impl/cloud: Add support for "memcached" memcache.

impl/cloud/context.go

Index: impl/cloud/context.go
diff --git a/impl/cloud/context.go b/impl/cloud/context.go
index f7525e439f0c62e9eefdab9155ecb83899863360..a4b19ea6990e1adbece421ee9dc7bafed5d184c6 100644
--- a/impl/cloud/context.go
+++ b/impl/cloud/context.go
@@ -5,26 +5,69 @@
 package cloud
 
 import (
+	"github.com/luci/gae/impl/dummy"
+	ds "github.com/luci/gae/service/datastore"
+	"github.com/luci/gae/service/mail"
+	mc "github.com/luci/gae/service/memcache"
+	"github.com/luci/gae/service/module"
+	"github.com/luci/gae/service/taskqueue"
+	"github.com/luci/gae/service/user"
+
 	"cloud.google.com/go/datastore"
+	"github.com/bradfitz/gomemcache/memcache"
 
 	"golang.org/x/net/context"
 )
 
-// Use installs the cloud services implementation into the supplied Context.
-//
-// This includes:
-//	- github.com/luci/gae/service/info
-//	- github.com/luci/gae/service/datastore
+// Config is a full-stack cloud service configuration. A user can selectively
+// populate its fields, and services for the populated fields will be installed
+// in the Context and available.
 //
-// This is built around the ability to use cloud datastore.
-func Use(c context.Context, client *datastore.Client) context.Context {
-	return UseDS(useInfo(c), client)
+// Because the "impl/cloud" service collection is a composite set of cloud
+// services, the user can choose services based on their configuration.
+type Config struct {
+	// DS is the cloud datastore client. If populated, the datastore service will
+	// be installed.
+	DS *datastore.Client
+
+	// MC is the memcache service client. If populated, the memcache service will
+	// be installed.
+	MC *memcache.Client
 }
 
-// UseDS installs the cloud datastore implementation into the supplied Context.
-func UseDS(c context.Context, client *datastore.Client) context.Context {
-	cds := cloudDatastore{
-		client: client,
+// Use installs the Config into the supplied Context. Services will be installed
+// based on the fields that are populated in Config.
+//
+// Any services that are missing will have "impl/dummy" stubs installed. These
+// stubs will panic if called.
+func (cfg Config) Use(c context.Context) context.Context {
+	// Dummy services that we don't support.
+	c = mail.Set(c, dummy.Mail())
+	c = module.Set(c, dummy.Module())
+	c = taskqueue.SetRaw(c, dummy.TaskQueue())
+	c = user.Set(c, dummy.User())
+
+	c = useInfo(c)
+
+	// datastore service
+	if cfg.DS != nil {
+		cds := cloudDatastore{
+			client: cfg.DS,
+		}
+		c = cds.use(c)
+	} else {
+		c = ds.SetRaw(c, dummy.Datastore())
+	}
+
+	// memcache service
+	if cfg.MC != nil {
+		mc := memcacheClient{
+			client: cfg.MC,
+		}
+		c = mc.use(c)
+	} else {
+		c = mc.SetRaw(c, dummy.Memcache())
 	}
-	return cds.use(c)
+
+	return c
 }