Handle colors

[iTrooz]

Currently, the encoder doesn't accept colors in field keys. Example:

package main

import (
	"os"

	"github.com/fatih/color"
	"github.com/go-logfmt/logfmt"
)

func main() {
	key := color.New(color.FgGreen).Sprintf("mykey")
	e := logfmt.NewEncoder(os.Stdout)
	e.EncodeKeyval(key, "myvalue")
	e.EndRecord()
        // will print "[32mmykey[0m=myvalue", without color
}

I'm not sure how to allow them, while keeping your invalid character filtering, but I think handling colors would have real use cases

[ChrisHines]

This package intends to produce output that is as machine parsable as possible while still being easy on human eyes. Adding the color codes defeats machine parsing. So this request is out of scope for this package.

I contributed colored logging to github.com/go-kit/log which uses this package for its logfmt logger. In that case, though the color is applied to entire log lines, not individual fields or keys. If that sounds useful then take a look at package github.com/go-kit/log/term.

[iTrooz]

Adding the color codes defeats machine parsing

It does if used carelessly. But if you look at https://github.com/Sirupsen/logrus, they are using coloured keys for ease of development, and disable it when running in a server environment, allowing for machine-parsable logs.

For now, I wrote a basic "implementation" of the encoder instead (ref: vmware-tanzu/velero#9317) to allow for these colored keys, but I hope you can reconsider this choice to help with development/other user-facing environments