Rewrite relay WS dialer URL prep using net/url to preserve non-standard ports

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

@@ -9,7 +9,6 @@ import (
 	"net"
 	"net/http"
 	"net/url"
-	"strings"
 
 	"github.com/coder/websocket"
 	log "github.com/sirupsen/logrus"
@@ -34,13 +33,7 @@ func (d Dialer) Dial(ctx context.Context, address string) (net.Conn, error) {
 
 	opts := createDialOptions()
 
-	parsedURL, err := url.Parse(wsURL)
-	if err != nil {
-		return nil, err
-	}
-	parsedURL.Path = relay.WebSocketURLPath
-
-	wsConn, resp, err := websocket.Dial(ctx, parsedURL.String(), opts)
+	wsConn, resp, err := websocket.Dial(ctx, wsURL, opts)
 	if err != nil {
 		if errors.Is(err, context.Canceled) {
 			return nil, err
@@ -56,12 +49,24 @@ func (d Dialer) Dial(ctx context.Context, address string) (net.Conn, error) {
 	return conn, nil
 }
 
+// prepareURL rewrites a rel://host[:port] or rels://host[:port] address into a
+// ws://host[:port]/relay or wss://host[:port]/relay URL, preserving any
+// non-standard port from the input.
 func prepareURL(address string) (string, error) {
-	if !strings.HasPrefix(address, "rel:") && !strings.HasPrefix(address, "rels:") {
-		return "", fmt.Errorf("unsupported scheme: %s", address)
+	parsed, err := url.Parse(address)
+	if err != nil {
+		return "", fmt.Errorf("parse relay address %q: %w", address, err)
 	}
-
-	return strings.Replace(address, "rel", "ws", 1), nil
+	switch parsed.Scheme {
+	case "rel":
+		parsed.Scheme = "ws"
+	case "rels":
+		parsed.Scheme = "wss"
+	default:
+		return "", fmt.Errorf("unsupported scheme: %s", parsed.Scheme)
+	}
+	parsed.Path = relay.WebSocketURLPath
+	return parsed.String(), nil
 }
 
 func httpClientNbDialer() *http.Client {

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

@@ -0,0 +1,66 @@
+package ws
+
+import (
+	"testing"
+)
+
+func TestPrepareURL(t *testing.T) {
+	tests := []struct {
+		name    string
+		input   string
+		want    string
+		wantErr bool
+	}{
+		{
+			name:  "rel scheme with non-standard port",
+			input: "rel://test-domain-2:45678",
+			want:  "ws://test-domain-2:45678/relay",
+		},
+		{
+			name:  "rels scheme with non-standard port",
+			input: "rels://test-domain-2:45678",
+			want:  "wss://test-domain-2:45678/relay",
+		},
+		{
+			name:  "rel scheme without port",
+			input: "rel://test-domain-2",
+			want:  "ws://test-domain-2/relay",
+		},
+		{
+			name:  "rels scheme without port",
+			input: "rels://test-domain-2",
+			want:  "wss://test-domain-2/relay",
+		},
+		{
+			name:  "rel scheme with IP and port",
+			input: "rel://1.2.3.4:45678",
+			want:  "ws://1.2.3.4:45678/relay",
+		},
+		{
+			name:  "rel scheme with hostname starting with rel",
+			input: "rel://relay.example.com:45678",
+			want:  "ws://relay.example.com:45678/relay",
+		},
+		{
+			name:    "unsupported scheme",
+			input:   "http://test-domain-2:45678",
+			wantErr: true,
+		},
+		{
+			name:    "no scheme",
+			input:   "test-domain-2:45678",
+			wantErr: true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := prepareURL(tt.input)
+			if (err != nil) != tt.wantErr {
+				t.Fatalf("prepareURL(%q) err = %v, wantErr %v", tt.input, err, tt.wantErr)
+			}
+			if got != tt.want {
+				t.Errorf("prepareURL(%q) = %q, want %q", tt.input, got, tt.want)
+			}
+		})
+	}
+}