logformat enhancement

[notzippy]

It would be nice if I could specify a series of keys into TerminalFormat so that I could layout the key values in a specific named order like

func TerminalFormat(contextKeys []string, "[%s] [%s] %s %s %-40s %s") log.Format { 

Missing context keys would be passed empty strings, unused context items would be added to the end

BTW noticed the following in format

    // try to justify the log output for short messages
    if len(r.Ctx) > 0 && len(r.Msg) < termMsgJust {
        b.Write(bytes.Repeat([]byte{' '}, termMsgJust-len(r.Msg)))
    }

That could be removed by changing the above format statements to

    if color > 0 {
        fmt.Fprintf(b, "\x1b[%dm%s\x1b[0m[%s] %-40s ", color, lvl, r.Time.Format(termTimeFormat), r.Msg)
    } else {
        fmt.Fprintf(b, "[%s] [%s] %-40s ", lvl, r.Time.Format(termTimeFormat), r.Msg)
    }

The "%-40s" provides the right pad

This is a great package, the value of the MatchFilterHandler is underated and makes this the perfect tool for module logs. thanks !

[ChrisHines]

Interesting idea. Have you seen the discussion on issue #14?

I'm on the fence here. On the one hand TerminalFormat is documented as not recommended for production uses because it isn't as machine parsable as other formats, so giving the developer some control seems reasonable. On the other hand it goes against log15's opinion that we should prefer machine parsable log formats.

If we did include a format like this in log15 we would prefer to create a new format rather than breaking the v2 API by changing the existing TerminalFormat.

[notzippy]

I looked at #14 and I agree that machine parsable code is far better to store historical data, that said watching an os.StdOut dump visually is far easier if we can specify the order. For example in my web application the logger will always have the ip, module and controller in the log context so I would like to be able to specify for the terminal output those items first, then the message then any other context.

And I am ok with a new Formatter implementing this.