Catch error on startup

[randomandy]

So I have something like this:

    func init() {
    ...
        server, err := machinery.NewServer(&cnf)
        if err != nil {
            // some error handling
        }

        server.RegisterTasks(tasks)

        worker = server.NewWorker("machinery_worker")
    ...

    func main() {
        err := worker.Launch()
        if err != nil {
            // some error handling
        }
    }

which leads to this if the worker cannot connect to the broker on startup:

    2016/04/20 16:01:59 Launching a worker with the following settings:
    2016/04/20 16:01:59 - Broker: amqp://some_url
    2016/04/20 16:01:59 - ResultBackend: amqp://some_url
    2016/04/20 16:01:59 - Exchange: machinery_exchange
    2016/04/20 16:01:59 - ExchangeType: direct
    2016/04/20 16:01:59 - DefaultQueue: machinery_tasks
    2016/04/20 16:01:59 - BindingKey: machinery_task
    panic: runtime error: invalid memory address or nil pointer dereference
    [signal 0xb code=0x1 addr=0x20 pc=0x3495e9]

    goroutine 5 [running]:
    panic(0x4d3680, 0xc82000a0d0)
        /usr/local/go/src/runtime/panic.go:464 +0x3e6
    github.com/RichardKnop/machinery/vendor/github.com/streadway/amqp.(*Channel).Close(0x0, 0x0, 0x0)
        /Users/andy/checkouts/golang/src/github.com/RichardKnop/machinery/vendor/github.com/streadway/amqp/channel.go:402 +0x39
    github.com/RichardKnop/machinery/v1/brokers.(*AMQPBroker).StartConsuming(0xc8200165c0, 0x5d7220, 0x10, 0xc44828, 0xc8200bd500, 0x1, 0xc40028, 0xc8200e2050)
        /Users/andy/checkouts/golang/src/github.com/RichardKnop/machinery/v1/brokers/amqp.go:57 +0x156
    github.com/RichardKnop/machinery/v1.(*Worker).Launch.func1(0xc44740, 0xc8200165c0, 0xc8200bd500, 0xc820010540)
        /Users/andy/checkouts/golang/src/github.com/RichardKnop/machinery/v1/worker.go:38 +0xa2
    created by github.com/RichardKnop/machinery/v1.(*Worker).Launch
        /Users/andy/checkouts/golang/src/github.com/RichardKnop/machinery/v1/worker.go:47 +0x67d

I'm trying to figure out where the process dies. server.RegisterTasks(tasks) or in worker = server.NewWorker("machinery_worker") (I'm catching all other errors).

Although the output would suggest that the error actually occurs during worker.Launch(), which leads me to believe that there's a bug in the error handling (because err comes back as nil)?

[randomandy]

Ok so I'm pretty sure it happens here:
broker.StartConsuming()
inside Launch()

[randomandy]

This fixes it:

func (worker *Worker) Launch() error {
    cnf := worker.server.GetConfig()
    broker := worker.server.GetBroker()

    log.Printf("Launching a worker with the following settings:")
    log.Printf("- Broker: %s", cnf.Broker)
    log.Printf("- ResultBackend: %s", cnf.ResultBackend)
    log.Printf("- Exchange: %s", cnf.Exchange)
    log.Printf("- ExchangeType: %s", cnf.ExchangeType)
    log.Printf("- DefaultQueue: %s", cnf.DefaultQueue)
    log.Printf("- BindingKey: %s", cnf.BindingKey)

    errorsChan := make(chan error)

    go func() {
        for {
            retry, err := broker.StartConsuming(worker.ConsumerTag, worker)
            if err != nil {
                errorsChan <- err
            }

            if retry {
                log.Printf("Going to retry launching the worker. Error: %v", err)
            }
        }
    }()

    return <-errorsChan
}

[RichardKnop]

@randomandy HI Andy. Thanks for catching this bug!

I'm quite busy at the moment so it might take me few days to take a look. If you want, create a PR with a fix and I will try to look at it and merge it this weekend if time allows.

[randomandy]

@RichardKnop Hey Richard. Sure thing, happy to help. Fix is in #76