Add support to restart on program exit

main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"fmt"
 	"os"
+	"os/exec"
 	"os/signal"
 	"path/filepath"
 	"syscall"
@@ -167,24 +168,40 @@ func runGaper(cfg *Config) error {
 		return fmt.Errorf("watcher error: %v", err)
 	}
 
+	var changeRestart bool
+
 	go watcher.Watch()
 	for {
 		select {
 		case event := <-watcher.Events:
 			logger.Debug("Detected new changed file: ", event)
+			changeRestart = true
 			restart(builder, runner)
 		case err := <-watcher.Errors:
 			return fmt.Errorf("error on watching files: %v", err)
+		case err := <-runner.Errors():
+			if changeRestart {
+				changeRestart = false
+			} else {
+				logger.Debug("Detected program exit: ", err)
+				if err = handleProgramExit(builder, runner, err); err != nil {
+					return err
+				}
+			}
 		default:
-			logger.Debug("Waiting watch event")
 			time.Sleep(time.Duration(cfg.PollInterval) * time.Millisecond)
 		}
 	}
 }
 
 func restart(builder Builder, runner Runner) error {
-	if err := runner.Kill(); err != nil {
+	logger.Debug("Restarting program")
-		return fmt.Errorf("kill error: %v", err)
+
+	// kill process if it is running
+	if !runner.Exited() {
+		if err := runner.Kill(); err != nil {
+			return fmt.Errorf("kill error: %v", err)
+		}
 	}
 
 	if err := builder.Build(); err != nil {
@@ -198,6 +215,16 @@ func restart(builder Builder, runner Runner) error {
 	return nil
 }
 
+func handleProgramExit(builder Builder, runner Runner, err error) error {
+	_, ok := err.(*exec.ExitError)
+	if !ok {
+		return fmt.Errorf("couldn't handle program crash restart: %v", err)
+	}
+
+	restart(builder, runner)
+	return nil
+}
+
 func shutdown(runner Runner) {
 	c := make(chan os.Signal, 2)
 	signal.Notify(c, os.Interrupt, syscall.SIGTERM)

runner.go

@@ -16,6 +16,8 @@ const OSWindows = "windows"
 type Runner interface {
 	Run() (*exec.Cmd, error)
 	Kill() error
+	Errors() chan error
+	Exited() bool
 }
 
 type runner struct {
@@ -24,6 +26,7 @@ type runner struct {
 	writer    io.Writer
 	command   *exec.Cmd
 	starttime time.Time
+	errors    chan error
 }
 
 // NewRunner ...
@@ -33,6 +36,7 @@ func NewRunner(writer io.Writer, bin string, args []string) Runner {
 		args:      args,
 		writer:    writer,
 		starttime: time.Now(),
+		errors:    make(chan error),
 	}
 }
 
@@ -91,6 +95,11 @@ func (r *runner) Exited() bool {
 	return r.command != nil && r.command.ProcessState != nil && r.command.ProcessState.Exited()
 }
 
+// Errors ...
+func (r *runner) Errors() chan error {
+	return r.errors
+}
+
 func (r *runner) runBin() error {
 	r.command = exec.Command(r.bin, r.args...) // nolint gas
 	stdout, err := r.command.StdoutPipe()
@@ -113,7 +122,13 @@ func (r *runner) runBin() error {
 	// TODO: handle or log errors
 	go io.Copy(r.writer, stdout) // nolint errcheck
 	go io.Copy(r.writer, stderr) // nolint errcheck
-	go r.command.Wait()          // nolint errcheck
+
+	// wait for exit errors
+	go func() {
+		if err := r.command.Wait(); err != nil {
+			r.errors <- err
+		}
+	}()
 
 	return nil
 }

testdata/server/main.go

@@ -8,10 +8,14 @@ import (
 )
 
 func main() {
-	http.HandleFunc("/bar", func(w http.ResponseWriter, r *http.Request) {
+	http.HandleFunc("/foo", func(w http.ResponseWriter, r *http.Request) {
 		fmt.Fprintf(w, "Hello, %q", html.EscapeString(r.URL.Path)) // nolint gas
 	})
 
+	http.HandleFunc("/bar", func(w http.ResponseWriter, r *http.Request) {
+		log.Fatal("Forced failure")
+	})
+
 	log.Println("Starting server")
 	log.Fatal(http.ListenAndServe(":8080", nil))
 }