feat: add CLI connector for unix domain socket (#186)

* feat: Add cli connector for unix domain socket

* Update cmd/uncloud/main.go

---------

Co-authored-by: Pasha Sviderski <me@psviderski.name>

pkg/client/connector/unix.go

@@ -0,0 +1,41 @@
+package connector
+
+import (
+	"context"
+	"fmt"
+
+	"golang.org/x/net/proxy"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials/insecure"
+)
+
+// UnixConnector establishes a connection to the machine API through a unix domain socket.
+type UnixConnector struct {
+	socketPath string
+}
+
+func NewUnixConnector(socketPath string) *UnixConnector {
+	return &UnixConnector{socketPath: socketPath}
+}
+
+func (c *UnixConnector) Connect(_ context.Context) (*grpc.ClientConn, error) {
+	// gRPC uses "unix:path" syntax for unix sockets.
+	target := "unix:" + c.socketPath
+
+	conn, err := grpc.NewClient(
+		target,
+		grpc.WithTransportCredentials(insecure.NewCredentials()),
+	)
+	if err != nil {
+		return nil, fmt.Errorf("create machine API client: %w", err)
+	}
+	return conn, nil
+}
+
+func (c *UnixConnector) Dialer() (proxy.ContextDialer, error) {
+	return nil, fmt.Errorf("proxy connections are not supported over a unix connection")
+}
+
+func (c *UnixConnector) Close() error {
+	return nil
+}