TUN-8728: implement diag/tunnel endpoint

## Summary
The new endpoint returns the current information to be used when calling the diagnostic procedure.
This also adds:
- add indexed connection info and method to extract active connections from connTracker
- add edge address to Event struct and conn tracker
- remove unnecessary event send
- add tunnel configuration handler
- adjust cmd and metrics to create diagnostic server

Closes TUN-8728

diagnostic/handlers_test.go

@@ -5,15 +5,19 @@ import (
 	"encoding/json"
 	"errors"
 	"io"
+	"net"
 	"net/http"
 	"net/http/httptest"
 	"testing"
 
+	"github.com/google/uuid"
 	"github.com/rs/zerolog"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
+	"github.com/cloudflare/cloudflared/connection"
 	"github.com/cloudflare/cloudflared/diagnostic"
+	"github.com/cloudflare/cloudflared/tunnelstate"
 )
 
 type SystemCollectorMock struct{}
@@ -24,6 +28,23 @@ const (
 	errorKey             = "errkey"
 )
 
+func newTrackerFromConns(t *testing.T, connections []tunnelstate.IndexedConnectionInfo) *tunnelstate.ConnTracker {
+	t.Helper()
+
+	log := zerolog.Nop()
+	tracker := tunnelstate.NewConnTracker(&log)
+
+	for _, conn := range connections {
+		tracker.OnTunnelEvent(connection.Event{
+			Index:       conn.Index,
+			EventType:   connection.Connected,
+			Protocol:    conn.Protocol,
+			EdgeAddress: conn.EdgeAddress,
+		})
+	}
+
+	return tracker
+}
 func setCtxValuesForSystemCollector(
 	systemInfo *diagnostic.SystemInformation,
 	rawInfo string,
@@ -83,7 +104,7 @@ func TestSystemHandler(t *testing.T) {
 	for _, tCase := range tests {
 		t.Run(tCase.name, func(t *testing.T) {
 			t.Parallel()
-			handler := diagnostic.NewDiagnosticHandler(&log, 0, &SystemCollectorMock{})
+			handler := diagnostic.NewDiagnosticHandler(&log, 0, &SystemCollectorMock{}, uuid.New(), uuid.New(), nil)
 			recorder := httptest.NewRecorder()
 			ctx := setCtxValuesForSystemCollector(tCase.systemInfo, tCase.rawInfo, tCase.err)
 			request, err := http.NewRequestWithContext(ctx, http.MethodGet, "/diag/syste,", nil)
@@ -106,3 +127,58 @@ func TestSystemHandler(t *testing.T) {
 		})
 	}
 }
+
+func TestTunnelStateHandler(t *testing.T) {
+	t.Parallel()
+
+	log := zerolog.Nop()
+	tests := []struct {
+		name        string
+		tunnelID    uuid.UUID
+		clientID    uuid.UUID
+		connections []tunnelstate.IndexedConnectionInfo
+	}{
+		{
+			name:     "case1",
+			tunnelID: uuid.New(),
+			clientID: uuid.New(),
+		},
+		{
+			name:     "case2",
+			tunnelID: uuid.New(),
+			clientID: uuid.New(),
+			connections: []tunnelstate.IndexedConnectionInfo{{
+				ConnectionInfo: tunnelstate.ConnectionInfo{
+					IsConnected: true,
+					Protocol:    connection.QUIC,
+					EdgeAddress: net.IPv4(100, 100, 100, 100),
+				},
+				Index: 0,
+			}},
+		},
+	}
+
+	for _, tCase := range tests {
+		t.Run(tCase.name, func(t *testing.T) {
+			t.Parallel()
+			tracker := newTrackerFromConns(t, tCase.connections)
+			handler := diagnostic.NewDiagnosticHandler(&log, 0, nil, tCase.tunnelID, tCase.clientID, tracker)
+			recorder := httptest.NewRecorder()
+			handler.TunnelStateHandler(recorder, nil)
+			decoder := json.NewDecoder(recorder.Body)
+
+			var response struct {
+				TunnelID    uuid.UUID                           `json:"tunnelID,omitempty"`
+				ConnectorID uuid.UUID                           `json:"connectorID,omitempty"`
+				Connections []tunnelstate.IndexedConnectionInfo `json:"connections,omitempty"`
+			}
+
+			err := decoder.Decode(&response)
+			require.NoError(t, err)
+			assert.Equal(t, http.StatusOK, recorder.Code)
+			assert.Equal(t, tCase.tunnelID, response.TunnelID)
+			assert.Equal(t, tCase.clientID, response.ConnectorID)
+			assert.Equal(t, tCase.connections, response.Connections)
+		})
+	}
+}