Initial distributor implementation

appengine/cmd/dm/distributor/task_description.go

Index: appengine/cmd/dm/distributor/task_description.go
diff --git a/appengine/cmd/dm/distributor/task_description.go b/appengine/cmd/dm/distributor/task_description.go
new file mode 100644
index 0000000000000000000000000000000000000000..baef72399e3a367a55b35f92caf44fefcfcefde3
--- /dev/null
+++ b/appengine/cmd/dm/distributor/task_description.go
@@ -0,0 +1,73 @@
+// Copyright 2016 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package distributor
+
+import (
+	"fmt"
+
+	"github.com/golang/protobuf/proto"
+	"github.com/luci/gae/service/info"
+	dm "github.com/luci/luci-go/common/api/dm/service/v1"
+	"github.com/luci/luci-go/common/gcloud/pubsub"
+	"golang.org/x/net/context"
+)
+
+// NewTaskDescription builds a new *TaskDescription.
+//
+// It's intended for use by the DM core logic, and not for use by distributor
+// implementations.
+func NewTaskDescription(c context.Context, payload *dm.Quest_Desc, exAuth *dm.Execution_Auth,
+	state PersistentState) *TaskDescription {
+	return &TaskDescription{
+		c:             c,
+		payload:       payload,
+		executionAuth: exAuth,
+		previousState: state,
+	}
+}
+
+// TaskDescription is the parameters for PrepareTask.
+type TaskDescription struct {
+	c             context.Context
+	payload       *dm.Quest_Desc
+	executionAuth *dm.Execution_Auth
+	previousState PersistentState
+}
+
+// PrepareTopic returns the pubsub topic that notifications should be sent to.
+//
+// It returns the full name of the topic and a token that will be used to route
+// PubSub messages back to the Distributor. The publisher to the topic must be
+// instructed to put the token into the 'auth_token' attribute of PubSub
+// messages. DM will know how to route such messages to D.HandleNotification.
+func (t *TaskDescription) PrepareTopic() (topic pubsub.Topic, token string, err error) {
+	topic = pubsub.NewTopic(info.Get(t.c).TrimmedAppID(), notifyTopicSuffix)
+	if err := topic.Validate(); err != nil {
+		panic(fmt.Errorf("failed to validate Topic %q: %s", topic, err))
+	}
+	token, err = encodeAuthToken(t.c, t.executionAuth.Id,
+		t.payload.DistributorConfigName)
+	return
+}
+
+// PreviousState is the current PersistentState of the Attempt (e.g. the
+// PersistentState returned by the previous Execution). This will be empty
+// for the first Execution.
+func (t *TaskDescription) PreviousState() PersistentState {
+	return t.previousState
+}
+
+// Payload is description of the job to run.
+func (t *TaskDescription) Payload() *dm.Quest_Desc {
+	return proto.Clone(t.payload).(*dm.Quest_Desc)
+}
+
+// ExecutionAuth is the combined execution_id+activation token that the
+// execution must use to call ActivateExecution before making further API calls
+// into DM.
+func (t *TaskDescription) ExecutionAuth() *dm.Execution_Auth {
+	ret := *t.executionAuth
+	return &ret
+}