iris/iris.go

// Package iris provides efficient and well-designed toolbox with robust set of features to
// create your own perfect high performance web application
// with unlimited portability using the Go Programming Language.
//
// For middleware, template engines, response engines, sessions, websockets, mails, subdomains,
// dynamic subdomains, routes, party of subdomains & routes and more
//
// visit https://docs.iris-go.com
package iris

import (
	"fmt"
	"io"
	"log"
	"net"
	"net/http"
	"net/url"
	"os"
	"os/signal"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/geekypanda/httpcache"
	"github.com/kataras/go-errors"
	"github.com/kataras/go-fs"
	"github.com/kataras/go-serializer"
	"github.com/kataras/go-sessions"
)

const (
	// Version is the current version number of the Iris web framework
	Version = "6.2.0"

	banner = `         _____      _
        |_   _|    (_)
          | |  ____ _  ___
          | | | __|| |/ __|
         _| |_| |  | |\__ \
        |_____|_|  |_||___/ ` + Version + ` `
)

// Default is the field which keeps an empty `Framework`
// instance with its default configuration (config can change at runtime).
//
// Use that as `iris.Default.Handle(...)`
// or create a new, ex: `app := iris.New(); app.Handle(...)`
var (
	Default *Framework
	// ResetDefault resets the `.Default`
	// to an empty *Framework with the default configuration.
	//
	// Note: ResetDefault field itself can be setted
	//       to custom function too.
	ResetDefault = func() { Default = New() }
)

func init() {
	ResetDefault()
}

// Framework is our God |\| Google.Search('Greek mythology Iris').
type Framework struct {
	*Router
	policies Policies

	// HTTP Server runtime fields is the iris' defined main server, developer can use unlimited number of servers
	// note: they're available after .Build, and .Serve/Listen/ListenTLS/ListenLETSENCRYPT/ListenUNIX
	ln             net.Listener
	closedManually bool

	once      sync.Once
	Config    *Configuration
	sessions  sessions.Sessions
	Websocket *WebsocketServer
}

var defaultGlobalLoggerOuput = log.New(os.Stdout, "[iris] ", log.LstdFlags)

// DevLogger returns a new Logger which prints both ProdMode and DevMode messages
// to the default global logger printer.
//
// Usage: app := iris.New()
//        app.Adapt(iris.DevLogger())
//
// Users can always ignore that and adapt a custom LoggerPolicy,
// which will use your custom printer instead.
func DevLogger() LoggerPolicy {
	return func(mode LogMode, logMessage string) {
		defaultGlobalLoggerOuput.Println(logMessage)
	}
}

// New creates and returns a fresh Iris *Framework instance
// with the default configuration if no 'setters' parameters passed.
func New(setters ...OptionSetter) *Framework {
	s := &Framework{}

	//  +------------------------------------------------------------+
	//  | Set the config passed from setters                         |
	//  | or use the default one                                     |
	//  +------------------------------------------------------------+
	s.Set(setters...)

	{
		//  +------------------------------------------------------------+
		//  | Module Name: Logger                                        |
		//  | On Init: If user didn't adapt a custom loggger then attach |
		//  |           a new logger using log.Logger as printer with    |
		//  |          some default options                              |
		//  +------------------------------------------------------------+

		// The logger policy is never nil and it doesn't defaults to an empty func,
		// instead it defaults to a logger with os.Stdout as the print target which prints
		// ONLY prodction level messages.
		// While in ProdMode Iris logs only panics and fatal errors.
		// You can override the default log policy with app.Adapt(iris.DevLogger())
		//                            or app.Adapt(iris.LoggerPolicy(customLogger))
		// to log both ProdMode and DevMode messages.
		//
		// Note:
		// The decision to not log everything and use middleware for http requests instead of built'n
		// is because I'm using Iris on production so I don't want many logs to my screens
		// while server is running.
		s.Adapt(LoggerPolicy(func(mode LogMode, logMessage string) {
			if mode == ProdMode {
				defaultGlobalLoggerOuput.Println(logMessage)
			}
		}))

	}

	//  +------------------------------------------------------------+
	//  |                                                            |
	//  | Please take a look at the policy.go file first.            |
	//  | The EventPolicy contains all the necessary information     |
	//  | user should know about the framework's flow.               |
	//  |                                                            |
	//  +------------------------------------------------------------+

	//  +------------------------------------------------------------+
	//  | On Boot: Set the VHost and VScheme config fields           |
	//  |           based on the net.Listener which (or not)         |
	//  |           setted on Serve and Listen funcs.                |
	//  |                                                            |
	//  |           It's the only pre-defined Boot event because of  |
	//  |           any user's custom 'Build' events should know     |
	//  |           the Host of the server.                          |
	//  +------------------------------------------------------------+
	s.Adapt(EventPolicy{Boot: func(s *Framework) {
		// set the host and scheme
		if s.Config.VHost == "" { // if not setted by Listen functions
			if s.ln != nil { // but user called .Serve
				// then take the listener's addr
				s.Config.VHost = s.ln.Addr().String()
			} else {
				// if no .Serve or .Listen called, then the user should set the VHost manually,
				// however set it to a default value here for any case
				s.Config.VHost = DefaultServerAddr
			}
		}
		// if user didn't specified a scheme then get it from the VHost, which is already setted at before statements
		if s.Config.VScheme == "" {
			s.Config.VScheme = ParseScheme(s.Config.VHost)
		}
	}})

	{
		//  +------------------------------------------------------------+
		//  | Module Name: Renderer                                      |
		//  | On Init: set templates and serializers                     |
		//  | and adapt the RenderPolicy for both                        |
		//  | templates and content-type specific renderer (serializer)  |
		//  | On Build: build the serializers and templates              |
		//  | based on the user's calls                                  |
		//  +------------------------------------------------------------+

		{
			//  +------------------------------------------------------------+
			//  | Module Name: Rich Content-Type Renderer                    |
			//  | On Init: Attach a new empty content-type serializers       |
			//  | On Build: register the default serializers  + the user's   |
			//  +------------------------------------------------------------+

			// prepare the serializers,
			// serializer content-types(json,jsonp,xml,markdown) the defaults are setted:
			serializers := serializer.Serializers{}
			serializer.RegisterDefaults(serializers)

			//
			// notes for me: Why not at the build state? in order to be overridable and not only them,
			// these are easy to be overriden by external adaptors too, no matter the order,
			// this is why the RenderPolicy last registration executing first and the first last.
			//

			// Adapt the RenderPolicy on the Build in order to be the last
			// render policy, so the users can adapt their own before the default(= to override json,xml,jsonp renderer).
			//
			// Notes: the Renderer of the view system is managed by the
			// adaptors because they are optional.
			// If templates are binded to the RenderPolicy then
			// If a key contains a dot('.') then is a template file
			// otherwise try to find a serializer, if contains error then we return false and the error
			// in order the renderer to continue to search for any other custom registerer RenderPolicy
			// if no error then check if it has written anything, if yes write the content
			// to the writer(which is the context.ResponseWriter or the gzip version of it)
			// if no error but nothing written then we return false and the error
			s.Adapt(RenderPolicy(func(out io.Writer, name string, bind interface{}, options ...map[string]interface{}) (error, bool) {
				b, err := serializers.Serialize(name, bind, options...)
				if err != nil {
					return err, false // errors should be wrapped
				}
				if len(b) > 0 {
					_, err = out.Write(b)
					return err, true
				}
				// continue to the next if any or notice there is no available renderer for that name
				return nil, false
			}))
		}
		{
			//  +------------------------------------------------------------+
			//  | Module Name: Template engine's funcs                       |
			//  | On Init: Use the template mux builder to                   |
			//  |         adapt the reverse routing tmpl funcs               |
			//  |          for any template engine that will be registered   |
			//  +------------------------------------------------------------+
			s.Adapt(TemplateFuncsPolicy{
				"url":     s.URL,
				"urlpath": s.policies.RouterReversionPolicy.URLPath,
			})

			// the entire template registration logic lives inside the ./adaptors/template now.

		}

	}

	{
		//  +------------------------------------------------------------+
		//  | Module Name: Sessions                                      |
		//  | On Init: Attach a session manager with empty config        |
		//  | On Build: Set the configuration if allowed                 |
		//  +------------------------------------------------------------+

		// set the sessions in order to UseSessionDB to work
		s.sessions = sessions.New()
		// On Build:
		s.Adapt(EventPolicy{Build: func(*Framework) {
			// re-set the configuration field to update users configuration
			s.sessions.Set(s.Config.Sessions)
		}})
	}

	{
		//  +------------------------------------------------------------+
		//  | Module Name: Websocket                                     |
		//  | On Init: Attach a new websocket server.                    |
		//  |         It starts on first callback registration           |
		//  +------------------------------------------------------------+

		// in order to be able to call $instance.Websocket.OnConnection.
		// The whole server's configuration will be
		// initialized on the first OnConnection registration (no runtime)
		s.Websocket = NewWebsocketServer(s)
	}

	{
		//  +------------------------------------------------------------+
		//  | Module Name: Router                                        |
		//  | On Init: Attach a new router, pass a new repository,       |
		//  |    an empty error handlers list, the context pool binded   |
		//  |    to the Framework and the root path "/"                  |
		//  | On Build: Use the policies to build the router's handler   |
		//  |            based on its route repository                   |
		//  +------------------------------------------------------------+

		s.Router = &Router{
			repository: new(routeRepository),
			Errors: &ErrorHandlers{
				handlers: make(map[int]Handler, 0),
			},
			Context: &contextPool{
				sync.Pool{New: func() interface{} { return &Context{framework: s} }},
			},
			relativePath: "/",
		}

		s.Adapt(EventPolicy{Build: func(*Framework) {
			// first check if it's not setted already by any Boot event.
			if s.Router.handler == nil {
				// and most importantly, check if the user has provided a router
				// adaptor, if not then it should panic here, iris can't run without a router attached to it
				// and default router not any more, user should select one from ./adaptors or
				// any other third-party adaptor may done by community.
				// I was coding the new iris version for more than 20 days(~200+ hours of code)
				// and I hope that once per application the addition of +1 line users have to put,
				// is not a big deal.
				if s.policies.RouterBuilderPolicy == nil {
					// this is important panic and app can't continue as we said.
					s.handlePanic(errRouterIsMissing.Format(s.Config.VHost))
					// don't trace anything else,
					// the detailed errRouterIsMissing message will tell the user what to do to fix that.
					os.Exit(0)

				}
				// buid the router using user's selection build policy
				s.Router.build(s.policies.RouterBuilderPolicy)
			}
		}})

	}

	{
		//  +------------------------------------------------------------+
		//  | Module Name: System                                        |
		//  | On Build: Check for updates on Build                       |
		//  +------------------------------------------------------------+

		// On Build: local repository updates
		s.Adapt(EventPolicy{Build: func(*Framework) {
			if s.Config.CheckForUpdatesSync {
				s.CheckForUpdates(false)
			} else if s.Config.CheckForUpdates {
				go s.CheckForUpdates(false)
			}
		}})
	}

	return s
}

// Set sets an option, configuration field to its Config
func (s *Framework) Set(setters ...OptionSetter) {
	if s.Config == nil {
		defaultConfiguration := DefaultConfiguration()
		s.Config = &defaultConfiguration
	}

	for _, setter := range setters {
		setter.Set(s.Config)
	}
}

// Log logs to the defined logger policy.
//
// The default outputs to the os.Stdout when EnvMode is 'ProductionEnv'
func (s *Framework) Log(mode LogMode, log string) {
	s.policies.LoggerPolicy(mode, log)
}

// Must checks if the error is not nil, if it isn't
// panics on registered iris' logger or
// to a recovery event handler, otherwise does nothing.
func (s *Framework) Must(err error) {
	if err != nil {
		s.handlePanic(err)
	}
}

func (s *Framework) handlePanic(err error) {
	if recoveryHandler := s.policies.EventPolicy.Recover; recoveryHandler != nil {
		recoveryHandler(s, err)
		return
	}
	// if not a registered recovery event handler found
	// then call the logger's Panic.
	s.Log(ProdMode, err.Error())
}

// Boot runs only once, automatically
//  when 'Serve/Listen/ListenTLS/ListenUNIX/ListenLETSENCRYPT' called.
// It's exported because you may want to build the router
//  and its components but not run the server.
//
// See ./httptest/httptest.go to understand its usage.
func (s *Framework) Boot() (firstTime bool) {
	s.once.Do(func() {
		// here execute the boot events, before build events, if exists, here is
		// where the user can make an event module to adapt custom routers and other things
		// fire the before build event
		s.policies.EventPolicy.Fire(s.policies.EventPolicy.Boot, s)

		// here execute the build events if exists
		// right before the Listen, all methods have been setted
		// usually is used to adapt third-party servers or proxies or load balancer(s)
		s.policies.EventPolicy.Fire(s.policies.EventPolicy.Build, s)

		firstTime = true
	})
	return
}

// Serve serves incoming connections from the given listener.
//
// Serve blocks until the given listener returns permanent error.
func (s *Framework) Serve(ln net.Listener) error {
	if s.isRunning() {
		return errors.New("Server is already started and listening")
	}
	// maybe a 'race' here but user should not call .Serve more than one time especially in more than one go routines...
	s.ln = ln
	s.Boot()

	// post any panics to the user defined logger.
	defer func() {
		if rerr := recover(); rerr != nil {
			if x, ok := rerr.(*net.OpError); ok && x.Op == "accept" && s.closedManually {
				///TODO:
				// here we don't report it back because the user called .Close manually.
				// NOTES:
				//
				// I know that the best option to actual Close a server is
				//  by using a custom net.Listener and do it via channels on its Accept.
				// BUT I am not doing this right now because as I'm learning the new go v1.8 will have a shutdown
				// options by-default and we will use that instead.
				// println("iris.go:355:recover but closed manually so we don't run the handler")
				return
			}
			if err, ok := rerr.(error); ok {
				s.handlePanic(err)
			}
		}
	}()

	srv := &http.Server{
		ReadTimeout:    s.Config.ReadTimeout,
		WriteTimeout:   s.Config.WriteTimeout,
		MaxHeaderBytes: s.Config.MaxHeaderBytes,
		TLSNextProto:   s.Config.TLSNextProto,
		ConnState:      s.Config.ConnState,
		Addr:           s.Config.VHost,
		ErrorLog:       s.policies.LoggerPolicy.ToLogger(log.LstdFlags),
		Handler:        s.Router,
	}

	if s.Config.TLSNextProto != nil {
		srv.TLSNextProto = s.Config.TLSNextProto
	}
	if s.Config.ConnState != nil {
		srv.ConnState = s.Config.ConnState
	}
	// print the banner and wait for system channel interrupt
	go s.postServe()
	// finally return the error or block here, remember,
	// until go1.8 these are our best options.
	return srv.Serve(s.ln)
}

func (s *Framework) postServe() {
	if !s.Config.DisableBanner {
		bannerMessage := fmt.Sprintf("%s: Running at %s", time.Now().Format(s.Config.TimeFormat), s.Config.VHost)
		// we don't print it via Logger because:
		// 1. The banner is only 'useful' when the developer logs to terminal and no file
		// 2. Prefix & LstdFlags options of the default s.Logger

		fmt.Printf("%s\n\n%s\n", banner, bannerMessage)
	}

	ch := make(chan os.Signal, 1)
	signal.Notify(ch, os.Interrupt)
	<-ch

	// fire any custom interrupted events and at the end close and exit
	// if the custom event blocks then it decides what to do next.
	s.policies.Fire(s.policies.Interrupted, s)
	// .Close doesn't really closes but it releases the ip:port, wait for go1.8 and see comments on IsRunning
	s.Close()
	os.Exit(1)
}

// Listen starts the standalone http server
// which listens to the addr parameter which as the form of
// host:port
//
// If you need to manually monitor any error please use `.Serve` instead.
func (s *Framework) Listen(addr string) {
	addr = ParseHost(addr)
	if s.Config.VHost == "" {
		s.Config.VHost = addr
		// this will be set as the front-end listening addr
	}
	// only here, other Listen functions should throw an error if port is missing.
	// User should know how to fix them on ListenUNIX/ListenTLS/ListenLETSENCRYPT/Serve,
	// they are used by more 'advanced' devs, mostly.

	if portIdx := strings.IndexByte(addr, ':'); portIdx < 0 {
		// missing port part, add it
		addr = addr + ":80"
	}

	ln, err := TCPKeepAlive(addr)
	if err != nil {
		s.handlePanic(err)
	}

	s.Must(s.Serve(ln))
}

// ListenTLS Starts a https server with certificates,
// if you use this method the requests of the form of 'http://' will fail
// only https:// connections are allowed
// which listens to the addr parameter which as the form of
// host:port
//
//
// If you need to manually monitor any error please use `.Serve` instead.
func (s *Framework) ListenTLS(addr string, certFile, keyFile string) {
	addr = ParseHost(addr)
	if s.Config.VHost == "" {
		s.Config.VHost = addr
		// this will be set as the front-end listening addr
	}

	ln, err := TLS(addr, certFile, keyFile)
	if err != nil {
		s.handlePanic(err)
	}
	s.Must(s.Serve(ln))
}

// ListenLETSENCRYPT starts a server listening at the specific nat address
// using key & certification taken from the letsencrypt.org 's servers
// it's also starts a second 'http' server to redirect all 'http://$ADDR_HOSTNAME:80' to the' https://$ADDR'
// it creates a cache file to store the certifications, for performance reasons, this file by-default is "./letsencrypt.cache"
// if you skip the second parameter then the cache file is "./letsencrypt.cache"
// if you want to disable cache then simple pass as second argument an empty empty string ""
//
// example: https://github.com/iris-contrib/examples/blob/master/letsencrypt/main.go
//
// supports localhost domains for testing,
// NOTE: if you are ready for production then use `$app.Serve(iris.LETSENCRYPTPROD("mydomain.com"))` instead
func (s *Framework) ListenLETSENCRYPT(addr string, cacheFileOptional ...string) {
	addr = ParseHost(addr)
	if s.Config.VHost == "" {
		s.Config.VHost = addr
		// this will be set as the front-end listening addr
	}
	ln, err := LETSENCRYPT(addr, cacheFileOptional...)
	if err != nil {
		s.handlePanic(err)
	}

	// starts a second server which listening on HOST:80 to redirect all requests to the HTTPS://HOST:PORT
	Proxy(ParseHostname(addr)+":80", "https://"+addr)
	s.Must(s.Serve(ln))
}

// ListenUNIX starts the process of listening to the new requests using a 'socket file', this works only on unix
//
//
// If you need to manually monitor any error please use `.Serve` instead.
func (s *Framework) ListenUNIX(addr string, mode os.FileMode) {
	// *on unix listen we don't parse the host, because sometimes it causes problems to the user
	if s.Config.VHost == "" {
		s.Config.VHost = addr
		// this will be set as the front-end listening addr
	}
	ln, err := UNIX(addr, mode)
	if err != nil {
		s.handlePanic(err)
	}

	s.Must(s.Serve(ln))
}

// IsRunning returns true if server is running
func (s *Framework) isRunning() bool {
	///TODO: this will change on gov1.8,
	// Reseve or Restart and Close will be re-added again when 1.8 final release.
	return s != nil && s.ln != nil && s.ln.Addr() != nil && s.ln.Addr().String() != ""
}

// Close is not working propetly but it releases the host:port.
func (s *Framework) Close() error {
	if s.isRunning() {
		///TODO:
		// This code below doesn't works without custom net listener which will work in a stop channel which will cost us performance.
		// This will work on go v1.8 BUT FOR NOW make unexported reserve/reboot/restart in order to be non confusual for the user.
		// Close need to be exported because whitebox tests are using this method to release the port.
		return s.ln.Close()
	}

	return nil
}

// restart re-starts the server using the last .Serve's listener
// func (s *Framework) restart() error {
// 	///TODO: See .close() notes
// 	return s.Serve(s.ln)
// }

func (s *Framework) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	s.Router.ServeHTTP(w, r)
}

// global once because is not necessary to check for updates on more than one iris station*
var updateOnce sync.Once

const (
	githubOwner = "kataras"
	githubRepo  = "iris"
)

// CheckForUpdates will try to search for newer version of Iris based on the https://github.com/kataras/iris/releases
// If a newer version found then the app will ask the he dev/user if want to update the 'x' version
// if 'y' is pressed then the updater will try to install the latest version
// the updater, will notify the dev/user that the update is finished and should restart the App manually.
// Note: exported func CheckForUpdates exists because of the reason that an update can be executed while Iris is running
func (s *Framework) CheckForUpdates(force bool) {
	updated := false
	checker := func() {

		fs.DefaultUpdaterAlreadyInstalledMessage = "Updater: Running with the latest version(%s)\n"
		updater, err := fs.GetUpdater(githubOwner, githubRepo, Version)

		if err != nil {
			// ignore writer's error
			s.Log(DevMode, "update failed: "+err.Error())
			return
		}

		updated = updater.Run(fs.Stdout(s.policies.LoggerPolicy), fs.Stderr(s.policies.LoggerPolicy), fs.Silent(false))

	}

	if force {
		checker()
	} else {
		updateOnce.Do(checker)
	}

	if updated { // if updated, then do not run the web server
		s.Log(DevMode, "exiting now...")
		os.Exit(1)
	}

}

// Adapt adapds a policy to the Framework.
// It accepts single or more objects that implements the iris.Policy.
// Iris provides some of them but you can build your own based on one or more of these:
// - iris.EventPolicy
// - iris.RouterReversionPolicy
// - iris.RouterBuilderPolicy
// - iris.RouterWrapperPolicy
// - iris.TemplateRenderPolicy
// - iris.TemplateFuncsPolicy
//
// With a Policy you can change the behavior of almost each of the existing Iris' features.
// See policy.go for more.
func (s *Framework) Adapt(policies ...Policy) {
	for i := range policies {
		policies[i].Adapt(&s.policies)
	}
}

// UseSessionDB registers a session database, you can register more than one
// accepts a session database which implements a Load(sid string) map[string]interface{} and an Update(sid string, newValues map[string]interface{})
// the only reason that a session database will be useful for you is when you want to keep the session's values/data after the app restart
// a session database doesn't have write access to the session, it doesn't accept the context, so forget 'cookie database' for sessions, I will never allow that, for your protection.
//
// Note: Don't worry if no session database is registered, your context.Session will continue to work.
func (s *Framework) UseSessionDB(db sessions.Database) {
	s.sessions.UseDatabase(db)
}

// DestroySessionByID removes the session entry
// from the server-side memory (and database if registered).
// Client's session cookie will still exist but it will be reseted on the next request.
//
// It's safe to use it even if you are not sure if a session with that id exists.
func (s *Framework) DestroySessionByID(sid string) {
	s.sessions.DestroyByID(sid)
}

// DestroyAllSessions removes all sessions
// from the server-side memory (and database if registered).
// Client's session cookie will still exist but it will be reseted on the next request.
func (s *Framework) DestroyAllSessions() {
	s.sessions.DestroyAll()
}

// cachedMuxEntry is just a wrapper for the Cache functionality
// it seems useless but I prefer to keep the cached handler on its own memory stack,
// reason:  no clojures hell in the Cache function
type cachedMuxEntry struct {
	cachedHandler http.Handler
}

func newCachedMuxEntry(s *Framework, bodyHandler HandlerFunc, expiration time.Duration) *cachedMuxEntry {
	httpHandler := ToNativeHandler(s, bodyHandler)

	cachedHandler := httpcache.Cache(httpHandler, expiration)
	return &cachedMuxEntry{
		cachedHandler: cachedHandler,
	}
}

func (c *cachedMuxEntry) Serve(ctx *Context) {
	c.cachedHandler.ServeHTTP(ctx.ResponseWriter, ctx.Request)
}

// Cache is just a wrapper for a route's handler which you want to enable body caching
// Usage: iris.Default.Get("/", iris.Cache(func(ctx *iris.Context){
//    ctx.WriteString("Hello, world!") // or a template or anything else
// }, time.Duration(10*time.Second))) // duration of expiration
// if <=time.Second then it tries to find it though request header's "cache-control" maxage value
//
// Note that it depends on a station instance's cache service.
// Do not try to call it from default' station if you use the form of app := iris.New(),
// use the app.Cache instead of iris.Cache
func (s *Framework) Cache(bodyHandler HandlerFunc, expiration time.Duration) HandlerFunc {
	ce := newCachedMuxEntry(s, bodyHandler, expiration)
	return ce.Serve
}

// Path used to check arguments with the route's named parameters and return the correct url
// if parse failed returns empty string
func (s *Framework) Path(routeName string, args ...interface{}) string {
	r := s.Router.Routes().Lookup(routeName)
	if r == nil {
		return ""
	}

	// why receive interface{}
	// but need string?
	// because the key:value are string for a route path
	// but in the template functions all works fine with ...string
	// except when the developer wants to pass that string from a binding
	// via Render, then the template will fail to render
	// because of expecting string; but got []string

	var argsString []string
	if len(args) > 0 {
		argsString = make([]string, len(args))
	}

	for i, v := range args {
		if s, ok := v.(string); ok {
			argsString[i] = s
		} else if num, ok := v.(int); ok {
			argsString[i] = strconv.Itoa(num)
		} else if b, ok := v.(bool); ok {
			argsString[i] = strconv.FormatBool(b)
		} else if arr, ok := v.([]string); ok {
			if len(arr) > 0 {
				argsString[i] = arr[0]
				argsString = append(argsString, arr[1:]...)
			}
		}
	}

	return s.policies.RouterReversionPolicy.URLPath(r, argsString...)
}

// DecodeQuery returns the uri parameter as url (string)
// useful when you want to pass something to a database and be valid to retrieve it via context.Param
// use it only for special cases, when the default behavior doesn't suits you.
//
// http://www.blooberry.com/indexdot/html/topics/urlencoding.htm
// it uses just the url.QueryUnescape
func DecodeQuery(path string) string {
	if path == "" {
		return ""
	}
	encodedPath, err := url.QueryUnescape(path)
	if err != nil {
		return path
	}
	return encodedPath
}

// DecodeURL returns the decoded uri
// useful when you want to pass something to a database and be valid to retrieve it via context.Param
// use it only for special cases, when the default behavior doesn't suits you.
//
// http://www.blooberry.com/indexdot/html/topics/urlencoding.htm
// it uses just the url.Parse
func DecodeURL(uri string) string {
	u, err := url.Parse(uri)
	if err != nil {
		return uri
	}
	return u.String()
}

// URL returns the subdomain+ host + Path(...optional named parameters if route is dynamic)
// returns an empty string if parse is failed
func (s *Framework) URL(routeName string, args ...interface{}) (url string) {
	r := s.Router.Routes().Lookup(routeName)
	if r == nil {
		return
	}

	scheme := s.Config.VScheme // if s.Config.VScheme was setted, that will be used instead of the real, in order to make easy to run behind nginx
	host := s.Config.VHost     // if s.Config.VHost was setted, that will be used instead of the real, in order to make easy to run behind nginx

	// if it's dynamic subdomain then the first argument is the subdomain part
	// for this part we are responsible not the custom routers
	if r.Subdomain() == DynamicSubdomainIndicator {
		if len(args) == 0 { // it's a wildcard subdomain but not arguments
			return
		}

		if subdomain, ok := args[0].(string); ok {
			host = subdomain + "." + host
		} else {
			// it is not array because we join them before. if not pass a string then this is not a subdomain part, return empty uri
			return
		}
		args = args[1:] // remove the subdomain part for the arguments,
	}

	if parsedPath := s.Path(routeName, args...); parsedPath != "" {
		url = scheme + host + parsedPath
	}

	return
}

var errTemplateRendererIsMissing = errors.New(
	`
manually call of Render for a template: '%s' without specified RenderPolicy!
Please .Adapt one of the available view engines inside 'kataras/iris/adaptors/view'.
By-default Iris supports five template engines:
 - standard html  | view.HTML(...)
 - django         | view.Django(...)
 - handlebars     | view.Handlebars(...)
 - pug(jade)      | view.Pug(...)
 - amber          | view.Amber(...)

Edit your main .go source file to adapt one of these and restart your app.
	i.e: lines (<---) were missing.
	-------------------------------------------------------------------
	import (
		"github.com/kataras/iris"
		"github.com/kataras/iris/adaptors/httprouter" // or gorillamux
		"github.com/kataras/iris/adaptors/view" // <--- this line
	)

	func main(){
		app := iris.New()
		app.Adapt(httprouter.New()) // or gorillamux.New()
		// right below the iris.New()
		app.Adapt(view.HTML("./templates", ".html")) // <--- and this line were missing.

		app.Listen("%s")
	}
	-------------------------------------------------------------------
 `)

// RenderOptions is a helper type for  the optional runtime options can be passed by user when Render called.
// I.e the "layout" or "gzip" option
// same as iris.Map but more specific name
type RenderOptions map[string]interface{}

// Render renders using the specific template or any other rich content renderer to the 'w'.
//
// Example of usage:
// - send an e-mail using a template engine that you already
//   adapted via: app.Adapt(view.HTML("./templates", ".html"))  or app.Adapt(iris.RenderPolicy(mycustomRenderer)).
//
// It can also render json,xml,jsonp and markdown by-default before or after .Build too.
func (s *Framework) Render(w io.Writer, name string, bind interface{}, options ...map[string]interface{}) error {
	err, ok := s.policies.RenderPolicy(w, name, bind, options...)
	if !ok {
		// ok is false ONLY WHEN there is no registered render policy
		// that is responsible for that 'name` (if contains dot '.' it's for templates).
		// We don't use default template engines on the new version,
		// so we should notice the user here, we could make it to panic but because that is on runtime
		// we don't want to panic for that, let's give a message if the user adapted a logger for dev.
		// And return that error in the case the user wasn't in dev mode, she/he can catch this error.

		// Also on the README we will add the .Adapt(iris.DevLogger()) to mention that
		// logging for any runtime info(except http server's panics and unexpected serious errors) is not enabled by-default.
		if strings.Contains(name, ".") {
			err = errTemplateRendererIsMissing.Format(name, s.Config.VHost)
			s.Log(DevMode, err.Error())
			return err
		}

	}
	return err
}