Restore Unix socket support (#498)

https://github.com/fullstorydev/grpcurl/issues/496

Restore -unix to working properly by default with the default dialer.

cmd/grpcurl/grpcurl.go

@@ -484,12 +484,12 @@ func main() {
 		if *maxMsgSz > 0 {
 			opts = append(opts, grpc.WithDefaultCallOptions(grpc.MaxCallRecvMsgSize(*maxMsgSz)))
 		}
-		network := "tcp"
+		if isUnixSocket != nil && isUnixSocket() && !strings.HasPrefix(target, "unix://") {
-		if isUnixSocket != nil && isUnixSocket() {
+			// prepend unix:// to the address if it's not already there
-			network = "unix"
+			// this is to maintain backwards compatibility because the custom dialer is replaced by
-			if *authority == "" {
+			// the default dialer in grpc-go.
-				*authority = "localhost"
+			// https://github.com/fullstorydev/grpcurl/pull/480
-			}
+			target = "unix://" + target
 		}
 		var creds credentials.TransportCredentials
 		if *plaintext {
@@ -557,7 +557,7 @@ func main() {
 
 		blockingDialTiming := dialTiming.Child("BlockingDial")
 		defer blockingDialTiming.Done()
-		cc, err := grpcurl.BlockingDial(ctx, network, target, creds, opts...)
+		cc, err := grpcurl.BlockingDial(ctx, "", target, creds, opts...)
 		if err != nil {
 			fail(err, "Failed to dial target host %q", target)
 		}

grpcurl.go

@@ -609,6 +609,8 @@ func ServerTransportCredentials(cacertFile, serverCertFile, serverKeyFile string
 // BlockingDial is a helper method to dial the given address, using optional TLS credentials,
 // and blocking until the returned connection is ready. If the given credentials are nil, the
 // connection will be insecure (plain-text).
+// The network parameter should be left empty in most cases when your address is a RFC 3986
+// compliant URI. The resolver from grpc-go will resolve the correct network type.
 func BlockingDial(ctx context.Context, network, address string, creds credentials.TransportCredentials, opts ...grpc.DialOption) (*grpc.ClientConn, error) {
 	if creds == nil {
 		creds = insecure.NewCredentials()
@@ -645,6 +647,34 @@ func BlockingDial(ctx context.Context, network, address string, creds credential
 		writeResult:          writeResult,
 	}
 
+	switch network {
+	case "":
+		// no-op, use address as-is
+	case "tcp":
+		if strings.HasPrefix(address, "unix://") {
+			return nil, fmt.Errorf("tcp network type cannot use unix address %s", address)
+		}
+	case "unix":
+		if !strings.HasPrefix(address, "unix://") {
+			// prepend unix:// to the address if it's not already there
+			// this is to maintain backwards compatibility because the custom dialer is replaced by
+			// the default dialer in grpc-go.
+			// https://github.com/fullstorydev/grpcurl/pull/480
+			address = "unix://" + address
+		}
+	default:
+		// custom dialer for other networks
+		dialer := func(ctx context.Context, address string) (net.Conn, error) {
+			conn, err := (&net.Dialer{}).DialContext(ctx, network, address)
+			if err != nil {
+				// capture the error so we can provide a better message
+				writeResult(err)
+			}
+			return conn, err
+		}
+		opts = append([]grpc.DialOption{grpc.WithContextDialer(dialer)}, opts...)
+	}
+
 	// Even with grpc.FailOnNonTempDialError, this call will usually timeout in
 	// the face of TLS handshake errors. So we can't rely on grpc.WithBlock() to
 	// know when we're done. So we run it in a goroutine and then use result