Add initial middleware package.

appengine/middleware/context.go

Index: appengine/middleware/context.go
diff --git a/appengine/middleware/context.go b/appengine/middleware/context.go
new file mode 100644
index 0000000000000000000000000000000000000000..c98aae895e93b7429565089e839a8aa4011f6601
--- /dev/null
+++ b/appengine/middleware/context.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 (
+	"net/http"
+
+	"github.com/julienschmidt/httprouter"
+	"github.com/luci/gae/impl/memory"
+	"github.com/luci/gae/impl/prod"
+	"github.com/luci/luci-go/appengine/gaelogger"
+	"github.com/luci/luci-go/common/logging/memlogger"
+	"golang.org/x/net/context"
+)
+
+// Handler is the type for all middleware handlers. Of particular note, it's the
+// same as httprouder.Handle, except that it also has a context parameter.
+type Handler func(context.Context, http.ResponseWriter, *http.Request, httprouter.Params)
+
+// Base adapts a middleware-style handler to a httprouter.Handle. It passes
+// a new, empty context to `h`.
+func Base(h Handler) httprouter.Handle {
+	return func(rw http.ResponseWriter, r *http.Request, p httprouter.Params) {
+		h(context.Background(), rw, r, p)
+	}
+}
+
+// BaseProd adapts a middleware-style handler to a httprouter.Handle. It passes
+// a new context to `h` with the following services installed:
+//   * github.com/luci/gae/impl/prod (production appengine services)
+//   * github.com/luci/luci-go/appengine/gaelogger (appengine logging service)
+func BaseProd(h Handler) httprouter.Handle {
+	return func(rw http.ResponseWriter, r *http.Request, p httprouter.Params) {
+		h(gaelogger.Use(prod.UseRequest(r)), rw, r, p)
+	}
+}
+
+// BaseTest adapts a middleware-style handler to a httprouter.Handle. It passes
+// a new context to `h` with the following services installed:
+//   * github.com/luci/gae/impl/memory (in-memory appengine services)
+//   * github.com/luci/luci-go/common/logging/memlogger (in-memory logging service)
+func BaseTest(h Handler) httprouter.Handle {
+	return func(rw http.ResponseWriter, r *http.Request, p httprouter.Params) {
+		h(memlogger.Use(memory.Use(context.Background())), rw, r, p)
+	}
+}