[client, relay] Expose relay transport and connection errors in status and metrics (#6342)

shared/relay/client/dialer/quic/conn.go

@@ -57,6 +57,11 @@ func (c *Conn) Write(b []byte) (int, error) {
 	return len(b), nil
 }
 
+// Protocol returns the transport name for this connection.
+func (c *Conn) Protocol() string {
+	return Network
+}
+
 func (c *Conn) RemoteAddr() net.Addr {
 	return c.session.RemoteAddr()
 }

shared/relay/client/dialer/quic/quic.go

@@ -59,14 +59,12 @@ func (d Dialer) Dial(ctx context.Context, address, serverName string) (net.Conn,
 
 	udpConn, err := nbnet.ListenUDP("udp", &net.UDPAddr{Port: 0})
 	if err != nil {
-		log.Errorf("failed to listen on UDP: %s", err)
-		return nil, err
+		return nil, fmt.Errorf("listen udp: %w", err)
 	}
 
 	udpAddr, err := net.ResolveUDPAddr("udp", quicURL)
 	if err != nil {
-		log.Errorf("failed to resolve UDP address: %s", err)
-		return nil, err
+		return nil, fmt.Errorf("resolve %s: %w", quicURL, err)
 	}
 
 	session, err := quic.Dial(ctx, udpConn, udpAddr, tlsClientConfig, quicConfig)
@@ -74,7 +72,7 @@ func (d Dialer) Dial(ctx context.Context, address, serverName string) (net.Conn,
 		if errors.Is(err, context.Canceled) {
 			return nil, err
 		}
-		log.Errorf("failed to dial to Relay server via QUIC '%s': %s", quicURL, err)
+		log.Debugf("failed to dial to Relay server via QUIC '%s': %s", quicURL, err)
 		return nil, err
 	}
 

shared/relay/client/dialer/race_dialer.go

@@ -3,6 +3,7 @@ package dialer
 import (
 	"context"
 	"errors"
+	"fmt"
 	"net"
 	"time"
 
@@ -71,6 +72,7 @@ func (r *RaceDial) Dial(ctx context.Context) (net.Conn, error) {
 
 	connChan := make(chan dialResult, len(r.dialerFns))
 	winnerConn := make(chan net.Conn, 1)
+	errChan := make(chan error, 1)
 	abortCtx, abort := context.WithCancel(ctx)
 	defer abort()
 
@@ -78,11 +80,11 @@ func (r *RaceDial) Dial(ctx context.Context) (net.Conn, error) {
 		go r.dial(dfn, abortCtx, connChan)
 	}
 
-	go r.processResults(connChan, winnerConn, abort)
+	go r.processResults(connChan, winnerConn, errChan, abort)
 
 	conn, ok := <-winnerConn
 	if !ok {
-		return nil, errors.New("failed to dial to Relay server on any protocol")
+		return nil, <-errChan
 	}
 	return conn, nil
 }
@@ -90,6 +92,7 @@ func (r *RaceDial) Dial(ctx context.Context) (net.Conn, error) {
 // dialSequential tries each dialer in order, returning the first connection and
 // falling back to the next on failure.
 func (r *RaceDial) dialSequential(ctx context.Context) (net.Conn, error) {
+	var errs []error
 	for _, dfn := range r.dialerFns {
 		if err := ctx.Err(); err != nil {
 			return nil, err
@@ -103,12 +106,13 @@ func (r *RaceDial) dialSequential(ctx context.Context) (net.Conn, error) {
 				return nil, err
 			}
 			r.log.Errorf("failed to dial via %s: %s", dfn.Protocol(), err)
+			errs = append(errs, fmt.Errorf("%s: %w", dfn.Protocol(), err))
 			continue
 		}
 		r.log.Infof("successfully dialed via: %s", dfn.Protocol())
 		return conn, nil
 	}
-	return nil, errors.New("failed to dial to Relay server on any protocol")
+	return nil, dialErr(errs)
 }
 
 func (r *RaceDial) dial(dfn DialeFn, abortCtx context.Context, connChan chan dialResult) {
@@ -120,8 +124,9 @@ func (r *RaceDial) dial(dfn DialeFn, abortCtx context.Context, connChan chan dia
 	connChan <- dialResult{Conn: conn, Protocol: dfn.Protocol(), Err: err}
 }
 
-func (r *RaceDial) processResults(connChan chan dialResult, winnerConn chan net.Conn, abort context.CancelFunc) {
+func (r *RaceDial) processResults(connChan chan dialResult, winnerConn chan net.Conn, errChan chan error, abort context.CancelFunc) {
 	var hasWinner bool
+	errsByProtocol := make(map[string]error)
 	for i := 0; i < len(r.dialerFns); i++ {
 		dr := <-connChan
 		if dr.Err != nil {
@@ -129,6 +134,7 @@ func (r *RaceDial) processResults(connChan chan dialResult, winnerConn chan net.
 				r.log.Infof("connection attempt aborted via: %s", dr.Protocol)
 			} else {
 				r.log.Errorf("failed to dial via %s: %s", dr.Protocol, dr.Err)
+				errsByProtocol[dr.Protocol] = fmt.Errorf("%s: %w", dr.Protocol, dr.Err)
 			}
 			continue
 		}
@@ -146,5 +152,29 @@ func (r *RaceDial) processResults(connChan chan dialResult, winnerConn chan net.
 		hasWinner = true
 		winnerConn <- dr.Conn
 	}
+	if !hasWinner {
+		errChan <- dialErr(r.orderedErrs(errsByProtocol))
+	}
 	close(winnerConn)
 }
+
+// orderedErrs returns the per-protocol errors in dialer order, so the combined
+// error is stable regardless of which attempt failed first.
+func (r *RaceDial) orderedErrs(byProtocol map[string]error) []error {
+	errs := make([]error, 0, len(byProtocol))
+	for _, dfn := range r.dialerFns {
+		if err, ok := byProtocol[dfn.Protocol()]; ok {
+			errs = append(errs, err)
+		}
+	}
+	return errs
+}
+
+// dialErr combines per-dialer failures, preserving the underlying reasons
+// (e.g. "connection refused") rather than a generic message.
+func dialErr(errs []error) error {
+	if len(errs) == 0 {
+		return errors.New("no relay transport available")
+	}
+	return errors.Join(errs...)
+}

shared/relay/client/dialer/ws/conn.go

@@ -33,6 +33,11 @@ func NewConn(wsConn *websocket.Conn, serverAddress string, underlying net.Conn)
 	}
 }
 
+// Protocol returns the transport name for this connection.
+func (c *Conn) Protocol() string {
+	return Network
+}
+
 func (c *Conn) Read(b []byte) (n int, err error) {
 	t, ioReader, err := c.Conn.Reader(c.ctx)
 	if err != nil {

shared/relay/client/dialer/ws/ws.go

@@ -22,7 +22,7 @@ type Dialer struct {
 }
 
 func (d Dialer) Protocol() string {
-	return "WS"
+	return Network
 }
 
 func (d Dialer) Dial(ctx context.Context, address, serverName string) (net.Conn, error) {
@@ -39,7 +39,12 @@ func (d Dialer) Dial(ctx context.Context, address, serverName string) (net.Conn,
 		if errors.Is(err, context.Canceled) {
 			return nil, err
 		}
-		log.Errorf("failed to dial to Relay server '%s': %s", wsURL, err)
+		// websocket.Dial wraps the cause in verbose layers; surface the
+		// underlying network error when present.
+		var opErr *net.OpError
+		if errors.As(err, &opErr) {
+			return nil, opErr
+		}
 		return nil, err
 	}
 	if resp.Body != nil {