TUN-8732: implement port selection algorithm

## Summary
Implements the discovery of the metrics server given an array of addresses (known addresses), tunnelID, and connectorID.

Closes TUN-8732

diagnostic/diagnostic_utils.go

@@ -2,12 +2,17 @@ package diagnostic
 
 import (
 	"archive/zip"
+	"context"
 	"fmt"
 	"io"
+	"net/url"
 	"os"
 	"path/filepath"
 	"strings"
 	"time"
+
+	"github.com/google/uuid"
+	"github.com/rs/zerolog"
 )
 
 // CreateDiagnosticZipFile create a zip file with the contents from the all
@@ -67,3 +72,69 @@ func CreateDiagnosticZipFile(base string, paths []string) (zipFileName string, e
 	zipFileName = archive.Name()
 	return zipFileName, nil
 }
+
+type AddressableTunnelState struct {
+	*TunnelState
+	URL *url.URL
+}
+
+func findMetricsServerPredicate(tunnelID, connectorID uuid.UUID) func(state *TunnelState) bool {
+	if tunnelID != uuid.Nil && connectorID != uuid.Nil {
+		return func(state *TunnelState) bool {
+			return state.ConnectorID == connectorID && state.TunnelID == tunnelID
+		}
+	} else if tunnelID == uuid.Nil && connectorID != uuid.Nil {
+		return func(state *TunnelState) bool {
+			return state.ConnectorID == connectorID
+		}
+	} else if tunnelID != uuid.Nil && connectorID == uuid.Nil {
+		return func(state *TunnelState) bool {
+			return state.TunnelID == tunnelID
+		}
+	}
+
+	return func(*TunnelState) bool {
+		return true
+	}
+}
+
+// The FindMetricsServer will try to find the metrics server url.
+// There are two possible error scenarios:
+// 1. No instance is found which will only return ErrMetricsServerNotFound
+// 2. Multiple instances are found which will return an array of state and ErrMultipleMetricsServerFound
+// In case of success, only the state for the instance is returned.
+func FindMetricsServer(
+	log *zerolog.Logger,
+	client *httpClient,
+	addresses []string,
+) (*AddressableTunnelState, []*AddressableTunnelState, error) {
+	instances := make([]*AddressableTunnelState, 0)
+
+	for _, address := range addresses {
+		url, err := url.Parse("http://" + address)
+		if err != nil {
+			log.Debug().Err(err).Msgf("error parsing address %s", address)
+
+			continue
+		}
+
+		client.SetBaseURL(url)
+
+		state, err := client.GetTunnelState(context.Background())
+		if err == nil {
+			instances = append(instances, &AddressableTunnelState{state, url})
+		} else {
+			log.Debug().Err(err).Msgf("error getting tunnel state from address %s", address)
+		}
+	}
+
+	if len(instances) == 0 {
+		return nil, nil, ErrMetricsServerNotFound
+	}
+
+	if len(instances) == 1 {
+		return instances[0], nil, nil
+	}
+
+	return nil, instances, ErrMultipleMetricsServerFound
+}

diagnostic/diagnostic_utils_test.go

@@ -0,0 +1,147 @@
+package diagnostic_test
+
+import (
+	"context"
+	"net/http"
+	"net/url"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/facebookgo/grace/gracenet"
+	"github.com/google/uuid"
+	"github.com/rs/zerolog"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/cloudflare/cloudflared/diagnostic"
+	"github.com/cloudflare/cloudflared/metrics"
+	"github.com/cloudflare/cloudflared/tunnelstate"
+)
+
+func helperCreateServer(t *testing.T, listeners *gracenet.Net, tunnelID uuid.UUID, connectorID uuid.UUID) func() {
+	t.Helper()
+	listener, err := metrics.CreateMetricsListener(listeners, "localhost:0")
+	require.NoError(t, err)
+	log := zerolog.Nop()
+	tracker := tunnelstate.NewConnTracker(&log)
+	handler := diagnostic.NewDiagnosticHandler(&log, 0, nil, tunnelID, connectorID, tracker, nil, []string{})
+	router := http.NewServeMux()
+	router.HandleFunc("/diag/tunnel", handler.TunnelStateHandler)
+	server := &http.Server{
+		ReadTimeout:  10 * time.Second,
+		WriteTimeout: 10 * time.Second,
+		Handler:      router,
+	}
+
+	var wgroup sync.WaitGroup
+
+	wgroup.Add(1)
+
+	go func() {
+		defer wgroup.Done()
+
+		_ = server.Serve(listener)
+	}()
+
+	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
+
+	cleanUp := func() {
+		_ = server.Shutdown(ctx)
+
+		cancel()
+		wgroup.Wait()
+	}
+
+	return cleanUp
+}
+
+func TestFindMetricsServer_WhenSingleServerIsRunning_ReturnState(t *testing.T) {
+	listeners := gracenet.Net{}
+	tid1 := uuid.New()
+	cid1 := uuid.New()
+
+	cleanUp := helperCreateServer(t, &listeners, tid1, cid1)
+	defer cleanUp()
+
+	log := zerolog.Nop()
+	client := diagnostic.NewHTTPClient()
+	addresses := metrics.GetMetricsKnownAddresses("host")
+	url1, err := url.Parse("http://localhost:20241")
+	require.NoError(t, err)
+
+	tunnel1 := &diagnostic.AddressableTunnelState{
+		TunnelState: &diagnostic.TunnelState{
+			TunnelID:    tid1,
+			ConnectorID: cid1,
+			Connections: nil,
+		},
+		URL: url1,
+	}
+
+	state, tunnels, err := diagnostic.FindMetricsServer(&log, client, addresses[:])
+	if err != nil {
+		require.ErrorIs(t, err, diagnostic.ErrMultipleMetricsServerFound)
+	}
+
+	assert.Equal(t, tunnel1, state)
+	assert.Nil(t, tunnels)
+}
+
+func TestFindMetricsServer_WhenMultipleServerAreRunning_ReturnError(t *testing.T) {
+	listeners := gracenet.Net{}
+	tid1 := uuid.New()
+	cid1 := uuid.New()
+	cid2 := uuid.New()
+
+	cleanUp := helperCreateServer(t, &listeners, tid1, cid1)
+	defer cleanUp()
+
+	cleanUp = helperCreateServer(t, &listeners, tid1, cid2)
+	defer cleanUp()
+
+	log := zerolog.Nop()
+	client := diagnostic.NewHTTPClient()
+	addresses := metrics.GetMetricsKnownAddresses("host")
+	url1, err := url.Parse("http://localhost:20241")
+	require.NoError(t, err)
+	url2, err := url.Parse("http://localhost:20242")
+	require.NoError(t, err)
+
+	tunnel1 := &diagnostic.AddressableTunnelState{
+		TunnelState: &diagnostic.TunnelState{
+			TunnelID:    tid1,
+			ConnectorID: cid1,
+			Connections: nil,
+		},
+		URL: url1,
+	}
+	tunnel2 := &diagnostic.AddressableTunnelState{
+		TunnelState: &diagnostic.TunnelState{
+			TunnelID:    tid1,
+			ConnectorID: cid2,
+			Connections: nil,
+		},
+		URL: url2,
+	}
+
+	state, tunnels, err := diagnostic.FindMetricsServer(&log, client, addresses[:])
+	if err != nil {
+		require.ErrorIs(t, err, diagnostic.ErrMultipleMetricsServerFound)
+	}
+
+	assert.Nil(t, state)
+	assert.Equal(t, []*diagnostic.AddressableTunnelState{tunnel1, tunnel2}, tunnels)
+}
+
+func TestFindMetricsServer_WhenNoInstanceIsRuning_ReturnError(t *testing.T) {
+	log := zerolog.Nop()
+	client := diagnostic.NewHTTPClient()
+	addresses := metrics.GetMetricsKnownAddresses("host")
+
+	state, tunnels, err := diagnostic.FindMetricsServer(&log, client, addresses[:])
+	require.ErrorIs(t, err, diagnostic.ErrMetricsServerNotFound)
+
+	assert.Nil(t, state)
+	assert.Nil(t, tunnels)
+}

diagnostic/error.go

@@ -19,4 +19,8 @@ var (
 	ErrNoVolumeFound = errors.New("no disk volume information found")
 	// Error user when the base url of the diagnostic client is not provided.
 	ErrNoBaseUrl = errors.New("no base url")
+	// Error used when no metrics server is found listening to the known addresses list (check [metrics.GetMetricsKnownAddresses])
+	ErrMetricsServerNotFound = errors.New("metrics server not found")
+	// Error used when multiple metrics server are found listening to the known addresses list (check [metrics.GetMetricsKnownAddresses])
+	ErrMultipleMetricsServerFound = errors.New("multiple metrics server found")
 )