A client/server helper wrapper for endpoints in Go.

go/src/infra/gae/epservice/example/service_cas.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 example
+
+import (
+        "golang.org/x/net/context"
+        "infra/gae/libs/wrapper"
+        "infra/gae/libs/wrapper/gae"
+
+        "github.com/GoogleCloudPlatform/go-endpoints/endpoints"
+)
+
+// CASReq is the input for the CAS RPC
+type CASReq struct {
+        Name string `endpoints:"required"`
+
+        OldVal int64 `json:",string"`
+        NewVal int64 `json:",string"`
+}
+
+// CAS does an atomic compare-and-swap on a counter.
+func (Example) CAS(c endpoints.Context, r *CASReq) (err error) {
+        success := false
+        ds := wrapper.GetDS(gae.Use(context.Background(), c))
+        err = ds.RunInTransaction(func(context.Context) error {
+                ctr := &Counter{ID: r.Name}
+                if err := ds.Get(ctr); err != nil {
+                        return err
+                }
+                if ctr.Val == r.OldVal {
+                        success = true
+                        ctr.Val = r.NewVal
+                        _, err := ds.Put(ctr)
+                        return err
+                }
+                success = false
+                return nil
+        }, nil)
+        if err == nil && !success {
+                err = endpoints.ConflictError
+        }
+        return
+}
+
+func init() {
+        mi["CAS"] = &endpoints.MethodInfo{
+                Path: "counter/{Name}/cas",
+                Desc: "Compare and swap a counter value",
+        }
+}