Initial distributor implementation

appengine/cmd/dm/distributor/task_description.go

+// Copyright 2016 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 distributor
+
+import (
+        dm "github.com/luci/luci-go/common/api/dm/service/v1"
+        "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, token string, err error) {
+        topic = pubsubTopic(t.c)
+        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 {
+        ret := *t.payload

[dnj (Google), 2016/06/09 18:00:56]

I think you should build "clone" into "Quest_Desc".

[iannucci, 2016/06/15 00:46:00]

yeah that's a better idea. I was tired :P. Done.

+        meta := *ret.Meta
+        retry := *meta.Retry
+
+        meta.Retry = &retry
+        ret.Meta = &meta
+        return &ret
+}
+
+// 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
+}