feat: implement headless server mode with API endpoints for metrics and process management

backend/sysinfo.go

@@ -313,6 +313,26 @@ func KillProcess(pid int32, force bool) error {
 	}
 	return p.Terminate()
 }
+// CollectFull gathers a complete metrics snapshot including GPU data.
+// Unlike NewSysInfo, it does not start a background emitter and does not
+// require a Wails runtime context — safe to call from server mode.
+func CollectFull(ctx context.Context) (*Metrics, error) {
+	s := &SysInfo{ctx: ctx}
+	m, err := s.CollectOnce()
+	if err != nil {
+		return nil, err
+	}
+	name, tot, used, util := queryGPU(ctx)
+	if name != "" {
+		m.GPUName = name
+		m.GPUTotal = tot
+		m.GPUUsed = used
+		m.GPUUtil = util
+		m.GPUProcesses = queryGPUProcesses(ctx)
+	}
+	return m, nil
+}
+
 // GetManPage returns the plain-text man page for the given command name.
 // Returns an empty string if man is not installed or the page does not exist.
 func GetManPage(name string) string {

main.go

@@ -2,6 +2,10 @@ package main
 
 import (
 	"embed"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
 
 	"github.com/wailsapp/wails/v2"
 	"github.com/wailsapp/wails/v2/pkg/options"
@@ -12,6 +16,18 @@ import (
 var assets embed.FS
 
 func main() {
+	noGUI, port, help := parseSysmonArgs()
+
+	if help {
+		printHelp()
+		os.Exit(0)
+	}
+
+	if noGUI {
+		runServer(port)
+		return
+	}
+
 	// Create an instance of the app structure
 	app := NewApp()
 
@@ -34,3 +50,56 @@ func main() {
 		println("Error:", err.Error())
 	}
 }
+
+// parseSysmonArgs scans os.Args manually so we don't call flag.Parse(),
+// which would conflict with flags that Wails injects in dev mode (e.g. -assetdir).
+func parseSysmonArgs() (noGUI bool, port int, help bool) {
+	port = 9731
+	args := os.Args[1:]
+	for i := 0; i < len(args); i++ {
+		arg := args[i]
+		switch arg {
+		case "--no-gui":
+			noGUI = true
+		case "--help", "-h":
+			help = true
+		case "--port":
+			if i+1 < len(args) {
+				i++
+				if p, err := strconv.Atoi(args[i]); err == nil && p > 0 && p <= 65535 {
+					port = p
+				}
+			}
+		default:
+			if strings.HasPrefix(arg, "--port=") {
+				if p, err := strconv.Atoi(strings.TrimPrefix(arg, "--port=")); err == nil && p > 0 && p <= 65535 {
+					port = p
+				}
+			}
+		}
+	}
+	return
+}
+
+func printHelp() {
+	fmt.Print(`sysmon — system monitor
+
+Usage:
+  sysmon                       Launch with graphical interface (default)
+  sysmon --no-gui              Run as headless HTTP API server (port 9731)
+  sysmon --no-gui --port N     Run server on port N
+
+Options:
+  --no-gui          Start without GUI, expose HTTP API instead
+  --port <number>   HTTP server port (default: 9731, requires --no-gui)
+  --help, -h        Show this help
+
+Server endpoints (--no-gui mode):
+  GET  /api/metrics              Latest metrics snapshot (JSON)
+  GET  /api/metrics/stream       Server-Sent Events stream (1 s interval)
+  GET  /api/process/<pid>        Process detail (JSON)
+  POST /api/process/<pid>/kill   Kill process  (?force=true → SIGKILL)
+  GET  /api/man/<name>           Manual page for a command
+`)
+}
+

server.go

@@ -0,0 +1,172 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"os"
+	"os/signal"
+	"strconv"
+	"strings"
+	"syscall"
+	"time"
+
+	"sysmon/backend"
+)
+
+func runServer(port int) {
+	_, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	mux := http.NewServeMux()
+
+	// GET /api/metrics — latest snapshot
+	mux.HandleFunc("/api/metrics", func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api/metrics" {
+			http.NotFound(w, r)
+			return
+		}
+		if r.Method != http.MethodGet {
+			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+			return
+		}
+		m, err := backend.CollectFull(r.Context())
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+		w.Header().Set("Content-Type", "application/json")
+		w.Header().Set("Access-Control-Allow-Origin", "*")
+		json.NewEncoder(w).Encode(m) //nolint:errcheck
+	})
+
+	// GET /api/metrics/stream — SSE push every 1 s
+	mux.HandleFunc("/api/metrics/stream", func(w http.ResponseWriter, r *http.Request) {
+		flusher, ok := w.(http.Flusher)
+		if !ok {
+			http.Error(w, "streaming unsupported", http.StatusInternalServerError)
+			return
+		}
+		w.Header().Set("Content-Type", "text/event-stream")
+		w.Header().Set("Cache-Control", "no-cache")
+		w.Header().Set("Connection", "keep-alive")
+		w.Header().Set("Access-Control-Allow-Origin", "*")
+
+		ticker := time.NewTicker(time.Second)
+		defer ticker.Stop()
+
+		for {
+			select {
+			case <-r.Context().Done():
+				return
+			case <-ticker.C:
+				m, err := backend.CollectFull(r.Context())
+				if err != nil {
+					continue
+				}
+				data, _ := json.Marshal(m)
+				fmt.Fprintf(w, "data: %s\n\n", data) //nolint:errcheck
+				flusher.Flush()
+			}
+		}
+	})
+
+	// GET  /api/process/<pid>
+	// POST /api/process/<pid>/kill[?force=true]
+	mux.HandleFunc("/api/process/", func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Access-Control-Allow-Origin", "*")
+		path := strings.TrimPrefix(r.URL.Path, "/api/process/")
+		parts := strings.SplitN(path, "/", 2)
+		if parts[0] == "" {
+			http.Error(w, "missing pid", http.StatusBadRequest)
+			return
+		}
+		pid64, err := strconv.ParseInt(parts[0], 10, 32)
+		if err != nil || pid64 <= 0 {
+			http.Error(w, "invalid pid", http.StatusBadRequest)
+			return
+		}
+
+		// Kill action
+		if len(parts) == 2 && parts[1] == "kill" {
+			if r.Method != http.MethodPost {
+				http.Error(w, "use POST /api/process/<pid>/kill", http.StatusMethodNotAllowed)
+				return
+			}
+			force := r.URL.Query().Get("force") == "true"
+			if err := backend.KillProcess(int32(pid64), force); err != nil {
+				http.Error(w, err.Error(), http.StatusInternalServerError)
+				return
+			}
+			w.WriteHeader(http.StatusNoContent)
+			return
+		}
+
+		// Process detail
+		if r.Method != http.MethodGet {
+			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+			return
+		}
+		detail, err := backend.FetchProcessDetail(int32(pid64))
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusNotFound)
+			return
+		}
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(detail) //nolint:errcheck
+	})
+
+	// GET /api/man/<name>
+	mux.HandleFunc("/api/man/", func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodGet {
+			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+			return
+		}
+		name := strings.TrimPrefix(r.URL.Path, "/api/man/")
+		// Strict validation: only allow characters common in command names.
+		// exec.Command passes the name as a separate arg (no shell), but we
+		// reject obviously bad input early to avoid surprising behaviour.
+		if name == "" || len(name) > 64 || strings.ContainsAny(name, "/ \t\n\r\\\"';|&`$<>(){}") {
+			http.Error(w, "invalid name", http.StatusBadRequest)
+			return
+		}
+		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+		w.Header().Set("Access-Control-Allow-Origin", "*")
+		fmt.Fprint(w, backend.GetManPage(name)) //nolint:errcheck
+	})
+
+	addr := fmt.Sprintf(":%d", port)
+	fmt.Printf("sysmon server  →  http://localhost%s\n\n", addr)
+	fmt.Println("Endpoints:")
+	fmt.Printf("  GET  /api/metrics              — latest metrics snapshot (JSON)\n")
+	fmt.Printf("  GET  /api/metrics/stream       — Server-Sent Events stream (1 s)\n")
+	fmt.Printf("  GET  /api/process/<pid>        — process detail (JSON)\n")
+	fmt.Printf("  POST /api/process/<pid>/kill   — kill process (?force=true → SIGKILL)\n")
+	fmt.Printf("  GET  /api/man/<name>           — manual page for a command\n")
+	fmt.Println("\nPress Ctrl+C to stop.")
+
+	srv := &http.Server{
+		Addr:         addr,
+		Handler:      mux,
+		ReadTimeout:  10 * time.Second,
+		WriteTimeout: 0, // disabled: SSE streams are long-lived
+		IdleTimeout:  60 * time.Second,
+	}
+
+	quit := make(chan os.Signal, 1)
+	signal.Notify(quit, syscall.SIGINT, syscall.SIGTERM)
+	go func() {
+		<-quit
+		fmt.Println("\nShutting down…")
+		cancel()
+		shutCtx, shutCancel := context.WithTimeout(context.Background(), 5*time.Second)
+		defer shutCancel()
+		srv.Shutdown(shutCtx) //nolint:errcheck
+	}()
+
+	if err := srv.ListenAndServe(); err != nil && err != http.ErrServerClosed {
+		fmt.Fprintf(os.Stderr, "server error: %v\n", err)
+		os.Exit(1)
+	}
+}