LogDog: BigTable batching schema.

common/gcloud/pubsub/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/pubsub"
         "golang.org/x/net/context"
 )
 
 // Source is used to pull Pub/Sub messages in batches.
 type Source interface {
-        // Pull retrieves a new batch of Pub/Sub messages to process.
-        Pull(context.Context) ([]*pubsub.Message, error)
+        // Pull retrieves up to the specified number of of Pub/Sub messages to
+        // process.
+        Pull(context.Context, int) ([]*pubsub.Message, error)
 }
 
 // PubSubSource is a Source implementation built on top of a pubsub.PubSub.
 type pubSubSource struct {
-        ps    pubsub.Connection
-        sub   pubsub.Subscription
-        batch int
+        ps  pubsub.Connection
+        sub pubsub.Subscription
 }
 
 // NewSource generates a new Source by wrapping a pubsub.Connection
 // implementation. 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 pubsub.Connection, s pubsub.Subscription, batch int) Source {
-        if batch <= 0 {
-                batch = pubsub.MaxSubscriptionPullSize
-        }
+func NewSource(ps pubsub.Connection, s pubsub.Subscription) Source {
         return &pubSubSource{
-                ps:    ps,
-                sub:   s,
-                batch: batch,
+                ps:  ps,
+                sub: s,
         }
 }
 
-func (s *pubSubSource) Pull(c context.Context) (msgs []*pubsub.Message, err error) {
-        return s.ps.Pull(c, s.sub, s.batch)
+func (s *pubSubSource) Pull(c context.Context, batchSize int) (msgs []*pubsub.Message, err error) {
+        return s.ps.Pull(c, s.sub, batchSize)
 }