vendor/github.com/Sirupsen/logrus/text_formatter.go

package logrus

import (
	"bytes"
	"fmt"
	"runtime"
	"sort"
	"strings"
	"time"
)

const (
	nocolor = 0
	red     = 31
	green   = 32
	yellow  = 33
	blue    = 34
	gray    = 37
)

var (
	baseTimestamp time.Time
	isTerminal    bool
)

func init() {
	baseTimestamp = time.Now()
	isTerminal = IsTerminal()
}

type TextFormatter struct {
	// Set to true to bypass checking for a TTY before outputting colors.
	ForceColors bool

	// Force disabling colors.
	DisableColors bool

	// Disable timestamp logging. useful when output is redirected to logging
	// system that already adds timestamps.
	DisableTimestamp bool

	// Enable logging the full timestamp when a TTY is attached instead of just
	// the time passed since beginning of execution.
	FullTimestamp bool

	// TimestampFormat to use for display when a full timestamp is printed
	TimestampFormat string

	// The fields are sorted by default for a consistent output. For applications
	// that log extremely frequently and don't use the JSON formatter this may not
	// be desired.
	DisableSorting bool
}

func (f *TextFormatter) Format(entry *Entry) ([]byte, error) {
	var b *bytes.Buffer
	keys := make([]string, 0, len(entry.Data))
	for k := range entry.Data {
		keys = append(keys, k)
	}

	if !f.DisableSorting {
		sort.Strings(keys)
	}
	if entry.Buffer != nil {
		b = entry.Buffer
	} else {
		b = &bytes.Buffer{}
	}

	prefixFieldClashes(entry.Data)

	isColorTerminal := isTerminal && (runtime.GOOS != "windows")
	isColored := (f.ForceColors || isColorTerminal) && !f.DisableColors

	timestampFormat := f.TimestampFormat
	if timestampFormat == "" {
		timestampFormat = DefaultTimestampFormat
	}
	if isColored {
		f.printColored(b, entry, keys, timestampFormat)
	} else {
		if !f.DisableTimestamp {
			f.appendKeyValue(b, "time", entry.Time.Format(timestampFormat))
		}
		f.appendKeyValue(b, "level", entry.Level.String())
		if entry.Message != "" {
			f.appendKeyValue(b, "msg", entry.Message)
		}
		for _, key := range keys {
			f.appendKeyValue(b, key, entry.Data[key])
		}
	}

	b.WriteByte('\n')
	return b.Bytes(), nil
}

func (f *TextFormatter) printColored(b *bytes.Buffer, entry *Entry, keys []string, timestampFormat string) {
	var levelColor int
	switch entry.Level {
	case DebugLevel:
		levelColor = gray
	case WarnLevel:
		levelColor = yellow
	case ErrorLevel, FatalLevel, PanicLevel:
		levelColor = red
	default:
		levelColor = blue
	}

	levelText := strings.ToUpper(entry.Level.String())[0:4]

	if f.DisableTimestamp {
		fmt.Fprintf(b, "\x1b[%dm%s\x1b[0m %-44s ", levelColor, levelText, entry.Message)
	} else if !f.FullTimestamp {
		fmt.Fprintf(b, "\x1b[%dm%s\x1b[0m[%04d] %-44s ", levelColor, levelText, int(entry.Time.Sub(baseTimestamp)/time.Second), entry.Message)
	} else {
		fmt.Fprintf(b, "\x1b[%dm%s\x1b[0m[%s] %-44s ", levelColor, levelText, entry.Time.Format(timestampFormat), entry.Message)
	}
	for _, k := range keys {
		v := entry.Data[k]
		fmt.Fprintf(b, " \x1b[%dm%s\x1b[0m=", levelColor, k)
		f.appendValue(b, v)
	}
}

func needsQuoting(text string) bool {
	for _, ch := range text {
		if !((ch >= 'a' && ch <= 'z') ||
			(ch >= 'A' && ch <= 'Z') ||
			(ch >= '0' && ch <= '9') ||
			ch == '-' || ch == '.') {
			return true
		}
	}
	return false
}

func (f *TextFormatter) appendKeyValue(b *bytes.Buffer, key string, value interface{}) {

	b.WriteString(key)
	b.WriteByte('=')
	f.appendValue(b, value)
	b.WriteByte(' ')
}

func (f *TextFormatter) appendValue(b *bytes.Buffer, value interface{}) {
	switch value := value.(type) {
	case string:
		if !needsQuoting(value) {
			b.WriteString(value)
		} else {
			fmt.Fprintf(b, "%q", value)
		}
	case error:
		errmsg := value.Error()
		if !needsQuoting(errmsg) {
			b.WriteString(errmsg)
		} else {
			fmt.Fprintf(b, "%q", errmsg)
		}
	default:
		fmt.Fprint(b, value)
	}
}