Ability to register a view engine per group of routes or for the current a chain of handlers

Example at: https://github.com/kataras/iris/tree/master/_examples/view/context-view-engine

context/configuration.go

@@ -51,6 +51,9 @@ type ConfigurationReadOnly interface {
 	GetLanguageContextKey() string
 	// GetVersionContextKey returns the VersionContextKey field.
 	GetVersionContextKey() string
+
+	// GetViewEngineContextKey returns the ViewEngineContextKey field.
+	GetViewEngineContextKey() string
 	// GetViewLayoutContextKey returns the ViewLayoutContextKey field.
 	GetViewLayoutContextKey() string
 	// GetViewDataContextKey returns the ViewDataContextKey field.

context/context.go

@@ -2392,16 +2392,22 @@ func (ctx *Context) CompressReader(enable bool) error {
 //  | Rich Body Content Writers/Renderers                        |
 //  +------------------------------------------------------------+
 
-const (
-	// NoLayout to disable layout for a particular template file
-	NoLayout = "iris.nolayout"
-)
+// ViewEngine registers a view engine for the current chain of handlers.
+// It overrides any previously registered engines, including the application's root ones.
+// Note that, because performance is everything,
+// the "engine" MUST be already ready-to-use,
+// meaning that its `Load` method should be called once before this method call.
+//
+// To register a view engine per-group of groups too see `Party.RegisterView` instead.
+func (ctx *Context) ViewEngine(engine ViewEngine) {
+	ctx.values.Set(ctx.app.ConfigurationReadOnly().GetViewEngineContextKey(), engine)
+}
 
 // ViewLayout sets the "layout" option if and when .View
 // is being called afterwards, in the same request.
 // Useful when need to set or/and change a layout based on the previous handlers in the chain.
 //
-// Note that the 'layoutTmplFile' argument can be set to iris.NoLayout || view.NoLayout || context.NoLayout
+// Note that the 'layoutTmplFile' argument can be set to iris.NoLayout
 // to disable the layout for a specific view render action,
 // it disables the engine's configuration's layout property.
 //
@@ -2418,7 +2424,7 @@ func (ctx *Context) ViewLayout(layoutTmplFile string) {
 //
 // If .View's "binding" argument is not nil and it's not a type of map
 // then these data are being ignored, binding has the priority, so the main route's handler can still decide.
-// If binding is a map or context.Map then these data are being added to the view data
+// If binding is a map or iris.Map then these data are being added to the view data
 // and passed to the template.
 //
 // After .View, the data are not destroyed, in order to be re-used if needed (again, in the same request as everything else),
@@ -2457,7 +2463,7 @@ func (ctx *Context) ViewData(key string, value interface{}) {
 // A check for nil is always a good practise if different
 // kind of values or no data are registered via `ViewData`.
 //
-// Similarly to `viewData := ctx.Values().Get("iris.viewData")` or
+// Similarly to `viewData := ctx.Values().Get("iris.view.data")` or
 // `viewData := ctx.Values().Get(ctx.Application().ConfigurationReadOnly().GetViewDataContextKey())`.
 func (ctx *Context) GetViewData() map[string]interface{} {
 	viewDataContextKey := ctx.app.ConfigurationReadOnly().GetViewDataContextKey()
@@ -2514,7 +2520,21 @@ func (ctx *Context) View(filename string, optionalViewModel ...interface{}) erro
 		bindingData = ctx.values.Get(cfg.GetViewDataContextKey())
 	}
 
-	err := ctx.app.View(ctx, filename, layout, bindingData)
+	if key := cfg.GetViewEngineContextKey(); key != "" {
+		if engineV := ctx.values.Get(key); engineV != nil {
+			if engine, ok := engineV.(ViewEngine); ok {
+				err := engine.ExecuteWriter(ctx, filename, layout, bindingData)
+				if err != nil {
+					ctx.app.Logger().Errorf("View [%v] [%T]: %v", ctx.getLogIdentifier(), engine, err)
+					return err
+				}
+
+				return nil
+			}
+		}
+	}
+
+	err := ctx.app.View(ctx, filename, layout, bindingData) // if failed it logs the error.
 	if err != nil {
 		ctx.StopWithStatus(http.StatusInternalServerError)
 	}
@@ -2522,6 +2542,16 @@ func (ctx *Context) View(filename string, optionalViewModel ...interface{}) erro
 	return err
 }
 
+// getLogIdentifier returns the ID, or the client remote IP address,
+// useful for internal logging of context's method failure.
+func (ctx *Context) getLogIdentifier() interface{} {
+	if id := ctx.GetID(); id != nil {
+		return id
+	}
+
+	return ctx.RemoteAddr()
+}
+
 const (
 	// ContentBinaryHeaderValue header value for binary data.
 	ContentBinaryHeaderValue = "application/octet-stream"

context/view.go

@@ -0,0 +1,22 @@
+package context
+
+import "io"
+
+// ViewEngine is the interface which all view engines should be implemented in order to be registered inside iris.
+type ViewEngine interface {
+	// Load should load the templates from a physical system directory or by an embedded one (assets/go-bindata).
+	Load() error
+	// ExecuteWriter should execute a template by its filename with an optional layout and bindingData.
+	ExecuteWriter(w io.Writer, filename string, layout string, bindingData interface{}) error
+	// Ext should return the final file extension which this view engine is responsible to render.
+	Ext() string
+}
+
+// ViewEngineFuncer is an addition of a view engine,
+// if a view engine implements that interface
+// then iris can add some closed-relative iris functions
+// like {{ url }}, {{ urlpath }} and {{ tr }}.
+type ViewEngineFuncer interface {
+	// AddFunc should adds a function to the template's function map.
+	AddFunc(funcName string, funcBody interface{})
+}