fix(outbound): return 403 instead of 500 for an unresolvable outbound host

pkg/gotenberg/outbound.go

@@ -338,8 +338,18 @@ func DecideOutbound(ctx context.Context, rawURL string, allowList, denyList []*r
 			return OutboundDecision{}, fmt.Errorf("'%s' targets a non-public address: %w", normalized, ErrFiltered)
 		case errors.Is(err, ErrPublicIP):
 			return OutboundDecision{}, fmt.Errorf("'%s' targets a public address: %w", normalized, ErrFiltered)
-		default:
+		case errors.Is(err, context.Canceled), errors.Is(err, context.DeadlineExceeded):
+			// A cancellation or timeout is not a policy decision; surface it
+			// as-is so callers do not report it as a filtered request.
 			return OutboundDecision{}, fmt.Errorf("validate '%s' host: %w", normalized, err)
+		default:
+			// The host could not be resolved, so its address class cannot be
+			// verified. Fail closed and treat it as filtered, the same as a
+			// host that resolves to a blocked address, so clients get a
+			// generic 403 rather than a 500. This also denies alternate IP
+			// encodings such as http://2130706433/ that the resolver rejects
+			// as a hostname but Chromium would read as a private IP.
+			return OutboundDecision{}, fmt.Errorf("validate '%s' host: %v: %w", normalized, err, ErrFiltered)
 		}
 	}
 

pkg/gotenberg/outbound_test.go

@@ -311,6 +311,39 @@ func TestFilterOutboundURL(t *testing.T) {
 	}
 }
 
+func TestDecideOutbound_UnresolvableHostFailsClosed(t *testing.T) {
+	withStubResolver(t, func(string) ([]netip.Addr, error) {
+		return nil, errors.New("no such host")
+	})
+
+	// An alternate IP encoding (decimal for 127.0.0.1) that the resolver
+	// rejects as a hostname must fail closed as filtered, not surface as a
+	// server error, so clients receive a generic 403.
+	_, err := DecideOutbound(context.Background(), "http://2130706433/", nil, nil, time.Now().Add(5*time.Second), WithDenyPrivateIPs(true))
+	if !errors.Is(err, ErrFiltered) {
+		t.Fatalf("expected ErrFiltered, got: %v", err)
+	}
+}
+
+func TestDecideOutbound_ResolverCancellationNotFiltered(t *testing.T) {
+	withStubResolver(t, func(string) ([]netip.Addr, error) {
+		return nil, context.Canceled
+	})
+
+	// A cancellation or timeout is not a policy decision and must not be
+	// reported as a filtered request.
+	_, err := DecideOutbound(context.Background(), "http://example.com/", nil, nil, time.Now().Add(5*time.Second), WithDenyPrivateIPs(true))
+	if err == nil {
+		t.Fatal("expected error, got nil")
+	}
+	if errors.Is(err, ErrFiltered) {
+		t.Fatalf("cancellation must not be filtered, got: %v", err)
+	}
+	if !errors.Is(err, context.Canceled) {
+		t.Fatalf("expected context.Canceled, got: %v", err)
+	}
+}
+
 func TestResolveAndCheckPublic_IPLiteralLoopback(t *testing.T) {
 	withStubResolver(t, func(host string) ([]netip.Addr, error) {
 		t.Fatalf("unexpected DNS lookup for %q", host)