Allow the timestamp field to be customized

[savaki]

Currently, the timestamp is defined to be unix nanos within the field, "ts". I'd like to be able to pump the logs directly into third party services like loggly which have a different naming requirement and format for the timestamp field.

Was thinking of something like this:

https://github.com/savaki/zap

[akshayjshah]

@savaki I've never used Loggly before. From https://www.loggly.com/docs/automated-parsing/#json, it looks we want the flexibility to (a) call the field timestamp, and (b) encode time.Times using ISO-8601. Is that right?

[savaki]

Correct. I'm using my forked version now to publish logs to loggly.

func appendTimestamp(data []byte, t time.Time) []byte {
    data = append(data, `,"timestamp":"`...)
    data = t.UTC().AppendFormat(data, "2006-01-02T15:04:05.000Z")
    return append(data, `"`...)
}

func sample() {
    logger = zap.NewJSON(zap.Output(output), zap.Append(appendTimestamp))
}

[akshayjshah]

Gotcha. I think we can actually provide a little more flexibility than that - it should be easy enough to allow users to configure nearly everything about the final message (time format, key names, etc.).

I'll try to open a PR this weekend. When I do, I'll tag you - let me know what you think.

[savaki]

awesome, thanks.

[akshayjshah]

Note to self: this should also replace the StubTime kludge currently in the Logger interface.

[garo]

+1 here, we require our 'ts' field to be ISO-8601 format (ie. "2006-01-02T15:04:05.000Z")

[akshayjshah]

Addressed in #115. You can now customize your timestamps with something like this:

logger := zap.New(
  zap.NewJSONEncoder(zap.RFC3339Formatter("@timestamp")),
  zap.ErrorLevel,
  zap.Output(someFile),
)

If your preferred time format isn't supported out of the box, it should be easy to plug in your own TimeFormatter.