accesslog: NEW log broker and many more features

some fixes about context clone, fix response recorder concurrent access, fix reload views with only ParseTemplate and more

HISTORY.md

@@ -364,6 +364,10 @@ Response:
 
 Other Improvements:
 
+- Add a `Response() *http.Response` to the Response Recorder.
+- Fix Response Recorder `Flush` when transfer-encoding is `chunked`.
+- Fix Response Recorder `Clone` concurrent access afterwards.
+
 - Add a `ParseTemplate` method on view engines to manually parse and add a template from a text as [requested](https://github.com/kataras/iris/issues/1617). [Examples](https://github.com/kataras/iris/tree/master/_examples/view/parse-template).
 - Full `http.FileSystem` interface support for all **view** engines as [requested](https://github.com/kataras/iris/issues/1575). The first argument of the functions(`HTML`, `Blocks`, `Pug`, `Amber`, `Ace`, `Jet`, `Django`, `Handlebars`) can now be either a directory of `string` type (like before) or a value which completes the `http.FileSystem` interface. The `.Binary` method of all view engines was removed: pass the go-bindata's latest version `AssetFile()` exported function as the first argument instead of string.
 
@@ -614,7 +618,7 @@ New Context Methods:
 - `Context.ViewEngine(ViewEngine)` to set a view engine on-fly for the current chain of handlers, responsible to render templates through `ctx.View`. [Example](_examples/view/context-view-engine).
 - `Context.SetErr(error)` and `Context.GetErr() error` helpers.
 - `Context.CompressWriter(bool) error` and `Context.CompressReader(bool) error`.
-- `Context.Clone() Context` returns a copy of the Context.
+- `Context.Clone() Context` returns a copy of the Context safe for concurrent access.
 - `Context.IsCanceled() bool` reports whether the request has been canceled by the client.
 - `Context.IsSSL() bool` reports whether the request is under HTTPS SSL (New `Configuration.SSLProxyHeaders` and `HostProxyHeaders` fields too).
 - `Context.CompressReader(enable bool)` method and `iris.CompressReader` middleware to enable future request read body calls to decompress data, [example](_examples/compression/main.go).

_examples/README.md

@@ -72,7 +72,8 @@
     * [Sitemap](routing/sitemap/main.go)
 * Logging
     * [Request Logger](logging/request-logger/main.go)
-        * [Log requests and responses to access.log](logging/request-logger/accesslog)
+        * [AccessLog: log request & response and more](logging/request-logger/accesslog)
+        * [AccessLog: listen to logs and render them](logging/request-logger/accesslog-broker/main.go)
         * [Log Requests to a JSON File](logging/request-logger/request-logger-file-json/main.go) 
     * [Application File Logger](logging/file-logger/main.go)
     * [Application JSON Logger](logging/json-logger/main.go)

_examples/logging/request-logger/accesslog-broker/main.go

@@ -0,0 +1,75 @@
+package main
+
+import (
+	"github.com/kataras/iris/v12"
+	"github.com/kataras/iris/v12/middleware/accesslog"
+)
+
+func main() {
+	/*
+		On this example we will make use of the logs broker.
+		A handler will listen for any incoming logs and render
+		those logs as chunks of JSON to the client (e.g. browser) at real-time.
+		Note that this ^ can be done with Server-Sent Events but for the
+		sake of the example we'll do it using Transfer-Encoding: chunked.
+	*/
+
+	ac := accesslog.File("./access.log")
+	ac.TimeFormat = "2006-01-02 15:04:05"
+	ac.Async = true
+	broker := ac.Broker() // <- IMPORTANT
+
+	app := iris.New()
+	app.UseRouter(ac.Handler)
+
+	app.Get("/", indexHandler)
+	app.Get("/profile/{username}", profileHandler)
+	app.Post("/read_body", readBodyHandler)
+	app.Get("/logs", logsHandler(broker))
+
+	// http://localhost:8080/logs to see the logs at real-time.
+	app.Listen(":8080")
+}
+
+func indexHandler(ctx iris.Context) {
+	ctx.HTML("<h1>Index</h1>")
+}
+
+func profileHandler(ctx iris.Context) {
+	username := ctx.Params().Get("username")
+	ctx.HTML("Hello, <strong>%s</strong>!", username)
+}
+
+func readBodyHandler(ctx iris.Context) {
+	var request interface{}
+	if err := ctx.ReadBody(&request); err != nil {
+		ctx.StopWithPlainError(iris.StatusBadRequest, err)
+		return
+	}
+
+	ctx.JSON(iris.Map{"message": "OK", "data": request})
+}
+
+func logsHandler(b *accesslog.Broker) iris.Handler {
+	return func(ctx iris.Context) {
+		accesslog.Skip(ctx) // skip logging this handler, optionally.
+
+		logs := b.NewListener() // <- IMPORTANT
+
+		ctx.Header("Transfer-Encoding", "chunked")
+		notifyClose := ctx.Request().Context().Done()
+		for {
+			select {
+			case <-notifyClose:
+				b.CloseListener(logs) // <- IMPORTANT
+
+				err := ctx.Request().Context().Err()
+				ctx.Application().Logger().Infof("Listener closed [%v], loop end.", err)
+				return
+			case log := <-logs: // <- IMPORTANT
+				ctx.JSON(log, iris.JSON{Indent: "  ", UnescapeHTML: true})
+				ctx.ResponseWriter().Flush()
+			}
+		}
+	}
+}

_examples/view/parse-template/amber/main.go

@@ -11,6 +11,7 @@ func main() {
 	if err != nil {
 		panic(err)
 	}
+	e.Reload(true)
 
 	app := iris.New()
 	app.RegisterView(e)

_examples/view/parse-template/django/main.go

@@ -11,6 +11,7 @@ func main() {
 	if err != nil {
 		panic(err)
 	}
+	e.Reload(true)
 
 	app := iris.New()
 	app.RegisterView(e)

_examples/view/parse-template/handlebars/main.go

@@ -9,6 +9,7 @@ func main() {
 			return "Hello, " + name + "!"
 		},
 	})
+	e.Reload(true)
 
 	app := iris.New()
 	app.RegisterView(e)

_examples/view/parse-template/jet/main.go

@@ -17,6 +17,7 @@ func main() {
 	if err != nil {
 		panic(err)
 	}
+	e.Reload(true)
 
 	app := iris.New()
 	app.RegisterView(e)

_examples/view/parse-template/main.go

@@ -19,6 +19,7 @@ func main() {
 			return "Hello, " + name + "!"
 		},
 	})
+	e.Reload(true)
 
 	app := iris.New()
 	app.RegisterView(e)

context/response_recorder.go

@@ -59,7 +59,7 @@ func (w *ResponseRecorder) Naive() http.ResponseWriter {
 // prepares itself, the response recorder, to record and send response to the client.
 func (w *ResponseRecorder) BeginRecord(underline ResponseWriter) {
 	w.ResponseWriter = underline
-	w.headers = underline.Header()
+	w.headers = underline.Header().Clone()
 	w.result = nil
 	w.ResetBody()
 }
@@ -67,8 +67,8 @@ func (w *ResponseRecorder) BeginRecord(underline ResponseWriter) {
 // EndResponse is auto-called when the whole client's request is done,
 // releases the response recorder and its underline ResponseWriter.
 func (w *ResponseRecorder) EndResponse() {
-	releaseResponseRecorder(w)
 	w.ResponseWriter.EndResponse()
+	releaseResponseRecorder(w)
 }
 
 // Write Adds the contents to the body reply, it writes the contents temporarily
@@ -99,6 +99,12 @@ func (w *ResponseRecorder) Write(contents []byte) (int, error) {
 	return len(contents), nil
 }
 
+// Header returns the temporary header map that, on flush response,
+// will be sent by the underline's ResponseWriter's WriteHeader method.
+func (w *ResponseRecorder) Header() http.Header {
+	return w.headers
+}
+
 // SetBody overrides the body and sets it to a slice of bytes value.
 func (w *ResponseRecorder) SetBody(b []byte) {
 	w.chunks = b
@@ -122,7 +128,7 @@ func (w *ResponseRecorder) ResetBody() {
 
 // ResetHeaders sets the headers to the underline's response writer's headers, may empty.
 func (w *ResponseRecorder) ResetHeaders() {
-	w.headers = w.ResponseWriter.Header()
+	w.headers = w.ResponseWriter.Header().Clone()
 }
 
 // ClearHeaders clears all headers, both temp and underline's response writer.
@@ -130,7 +136,7 @@ func (w *ResponseRecorder) ClearHeaders() {
 	w.headers = http.Header{}
 	h := w.ResponseWriter.Header()
 	for k := range h {
-		h[k] = nil
+		delete(h, k)
 	}
 }
 
@@ -151,12 +157,9 @@ func (w *ResponseRecorder) FlushResponse() {
 	// copy the headers to the underline response writer
 	if w.headers != nil {
 		h := w.ResponseWriter.Header()
-
-		for k, values := range w.headers {
-			h[k] = nil
-			for i := range values {
-				h.Add(k, values[i])
-			}
+		// note: we don't reset the current underline's headers.
+		for k, v := range w.headers {
+			h[k] = v
 		}
 	}
 
@@ -184,8 +187,15 @@ func (w *ResponseRecorder) FlushResponse() {
 // it copies the header, status code, headers and the beforeFlush finally  returns a new ResponseRecorder
 func (w *ResponseRecorder) Clone() ResponseWriter {
 	wc := &ResponseRecorder{}
-	wc.headers = w.headers
-	wc.chunks = w.chunks[0:]
+
+	// copy headers.
+	wc.headers = w.headers.Clone()
+
+	// copy body.
+	chunksCopy := make([]byte, len(w.chunks))
+	copy(chunksCopy, w.chunks)
+	wc.chunks = chunksCopy
+
 	if resW, ok := w.ResponseWriter.(*responseWriter); ok {
 		wc.ResponseWriter = &responseWriter{
 			ResponseWriter: resW.ResponseWriter,
@@ -252,6 +262,23 @@ func (w *ResponseRecorder) CopyTo(res ResponseWriter) {
 
 // Flush sends any buffered data to the client.
 func (w *ResponseRecorder) Flush() {
+	// This fixes response recorder when chunked + Flush is used.
+	if w.headers.Get("Transfer-Encoding") == "chunked" {
+		if w.Written() == NoWritten {
+			if len(w.headers) > 0 {
+				h := w.ResponseWriter.Header()
+				// note: we don't reset the current underline's headers.
+				for k, v := range w.headers {
+					h[k] = v
+				}
+			}
+		}
+
+		if len(w.chunks) > 0 {
+			w.ResponseWriter.Write(w.chunks)
+		}
+	}
+
 	w.ResponseWriter.Flush()
 	w.ResetBody()
 }
@@ -308,9 +335,9 @@ func (w *ResponseRecorder) Result() *http.Response { // a modified copy of net/h
 
 	headers := w.headers.Clone()
 
-	for k, v := range w.ResponseWriter.Header() {
-		headers[k] = v
-	}
+	// for k, v := range w.ResponseWriter.Header() {
+	// 	headers[k] = v
+	// }
 	/*
 		dateFound := false
 		for k := range headers {

middleware/accesslog/accesslog.go

@@ -18,22 +18,35 @@ func init() {
 	context.SetHandlerName("iris/middleware/accesslog.*", "iris.accesslog")
 }
 
-const accessLogFieldsContextKey = "iris.accesslog.request.fields"
+const (
+	fieldsContextKey  = "iris.accesslog.request.fields"
+	skipLogContextKey = "iris.accesslog.request.skip"
+)
 
 // GetFields returns the accesslog fields for this request.
 // Returns a store which the caller can use to
 // set/get/remove custom log fields. Use its `Set` method.
 func GetFields(ctx iris.Context) (fields *Fields) {
-	if v := ctx.Values().Get(accessLogFieldsContextKey); v != nil {
+	if v := ctx.Values().Get(fieldsContextKey); v != nil {
 		fields = v.(*Fields)
 	} else {
 		fields = new(Fields)
-		ctx.Values().Set(accessLogFieldsContextKey, fields)
+		ctx.Values().Set(fieldsContextKey, fields)
 	}
 
 	return
 }
 
+// Skip called when a specific route should be skipped from the logging process.
+// It's an easy to use alternative for iris.NewConditionalHandler.
+func Skip(ctx iris.Context) {
+	ctx.Values().Set(skipLogContextKey, struct{}{})
+}
+
+func shouldSkip(ctx iris.Context) bool {
+	return ctx.Values().Get(skipLogContextKey) != nil
+}
+
 type (
 
 	// Fields is a type alias for memstore.Store, used to set
@@ -137,6 +150,7 @@ type AccessLog struct {
 	// order of registration so use a slice and
 	// take the field key from the extractor itself.
 	formatter Formatter
+	broker    *Broker
 }
 
 // New returns a new AccessLog value with the default values.
@@ -179,6 +193,28 @@ func File(path string) *AccessLog {
 	return New(f)
 }
 
+// Broker creates or returns the broker.
+// Use its `NewListener` and `CloseListener`
+// to listen and unlisten for incoming logs.
+//
+// Should be called before serve-time.
+func (ac *AccessLog) Broker() *Broker {
+	ac.mu.Lock()
+	if ac.broker == nil {
+		ac.broker = newBroker()
+		// atomic.StoreUint32(&ac.brokerActive, 1)
+	}
+	ac.mu.Unlock()
+	return ac.broker
+}
+
+// func (ac *AccessLog) isBrokerActive() bool { // see `Print` method.
+// 	return atomic.LoadUint32(&ac.brokerActive) > 0
+// }
+// ^ No need, we declare that the Broker should be called
+// before serve-time. Let's respect our comment
+// and don't try to make it safe for write and read concurrent access.
+
 // Write writes to the log destination.
 // It completes the io.Writer interface.
 // Safe for concurrent use.
@@ -294,6 +330,11 @@ func (ac *AccessLog) shouldReadResponseBody() bool {
 // defer ac.Close()
 // app.UseRouter(ac.Handler)
 func (ac *AccessLog) Handler(ctx *context.Context) {
+	if shouldSkip(ctx) { // usage: another middleware before that one disables logging.
+		ctx.Next()
+		return
+	}
+
 	var (
 		startTime = time.Now()
 		// Store some values, as future handler chain
@@ -314,13 +355,17 @@ func (ac *AccessLog) Handler(ctx *context.Context) {
 
 	// Set the fields context value so they can be modified
 	// on the following handlers chain. Same as `AddFields` but per-request.
-	// ctx.Values().Set(accessLogFieldsContextKey, new(Fields))
+	// ctx.Values().Set(fieldsContextKey, new(Fields))
 	// No need ^ The GetFields will set it if it's missing.
 	// So we initialize them whenever, and if, asked.
 
 	// Proceed to the handlers chain.
 	ctx.Next()
 
+	if shouldSkip(ctx) { // normal flow, we can get the context by executing the handler first.
+		return
+	}
+
 	latency := time.Since(startTime)
 	if ac.Async {
 		ctxCopy := ctx.Clone()
@@ -435,7 +480,7 @@ func (ac *AccessLog) after(ctx *context.Context, lat time.Duration, method, path
 
 // Print writes a log manually.
 // The `Handler` method calls it.
-func (ac *AccessLog) Print(ctx *context.Context, latency time.Duration, timeFormat string, code int, method, path, reqBody, respBody string, bytesReceived, bytesSent int, params *context.RequestParams, query []memstore.StringEntry, fields []memstore.Entry) error {
+func (ac *AccessLog) Print(ctx *context.Context, latency time.Duration, timeFormat string, code int, method, path, reqBody, respBody string, bytesReceived, bytesSent int, params *context.RequestParams, query []memstore.StringEntry, fields []memstore.Entry) (err error) {
 	var now time.Time
 
 	if ac.Clock != nil {
@@ -444,7 +489,7 @@ func (ac *AccessLog) Print(ctx *context.Context, latency time.Duration, timeForm
 		now = time.Now()
 	}
 
-	if f := ac.formatter; f != nil {
+	if hasFormatter, hasBroker := ac.formatter != nil, ac.broker != nil; hasFormatter || hasBroker {
 		log := &Log{
 			Logger:        ac,
 			Now:           now,
@@ -464,12 +509,21 @@ func (ac *AccessLog) Print(ctx *context.Context, latency time.Duration, timeForm
 			Ctx:           ctx, // ctx should only be used here, it may be nil on testing.
 		}
 
-		if err := f.Format(log); err != nil {
-			return err
+		var handled bool
+		if hasFormatter {
+			handled, err = ac.formatter.Format(log)
+			if err != nil {
+				return
+			}
 		}
 
-		// OK, it's handled, exit now.
-		return nil
+		if hasBroker { // after Format, it may want to customize the log's fields.
+			ac.broker.notify(log)
+		}
+
+		if handled {
+			return // OK, it's handled, exit now.
+		}
 	}
 
 	// url parameters, path parameters and custom fields separated by space,
@@ -478,7 +532,7 @@ func (ac *AccessLog) Print(ctx *context.Context, latency time.Duration, timeForm
 
 	// the number of separators are the same, in order to be easier
 	// for 3rd-party programs to read the result log file.
-	_, err := fmt.Fprintf(ac, "%s|%s|%s|%s|%s|%d|%s|%s|%s|%s|\n",
+	_, err = fmt.Fprintf(ac, "%s|%s|%s|%s|%s|%d|%s|%s|%s|%s|\n",
 		now.Format(timeFormat),
 		latency,
 		method,
@@ -491,5 +545,5 @@ func (ac *AccessLog) Print(ctx *context.Context, latency time.Duration, timeForm
 		respBody,
 	)
 
-	return err
+	return
 }

middleware/accesslog/broker.go

@@ -0,0 +1,90 @@
+package accesslog
+
+// LogChan describes the log channel.
+// See `Broker` for details.
+type LogChan chan *Log
+
+// A Broker holds the active listeners,
+// incoming logs on its Notifier channel
+// and broadcast event data to all registered listeners.
+//
+// Exports the `NewListener` and `CloseListener` methods.
+type Broker struct {
+	// Logs are pushed to this channel
+	// by the main events-gathering `run` routine.
+	Notifier LogChan
+
+	// NewListener action.
+	newListeners chan LogChan
+
+	// CloseListener action.
+	closingListeners chan chan *Log
+
+	// listeners store.
+	listeners map[LogChan]bool
+}
+
+// newBroker returns a new broker factory.
+func newBroker() *Broker {
+	b := &Broker{
+		Notifier:         make(LogChan, 1),
+		newListeners:     make(chan LogChan),
+		closingListeners: make(chan chan *Log),
+		listeners:        make(map[LogChan]bool),
+	}
+
+	// Listens and Broadcasts events.
+	go b.run()
+
+	return b
+}
+
+// run listens on different channels and act accordingly.
+func (b *Broker) run() {
+	for {
+		select {
+		case s := <-b.newListeners:
+			// A new channel has started to listen.
+			b.listeners[s] = true
+
+		case s := <-b.closingListeners:
+			// A listener has dettached.
+			// Stop sending them the logs.
+			delete(b.listeners, s)
+
+		case log := <-b.Notifier:
+			// A new log sent by the logger.
+			// Send it to all active listeners.
+			for clientMessageChan := range b.listeners {
+				clientMessageChan <- log
+			}
+		}
+	}
+}
+
+// notify sends the "log" to all active listeners.
+func (b *Broker) notify(log *Log) {
+	b.Notifier <- log
+}
+
+// NewListener returns a new log channel listener.
+// The caller SHALL NOT use this to write logs.
+func (b *Broker) NewListener() LogChan {
+	// Each listener registers its own message channel with the Broker's connections registry.
+	logs := make(LogChan)
+	// Signal the broker that we have a new listener.
+	b.newListeners <- logs
+	return logs
+}
+
+// CloseListener removes the "ln" listener from the active listeners.
+func (b *Broker) CloseListener(ln LogChan) {
+	b.closingListeners <- ln
+}
+
+// As we cant export a read-only and pass it as closing client
+// we will return a read-write channel on NewListener and add a note that the user
+// should NOT send data back to the channel, its use is read-only.
+// func (b *Broker) CloseListener(ln <-chan *Log) {
+// 	b.closingListeners <- ln
+// }

middleware/accesslog/log.go

@@ -34,9 +34,9 @@ type Log struct {
 	// The response status code.
 	Code int `json:"code"`
 	// Sorted URL Query arguments.
-	Query []memstore.StringEntry `json:"query"`
+	Query []memstore.StringEntry `json:"query,omitempty"`
 	// Dynamic path parameters.
-	PathParams []memstore.Entry `json:"params"`
+	PathParams []memstore.Entry `json:"params,omitempty"`
 	// Fields any data information useful to represent this Log.
 	Fields []memstore.Entry `json:"fields,omitempty"`
 
@@ -127,15 +127,17 @@ func parseRequestValues(code int, pathParams *context.RequestParams, query []mem
 
 // Formatter is responsible to print a Log to the accesslog's writer.
 type Formatter interface {
+	// SetOutput should inject the accesslog's direct output,
+	// if this "dest" is used then the Formatter
+	// should manually control its concurrent use.
+	SetOutput(dest io.Writer)
 	// Format should print the Log.
 	// Returns nil error on handle successfully,
 	// otherwise the log will be printed using the default formatter
 	// and the error will be printed to the Iris Application's error log level.
-	Format(log *Log) error
-	// SetWriter should inject the accesslog's direct output,
-	// if this "dest" is used then the Formatter
-	// should manually control its concurrent use.
-	SetOutput(dest io.Writer)
+	// Should return true if this handled the logging, otherwise false to
+	// continue with the default print format.
+	Format(log *Log) (bool, error)
 }
 
 var (
@@ -169,12 +171,12 @@ func (f *JSON) SetOutput(dest io.Writer) {
 // Format prints the logs in JSON format.
 // Writes to the destination directly,
 // locks on each Format call.
-func (f *JSON) Format(log *Log) error {
+func (f *JSON) Format(log *Log) (bool, error) {
 	f.mu.Lock()
 	err := f.enc.Encode(log)
 	f.mu.Unlock()
 
-	return err
+	return true, err
 }
 
 // Template is a Formatter.
@@ -213,7 +215,7 @@ func (f *Template) SetOutput(dest io.Writer) {
 const defaultTmplText = "{{.Now.Format .TimeFormat}}|{{.Latency}}|{{.Method}}|{{.Path}}|{{.RequestValuesLine}}|{{.Code}}|{{.BytesReceivedLine}}|{{.BytesSentLine}}|{{.Request}}|{{.Response}}|\n"
 
 // Format prints the logs in text/template format.
-func (f *Template) Format(log *Log) error {
+func (f *Template) Format(log *Log) (bool, error) {
 	var err error
 
 	// A template may be executed safely in parallel, although if parallel
@@ -226,5 +228,5 @@ func (f *Template) Format(log *Log) error {
 	}
 	f.mu.Unlock()
 
-	return err
+	return true, err
 }

view/fs.go

@@ -110,6 +110,11 @@ type noOpFS struct{}
 
 func (fs noOpFS) Open(name string) (http.File, error) { return nil, nil }
 
+func isNoOpFS(fs http.FileSystem) bool {
+	_, ok := fs.(noOpFS)
+	return ok
+}
+
 // fixes: "invalid character in file path"
 // on amber engine (it uses the virtual fs directly
 // and it uses filepath instead of the path package...).

view/html.go

@@ -34,9 +34,16 @@ type HTMLEngine struct {
 	//
 	middleware  func(name string, contents []byte) (string, error)
 	Templates   *template.Template
+	customCache []customTmp // required to load them again if reload is true.
 	//
 }
 
+type customTmp struct {
+	name     string
+	contents []byte
+	funcs    template.FuncMap
+}
+
 var (
 	_ Engine       = (*HTMLEngine)(nil)
 	_ EngineFuncer = (*HTMLEngine)(nil)
@@ -215,6 +222,17 @@ func (s *HTMLEngine) Funcs(funcMap template.FuncMap) *HTMLEngine {
 //
 // Returns an error if something bad happens, caller is responsible to handle that.
 func (s *HTMLEngine) Load() error {
+	s.rmu.Lock()
+	defer s.rmu.Unlock()
+
+	return s.load()
+}
+
+func (s *HTMLEngine) load() error {
+	if err := s.reloadCustomTemplates(); err != nil {
+		return err
+	}
+
 	return walk(s.fs, s.rootDir, func(path string, info os.FileInfo, err error) error {
 		if info == nil || info.IsDir() {
 			return nil
@@ -231,15 +249,35 @@ func (s *HTMLEngine) Load() error {
 			return fmt.Errorf("%s: %w", path, err)
 		}
 
-		return s.ParseTemplate(path, buf, nil)
+		return s.parseTemplate(path, buf, nil)
 	})
 }
 
+func (s *HTMLEngine) reloadCustomTemplates() error {
+	for _, tmpl := range s.customCache {
+		if err := s.parseTemplate(tmpl.name, tmpl.contents, tmpl.funcs); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
 // ParseTemplate adds a custom template to the root template.
 func (s *HTMLEngine) ParseTemplate(name string, contents []byte, funcs template.FuncMap) (err error) {
 	s.rmu.Lock()
 	defer s.rmu.Unlock()
 
+	s.customCache = append(s.customCache, customTmp{
+		name:     name,
+		contents: contents,
+		funcs:    funcs,
+	})
+
+	return s.parseTemplate(name, contents, funcs)
+}
+
+func (s *HTMLEngine) parseTemplate(name string, contents []byte, funcs template.FuncMap) (err error) {
 	s.initRootTmpl()
 
 	name = strings.TrimPrefix(name, "/")
@@ -270,6 +308,7 @@ func (s *HTMLEngine) initRootTmpl() { // protected by the caller.
 		// the root template should be the same,
 		// no matter how many reloads as the
 		// following unexported fields cannot be modified.
+		// However, on reload they should be cleared otherwise we get an error.
 		s.Templates = template.New(s.rootDir)
 		s.Templates.Delims(s.left, s.right)
 	}
@@ -349,7 +388,14 @@ func (s *HTMLEngine) runtimeFuncsFor(t *template.Template, name string, binding
 func (s *HTMLEngine) ExecuteWriter(w io.Writer, name string, layout string, bindingData interface{}) error {
 	// re-parse the templates if reload is enabled.
 	if s.reload {
-		if err := s.Load(); err != nil {
+		s.rmu.Lock()
+		defer s.rmu.Unlock()
+
+		s.Templates = nil
+		// we lose the templates parsed manually, so store them when it's called
+		// in order for load to take care of them too.
+
+		if err := s.load(); err != nil {
 			return err
 		}
 	}

view/jet.go

@@ -178,9 +178,6 @@ func (s *JetEngine) AddVar(key string, value interface{}) {
 // not safe concurrent access across clients, use it only on development state.
 func (s *JetEngine) Reload(developmentMode bool) *JetEngine {
 	s.developmentMode = developmentMode
-	if s.Set != nil {
-		s.Set.SetDevelopmentMode(developmentMode)
-	}
 	return s
 }
 
@@ -215,7 +212,6 @@ func (l *jetLoader) Exists(name string) (string, bool) {
 // Load should load the templates from a physical system directory or by an embedded one (assets/go-bindata).
 func (s *JetEngine) Load() error {
 	s.initSet()
-
 	// Note that, unlike the rest of template engines implementations,
 	// we don't call the Set.GetTemplate to parse the templates,
 	// we let it to the jet template parser itself which does that at serve-time and caches each template by itself.
@@ -236,7 +232,12 @@ func (s *JetEngine) initSet() {
 	s.mu.Lock()
 	if s.Set == nil {
 		s.Set = jet.NewHTMLSetLoader(s.loader)
-		s.Set.SetDevelopmentMode(s.developmentMode)
+		if s.developmentMode && !isNoOpFS(s.fs) {
+			// this check is made to avoid jet's fs lookup on noOp fs (nil passed by the developer).
+			// This can be produced when nil fs passed
+			// and only `ParseTemplate` is used.
+			s.Set.SetDevelopmentMode(true)
+		}
 
 		if s.vars != nil {
 			for key, value := range s.vars {