Make HTTP middleware easier to use

server/router/router.go

Index: server/router/router.go
diff --git a/server/router/router.go b/server/router/router.go
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+// Copyright 2016 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+// Package router provides a HTTP router with support for middleware and groups.
+//
+// Usage:
+//
+//	   r := router.New()
+//	   r.UseHandlers(Logger())
+//	   r.GET("/", rootHandler) // Type of rootHandler TBD
+//
+//	   authorized := r.Group("authorized")
+//	   authorized.UseHandler(Authenticator()) // Authenticator has signature similar to Logger
+//	   authorized.DELETE("/comment/:id", commentDeleteHandler) // Executes Logger and Authenticator middlewares in order before commentDeleteHandler
+//                                                             // Full path for above: /authorized/comment/:id
+//
+//	   func Logger() middleware.ChainedHandler {
+//		  return func(ctx context.Context, rw http.ResponseWriter, r *http.Request, p httprouter.Params, next middleware.Handler) {
+//			  log.Println("before")
+//			  next(ctx, rw, r, p)
+//			  log.Println("after")
+//		  }
+//	   }
+//
+package router
+
+import (
+	"github.com/julienschmidt/httprouter"
+	"github.com/luci/luci-go/server/middleware"
+)
+
+// Router represents the main router type.
+type Router struct {
+	Group
+}
+
+// Group represents a router configuration. It has a base path
+// and a list of middleware for the path.
+type Group struct {
+	hrouter  *httprouter.Router
+	handlers middleware.Chain
+	basePath string
+	router   *Router
+	root     bool
+}
+
+// New creates a Router.
+func New() *Router {
+	r := &Router{
+		Group: Group{
+			hrouter:  httprouter.New(),
+			basePath: "/",
+			root:     true,
+		},
+	}
+	r.Group.router = r
+	return r
+}
+
+// UseHandlers adds handlers as middleware to the group. The added middleware applies to
+// all routes in the current group and in groups derived from the current group.
+func (g *Group) UseHandlers(handlers ...middleware.ChainedHandler) {
+	g.handlers.Add(middleware.NewChain(handlers...))
+}
+
+// Use adds middleware chains to the group. The added middleware applies to
+// all routes in the current group and in groups derived from the current group.
+func (g *Group) Use(chains ...middleware.Chain) {
+	g.handlers.Add(chains...)
+}
+
+// Group creates a new router group, extended by the provided relativePath.
+// The new group has configuration such as handlers from the current group.
+func (g *Group) Group(relativePath string) *Group {
+	return &Group{
+		hrouter:  g.hrouter,
+		handlers: g.handlers,
+		basePath: g.basePath + relativePath,
+		router:   g.router,
+		root:     false,
+	}
+}
+
+// TODO(nishanths): Write wrappers for GET, POST, Handle and other httrouter.Router's public
+// methods. These will need to execute middleware before delegating to
+// hrouter.GET(..), etc.