rootless_docker_socat.go

package main

import (
	"context"
	"fmt"
	"log"
	"os"
	"os/exec"
	"strings"
	"sync"
)

func runDockerPs(ctx context.Context) (string, error) {
	cmd := exec.CommandContext(ctx, "docker", "ps", `--format`, `"{{.Ports}}"`)
	out, err := cmd.Output()
	return string(out), err
}

func runSocat(ctx context.Context, port string) error {
	xdgRuntimeDir := os.Getenv("XDG_RUNTIME_DIR")
	cmdCatDockerPid := exec.Command("cat", fmt.Sprintf("%s/docker.pid", xdgRuntimeDir))
	pid, err := cmdCatDockerPid.Output()
	if err != nil {
		return err
	}
	cmd := exec.CommandContext(ctx, "socat",
		`-t`,
		`--`,
		fmt.Sprintf(`TCP-LISTEN:%s,reuseaddr,fork`, port),
		fmt.Sprintf(`EXEC:"nsenter -U -n -t %s socat -t -- STDIN TCP4\:127.0.0.1\:%s"`, pid, port),
	)
	if err := cmd.Run(); err != nil {
		return err
	}
	return nil
}

func filterPort(out string) []string {
	portSet := map[string]bool{}
	ports := []string{}

	lines := strings.Split(out, "\n")
	for _, line := range lines {
		fwds := strings.Split(line, ",")
		for _, fwd := range fwds {
			hostContainer := strings.Split(fwd, "->")
			if len(hostContainer) == 2 {
				host := hostContainer[0]
				urlPort := strings.Split(host, ":")
				port := urlPort[1]
				if !portSet[port] {
					portSet[port] = true
					ports = append(ports, port)
				}
			}
		}
	}
	return ports
}

func main() {
	ctx := context.Background()
	out, err := runDockerPs(ctx)
	if err != nil {
		log.Print(err)
		return
	}
	ports := filterPort(out)
	log.Print(ports)
	wg := &sync.WaitGroup{}
	for _, port := range ports {
		log.Printf("socat: %s", port)
		wg.Add(1)
		go func(port string) {
			if err = runSocat(context.Background(), port); err != nil {
				log.Print(err)
			}
		}(port)
	}
	wg.Wait()
}