feat: completely new approach

Instead of building new images, we just run them with a tiny
mount that contains a statically-linked binary that wraps the
entry point and launches a signaling ws server.

Author: aslushnikov

.gitignore

@@ -2,3 +2,5 @@ node_modules/
 test-results/
 lib/
 types/
+deadmanswitch/bin/*
+deadmanswitch/deadmanswitch

.npmignore

@@ -1,7 +1,4 @@
 *
-!lib/
 !lib/**
-!types/
 !types/**
-!docker/
-!docker/**
+!deadmanswitch/bin/*

deadmanswitch/build.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+set -e
+set +x
+
+trap "cd $(pwd -P)" EXIT
+cd $(dirname "$0")
+
+rm -rf ./bin
+mkdir bin
+
+CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -ldflags="-s -w" -o bin/deadmanswitch_linux_x86_64
+CGO_ENABLED=0 GOOS=linux GOARCH=arm64 go build -ldflags="-s -w" -o bin/deadmanswitch_linux_aarch64
+
+# https://upx.github.io/ - 30% less file size.
+upx --best --ultra-brute bin/*

deadmanswitch/go.mod

@@ -0,0 +1,5 @@
+module deadmanswitch
+
+go 1.21.3
+
+require github.com/gorilla/websocket v1.5.3

deadmanswitch/go.sum

@@ -0,0 +1,2 @@
+github.com/gorilla/websocket v1.5.3 h1:saDtZ6Pbx/0u+bgYQ3q96pZgCzfhKXGPqt7kZ72aNNg=
+github.com/gorilla/websocket v1.5.3/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=

deadmanswitch/main.go

@@ -0,0 +1,164 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+	"os/exec"
+	"os/signal"
+	"strconv"
+	"sync"
+	"syscall"
+	"time"
+
+	"github.com/gorilla/websocket"
+)
+
+var upgrader = websocket.Upgrader{
+	ReadBufferSize:  1024,
+	WriteBufferSize: 1024,
+	CheckOrigin: func(r *http.Request) bool {
+		return true // Allow all connections for this example
+	},
+}
+
+func printUsage() {
+	fmt.Println("Usage: process_manager <command-to-run>")
+	fmt.Println("Example: process_manager python3 script.py")
+}
+
+func getEnvWithDefault(key, defaultValue string) string {
+	if value, exists := os.LookupEnv(key); exists {
+		return value
+	}
+	return defaultValue
+}
+
+func main() {
+	if len(os.Args) <= 1 {
+		printUsage()
+		os.Exit(1)
+	}
+
+	// Parse command line arguments
+	command := os.Args[1]
+	args := os.Args[2:]
+
+	// Get configuration from environment variables
+	port, _ := strconv.Atoi(getEnvWithDefault("DEADMANSWITCH_PORT", "54321"))
+	wsSuffix := getEnvWithDefault("DEADMANSWITCH_SUFFIX", "")
+
+	connectionTimeoutSeconds, _ := strconv.Atoi(getEnvWithDefault("DEADMANSWITCH_TIMEOUT", "10"))
+
+	// Channel to coordinate shutdown
+	cmdFinished := make(chan struct{})
+	clientConnected := make(chan struct{})
+	clientDisconnected := make(chan struct{})
+
+	// Start the child process
+	cmd := exec.Command(command, args...)
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	cmd.Stdin = os.Stdin
+
+	if err := cmd.Start(); err != nil {
+		log.Fatalf("Failed to start process: %v", err)
+	}
+
+	// Handle process completion
+	go func() {
+		cmd.Wait()
+		close(cmdFinished)
+	}()
+
+	// Setup WebSocket handler
+	var mutex sync.Mutex
+	has_client := false
+	http.HandleFunc("/"+wsSuffix, func(w http.ResponseWriter, r *http.Request) {
+		var had_clients bool
+		mutex.Lock()
+		had_clients = has_client
+		mutex.Unlock()
+
+		if had_clients {
+			http.NotFound(w, r)
+			return
+		}
+		conn, err := upgrader.Upgrade(w, r, nil)
+		if err != nil {
+			log.Printf("[deadmanswitch] Failed to upgrade connection: %v", err)
+			return
+		}
+		defer conn.Close()
+
+		mutex.Lock()
+		has_client = true
+		mutex.Unlock()
+
+		close(clientConnected)
+
+		for {
+			_, _, err := conn.ReadMessage()
+			if err != nil {
+				// Break the loop if an error occurs (e.g., if the connection is closed)
+				close(clientDisconnected)
+				break
+			}
+		}
+	})
+
+	// Start HTTP server
+	server := &http.Server{
+		Addr: fmt.Sprintf(":%d", port),
+	}
+
+	go func() {
+		if err := server.ListenAndServe(); err != http.ErrServerClosed {
+			log.Printf("[deadmanswitch] Server error: %v", err)
+		}
+	}()
+
+	log.Printf("[deadmanswitch] Waiting %d seconds on ws://localhost:%d/%s for client", connectionTimeoutSeconds, port, wsSuffix)
+	// Handle OS signals
+	sigChan := make(chan os.Signal, 1)
+	signal.Notify(sigChan, syscall.SIGINT, syscall.SIGTERM)
+
+	// Set up connection timeout
+	connetionTimer := time.NewTimer(time.Duration(connectionTimeoutSeconds) * time.Second)
+	go func() {
+		log.Printf("[deadmanswitch] expecting client connect...")
+		<-clientConnected
+		log.Printf("[deadmanswitch] yeah client connected")
+		connetionTimer.Stop()
+	}()
+
+	select {
+	case <-connetionTimer.C:
+		log.Printf("[deadmanswitch] still no client after %d seconds - closing.", connectionTimeoutSeconds)
+	case sig := <-sigChan:
+		log.Printf("[deadmanswitch] Received %v, exiting", sig)
+	case <-clientDisconnected:
+		log.Println("[deadmanswitch] client disconnected, terminating process")
+	case <-cmdFinished:
+		log.Println("[deadmanswitch] process finished")
+	}
+
+	log.Println("[deadmanswitch] Shutting down...")
+
+	// Shutdown the server
+	server.Close()
+	connetionTimer.Stop()
+
+	// Give the process a chance to terminate gracefully
+	if cmd.Process != nil {
+		processShutdownTimer := time.NewTimer(time.Duration(connectionTimeoutSeconds) * time.Second)
+		cmd.Process.Signal(syscall.SIGTERM)
+		select {
+		case <-processShutdownTimer.C:
+			cmd.Process.Kill()
+		case <-cmdFinished:
+			processShutdownTimer.Stop()
+		}
+	}
+}