feat(protbot): add headless MHF protocol bot as cmd/protbot

Copy MHBridge into the Erupe module as cmd/protbot/ so it can be
built, tested, and maintained alongside the server. The bot
implements the full sign → entrance → channel login flow and
supports lobby entry, chat, session setup, and quest enumeration.

The conn/ package keeps its own Blowfish crypto primitives to avoid
importing erupe-ce/config (which requires a config file at init).

cmd/protbot/conn/crypt_conn_test.go

@@ -0,0 +1,152 @@
+package conn
+
+import (
+	"io"
+	"net"
+	"testing"
+)
+
+// TestCryptConnRoundTrip verifies that encrypting and decrypting a packet
+// through a pair of CryptConn instances produces the original data.
+func TestCryptConnRoundTrip(t *testing.T) {
+	// Create an in-process TCP pipe.
+	server, client := net.Pipe()
+	defer server.Close()
+	defer client.Close()
+
+	sender := NewCryptConn(client)
+	receiver := NewCryptConn(server)
+
+	testCases := [][]byte{
+		{0x00, 0x14, 0x00, 0x00, 0x00, 0x01}, // Minimal login-like packet
+		{0xDE, 0xAD, 0xBE, 0xEF},
+		make([]byte, 256), // Larger packet
+	}
+
+	for i, original := range testCases {
+		// Send in a goroutine to avoid blocking.
+		errCh := make(chan error, 1)
+		go func() {
+			errCh <- sender.SendPacket(original)
+		}()
+
+		received, err := receiver.ReadPacket()
+		if err != nil {
+			t.Fatalf("case %d: ReadPacket error: %v", i, err)
+		}
+
+		if err := <-errCh; err != nil {
+			t.Fatalf("case %d: SendPacket error: %v", i, err)
+		}
+
+		if len(received) != len(original) {
+			t.Fatalf("case %d: length mismatch: got %d, want %d", i, len(received), len(original))
+		}
+		for j := range original {
+			if received[j] != original[j] {
+				t.Fatalf("case %d: byte %d mismatch: got 0x%02X, want 0x%02X", i, j, received[j], original[j])
+			}
+		}
+	}
+}
+
+// TestCryptPacketHeaderRoundTrip verifies header encode/decode.
+func TestCryptPacketHeaderRoundTrip(t *testing.T) {
+	original := &CryptPacketHeader{
+		Pf0:                     0x03,
+		KeyRotDelta:             0x03,
+		PacketNum:               42,
+		DataSize:                100,
+		PrevPacketCombinedCheck: 0x1234,
+		Check0:                 0xAAAA,
+		Check1:                 0xBBBB,
+		Check2:                 0xCCCC,
+	}
+
+	encoded, err := original.Encode()
+	if err != nil {
+		t.Fatalf("Encode error: %v", err)
+	}
+
+	if len(encoded) != CryptPacketHeaderLength {
+		t.Fatalf("encoded length: got %d, want %d", len(encoded), CryptPacketHeaderLength)
+	}
+
+	decoded, err := NewCryptPacketHeader(encoded)
+	if err != nil {
+		t.Fatalf("NewCryptPacketHeader error: %v", err)
+	}
+
+	if *decoded != *original {
+		t.Fatalf("header mismatch:\ngot  %+v\nwant %+v", *decoded, *original)
+	}
+}
+
+// TestMultiPacketSequence verifies that key rotation stays in sync across
+// multiple sequential packets.
+func TestMultiPacketSequence(t *testing.T) {
+	server, client := net.Pipe()
+	defer server.Close()
+	defer client.Close()
+
+	sender := NewCryptConn(client)
+	receiver := NewCryptConn(server)
+
+	for i := 0; i < 10; i++ {
+		data := []byte{byte(i), byte(i + 1), byte(i + 2), byte(i + 3)}
+
+		errCh := make(chan error, 1)
+		go func() {
+			errCh <- sender.SendPacket(data)
+		}()
+
+		received, err := receiver.ReadPacket()
+		if err != nil {
+			t.Fatalf("packet %d: ReadPacket error: %v", i, err)
+		}
+
+		if err := <-errCh; err != nil {
+			t.Fatalf("packet %d: SendPacket error: %v", i, err)
+		}
+
+		for j := range data {
+			if received[j] != data[j] {
+				t.Fatalf("packet %d byte %d: got 0x%02X, want 0x%02X", i, j, received[j], data[j])
+			}
+		}
+	}
+}
+
+// TestDialWithInit verifies that DialWithInit sends 8 NULL bytes on connect.
+func TestDialWithInit(t *testing.T) {
+	listener, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer listener.Close()
+
+	done := make(chan []byte, 1)
+	go func() {
+		conn, err := listener.Accept()
+		if err != nil {
+			return
+		}
+		defer conn.Close()
+		buf := make([]byte, 8)
+		_, _ = io.ReadFull(conn, buf)
+		done <- buf
+	}()
+
+	c, err := DialWithInit(listener.Addr().String())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer c.Close()
+
+	initBytes := <-done
+	for i, b := range initBytes {
+		if b != 0 {
+			t.Fatalf("init byte %d: got 0x%02X, want 0x00", i, b)
+		}
+	}
+}