| // Copyright 2016 Google Inc. All Rights Reserved. |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| package pubsub |
| |
| import ( |
| "sync" |
| |
| "golang.org/x/net/context" |
| ) |
| |
| // puller fetches messages from the server in a batch. |
| type puller struct { |
| Client *Client |
| Sub string |
| |
| // The maximum number of messages to fetch at once. |
| // No more than BatchSize messages will be outstanding at any time. |
| BatchSize int64 |
| |
| // A function to call when a new message is fetched from the server, but not yet returned from Next. |
| Notify func(ackID string) |
| |
| mu sync.Mutex |
| buf []*Message |
| } |
| |
| // Next returns the next message from the server, fetching a new batch if necessary. |
| // Notify is called with the ackIDs of newly fetched messages. |
| func (p *puller) Next(ctx context.Context) (*Message, error) { |
| p.mu.Lock() |
| defer p.mu.Unlock() |
| |
| for len(p.buf) == 0 { |
| var err error |
| p.buf, err = p.Client.s.fetchMessages(ctx, p.Sub, p.BatchSize) |
| if err != nil { |
| // TODO: retry before giving up. |
| return nil, err |
| } |
| for _, m := range p.buf { |
| p.Notify(m.AckID) |
| } |
| } |
| m := p.buf[0] |
| p.buf = p.buf[1:] |
| return m, nil |
| } |
| |
| // Pending returns the list of messages that have been fetched from the server |
| // but not yet returned via Next. |
| func (p *puller) Pending() []*Message { |
| p.mu.Lock() |
| defer p.mu.Unlock() |
| return p.buf |
| } |