Go logging with multiple backend

Question

I'm using go-logging and I'm trying to build a logger with a variable number of Backends (i.e. stderr + file + syslog + ...). So my program reads a configuration file, and create the logger according to what's defined.

As SetBackend is a variadic function, I thought I could use a slice as argument, but I was wrong.

Here is an example of my code:

func configureLogger(debug, file bool) {
    var backendList = []logging.Backend{}
    var format = logging.MustStringFormatter(
        `%{color}%{time:15:04:05.000} [%{level:.4s}] %{shortfunc}%{color:reset}: %{message}`,
    )

    if debug {
        consoleBackend := logging.NewLogBackend(os.Stderr, "", 0)
        consoleBackendFormatter := logging.NewBackendFormatter(consoleBackend, format)
        consoleBackendLeveled := logging.AddModuleLevel(consoleBackendFormatter)
        consoleBackendLeveled.SetLevel(logging.DEBUG, "")
        backendList = append(backendList, consoleBackendLeveled)
    }

    if file {
        f, err := os.OpenFile("file.log", os.O_APPEND|os.O_CREATE|os.O_RDWR, 0644)
        filebackend := logging.NewLogBackend(f, "", 0)
        filebackendFormatter := logging.NewBackendFormatter(filebackend, format)
        filebackendLeveled := logging.AddModuleLevel(filebackendFormatter)
        filebackendLeveled.SetLevel(logging.DEBUG, "")
        backendList = append(backendList, filebackendLeveled)
    }

    logging.SetBackend(backendList)
}

This end up with the following error:

cannot use backendList (type []logging.Backend) as type logging.Backend in argument to logging.SetBackend:
    []logging.Backend does not implement logging.Backend (missing Log method)

What am I missing?

chilladx · Accepted Answer · 2017-05-18 14:58:32Z

2

I was missing the good syntax. When passing a slice to a variadic function, you need to add ... after your slice name, as shown in the specs: https://golang.org/ref/spec#Passing_arguments_to_..._parameters

The right syntax is:

logging.SetBackend(backendList...)

answered May 18, 2017 at 14:58

chilladx

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