Add initial middleware package.

appengine/middleware/appengine.go

Index: appengine/middleware/appengine.go
diff --git a/appengine/middleware/appengine.go b/appengine/middleware/appengine.go
new file mode 100644
index 0000000000000000000000000000000000000000..261fe8bb72a42a0f3860d37b87bdcd7120b9451d
--- /dev/null
+++ b/appengine/middleware/appengine.go
@@ -0,0 +1,48 @@
+// 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
+
+import (
+	"fmt"
+	"net/http"
+
+	"github.com/julienschmidt/httprouter"
+	"golang.org/x/net/context"
+)
+
+// RequireCron ensures that this handler was run from the appengine 'cron'
+// service. Otherwise it aborts the request with a StatusForbidden.
+func RequireCron(h Handler) Handler {
+	return func(c context.Context, rw http.ResponseWriter, r *http.Request, p httprouter.Params) {
+		if r.Header.Get("X-Appengine-Cron") != "true" {

[Vadim Sh., 2015/10/13 01:29:14]

consider adding "&& !IsDevAppServer()"

it simplifies local manual testing

[iannucci, 2015/10/13 01:37:17]

WDYT about just adding this header in BaseTest?

[Vadim Sh., 2015/10/13 01:40:26]

What do you mean?

By "local manual testing" I meant when running an app on devserver for real (not
in unit tests). BaseProd is used in that case. There's no UI on devserver to
trigger cron jobs. And doing GET's with headers is trickier than just hitting an
URL in browser.

+			rw.WriteHeader(http.StatusForbidden)
+			fmt.Fprint(rw, "error: must be run from cron")

[dnj, 2015/10/13 01:44:49]

Worth logging, too.

[iannucci, 2015/10/13 01:56:34]

Ah, right, meant to do that. Done.

+			return
+		}
+		h(c, rw, r, p)
+	}
+}
+
+// RequireTaskQueue ensures that this handler was run from the specified
+// appengine 'taskqueue' queue. Otherwise it aborts the request with
+// a StatusForbidden.
+//
+// if `queue` is the empty string, than this simply checks that this handler was
+// run from ANY appengine taskqueue.
+func RequireTaskQueue(queue string, h Handler) Handler {
+	return func(c context.Context, rw http.ResponseWriter, r *http.Request, p httprouter.Params) {
+		qName := r.Header.Get("X-AppEngine-QueueName")
+		if qName == "" || (queue != "" && queue != qName) {

[dnj, 2015/10/13 01:44:49]

Why have "" be special? IMO should be simple:
if queue != r.Header.Get("X-AppEngine-QueueName") {...}

[iannucci, 2015/10/13 01:56:34]

Docs explain it pretty well I think?

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

Ah okay, makes sense. Sorry was on a bus.

+			rw.WriteHeader(http.StatusForbidden)
+			if queue == "" {
+				fmt.Fprintf(rw, "error: must be run from a taskqueue")
+			} else {
+				fmt.Fprintf(rw, "error: must be run from the taskqueue %q", queue)

[dnj, 2015/10/13 01:44:49]

This could leak internal task queue names. Maybe log the task queue name
instead.

[iannucci, 2015/10/13 01:56:34]

done

+			}
+			return
+		}
+		h(c, rw, r, p)
+	}
+}