caddyhttp: Implement named routes, invoke directive (#5107)

* caddyhttp: Implement named routes, `invoke` directive

* gofmt

* Add experimental marker

* Adjust route compile comments

modules/caddyhttp/invoke.go

@@ -0,0 +1,56 @@
+// Copyright 2015 Matthew Holt and The Caddy Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package caddyhttp
+
+import (
+	"fmt"
+	"net/http"
+
+	"github.com/caddyserver/caddy/v2"
+)
+
+func init() {
+	caddy.RegisterModule(Invoke{})
+}
+
+// Invoke implements a handler that compiles and executes a
+// named route that was defined on the server.
+//
+// EXPERIMENTAL: Subject to change or removal.
+type Invoke struct {
+	// Name is the key of the named route to execute
+	Name string `json:"name,omitempty"`
+}
+
+// CaddyModule returns the Caddy module information.
+func (Invoke) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		ID:  "http.handlers.invoke",
+		New: func() caddy.Module { return new(Invoke) },
+	}
+}
+
+func (invoke *Invoke) ServeHTTP(w http.ResponseWriter, r *http.Request, next Handler) error {
+	server := r.Context().Value(ServerCtxKey).(*Server)
+	if route, ok := server.NamedRoutes[invoke.Name]; ok {
+		return route.Compile(next).ServeHTTP(w, r)
+	}
+	return fmt.Errorf("invoke: route '%s' not found", invoke.Name)
+}
+
+// Interface guards
+var (
+	_ MiddlewareHandler = (*Invoke)(nil)
+)