http: add Engine.OnRequest

nbhttp/engine.go

@@ -160,6 +160,15 @@ type Config struct {
 	// Handler sets HTTP handler for Engine.
 	Handler http.Handler
 
+	// `OnRequest` sets HTTP handler which will be called before `Handler.ServeHTTP`.
+	//
+	// A `Request` is pushed into a task queue and waits to be executed by the goroutine pool by default, which means the `Request`
+	// may not be executed at once and may wait for long to be executed: if the client-side supports `pipeline` and the previous
+	// `Requests` are handled for long. In some scenarios, we need to know when the `Request` is received, then we can control and
+	// customize whether we should drop the task or record the real processing time for the `Request`. That is what this func should
+	// be used for.
+	OnRequest http.HandlerFunc
+
 	// ServerExecutor sets the executor for data reading callbacks.
 	ServerExecutor func(f func())
 

nbhttp/processor.go

@@ -240,6 +240,10 @@ func (p *ServerProcessor) OnComplete(parser *Parser) {
 	}
 
 	response := NewResponse(parser, request)
+
+	if engine.OnRequest != nil {
+		engine.OnRequest(response, request)
+	}
 	if !parser.Execute(func() {
 		engine.Handler.ServeHTTP(response, request)
 		p.flushResponse(parser, response)