safely capture and display panics while rendering any pages in the web http view. safely print out stack traces from crashed goroutines without destroying the terminal

src/ngrok/client/controller.go

@@ -85,14 +85,17 @@ func (ctl *Controller) PlayRequest(tunnel mvc.Tunnel, payload []byte) {
 }
 
 func (ctl *Controller) Go(fn func()) {
-	defer func() {
-		if r := recover(); r != nil {
-			ctl.Error("goroutine crashed: %v", r)
-			// XXX
-		}
-	}()
+	go func() {
+		defer func() {
+			if r := recover(); r != nil {
+				err := util.MakePanicTrace(r)
+				ctl.Error(err)
+				ctl.Shutdown(err)
+			}
+		}()
 
-	go fn()
+		fn()
+	}()
 }
 
 // private functions

src/ngrok/client/update_release.go

@@ -26,7 +26,7 @@ func autoUpdate(ctl mvc.Controller, token string) {
 
 		download := update.NewDownload()
 		downloadComplete := make(chan int)
-		go func() {
+		ctl.Go(func() {
 			for {
 				select {
 				case progress, ok := <-download.Progress:
@@ -47,7 +47,7 @@ func autoUpdate(ctl mvc.Controller, token string) {
 					}
 				}
 			}
-		}()
+		})
 
 		log.Info("Checking for update")
 		err := download.UpdateFromUrl(updateEndpoint + "?" + params.Encode())

src/ngrok/client/views/term/http.go

@@ -44,7 +44,7 @@ func newTermHttpView(ctl mvc.Controller, termView *TermView, proto *proto.Http,
 		termView:     termView,
 		Logger:       log.NewPrefixLogger("view", "term", "http"),
 	}
-	go v.Run()
+	ctl.Go(v.Run)
 	return v
 }
 

src/ngrok/client/views/web/http.go

@@ -214,6 +214,14 @@ func (whv *WebHttpView) updateHttp() {
 
 func (whv *WebHttpView) register() {
 	http.HandleFunc("/http/in/replay", func(w http.ResponseWriter, r *http.Request) {
+		defer func() {
+			if r := recover(); r != nil {
+				err := util.MakePanicTrace(r)
+				whv.Error("Replay failed: %v", err)
+				http.Error(w, err, 500)
+			}
+		}()
+
 		r.ParseForm()
 		txnid := r.Form.Get("txnid")
 		if txn, ok := whv.idToTxn[txnid]; ok {
@@ -232,6 +240,14 @@ func (whv *WebHttpView) register() {
 	})
 
 	http.HandleFunc("/http/in", func(w http.ResponseWriter, r *http.Request) {
+		defer func() {
+			if r := recover(); r != nil {
+				err := util.MakePanicTrace(r)
+				whv.Error("HTTP web view failed: %v", err)
+				http.Error(w, err, 500)
+			}
+		}()
+
 		pageTmpl, err := assets.ReadAsset("assets/client/page.html")
 		if err != nil {
 			panic(err)

src/ngrok/client/views/web/view.go

@@ -16,7 +16,6 @@ import (
 type WebView struct {
 	log.Logger
 
-	// saved only for creating subviews
 	ctl mvc.Controller
 
 	// messages sent over this broadcast are sent too all websocket connections
@@ -68,7 +67,7 @@ func NewWebView(ctl mvc.Controller, port int) *WebView {
 	})
 
 	wv.Info("Serving web interface on localhost:%d", port)
-	go http.ListenAndServe(fmt.Sprintf(":%d", port), nil)
+	wv.ctl.Go(func() { http.ListenAndServe(fmt.Sprintf(":%d", port), nil) })
 	return wv
 }
 

src/ngrok/util/trace.go

@@ -0,0 +1,12 @@
+package util
+
+import (
+	"fmt"
+	"runtime"
+)
+
+func MakePanicTrace(err interface{}) string {
+	stackBuf := make([]byte, 4096)
+	n := runtime.Stack(stackBuf, false)
+	return fmt.Sprintf("panic: %v\n\n%s", err, stackBuf[:n])
+}