A robust rabbitmq client for Go

caller.go

go func() {
	for {
		err = rmq.Stream(cancelCtx)
		if errors.Is(err, rabbitmq.ErrDisconnected) {
			continue
		}
		break
	}
}()

rabbitmq.go

var (
	ErrDisconnected             = errors.New("disconnected from rabbitmq, trying to reconnect")
)

const (
    // When reconnecting to the server after connection failure
    reconnectDelay = 5 * time.Second

    // When resending messages the server didn't confirm
    resendDelay = 5 * time.Second
)

// Client holds necessery information for rabbitMQ
type Client struct {
    pushQueue     string
    streamQueue   string
    logger        zerolog.Logger
    connection    *amqp.Connection
    channel       *amqp.Channel
    done          chan os.Signal
    notifyClose   chan *amqp.Error
    notifyConfirm chan amqp.Confirmation
    isConnected   bool
    alive         bool
    threads       int
    wg            *sync.WaitGroup
}

// New is a constructor that takes address, push and listen queue names, logger, and a channel that will notify rabbitmq client on server shutdown. We calculate the number of threads, create the client, and start the connection process. Connect method connects to the rabbitmq server and creates push/listen channels if they don't exist.
func New(streamQueue, pushQueue, addr string, l zerolog.Logger, done chan os.Signal) *Client {
    threads := runtime.GOMAXPROCS(0)
    if numCPU := runtime.NumCPU(); numCPU > threads {
        threads = numCPU
    }

    client := Client{
        logger:       l,
        threads:      threads,
        pushQueue:    pushQueue,
	streamQueue:  streamQueue,
        done:         done,
        alive:        true,
        wg:           &sync.WaitGroup{},
    }

    go client.handleReconnect(addr)
    return &client
}

// handleReconnect will wait for a connection error on
// notifyClose, and then continuously attempt to reconnect.
func (c *Client) handleReconnect(addr string) {
    for c.alive {
        c.isConnected = false
        t := time.Now()
        fmt.Printf("Attempting to connect to rabbitMQ: %s\n", addr)
        var retryCount int
        for !c.connect(addr) {
            if !c.alive {
				return
			}
            select {
			case <-c.done:
				return
			case <-time.After(reconnectDelay + time.Duration(retryCount)*time.Second):
                c.logger.Printf("disconnected from rabbitMQ and failed to connect")
				retryCount++
			}
        }
        c.logger.Printf("Connected to rabbitMQ in: %vms", time.Since(t).Milliseconds())
        select {
        case <-c.done:
            return
        case <-c.notifyClose:
        }
    }
}

// connect will make a single attempt to connect to
// RabbitMq. It returns the success of the attempt.
func (c *Client) connect(addr string) bool {
    conn, err := amqp.Dial(addr)
    if err != nil {
        c.logger.Printf("failed to dial rabbitMQ server: %v", err)
        return false
    }
    ch, err := conn.Channel()
    if err != nil {
        c.logger.Printf("failed connecting to channel: %v", err)
        return false
    }
    ch.Confirm(false)
    _, err = ch.QueueDeclare(
        c.streamQueue,
        true,  // Durable
        false, // Delete when unused
        false, // Exclusive
        false, // No-wait
        nil,   // Arguments
    )
    if err != nil {
        c.logger.Printf("failed to declare stream queue: %v", err)
        return false
    }

    _, err = ch.QueueDeclare(
        c.pushQueue,
        true,  // Durable
        false, // Delete when unused
        false, // Exclusive
        false, // No-wait
        nil,   // Arguments
    )
    if err != nil {
        c.logger.Printf("failed to declare push queue: %v", err)
        return false
    }
    c.changeConnection(conn, ch)
    c.isConnected = true
    return true
}

// changeConnection takes a new connection to the queue,
// and updates the channel listeners to reflect this.
func (c *Client) changeConnection(connection *amqp.Connection, channel *amqp.Channel) {
    c.connection = connection
    c.channel = channel
    c.notifyClose = make(chan *amqp.Error)
    c.notifyConfirm = make(chan amqp.Confirmation)
    c.channel.NotifyClose(c.notifyClose)
    c.channel.NotifyPublish(c.notifyConfirm)
}

// Push will push data onto the queue, and wait for a confirmation.
// If no confirms are received until within the resendTimeout,
// it continuously resends messages until a confirmation is received.
// This will block until the server sends a confirm.
func (c *Client) Push(data []byte) error {
    if !c.isConnected {
        return errors.New("failed to push push: not connected")
    }
    for {
        err := c.UnsafePush(data)
        if err != nil {
            if err == ErrDisconnected {
                continue
            }
            return err
        }
        select {
        case confirm := <-c.notifyConfirm:
            if confirm.Ack {
                return nil
            }
        case <-time.After(resendDelay):
        }
    }
}

// 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
// receive the message.
func (c *Client) UnsafePush(data []byte) error {
    if !c.isConnected {
        return ErrDisconnected
    }
    return c.channel.Publish(
        "",     // Exchange
        c.pushQueue, // Routing key
        false,  // Mandatory
        false,  // Immediate
        amqp.Publishing{
            ContentType: "text/plain",
            Body:        data,
        },
    )
}

func (c *Client) Stream(cancelCtx context.Context) error {
    c.wg.Add(threads)

    for {
        if c.isConnected {
            break
        }
        time.Sleep(1 * time.Second)
    }

    err := c.channel.Qos(1, 0, false)
    if err != nil {
        return err
    }

    var connectionDropped bool

    for i := 1; i <= c.threads; i++ {
        msgs, err := c.channel.Consume(
            c.streamQueue,
            consumerName(i), // Consumer
            false,           // Auto-Ack
            false,           // Exclusive
            false,           // No-local
            false,           // No-Wait
            nil,             // Args
        )
        if err != nil {
            return err
        }

        go func() {
            defer c.wg.Done()
            for {
                select {
                    case <-cancelCtx.Done():
                    	return
                    case msg, ok := <-msgs:
                    	if !ok {
                            connectionDropped = true
                            return
                    	}
                    	c.parseEvent(msg)
                    }
                }
        }()

    }

    c.wg.Wait()

    if connectionDropped {
        return ErrDisconnected
    }

    return nil
}

type event struct{
    Job string `json:"job"`
    Data string `json:"data"`
}

func (c *Client) parseEvent(msg amqp.Delivery) {
    l := c.logger.Log().Timestamp()
    startTime := time.Now()

    var evt event
    err := json.Unmarshal(msg.Body, &evt)
    if err != nil {
        logAndNack(msg, l, startTime, "unmarshalling body: %s - %s", string(msg.Body), err.Error())
        return
    }

    if evt.Data == "" {
        logAndNack(msg, l, startTime, "received event without data")
        return
    }

    defer func(ctx context.Context, e event, m amqp.Delivery, logger *zerolog.Event) {
        if err := recover(); err != nil {
            stack := make([]byte, 8096)
            stack = stack[:runtime.Stack(stack, false)]
            l.Bytes("stack", stack).Str("level", "fatal").Interface("error", err).Msg("panic recovery for rabbitMQ message")
            msg.Nack(false, false)
        }
    }(ctx, evt, msg, l)

    switch evt.Job {
    case "job1":
        // Call an actual function
        err = func()
    case "job1":
        err = func()
    default:
        msg.Reject(false)
        return
    }

    if err != nil {
        logAndNack(msg, l, startTime, err.Error())
        return
    }

    l.Str("level", "info").Int64("took-ms", time.Since(startTime).Milliseconds()).Msgf("%s succeeded", evt.Job)
    msg.Ack(false)
}

func logAndNack(msg amqp.Delivery, l *zerolog.Event, t time.Time, err string, args ...interface{}) {
    msg.Nack(false, false)
    l.Int64("took-ms", time.Since(t).Milliseconds()).Str("level", "error").Msg(fmt.Sprintf(err, args...))
}

func (c *Client) Close() error {
    if !c.isConnected {
        return nil
    }
    c.alive = false
    fmt.Println("Waiting for current messages to be processed...")
    c.wg.Wait()
    for i := 1; i <= c.threads; i++ {
        fmt.Println("Closing consumer: ", i)
        err := c.channel.Cancel(consumerName(i), false)
        if err != nil {
            return fmt.Errorf("error canceling consumer %s: %v", consumerName(i), err)
        }
    }
    err := c.channel.Close()
    if err != nil {
        return err
    }
    err = c.connection.Close()
    if err != nil {
        return err
    }
    c.isConnected = false
    fmt.Println("gracefully stopped rabbitMQ connection")
    return nil
}

func consumerName(i int) string {
    return fmt.Sprintf("go-consumer-%v", i)
}

What's the q in L#55?

What's the q in L#55?

Thanks for noticing, fixed this! Receiver in my actual code is named q and not c, thus this typo.

Wow, your code looks great. I am starting to use go for my personal projects with rest api and i was looking for more in depth proof of concepts

@ribice Can you look at this please ? I do not understand you hadlereconnect logic. How do i properly instatie my client so it ca be used any time i need ? https://gist.github.com/s0j0hn/06492e218e51bfd67421450aa66c586c

	goChan := make(chan os.Signal, 1)
	clientV2 := V2.New("listenqueue", "pushqueue", config.GetRabbitMQAccess(), log.Logger, goChan)

	go func() {
		for {
			select {
			case <- goChan:
				taskBytes := rabbitmq.CreateNewTaskV2([]string{"test", "test2"}, "Status is OK")
				err = clientV2.UnsafePush(taskBytes)
				if err != nil {
					echoServer.Logger.Fatal(err)
					os.Exit(1)
				}
				return
			default:
				// Do other stuff
			}
		}
	}()

EDIT: I updated my version and everything works

@ribice, Thank you very much for the example. I would like just to add a note about the following error which could occur after reconnecting to a RabbitMQ server:

panic: sync: negative WaitGroup counter

When the connection drops, c.wg.Done() on L222 will decrease the counter in WaitGroup to 0. After reconnecting to the server, the counter remains 0 because there isn't a c.wg.Add() call to increase it. When the connection drops again or you try to shut down the application, c.wg.Done() is called again and panic occurs.

I have managed to fix the problem by deleting client.wg.Add(threads) from L40 and putting c.wg.Add(1) before calling the goroutine in Stream() function.

Cheers 🍻

There's a duplicated UnsafePush() method https://gist.github.com/ribice/20951bd1c84d714ff2476465c0c0653f#file-rabbitmq-go-L156-L190

hai, where is this c.streamQueue come from?

Thanks for reporting @sundowndev and @mshddev, I fixed both issues.

1. missing a comma
2. undefined variable resendDelay
3. undefined variable name in client struct

@dikkini: Thanks, addressed those.

What is recover() at L259?

another thing is that can we use the raw type to communicate between the goroutine? I mean the alive and isConnected

https://golangbyexample.com/recover-example-go/

@ribice, Thank you very much for the example. I would like just to add a note about the following error which could occur after reconnecting to a RabbitMQ server:

panic: sync: negative WaitGroup counter

When the connection drops, c.wg.Done() on L222 will decrease the counter in WaitGroup to 0. After reconnecting to the server, the counter remains 0 because there isn't a c.wg.Add() call to increase it. When the connection drops again or you try to shut down the application, c.wg.Done() is called again and panic occurs.

I have managed to fix the problem by deleting client.wg.Add(threads) from L40 and putting c.wg.Add(1) before calling the goroutine in Stream() function.

Cheers 🍻

Awesome fix.

@ribice, Thank you very much for the example. I would like just to add a note about the following error which could occur after reconnecting to a RabbitMQ server:

panic: sync: negative WaitGroup counter

When the connection drops, c.wg.Done() on L222 will decrease the counter in WaitGroup to 0. After reconnecting to the server, the counter remains 0 because there isn't a c.wg.Add() call to increase it. When the connection drops again or you try to shut down the application, c.wg.Done() is called again and panic occurs.

I have managed to fix the problem by deleting client.wg.Add(threads) from L40 and putting c.wg.Add(1) before calling the goroutine in Stream() function.

Cheers 🍻

Thanks. I noticed that I did this change long ago on my environment, but forgot to update Gist. Will do that today.

I update Gist, hope that's correct now.

Hey, how should I use this library in an architecture that consists of 1 producer and 3 subscriber? Basically my producer microservice will publish a message and 3 of the receiver services will consume it. There will be only one queue and it is fanout type. How should I structure my code regarding this library? It looks a bit complicated to me.

Could you explain a bit more how does handleReconnect function work? And why do we need both alive and isConnected booleans?

L181: I assume threads is c.threads?