Feature/download router (#15)

* Add Download file helper in response and a express.Router instance based app.use()

* update readme

Author: DronRathore

README.md

@@ -31,6 +31,29 @@ func main (){
   app.Start("8080")
 }
 ```
+
+__Note__: You can also adhoc an ```express.Router()``` instance too much like it is done in expressjs
+```go
+package main
+import (
+  express "github.com/DronRathore/goexpress"
+  request "github.com/DronRathore/goexpress/request"
+  response "github.com/DronRathore/goexpress/response"
+)
+var LibRoutes = func (){
+  // create a new Router instance which works in similar way as app.Get/Post etc
+  var LibRouter = express.Router()
+  LibRouter.Get("/lib/:api_version", func(req *request.Request, res *response.Response, next func()){
+    res.Json(req.Params["api_version"])
+  })
+  return *LibRoutes
+}() // immediate invocation
+func main(){
+  var app = express.Express()
+  app.Use(LibRoutes) // attaches the Library Routes
+  app.Start("8080")
+}
+```
 ## Middleware
 You can write custom middlewares, wrappers in the similar fashion. Middlewares can be used to add websocket upgradation lib, session handling lib, static assets server handler
 ```go
@@ -86,6 +109,15 @@ func main (){
   app.Start("8080")
 }
 ```
+__Note__: You can now also send an auto downloadable file too using ```res.Download``` api
+```go
+/*
+  @params:
+    path: Full path to the file in local machine
+    filename: The name to be sent to the client
+*/
+res.Download(path string, filename string)
+```
 
 ## Post Body
 ```go

express.go

@@ -121,11 +121,18 @@ func (e *express) Delete(url string, middleware router.Middleware) *express{
 }
 
 // Extension to provide Router.Use functionality
-func (e *express) Use(middleware router.Middleware) *express{
+func (e *express) Use(middleware interface{}) *express{
 	e.router.Use(middleware)
 	return e
 }
 
+// Returns a new instance of express Router
+func Router() *router.Router {
+	var route *router.Router = &router.Router{}
+	route.Init()
+	return route;
+}
+
 // Sets global app properties that can be accessed under express struct
 func (e *express) SetProp(key string, value interface{}) *express{
 	e.properties[key] = value

response/response.go

@@ -222,6 +222,17 @@ func (res *Response) SendFile(url string, noCache bool) bool {
 	<-channel
 	return true
 }
+// Send a download file to the client
+func (res *Response) Download(path string, file_name string) bool {
+	if res.Header.CanSendHeader() == true {
+		res.Header.Set("Content-Disposition", "attachment; filename=\"" + file_name+ "\"")
+		return res.SendFile(path, false)
+	} else {
+		log.Print("Cannot Send header after being flushed")
+		res.End()
+		return false
+	}
+}
 
 // Ends a response and drops the connection with client
 func (res *Response) End(){

router/router.go

@@ -71,18 +71,42 @@ func (r* Router) Delete(url string, middleware Middleware) *Router{
 	r.addHandler("delete", false, compileRegex(url), middleware)
 	return r
 }
-
-func (r* Router) Use(middleware Middleware) *Router{
-	var regex = compileRegex("(.*)")
-	// A middleware is for all type of routes
-	r.addHandler("get", true, regex, middleware)
-	r.addHandler("post", true, regex, middleware)
-	r.addHandler("put", true, regex, middleware)
-	r.addHandler("patch", true, regex, middleware)
-	r.addHandler("delete", true, regex, middleware)
+// Router.Use can take a function or a new express.Router() instance as argument
+func (r* Router) Use(middleware interface{}) *Router{
+	router, ok := middleware.(Router)
+	if ok {
+		r.useRouter(router)
+	} else {
+		mware, ok := middleware.(func(request *request.Request, response *response.Response, next func()))
+		if ok {
+			var regex = compileRegex("(.*)")
+			// A middleware is for all type of routes
+			r.addHandler("get", true, regex, mware)
+			r.addHandler("post", true, regex, mware)
+			r.addHandler("put", true, regex, mware)
+			r.addHandler("patch", true, regex, mware)
+			r.addHandler("delete", true, regex, mware)
+		} else {
+			panic("express.Router.Use can only take a function or a Router instance")
+		}
+	}
 	return r
 }
 
+func (r* Router) useRouter(router Router) *Router {
+	routes := router.getRoutes()
+	for route_type, list := range routes {
+		if r.routes[route_type] == nil {
+			r.routes[route_type] = []*Route{}
+		}
+		r.routes[route_type] = append(r.routes[route_type], list...)
+	}
+	return r;
+}
+
+func (r* Router) getRoutes() map[string][]*Route {
+	return r.routes
+}
 // Finds the suitable router for given url and method
 // It returns the middleware if found and a cursor index of array
 func (r* Router) FindNext(index int, method string, url string, request *request.Request) (Middleware, int, bool){