feat(agent): agent stream tunneling with TLS and dTLS (UDP) (#188)

* **New Features**
  * Multiplexed TLS port: HTTP API and a custom stream protocol can share one port via ALPN.
  * Agent-side TCP and DTLS/UDP stream tunneling with health-check support and runtime capability detection.
  * Agents now advertise per-agent stream support (TCP/UDP).

* **Documentation**
  * Added comprehensive stream protocol documentation.

* **Tests**
  * Extended integration and concurrency tests covering multiplexing, TCP/UDP streams, and health checks.

* **Chores**
  * Compose/template updated to expose both TCP and UDP ports.

agent/pkg/agent/stream/tests/mux_test.go

@@ -0,0 +1,94 @@
+package stream_test
+
+import (
+	"bufio"
+	"context"
+	"crypto/tls"
+	"crypto/x509"
+	"io"
+	"net"
+	"net/http"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+	"github.com/yusing/godoxy/agent/pkg/agent/common"
+	"github.com/yusing/godoxy/agent/pkg/agent/stream"
+)
+
+func TestTLSALPNMux_HTTPAndStreamShareOnePort(t *testing.T) {
+	certs := genTestCerts(t)
+
+	baseLn, err := net.ListenTCP("tcp", &net.TCPAddr{IP: net.ParseIP("127.0.0.1"), Port: 0})
+	require.NoError(t, err, "listen tcp")
+	defer baseLn.Close()
+	baseAddr := baseLn.Addr().String()
+
+	caCertPool := x509.NewCertPool()
+	caCertPool.AddCert(certs.CaCert)
+
+	serverTLS := &tls.Config{
+		Certificates: []tls.Certificate{*certs.SrvCert},
+		ClientCAs:    caCertPool,
+		ClientAuth:   tls.RequireAndVerifyClientCert,
+		MinVersion:   tls.VersionTLS12,
+		NextProtos:   []string{"http/1.1", stream.StreamALPN},
+	}
+
+	ctx, cancel := context.WithCancel(t.Context())
+	defer cancel()
+
+	streamSrv := stream.NewTCPServerHandler(ctx)
+	defer func() { _ = streamSrv.Close() }()
+
+	tlsLn := tls.NewListener(baseLn, serverTLS)
+	defer func() { _ = tlsLn.Close() }()
+
+	// HTTP server
+	httpSrv := &http.Server{Handler: http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		_, _ = w.Write([]byte("ok"))
+	}),
+		TLSNextProto: map[string]func(*http.Server, *tls.Conn, http.Handler){
+			stream.StreamALPN: func(_ *http.Server, conn *tls.Conn, _ http.Handler) {
+				streamSrv.ServeConn(conn)
+			},
+		},
+	}
+	go func() { _ = httpSrv.Serve(tlsLn) }()
+	defer func() { _ = httpSrv.Close() }()
+
+	// Stream destination
+	dstAddr, closeDst := startTCPEcho(t)
+	defer closeDst()
+
+	// HTTP client over the same port
+	clientTLS := &tls.Config{
+		Certificates: []tls.Certificate{*certs.ClientCert},
+		RootCAs:      caCertPool,
+		MinVersion:   tls.VersionTLS12,
+		NextProtos:   []string{"http/1.1"},
+		ServerName:   common.CertsDNSName,
+	}
+	hc, err := tls.Dial("tcp", baseAddr, clientTLS)
+	require.NoError(t, err, "dial https")
+	defer hc.Close()
+	_ = hc.SetDeadline(time.Now().Add(2 * time.Second))
+	_, err = hc.Write([]byte("GET / HTTP/1.1\r\nHost: godoxy-agent\r\n\r\n"))
+	require.NoError(t, err, "write http request")
+	r := bufio.NewReader(hc)
+	statusLine, err := r.ReadString('\n')
+	require.NoError(t, err, "read status line")
+	require.Contains(t, statusLine, "200", "expected 200")
+
+	// Stream client over the same port
+	client := NewTCPClient(t, baseAddr, dstAddr, certs)
+	defer client.Close()
+	_ = client.SetDeadline(time.Now().Add(2 * time.Second))
+	msg := []byte("ping over mux")
+	_, err = client.Write(msg)
+	require.NoError(t, err, "write stream payload")
+	buf := make([]byte, len(msg))
+	_, err = io.ReadFull(client, buf)
+	require.NoError(t, err, "read stream payload")
+	require.Equal(t, msg, buf)
+}