Add remote_api support

impl/prod/context.go

 // 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 prod
 
 import (
         "net/http"
 
         "github.com/luci/gae/service/info"
         "golang.org/x/net/context"
+        gOAuth "golang.org/x/oauth2/google"
         "google.golang.org/appengine"
+        "google.golang.org/appengine/remote_api"
 )
 
 type key int
 
 var (
         prodContextKey      key
         prodContextNoTxnKey key = 1
         probeCacheKey       key = 2
 )
 
@@ skipping 17 matching lines @@
         aeCtx, err := appengine.Namespace(aeCtx, info.Get(c).GetNamespace())
         if err != nil {
                 panic(err)
         }
         if deadline, ok := c.Deadline(); ok {
                 aeCtx, _ = context.WithDeadline(aeCtx, deadline)
         }
         return aeCtx
 }
 
+func setupAECtx(c, aeCtx context.Context) context.Context {
+        c = context.WithValue(c, prodContextKey, aeCtx)
+        c = context.WithValue(c, prodContextNoTxnKey, aeCtx)
+        return useMail(useUser(useURLFetch(useRDS(useMC(useTQ(useGI(useLogging(c))))))))
+}
+
 // Use adds production implementations for all the gae services to the
 // context.
 //
 // The services added are:
 //   - github.com/luci-go/common/logging
 //   - github.com/luci/gae/service/datastore
 //   - github.com/luci/gae/service/info
 //   - github.com/luci/gae/service/mail
 //   - github.com/luci/gae/service/memcache
 //   - github.com/luci/gae/service/taskqueue
 //   - github.com/luci/gae/service/urlfetch
 //   - github.com/luci/gae/service/user
 //
 // These can be retrieved with the <service>.Get functions.
 //
 // The implementations are all backed by the real appengine SDK functionality,
 func Use(c context.Context, r *http.Request) context.Context {
-        aeCtx := appengine.NewContext(r)
-        c = context.WithValue(c, prodContextKey, aeCtx)
-        c = context.WithValue(c, prodContextNoTxnKey, aeCtx)
-        return useMail(useUser(useURLFetch(useRDS(useMC(useTQ(useGI(useLogging(c))))))))
+        return setupAECtx(c, appengine.NewContext(r))
 }
+
+// UseRemote is the same as Use, except that it lets you attach a context to
+// a remote host using the Remote API feature. See the docs for the
+// prerequisites.
+//
+// docs: https://cloud.google.com/appengine/docs/go/tools/remoteapi
+//
+// If client is nil, this will use a default Google OAuth2 client. Otherwise the
+// client must be configured to have the following OAuth2 scopes:
+//              "https://www.googleapis.com/auth/appengine.apis"
+//              "https://www.googleapis.com/auth/userinfo.email"
+//              "https://www.googleapis.com/auth/cloud.platform"
+func UseRemote(c context.Context, host string, client *http.Client) (context.Context, error) {
+        err := error(nil)
+        if client == nil {
+                client, err = gOAuth.DefaultClient(context.Background(),
+                        "https://www.googleapis.com/auth/appengine.apis",
+                        "https://www.googleapis.com/auth/userinfo.email",
+                        "https://www.googleapis.com/auth/cloud.platform",
+                )
+                if err != nil {
+                        return nil, err
+                }
+        }
+
+        aeCtx, err := remote_api.NewRemoteContext(host, client)
+        if err != nil {
+                return nil, err
+        }
+        return setupAECtx(c, aeCtx), nil
+}