Add initial middleware package.

appengine/middleware/doc.go

Index: appengine/middleware/doc.go
diff --git a/appengine/middleware/doc.go b/appengine/middleware/doc.go
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+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Package middleware provides a standard set of middleware tools for luci
+// appengine apps. It's built around "github.com/julienschmidt/httprouter".
+//
+// Usage Example
+//
+// Middleware is pretty basic to use. You pick one of the 'Base' functions,
+// then layer middlewares, making the innermost middleware your actual handler
+// function.
+//
+// BaseProd and BaseTest ensure that the context has a full compliment of
+// luci/gae services, as well as a luci-go/common/logging service.
+//
+//   import (

[dnj, 2015/10/13 04:39:10]

WDYT about moving this into a test example?

[iannucci, 2015/10/13 04:52:29]

I don't think it would work? Is there a way to do an example with data types and
init functions?

+//     "log"
+//
+//     "github.com/julienschmidt/httprouter"
+//     "github.com/luci/gae/service/datastore"
+//     "github.com/luci/luci-go/appengine/middleware"
+//     "github.com/luci/luci-go/common/logging"
+//   )
+//
+//   // Thing is just a silly datastore model for the example.
+//   type Thing struct{
+//     ID string `gae:"$id"`
+//   }
+//
+//   func myHandler(c context.Context, rw http.ResponseWriter, r *http.Request, p httprouter.Params) {
+//     if err := datastore.Get(c).Put(&Thing{ID: p.ByName("thing_id")}); err != nil {
+//       logging.Errorf(c, "failed to put thing: %s", err)
+//       fmt.Fprintf("error: %s", err)
+//       rw.WriteHeader(500)
+//       return
+//     }
+//     rw.Write([]byte("ok"))
+//   }
+//
+//   func init() {
+//     router := httprouter.New()
+//     router.GET("/internal/make_thing/:obj_id",
+//       middleware.BaseProd(middleware.RequireCron(myHandler)))
+//
+//     log.Fatal(http.ListenAndServe(":8080", router))
+//   }
+package middleware