From 8415124ff109a5ac94437ebb4de1886e5ff308a9 Mon Sep 17 00:00:00 2001
From: Nick Santos <nicholas.j.santos@gmail.com>
Date: Wed, 3 Feb 2021 16:29:13 -0500
Subject: [PATCH] socat: add a utility to forward ports to a remote docker
 server (#94)

---
 internal/socat/socat.go | 92 +++++++++++++++++++++++++++++++++++++++++
 pkg/cmd/root.go         |  1 +
 pkg/cmd/socat.go        | 49 ++++++++++++++++++++++
 3 files changed, 142 insertions(+)
 create mode 100644 internal/socat/socat.go
 create mode 100644 pkg/cmd/socat.go

diff --git a/internal/socat/socat.go b/internal/socat/socat.go
new file mode 100644
index 0000000..1a3f3fa
--- /dev/null
+++ b/internal/socat/socat.go
@@ -0,0 +1,92 @@
+// Manage socat network routers for remote docker instances.
+package socat
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"os/exec"
+	"time"
+
+	"github.com/docker/docker/api/types"
+	"github.com/docker/docker/client"
+)
+
+const serviceName = "ctlptl-portforward-service"
+
+type ContainerClient interface {
+	ContainerInspect(ctx context.Context, containerID string) (types.ContainerJSON, error)
+	ContainerRemove(ctx context.Context, id string, options types.ContainerRemoveOptions) error
+}
+
+type Controller struct {
+	client ContainerClient
+}
+
+func NewController(client ContainerClient) *Controller {
+	return &Controller{client: client}
+}
+
+func DefaultController(ctx context.Context) (*Controller, error) {
+	client, err := client.NewClientWithOpts(client.FromEnv)
+	if err != nil {
+		return nil, err
+	}
+
+	client.NegotiateAPIVersion(ctx)
+	return NewController(client), nil
+}
+
+// Connect a port on the local machine to a port on a remote docker machine.
+func (c *Controller) ConnectRemoteDockerPort(ctx context.Context, port int) error {
+	err := c.StartRemotePortforwarder(ctx)
+	if err != nil {
+		return err
+	}
+	return c.StartLocalPortforwarder(ctx, port)
+}
+
+// Create a port-forwarding server on the same machine that's running
+// Docker. This server accepts connections and routes them to localhost ports
+// on the same machine.
+func (c *Controller) StartRemotePortforwarder(ctx context.Context) error {
+	container, err := c.client.ContainerInspect(ctx, serviceName)
+	if err == nil && container.State.Running {
+		// The service is already running!
+		return nil
+	} else if err == nil {
+		// The service exists, but is not running
+		err := c.client.ContainerRemove(ctx, serviceName, types.ContainerRemoveOptions{Force: true})
+		if err != nil {
+			return fmt.Errorf("creating remote portforwarder: %v", err)
+		}
+	} else if !client.IsErrNotFound(err) {
+		return fmt.Errorf("inspecting remote portforwarder: %v", err)
+	}
+
+	cmd := exec.Command("docker", "run", "-d", "-it",
+		"--name", serviceName, "--net=host", "--restart=always",
+		"--entrypoint", "/bin/sh", "alpine/socat", "-c", "while true; do sleep 1000; done")
+	return cmd.Run()
+}
+
+// Create a port-forwarding server on the local machine, forwarding connections
+// to the same port on the remote Docker server.
+func (c *Controller) StartLocalPortforwarder(ctx context.Context, port int) error {
+	cmd := exec.Command("socat", fmt.Sprintf("TCP-LISTEN:%d,reuseaddr,fork", port),
+		fmt.Sprintf("EXEC:'docker exec -i %s socat STDIO TCP:localhost:%d'", serviceName, port))
+	err := cmd.Start()
+	if err != nil {
+		return fmt.Errorf("creating local portforwarder: %v", err)
+	}
+
+	for i := 0; i < 100; i++ {
+		conn, err := net.Dial("tcp", fmt.Sprintf("localhost:%d", port))
+		if err == nil {
+			_ = conn.Close()
+			return nil
+		}
+		time.Sleep(100 * time.Millisecond)
+	}
+	return fmt.Errorf("timed out waiting for local portforwarder")
+}
diff --git a/pkg/cmd/root.go b/pkg/cmd/root.go
index e62aae9..f1b6dcf 100644
--- a/pkg/cmd/root.go
+++ b/pkg/cmd/root.go
@@ -20,6 +20,7 @@ func NewRootCommand() *cobra.Command {
 	rootCmd.AddCommand(NewDockerDesktopCommand())
 	rootCmd.AddCommand(newDocsCommand(rootCmd))
 	rootCmd.AddCommand(analytics.NewCommand())
+	rootCmd.AddCommand(NewSocatCommand())
 
 	return rootCmd
 }
diff --git a/pkg/cmd/socat.go b/pkg/cmd/socat.go
new file mode 100644
index 0000000..3adffc8
--- /dev/null
+++ b/pkg/cmd/socat.go
@@ -0,0 +1,49 @@
+package cmd
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"strconv"
+
+	"github.com/spf13/cobra"
+	"github.com/tilt-dev/ctlptl/internal/socat"
+)
+
+func NewSocatCommand() *cobra.Command {
+	var cmd = &cobra.Command{
+		Use:   "socat",
+		Short: "Use socat to connect components. Experimental.",
+	}
+
+	cmd.AddCommand(&cobra.Command{
+		Use:     "connect-remote-docker",
+		Short:   "Connects a local port to a remote port on a machine running Docker",
+		Example: "  ctlptl socat connect-remote-docker [port]\n",
+		Run:     connectRemoteDocker,
+		Args:    cobra.ExactArgs(1),
+	})
+
+	return cmd
+}
+
+func connectRemoteDocker(cmd *cobra.Command, args []string) {
+	port, err := strconv.Atoi(args[0])
+	if err != nil {
+		_, _ = fmt.Fprintf(os.Stderr, "connect-remote-docker: %v\n", err)
+		os.Exit(1)
+	}
+
+	ctx := context.Background()
+	c, err := socat.DefaultController(ctx)
+	if err != nil {
+		_, _ = fmt.Fprintf(os.Stderr, "connect-remote-docker: %v\n", err)
+		os.Exit(1)
+	}
+
+	err = c.ConnectRemoteDockerPort(ctx, port)
+	if err != nil {
+		_, _ = fmt.Fprintf(os.Stderr, "connect-remote-docker: %v\n", err)
+		os.Exit(1)
+	}
+}