Give TCP flags a dedicated type

- Implement Stringer for it so that we can improve error messages.
- Use TCPFlags through the code base. There used to be a mixed usage of byte,
  uint8 and int as TCP flags.

PiperOrigin-RevId: 361940150

3 files changed, 19 insertions, 13 deletions

diff --git a/test/packetimpact/testbench/connections.go b/test/packetimpact/testbench/connections.go
index 15e1a51de..bafc45d3b 100644
--- a/test/packetimpact/testbench/connections.go
+++ b/test/packetimpact/testbench/connections.go
@@ -677,17 +677,17 @@ func (conn *TCPIPv4) Connect(t *testing.T) {
 	t.Helper()
 
 	// Send the SYN.
-	conn.Send(t, TCP{Flags: Uint8(header.TCPFlagSyn)})
+	conn.Send(t, TCP{Flags: TCPFlags(header.TCPFlagSyn)})
 
 	// Wait for the SYN-ACK.
-	synAck, err := conn.Expect(t, TCP{Flags: Uint8(header.TCPFlagSyn | header.TCPFlagAck)}, time.Second)
+	synAck, err := conn.Expect(t, TCP{Flags: TCPFlags(header.TCPFlagSyn | header.TCPFlagAck)}, time.Second)
 	if err != nil {
 		t.Fatalf("didn't get synack during handshake: %s", err)
 	}
 	conn.layerStates[len(conn.layerStates)-1].(*tcpState).synAck = synAck
 
 	// Send an ACK.
-	conn.Send(t, TCP{Flags: Uint8(header.TCPFlagAck)})
+	conn.Send(t, TCP{Flags: TCPFlags(header.TCPFlagAck)})
 }
 
 // ConnectWithOptions performs a TCP 3-way handshake with given TCP options.
@@ -696,17 +696,17 @@ func (conn *TCPIPv4) ConnectWithOptions(t *testing.T, options []byte) {
 	t.Helper()
 
 	// Send the SYN.
-	conn.Send(t, TCP{Flags: Uint8(header.TCPFlagSyn), Options: options})
+	conn.Send(t, TCP{Flags: TCPFlags(header.TCPFlagSyn), Options: options})
 
 	// Wait for the SYN-ACK.
-	synAck, err := conn.Expect(t, TCP{Flags: Uint8(header.TCPFlagSyn | header.TCPFlagAck)}, time.Second)
+	synAck, err := conn.Expect(t, TCP{Flags: TCPFlags(header.TCPFlagSyn | header.TCPFlagAck)}, time.Second)
 	if err != nil {
 		t.Fatalf("didn't get synack during handshake: %s", err)
 	}
 	conn.layerStates[len(conn.layerStates)-1].(*tcpState).synAck = synAck
 
 	// Send an ACK.
-	conn.Send(t, TCP{Flags: Uint8(header.TCPFlagAck)})
+	conn.Send(t, TCP{Flags: TCPFlags(header.TCPFlagAck)})
 }
 
 // ExpectData is a convenient method that expects a Layer and the Layer after
diff --git a/test/packetimpact/testbench/layers.go b/test/packetimpact/testbench/layers.go
index 64a7a171a..2311f7686 100644
--- a/test/packetimpact/testbench/layers.go
+++ b/test/packetimpact/testbench/layers.go
@@ -407,6 +407,12 @@ func Uint8(v uint8) *uint8 {
 	return &v
 }
 
+// TCPFlags is a helper routine that allocates a new
+// header.TCPFlags value to store v and returns a pointer to it.
+func TCPFlags(v header.TCPFlags) *header.TCPFlags {
+	return &v
+}
+
 // Address is a helper routine that allocates a new tcpip.Address value to
 // store v and returns a pointer to it.
 func Address(v tcpip.Address) *tcpip.Address {
@@ -1030,7 +1036,7 @@ type TCP struct {
 	SeqNum        *uint32
 	AckNum        *uint32
 	DataOffset    *uint8
-	Flags         *uint8
+	Flags         *header.TCPFlags
 	WindowSize    *uint16
 	Checksum      *uint16
 	UrgentPointer *uint16
@@ -1063,7 +1069,7 @@ func (l *TCP) ToBytes() ([]byte, error) {
 		h.SetDataOffset(uint8(l.length()))
 	}
 	if l.Flags != nil {
-		h.SetFlags(*l.Flags)
+		h.SetFlags(uint8(*l.Flags))
 	}
 	if l.WindowSize != nil {
 		h.SetWindowSize(*l.WindowSize)
@@ -1157,7 +1163,7 @@ func parseTCP(b []byte) (Layer, layerParser) {
 		SeqNum:        Uint32(h.SequenceNumber()),
 		AckNum:        Uint32(h.AckNumber()),
 		DataOffset:    Uint8(h.DataOffset()),
-		Flags:         Uint8(h.Flags()),
+		Flags:         TCPFlags(h.Flags()),
 		WindowSize:    Uint16(h.WindowSize()),
 		Checksum:      Uint16(h.Checksum()),
 		UrgentPointer: Uint16(h.UrgentPointer()),
diff --git a/test/packetimpact/testbench/layers_test.go b/test/packetimpact/testbench/layers_test.go
index eca0780b5..614a5de1e 100644
--- a/test/packetimpact/testbench/layers_test.go
+++ b/test/packetimpact/testbench/layers_test.go
@@ -178,7 +178,7 @@ func TestLayerStringFormat(t *testing.T) {
 				SeqNum:     Uint32(3452155723),
 				AckNum:     Uint32(2596996163),
 				DataOffset: Uint8(5),
-				Flags:      Uint8(20),
+				Flags:      TCPFlags(header.TCPFlagRst | header.TCPFlagAck),
 				WindowSize: Uint16(64240),
 				Checksum:   Uint16(0x2e2b),
 			},
@@ -188,7 +188,7 @@ func TestLayerStringFormat(t *testing.T) {
 				"SeqNum:3452155723 " +
 				"AckNum:2596996163 " +
 				"DataOffset:5 " +
-				"Flags:20 " +
+				"Flags:  R A  " +
 				"WindowSize:64240 " +
 				"Checksum:11819" +
 				"}",
@@ -436,7 +436,7 @@ func TestTCPOptions(t *testing.T) {
 					DstPort:       Uint16(54321),
 					SeqNum:        Uint32(0),
 					AckNum:        Uint32(0),
-					Flags:         Uint8(header.TCPFlagSyn),
+					Flags:         TCPFlags(header.TCPFlagSyn),
 					WindowSize:    Uint16(8192),
 					Checksum:      Uint16(0xf51c),
 					UrgentPointer: Uint16(0),
@@ -480,7 +480,7 @@ func TestTCPOptions(t *testing.T) {
 					DstPort:       Uint16(54321),
 					SeqNum:        Uint32(0),
 					AckNum:        Uint32(0),
-					Flags:         Uint8(header.TCPFlagSyn),
+					Flags:         TCPFlags(header.TCPFlagSyn),
 					WindowSize:    Uint16(8192),
 					Checksum:      Uint16(0xe521),
 					UrgentPointer: Uint16(0),