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example_client_test.go
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example_client_test.go
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package amqp_test
import (
"errors"
"fmt"
"log"
"os"
"time"
"github.com/streadway/amqp"
)
// This exports a Session object that wraps this library. It
// automatically reconnects when the connection fails, and
// blocks all pushes until the connection succeeds. It also
// confirms every outgoing message, so none are lost.
// It doesn't automatically ack each message, but leaves that
// to the parent process, since it is usage-dependent.
//
// Try running this in one terminal, and `rabbitmq-server` in another.
// Stop & restart RabbitMQ to see how the queue reacts.
func Example() {
name := "job_queue"
addr := "amqp://guest:guest@localhost:5672/"
queue := New(name, addr)
message := []byte("message")
// Attempt to push a message every 2 seconds
for {
time.Sleep(time.Second * 2)
if err := queue.Push(message); err != nil {
fmt.Printf("Push failed: %s\n", err)
} else {
fmt.Println("Push succeeded!")
}
}
}
type Session struct {
name string
logger *log.Logger
connection *amqp.Connection
channel *amqp.Channel
done chan bool
notifyConnClose chan *amqp.Error
notifyChanClose chan *amqp.Error
notifyConfirm chan amqp.Confirmation
isReady bool
}
const (
// When reconnecting to the server after connection failure
reconnectDelay = 5 * time.Second
// When setting up the channel after a channel exception
reInitDelay = 2 * time.Second
// When resending messages the server didn't confirm
resendDelay = 5 * time.Second
)
var (
errNotConnected = errors.New("not connected to a server")
errAlreadyClosed = errors.New("already closed: not connected to the server")
errShutdown = errors.New("session is shutting down")
)
// New creates a new consumer state instance, and automatically
// attempts to connect to the server.
func New(name string, addr string) *Session {
session := Session{
logger: log.New(os.Stdout, "", log.LstdFlags),
name: name,
done: make(chan bool),
}
go session.handleReconnect(addr)
return &session
}
// handleReconnect will wait for a connection error on
// notifyConnClose, and then continuously attempt to reconnect.
func (session *Session) handleReconnect(addr string) {
for {
session.isReady = false
log.Println("Attempting to connect")
conn, err := session.connect(addr)
if err != nil {
log.Println("Failed to connect. Retrying...")
select {
case <-session.done:
return
case <-time.After(reconnectDelay):
}
continue
}
if done := session.handleReInit(conn); done {
break
}
}
}
// connect will create a new AMQP connection
func (session *Session) connect(addr string) (*amqp.Connection, error) {
conn, err := amqp.Dial(addr)
if err != nil {
return nil, err
}
session.changeConnection(conn)
log.Println("Connected!")
return conn, nil
}
// handleReconnect will wait for a channel error
// and then continuously attempt to re-initialize both channels
func (session *Session) handleReInit(conn *amqp.Connection) bool {
for {
session.isReady = false
err := session.init(conn)
if err != nil {
log.Println("Failed to initialize channel. Retrying...")
select {
case <-session.done:
return true
case <-time.After(reInitDelay):
}
continue
}
select {
case <-session.done:
return true
case <-session.notifyConnClose:
log.Println("Connection closed. Reconnecting...")
return false
case <-session.notifyChanClose:
log.Println("Channel closed. Re-running init...")
}
}
}
// init will initialize channel & declare queue
func (session *Session) init(conn *amqp.Connection) error {
ch, err := conn.Channel()
if err != nil {
return err
}
err = ch.Confirm(false)
if err != nil {
return err
}
_, err = ch.QueueDeclare(
session.name,
false, // Durable
false, // Delete when unused
false, // Exclusive
false, // No-wait
nil, // Arguments
)
if err != nil {
return err
}
session.changeChannel(ch)
session.isReady = true
log.Println("Setup!")
return nil
}
// changeConnection takes a new connection to the queue,
// and updates the close listener to reflect this.
func (session *Session) changeConnection(connection *amqp.Connection) {
session.connection = connection
session.notifyConnClose = make(chan *amqp.Error)
session.connection.NotifyClose(session.notifyConnClose)
}
// changeChannel takes a new channel to the queue,
// and updates the channel listeners to reflect this.
func (session *Session) changeChannel(channel *amqp.Channel) {
session.channel = channel
session.notifyChanClose = make(chan *amqp.Error)
session.notifyConfirm = make(chan amqp.Confirmation, 1)
session.channel.NotifyClose(session.notifyChanClose)
session.channel.NotifyPublish(session.notifyConfirm)
}
// Push will push data onto the queue, and wait for a confirm.
// If no confirms are received until within the resendTimeout,
// it continuously re-sends messages until a confirm is received.
// This will block until the server sends a confirm. Errors are
// only returned if the push action itself fails, see UnsafePush.
func (session *Session) Push(data []byte) error {
if !session.isReady {
return errors.New("failed to push: not connected")
}
for {
err := session.UnsafePush(data)
if err != nil {
session.logger.Println("Push failed. Retrying...")
select {
case <-session.done:
return errShutdown
case <-time.After(resendDelay):
}
continue
}
select {
case confirm := <-session.notifyConfirm:
if confirm.Ack {
session.logger.Println("Push confirmed!")
return nil
}
case <-time.After(resendDelay):
}
session.logger.Println("Push didn't confirm. Retrying...")
}
}
// UnsafePush will push to the queue without checking for
// confirmation. It returns an error if it fails to connect.
// No guarantees are provided for whether the server will
// recieve the message.
func (session *Session) UnsafePush(data []byte) error {
if !session.isReady {
return errNotConnected
}
return session.channel.Publish(
"", // Exchange
session.name, // Routing key
false, // Mandatory
false, // Immediate
amqp.Publishing{
ContentType: "text/plain",
Body: data,
},
)
}
// Stream will continuously put queue items on the channel.
// It is required to call delivery.Ack when it has been
// successfully processed, or delivery.Nack when it fails.
// Ignoring this will cause data to build up on the server.
func (session *Session) Stream() (<-chan amqp.Delivery, error) {
if !session.isReady {
return nil, errNotConnected
}
return session.channel.Consume(
session.name,
"", // Consumer
false, // Auto-Ack
false, // Exclusive
false, // No-local
false, // No-Wait
nil, // Args
)
}
// Close will cleanly shutdown the channel and connection.
func (session *Session) Close() error {
if !session.isReady {
return errAlreadyClosed
}
err := session.channel.Close()
if err != nil {
return err
}
err = session.connection.Close()
if err != nil {
return err
}
close(session.done)
session.isReady = false
return nil
}