Allow internal server error using panic()

assets/templates/html/index.html.tmpl

@@ -9,12 +9,12 @@ the command line.
 ## USAGE
 
     # Upload a file
-    curl -F'file=@yourfile.png' <a href="{{Request.Host}}">{{Request.Host}}</a>
+    curl -F'file=@yourfile.png' <a href="{{.Request.Host}}">{{.Request.Host}}</a>
 
     # Shorten a URL
-    curl -F'shorten=http://example.com/some/long/url' <a href="{{Request.Host}}">{{Request.Host}}</a>
+    curl -F'shorten=http://example.com/some/long/url' <a href="{{.Request.Host}}">{{.Request.Host}}</a>
 
     # Shorten a URL with a token to delete it later
-    curl -F'shorten=http://example.com/some/long/url' -F'deleteToken=' <a href="{{Request.Host}}">{{Request.Host}}</a>
+    curl -F'shorten=http://example.com/some/long/url' -F'deleteToken=' <a href="{{.Request.Host}}">{{.Request.Host}}</a>
 </pre>
 {{end}}

assets/templates/txt/index.txt.tmpl

@@ -7,10 +7,10 @@ the command line.
 ## USAGE
 
     # Upload a file
-    curl -F'file=@yourfile.png' {{Request.Host}}
+    curl -F'file=@yourfile.png' {{.Request.Host}}
 
     # Shorten a URL
-    curl -F'shorten=http://example.com/some/long/url' {{Request.Host}}
+    curl -F'shorten=http://example.com/some/long/url' {{.Request.Host}}
 
     # Shorten a URL with a token to delete it later
-    curl -F'shorten=http://example.com/some/long/url' -F'deleteToken=' {{Request.Host}}
+    curl -F'shorten=http://example.com/some/long/url' -F'deleteToken=' {{.Request.Host}}

go.mod

@@ -4,6 +4,7 @@ go 1.12
 
 require (
 	github.com/go-bindata/go-bindata v3.1.2+incompatible // indirect
+	github.com/gorilla/handlers v1.4.2
 	github.com/gorilla/mux v1.7.3
 	github.com/pkg/errors v0.8.1
 	github.com/prometheus/client_golang v1.1.0

go.sum

@@ -18,6 +18,8 @@ github.com/golang/protobuf v1.3.2 h1:6nsPYzhq5kReh6QImI3k5qWzO4PEbvbIW2cwSfR/6xs
 github.com/golang/protobuf v1.3.2/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
 github.com/google/go-cmp v0.3.0/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
 github.com/google/gofuzz v1.0.0/go.mod h1:dBl0BpW6vV/+mYPU4Po3pmUjxk6FQPldtuIdl/M65Eg=
+github.com/gorilla/handlers v1.4.2 h1:0QniY0USkHQ1RGCLfKxeNHK9bkDHGRYGNDFBCS+YARg=
+github.com/gorilla/handlers v1.4.2/go.mod h1:Qkdc/uu4tH4g6mTK6auzZ766c4CA0Ng8+o/OAirnOIQ=
 github.com/gorilla/mux v1.7.3 h1:gnP5JzjVOuiZD07fKKToCAOjS0yOpj/qPETTXCCS6hw=
 github.com/gorilla/mux v1.7.3/go.mod h1:1lud6UwP+6orDFRuTfBEV8e9/aOM/c4fVVCaMa2zaAs=
 github.com/json-iterator/go v1.1.6/go.mod h1:+SdeFBvtyEkXs7REEP0seUULqWtbJapLOCVDaaPEHmU=

handlers/handlers.go

@@ -84,8 +84,7 @@ func viewPasteHandlerInner(w http.ResponseWriter, r *http.Request, flags viewPas
 		p, err = getPaste(tx, key)
 		return err
 	}); err != nil {
-		log.Printf("error: %v\n", err)
+		panic(err)
-		renderInternalServerError(w, r, err)
 		return
 	}
 	if p == nil {
@@ -124,9 +123,7 @@ func viewPasteHandlerInner(w http.ResponseWriter, r *http.Request, flags viewPas
 			rawurl := string(p.Content)
 			urlParse, err := url.Parse(rawurl)
 			if err != nil {
-				log.Printf("error: invalid URL ('%v') in database for key '%v': %v\n", rawurl, p.Key, err)
+				panic(errors.Wrapf(err, "invalid URL ('%v') in database for key '%v'", rawurl, p.Key))
-				renderInternalServerError(w, r, "invalid url in database")
-				return
 			}
 			http.Redirect(w, r, urlParse.String(), http.StatusSeeOther)
 		}
@@ -134,17 +131,13 @@ func viewPasteHandlerInner(w http.ResponseWriter, r *http.Request, flags viewPas
 	case stateDeleted:
 		renderError(w, r, http.StatusGone, "paste has been deleted")
 	default:
-		log.Printf("error: invalid paste.State (%v) for key '%v'\n", p.State, p.Key)
+		panic(errors.Errorf("invalid paste.State (%v) for key '%v'", p.State, p.Key))
-		msg := fmt.Sprintf("internal server error: invalid paste.State (%v\n)", p.State)
-		renderInternalServerError(w, r, msg)
 	}
 }
 
 func newPasteHandler(w http.ResponseWriter, r *http.Request) {
 	if err := r.ParseMultipartForm(50 * 1000 * 1000); err != nil {
-		log.Printf("error: %v\n", err)
+		panic(err)
-		renderInternalServerError(w, r, err)
-		return
 	}
 
 	// Determine what kind of post this is, currently only `shorten=...`
@@ -189,9 +182,7 @@ func newRedirectPasteHandler(w http.ResponseWriter, r *http.Request) {
 		paste, err = shortenURL(tx, userURL)
 		return err
 	}); err != nil {
-		log.Printf("error: %v\n", err)
+		panic(err)
-		renderInternalServerError(w, r, err)
-		return
 	}
 	data := map[string]interface{}{"Paste": paste}
 	render(w, r, "newRedirectPasteSuccess", data)

handlers/router.go

@@ -1,6 +1,7 @@
 package handlers
 
 import (
+	"fmt"
 	"log"
 	"net/http"
 	"time"
@@ -8,9 +9,29 @@ import (
 	"github.com/gorilla/mux"
 )
 
+func recoveryMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		defer func() {
+			defer func() {
+				if err := recover(); err != nil {
+					log.Printf("error: panic while recovering from another panic: %v\n", err)
+					fmt.Fprintf(w, "internal server error: %v\n", err)
+				}
+			}()
+
+			if err := recover(); err != nil {
+				log.Printf("error: %v\n", err)
+				renderInternalServerError(w, r, err)
+			}
+		}()
+		next.ServeHTTP(w, r)
+	})
+}
+
 func StartMainServer() {
 	// Initialize Gorilla router
 	router := mux.NewRouter()
+	router.Use(recoveryMiddleware)
 	router.HandleFunc("/", indexGetHandler).Methods("GET")
 	router.HandleFunc("/", newPasteHandler).Methods("POST")
 	router.HandleFunc("/{key:[A-Za-z0-9-_]{4,}}", viewPasteHandler).Methods("GET")

handlers/views.go

@@ -40,14 +40,20 @@ func init() {
 	for _, tmplPath := range AssetNames() {
 		if mustMatch("templates/txt/*.txt.tmpl", tmplPath) {
 			base := text.Must(textBaseTemplate.Clone())
-			tmpl := text.Must(base.Parse(string(MustAsset(tmplPath))))
+			tmpl, err := base.Parse(string(MustAsset(tmplPath)))
+			if err != nil {
+				panic(errors.Wrapf(err, "parsing %v", tmplPath))
+			}
 			tmplName := strings.TrimSuffix(filepath.Base(tmplPath), ".txt.tmpl")
 			textTemplates[tmplName] = tmpl
 			continue
 		}
 		if mustMatch("templates/html/*.html.tmpl", tmplPath) {
 			base := html.Must(htmlBaseTemplate.Clone())
-			tmpl := html.Must(base.Parse(string(MustAsset(tmplPath))))
+			tmpl, err := base.Parse(string(MustAsset(tmplPath)))
+			if err != nil {
+				panic(errors.Wrapf(err, "parsing %v", tmplPath))
+			}
 			tmplName := strings.TrimSuffix(filepath.Base(tmplPath), ".html.tmpl")
 			htmlTemplates[tmplName] = tmpl
 			continue