初版功能完成

internal/protocol/session_header_test.go

@@ -0,0 +1,88 @@
+package protocol
+
+import (
+	"bytes"
+	"errors"
+	"testing"
+)
+
+func TestSessionHeaderGoldenBytes(t *testing.T) {
+	t.Parallel()
+	header := NewIPv4SessionHeader(0x0102030405060708, 0x0014)
+	got, err := header.MarshalBinary()
+	if err != nil {
+		t.Fatalf("MarshalBinary() error = %v", err)
+	}
+	want := []byte{
+		'R', 'M', 'L', 'K',
+		0x01, 0x01,
+		0x00, 0x00,
+		0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
+		0x00, 0x14,
+		0x00, 0x00,
+	}
+	if !bytes.Equal(got, want) {
+		t.Fatalf("MarshalBinary() = %x, want %x", got, want)
+	}
+}
+
+func TestIPv4SessionRoundTrip(t *testing.T) {
+	t.Parallel()
+	packet := []byte{0x45, 0x00, 0x00, 0x04}
+	encoded, err := EncodeIPv4Session(42, packet)
+	if err != nil {
+		t.Fatalf("EncodeIPv4Session() error = %v", err)
+	}
+	header, decoded, err := DecodeIPv4Session(encoded)
+	if err != nil {
+		t.Fatalf("DecodeIPv4Session() error = %v", err)
+	}
+	if header.SessionID != 42 {
+		t.Fatalf("SessionID = %d, want 42", header.SessionID)
+	}
+	if !bytes.Equal(decoded, packet) {
+		t.Fatalf("decoded payload = %x, want %x", decoded, packet)
+	}
+}
+
+func TestDecodeIPv4SessionRejectsInvalidFraming(t *testing.T) {
+	t.Parallel()
+	valid, err := EncodeIPv4Session(7, []byte{0x45})
+	if err != nil {
+		t.Fatalf("EncodeIPv4Session() error = %v", err)
+	}
+
+	tests := []struct {
+		name   string
+		mutate func([]byte) []byte
+		want   error
+	}{
+		{name: "short", mutate: func(data []byte) []byte { return data[:19] }, want: ErrSessionHeaderTooShort},
+		{name: "magic", mutate: func(data []byte) []byte { data[0] = 'X'; return data }, want: ErrSessionMagic},
+		{name: "version", mutate: func(data []byte) []byte { data[4] = 2; return data }, want: ErrSessionVersion},
+		{name: "type", mutate: func(data []byte) []byte { data[5] = 2; return data }, want: ErrSessionType},
+		{name: "flags", mutate: func(data []byte) []byte { data[7] = 1; return data }, want: ErrSessionFlags},
+		{name: "reserved", mutate: func(data []byte) []byte { data[19] = 1; return data }, want: ErrSessionReserved},
+		{name: "payload length", mutate: func(data []byte) []byte { data[17] = 2; return data }, want: ErrSessionPayloadLength},
+	}
+
+	for _, test := range tests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+			input := append([]byte(nil), valid...)
+			_, _, gotErr := DecodeIPv4Session(test.mutate(input))
+			if !errors.Is(gotErr, test.want) {
+				t.Fatalf("DecodeIPv4Session() error = %v, want %v", gotErr, test.want)
+			}
+		})
+	}
+}
+
+func TestEncodeIPv4SessionRejectsOversizedPayload(t *testing.T) {
+	t.Parallel()
+	_, err := EncodeIPv4Session(1, make([]byte, 1<<16))
+	if !errors.Is(err, ErrSessionPayloadTooLong) {
+		t.Fatalf("EncodeIPv4Session() error = %v, want %v", err, ErrSessionPayloadTooLong)
+	}
+}