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// Copyright 2012 Gary Burd
//
// 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.
// +build go1.7
package redis_test
import (
"context"
"fmt"
"time"
"github.com/gomodule/redigo/redis"
)
// listenPubSubChannels listens for messages on Redis pubsub channels. The
// onStart function is called after the channels are subscribed. The onMessage
// function is called for each message.
func listenPubSubChannels(ctx context.Context, redisServerAddr string,
onStart func() error,
onMessage func(channel string, data []byte) error,
channels ...string) error {
// A ping is set to the server with this period to test for the health of
// the connection and server.
const healthCheckPeriod = time.Minute
c, err := redis.Dial("tcp", redisServerAddr,
// Read timeout on server should be greater than ping period.
redis.DialReadTimeout(healthCheckPeriod+10*time.Second),
redis.DialWriteTimeout(10*time.Second))
if err != nil {
return err
}
defer c.Close()
psc := redis.PubSubConn{Conn: c}
if err := psc.Subscribe(redis.Args{}.AddFlat(channels)...); err != nil {
return err
}
done := make(chan error, 1)
// Start a goroutine to receive notifications from the server.
go func() {
for {
switch n := psc.Receive().(type) {
case error:
done <- n
return
case redis.Message:
if err := onMessage(n.Channel, n.Data); err != nil {
done <- err
return
}
case redis.Subscription:
switch n.Count {
case len(channels):
// Notify application when all channels are subscribed.
if err := onStart(); err != nil {
done <- err
return
}
case 0:
// Return from the goroutine when all channels are unsubscribed.
done <- nil
return
}
}
}
}()
ticker := time.NewTicker(healthCheckPeriod)
defer ticker.Stop()
loop:
for {
select {
case <-ticker.C:
// Send ping to test health of connection and server. If
// corresponding pong is not received, then receive on the
// connection will timeout and the receive goroutine will exit.
if err = psc.Ping(""); err != nil {
break loop
}
case <-ctx.Done():
break loop
case err := <-done:
// Return error from the receive goroutine.
return err
}
}
// Signal the receiving goroutine to exit by unsubscribing from all channels.
if err := psc.Unsubscribe(); err != nil {
return err
}
// Wait for goroutine to complete.
return <-done
}
func publish() {
c, err := dial()
if err != nil {
fmt.Println(err)
return
}
defer c.Close()
if _, err = c.Do("PUBLISH", "c1", "hello"); err != nil {
fmt.Println(err)
return
}
if _, err = c.Do("PUBLISH", "c2", "world"); err != nil {
fmt.Println(err)
return
}
if _, err = c.Do("PUBLISH", "c1", "goodbye"); err != nil {
fmt.Println(err)
return
}
}
// This example shows how receive pubsub notifications with cancelation and
// health checks.
func ExamplePubSubConn() {
redisServerAddr, err := serverAddr()
if err != nil {
fmt.Println(err)
return
}
ctx, cancel := context.WithCancel(context.Background())
err = listenPubSubChannels(ctx,
redisServerAddr,
func() error {
// The start callback is a good place to backfill missed
// notifications. For the purpose of this example, a goroutine is
// started to send notifications.
go publish()
return nil
},
func(channel string, message []byte) error {
fmt.Printf("channel: %s, message: %s\n", channel, message)
// For the purpose of this example, cancel the listener's context
// after receiving last message sent by publish().
if string(message) == "goodbye" {
cancel()
}
return nil
},
"c1", "c2")
if err != nil {
fmt.Println(err)
return
}
// Output:
// channel: c1, message: hello
// channel: c2, message: world
// channel: c1, message: goodbye
}
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