LogDog: Add collector service implementation.

common/gcloud/gcps/subscriber/source.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 subscriber
+
+import (
+        "github.com/luci/luci-go/common/gcloud/gcps"
+        "golang.org/x/net/context"
+        "google.golang.org/cloud/pubsub"
+)
+
+// Source is used to pull Pub/Sub messages in batches.
+type Source interface {

[dnj (Google), 2016/01/21 04:36:24]

Generalized Source allows for greater interoperability. NewSource below wraps a
Pub/Sub instance, making it easy to get a Source instance.

+        // Pull retrieves a new batch of Pub/Sub messages to process.
+        Pull(context.Context) ([]*pubsub.Message, error)
+}
+
+// PubSubSource is a Source implementation built on top of a gcps.PubSub.
+type pubSubSource struct {
+        ps    gcps.PubSub
+        sub   gcps.Subscription
+        batch int
+}
+
+// NewSource generates a new Source by wrapping a gcps.PubSub method. This
+// Source is bound to a single subscription.
+//
+// If the supplied batch size is <= 0, the maximum allowed Pub/Sub batch size
+// will be used.
+func NewSource(ps gcps.PubSub, s gcps.Subscription, batch int) Source {
+        if batch <= 0 {
+                batch = gcps.MaxSubscriptionPullSize
+        }
+        return &pubSubSource{
+                ps:    ps,
+                sub:   s,
+                batch: batch,
+        }
+}
+
+func (s *pubSubSource) Pull(c context.Context) (msgs []*pubsub.Message, err error) {
+        return s.ps.Pull(c, s.sub, s.batch)
+}