	if err != nil {
+		t.Fatal(err)
+	}
 
 	if !reflect.DeepEqual(packet, decoded) {
 		t.Error("Encoded and decoded IPv4 packets not equal:", decoded, packet)

ipv6.go

@@ -16,9 +16,16 @@ type IPv6Packet struct {
 	Payload      []byte `json:"payload"`
 }
 
-func DecodeIPv6(b []byte) IPv6Packet {
+const minIPv6PacketSize = 1 + 1 + 4 + 2 + 1 + 1 + 16 + 16
+
+// DecodeIPv6 decodes an IPv6 packet.
+func DecodeIPv6(b []byte) (IPv6Packet, error) {
 	packet := IPv6Packet{}
 
+	if len(b) < minIPv6PacketSize {
+		return packet, ErrorNotEnoughBytes
+	}
+
 	i := 0
 
 	packet.Version = b[i] >> 4
@@ -45,9 +52,10 @@ func DecodeIPv6(b []byte) IPv6Packet {
 
 	packet.Payload = b[i:]
 
-	return packet
+	return packet, nil
 }
 
+// Bytes returns an encoded IPv6 packet.
 func (p IPv6Packet) Bytes() []byte {
 	i := 0
 	b := make([]byte, 40+len(p.Payload))

ipv6_test.go

@@ -16,7 +16,10 @@ func TestIPv6(t *testing.T) {
 		187, 0, 0, 0, 0, 1, 3, 3, 7,
 	}
 
-	packet := DecodeIPv6(b)
+	packet, err := DecodeIPv6(b)
+	if err != nil {
+		t.Fatal(err)
+	}
 
 	if packet.Destination.String() != "2620:100:5007:2::2" {
 		t.Errorf("expected destination address %v, got %v",
@@ -42,7 +45,10 @@ func TestIPv6Encode(t *testing.T) {
 		},
 	}
 
-	p := DecodeIPv6(packet.Bytes())
+	p, err := DecodeIPv6(packet.Bytes())
+	if err != nil {
+		t.Fatal(err)
+	}
 
 	if !reflect.DeepEqual(packet, p) {
 		t.Error("Encoded and decoded IPv6 packets not equal:", packet, p)

tcp.go

@@ -21,6 +21,8 @@ type TCPPacket struct {
 	Payload []byte `json:"payload"`
 }
 
+const minTCPPacketSize = 2 + 2 + 4 + 4 + 1 + 2 + 2 + 2 + 2
+
 func (p TCPPacket) HasFIN() bool {
 	return p.Flags&(1<<0) > 0
 }
@@ -57,9 +59,14 @@ func (p TCPPacket) HasNS() bool {
 	return p.Flags>>8 > 0
 }
 
-func DecodeTCP(b []byte) TCPPacket {
+// DecodeTCP decodes an TCP packet.
+func DecodeTCP(b []byte) (TCPPacket, error) {
 	packet := TCPPacket{}
 
+	if len(b) < minTCPPacketSize {
+		return packet, ErrorNotEnoughBytes
+	}
+
 	i := 0
 
 	packet.SourcePort = uint16(b[i])<<8 | uint16(b[i+1])
@@ -93,5 +100,5 @@ func DecodeTCP(b []byte) TCPPacket {
 
 	packet.Payload = b[i:]
 
-	return packet
+	return packet, nil
 }

tcp_test.go

@@ -16,7 +16,10 @@ func TestTCP(t *testing.T) {
 		13, 10,
 	}
 
-	tcpPacket := DecodeTCP(b)
+	tcpPacket, err := DecodeTCP(b)
+	if err != nil {
+		t.Fatal(err)
+	}
 
 	if tcpPacket.DestinationPort != 80 {
 		t.Errorf("expected destination port %v, got %v", 80, tcpPacket.DestinationPort)