worker: use openapi spec and generated code

Write an openapi spec for the worker API and use `deepmap/oapi-codegen`
to generate scaffolding for the server-side using the `labstack/echo`
server.

Incidentally, echo by default returns the errors in the same format that
worker API always has:

    { "message": "..." }

The API itself is unchanged to make this change easier to understand. It
will be changed to better suit our needs in future commits.

vendor/github.com/labstack/gommon/LICENSE

@@ -0,0 +1,22 @@
+The MIT License (MIT)
+
+Copyright (c) 2018 labstack
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+

vendor/github.com/labstack/gommon/color/README.md

@@ -0,0 +1,86 @@
+# Color
+
+Style terminal text.
+
+## Installation
+
+```sh
+go get github.com/labstack/gommon/color
+```
+
+## Windows?
+
+Try [cmder](http://bliker.github.io/cmder) or https://github.com/mattn/go-colorable
+
+## [Usage](https://github.com/labstack/gommon/blob/master/color/color_test.go)
+
+```sh
+import github.com/labstack/gommon/color
+```
+
+### Colored text
+
+```go
+color.Println(color.Black("black"))
+color.Println(color.Red("red"))
+color.Println(color.Green("green"))
+color.Println(color.Yellow("yellow"))
+color.Println(color.Blue("blue"))
+color.Println(color.Magenta("magenta"))
+color.Println(color.Cyan("cyan"))
+color.Println(color.White("white"))
+color.Println(color.Grey("grey"))
+```
+![Colored Text](http://i.imgur.com/8RtY1QR.png)
+
+### Colored background
+
+```go
+color.Println(color.BlackBg("black background", color.Wht))
+color.Println(color.RedBg("red background"))
+color.Println(color.GreenBg("green background"))
+color.Println(color.YellowBg("yellow background"))
+color.Println(color.BlueBg("blue background"))
+color.Println(color.MagentaBg("magenta background"))
+color.Println(color.CyanBg("cyan background"))
+color.Println(color.WhiteBg("white background"))
+```
+![Colored Background](http://i.imgur.com/SrrS6lw.png)
+
+### Emphasis
+
+```go
+color.Println(color.Bold("bold"))
+color.Println(color.Dim("dim"))
+color.Println(color.Italic("italic"))
+color.Println(color.Underline("underline"))
+color.Println(color.Inverse("inverse"))
+color.Println(color.Hidden("hidden"))
+color.Println(color.Strikeout("strikeout"))
+```
+![Emphasis](http://i.imgur.com/3RSJBbc.png)
+
+### Mix and match
+
+```go
+color.Println(color.Green("bold green with white background", color.B, color.WhtBg))
+color.Println(color.Red("underline red", color.U))
+color.Println(color.Yellow("dim yellow", color.D))
+color.Println(color.Cyan("inverse cyan", color.In))
+color.Println(color.Blue("bold underline dim blue", color.B, color.U, color.D))
+```
+![Mix and match](http://i.imgur.com/jWGq9Ca.png)
+
+### Enable/Disable the package
+
+```go
+color.Disable()
+color.Enable()
+```
+
+### New instance
+
+```go
+c := New()
+c.Green("green")
+```

vendor/github.com/labstack/gommon/color/color.go

@@ -0,0 +1,407 @@
+package color
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+
+	"github.com/mattn/go-colorable"
+	"github.com/mattn/go-isatty"
+)
+
+type (
+	inner func(interface{}, []string, *Color) string
+)
+
+// Color styles
+const (
+	// Blk Black text style
+	Blk = "30"
+	// Rd red text style
+	Rd = "31"
+	// Grn green text style
+	Grn = "32"
+	// Yel yellow text style
+	Yel = "33"
+	// Blu blue text style
+	Blu = "34"
+	// Mgn magenta text style
+	Mgn = "35"
+	// Cyn cyan text style
+	Cyn = "36"
+	// Wht white text style
+	Wht = "37"
+	// Gry grey text style
+	Gry = "90"
+
+	// BlkBg black background style
+	BlkBg = "40"
+	// RdBg red background style
+	RdBg = "41"
+	// GrnBg green background style
+	GrnBg = "42"
+	// YelBg yellow background style
+	YelBg = "43"
+	// BluBg blue background style
+	BluBg = "44"
+	// MgnBg magenta background style
+	MgnBg = "45"
+	// CynBg cyan background style
+	CynBg = "46"
+	// WhtBg white background style
+	WhtBg = "47"
+
+	// R reset emphasis style
+	R = "0"
+	// B bold emphasis style
+	B = "1"
+	// D dim emphasis style
+	D = "2"
+	// I italic emphasis style
+	I = "3"
+	// U underline emphasis style
+	U = "4"
+	// In inverse emphasis style
+	In = "7"
+	// H hidden emphasis style
+	H = "8"
+	// S strikeout emphasis style
+	S = "9"
+)
+
+var (
+	black   = outer(Blk)
+	red     = outer(Rd)
+	green   = outer(Grn)
+	yellow  = outer(Yel)
+	blue    = outer(Blu)
+	magenta = outer(Mgn)
+	cyan    = outer(Cyn)
+	white   = outer(Wht)
+	grey    = outer(Gry)
+
+	blackBg   = outer(BlkBg)
+	redBg     = outer(RdBg)
+	greenBg   = outer(GrnBg)
+	yellowBg  = outer(YelBg)
+	blueBg    = outer(BluBg)
+	magentaBg = outer(MgnBg)
+	cyanBg    = outer(CynBg)
+	whiteBg   = outer(WhtBg)
+
+	reset     = outer(R)
+	bold      = outer(B)
+	dim       = outer(D)
+	italic    = outer(I)
+	underline = outer(U)
+	inverse   = outer(In)
+	hidden    = outer(H)
+	strikeout = outer(S)
+
+	global = New()
+)
+
+func outer(n string) inner {
+	return func(msg interface{}, styles []string, c *Color) string {
+		// TODO: Drop fmt to boost performance?
+		if c.disabled {
+			return fmt.Sprintf("%v", msg)
+		}
+
+		b := new(bytes.Buffer)
+		b.WriteString("\x1b[")
+		b.WriteString(n)
+		for _, s := range styles {
+			b.WriteString(";")
+			b.WriteString(s)
+		}
+		b.WriteString("m")
+		return fmt.Sprintf("%s%v\x1b[0m", b.String(), msg)
+	}
+}
+
+type (
+	Color struct {
+		output   io.Writer
+		disabled bool
+	}
+)
+
+// New creates a Color instance.
+func New() (c *Color) {
+	c = new(Color)
+	c.SetOutput(colorable.NewColorableStdout())
+	return
+}
+
+// Output returns the output.
+func (c *Color) Output() io.Writer {
+	return c.output
+}
+
+// SetOutput sets the output.
+func (c *Color) SetOutput(w io.Writer) {
+	c.output = w
+	if w, ok := w.(*os.File); !ok || !isatty.IsTerminal(w.Fd()) {
+		c.disabled = true
+	}
+}
+
+// Disable disables the colors and styles.
+func (c *Color) Disable() {
+	c.disabled = true
+}
+
+// Enable enables the colors and styles.
+func (c *Color) Enable() {
+	c.disabled = false
+}
+
+// Print is analogous to `fmt.Print` with termial detection.
+func (c *Color) Print(args ...interface{}) {
+	fmt.Fprint(c.output, args...)
+}
+
+// Println is analogous to `fmt.Println` with termial detection.
+func (c *Color) Println(args ...interface{}) {
+	fmt.Fprintln(c.output, args...)
+}
+
+// Printf is analogous to `fmt.Printf` with termial detection.
+func (c *Color) Printf(format string, args ...interface{}) {
+	fmt.Fprintf(c.output, format, args...)
+}
+
+func (c *Color) Black(msg interface{}, styles ...string) string {
+	return black(msg, styles, c)
+}
+
+func (c *Color) Red(msg interface{}, styles ...string) string {
+	return red(msg, styles, c)
+}
+
+func (c *Color) Green(msg interface{}, styles ...string) string {
+	return green(msg, styles, c)
+}
+
+func (c *Color) Yellow(msg interface{}, styles ...string) string {
+	return yellow(msg, styles, c)
+}
+
+func (c *Color) Blue(msg interface{}, styles ...string) string {
+	return blue(msg, styles, c)
+}
+
+func (c *Color) Magenta(msg interface{}, styles ...string) string {
+	return magenta(msg, styles, c)
+}
+
+func (c *Color) Cyan(msg interface{}, styles ...string) string {
+	return cyan(msg, styles, c)
+}
+
+func (c *Color) White(msg interface{}, styles ...string) string {
+	return white(msg, styles, c)
+}
+
+func (c *Color) Grey(msg interface{}, styles ...string) string {
+	return grey(msg, styles, c)
+}
+
+func (c *Color) BlackBg(msg interface{}, styles ...string) string {
+	return blackBg(msg, styles, c)
+}
+
+func (c *Color) RedBg(msg interface{}, styles ...string) string {
+	return redBg(msg, styles, c)
+}
+
+func (c *Color) GreenBg(msg interface{}, styles ...string) string {
+	return greenBg(msg, styles, c)
+}
+
+func (c *Color) YellowBg(msg interface{}, styles ...string) string {
+	return yellowBg(msg, styles, c)
+}
+
+func (c *Color) BlueBg(msg interface{}, styles ...string) string {
+	return blueBg(msg, styles, c)
+}
+
+func (c *Color) MagentaBg(msg interface{}, styles ...string) string {
+	return magentaBg(msg, styles, c)
+}
+
+func (c *Color) CyanBg(msg interface{}, styles ...string) string {
+	return cyanBg(msg, styles, c)
+}
+
+func (c *Color) WhiteBg(msg interface{}, styles ...string) string {
+	return whiteBg(msg, styles, c)
+}
+
+func (c *Color) Reset(msg interface{}, styles ...string) string {
+	return reset(msg, styles, c)
+}
+
+func (c *Color) Bold(msg interface{}, styles ...string) string {
+	return bold(msg, styles, c)
+}
+
+func (c *Color) Dim(msg interface{}, styles ...string) string {
+	return dim(msg, styles, c)
+}
+
+func (c *Color) Italic(msg interface{}, styles ...string) string {
+	return italic(msg, styles, c)
+}
+
+func (c *Color) Underline(msg interface{}, styles ...string) string {
+	return underline(msg, styles, c)
+}
+
+func (c *Color) Inverse(msg interface{}, styles ...string) string {
+	return inverse(msg, styles, c)
+}
+
+func (c *Color) Hidden(msg interface{}, styles ...string) string {
+	return hidden(msg, styles, c)
+}
+
+func (c *Color) Strikeout(msg interface{}, styles ...string) string {
+	return strikeout(msg, styles, c)
+}
+
+// Output returns the output.
+func Output() io.Writer {
+	return global.output
+}
+
+// SetOutput sets the output.
+func SetOutput(w io.Writer) {
+	global.SetOutput(w)
+}
+
+func Disable() {
+	global.Disable()
+}
+
+func Enable() {
+	global.Enable()
+}
+
+// Print is analogous to `fmt.Print` with termial detection.
+func Print(args ...interface{}) {
+	global.Print(args...)
+}
+
+// Println is analogous to `fmt.Println` with termial detection.
+func Println(args ...interface{}) {
+	global.Println(args...)
+}
+
+// Printf is analogous to `fmt.Printf` with termial detection.
+func Printf(format string, args ...interface{}) {
+	global.Printf(format, args...)
+}
+
+func Black(msg interface{}, styles ...string) string {
+	return global.Black(msg, styles...)
+}
+
+func Red(msg interface{}, styles ...string) string {
+	return global.Red(msg, styles...)
+}
+
+func Green(msg interface{}, styles ...string) string {
+	return global.Green(msg, styles...)
+}
+
+func Yellow(msg interface{}, styles ...string) string {
+	return global.Yellow(msg, styles...)
+}
+
+func Blue(msg interface{}, styles ...string) string {
+	return global.Blue(msg, styles...)
+}
+
+func Magenta(msg interface{}, styles ...string) string {
+	return global.Magenta(msg, styles...)
+}
+
+func Cyan(msg interface{}, styles ...string) string {
+	return global.Cyan(msg, styles...)
+}
+
+func White(msg interface{}, styles ...string) string {
+	return global.White(msg, styles...)
+}
+
+func Grey(msg interface{}, styles ...string) string {
+	return global.Grey(msg, styles...)
+}
+
+func BlackBg(msg interface{}, styles ...string) string {
+	return global.BlackBg(msg, styles...)
+}
+
+func RedBg(msg interface{}, styles ...string) string {
+	return global.RedBg(msg, styles...)
+}
+
+func GreenBg(msg interface{}, styles ...string) string {
+	return global.GreenBg(msg, styles...)
+}
+
+func YellowBg(msg interface{}, styles ...string) string {
+	return global.YellowBg(msg, styles...)
+}
+
+func BlueBg(msg interface{}, styles ...string) string {
+	return global.BlueBg(msg, styles...)
+}
+
+func MagentaBg(msg interface{}, styles ...string) string {
+	return global.MagentaBg(msg, styles...)
+}
+
+func CyanBg(msg interface{}, styles ...string) string {
+	return global.CyanBg(msg, styles...)
+}
+
+func WhiteBg(msg interface{}, styles ...string) string {
+	return global.WhiteBg(msg, styles...)
+}
+
+func Reset(msg interface{}, styles ...string) string {
+	return global.Reset(msg, styles...)
+}
+
+func Bold(msg interface{}, styles ...string) string {
+	return global.Bold(msg, styles...)
+}
+
+func Dim(msg interface{}, styles ...string) string {
+	return global.Dim(msg, styles...)
+}
+
+func Italic(msg interface{}, styles ...string) string {
+	return global.Italic(msg, styles...)
+}
+
+func Underline(msg interface{}, styles ...string) string {
+	return global.Underline(msg, styles...)
+}
+
+func Inverse(msg interface{}, styles ...string) string {
+	return global.Inverse(msg, styles...)
+}
+
+func Hidden(msg interface{}, styles ...string) string {
+	return global.Hidden(msg, styles...)
+}
+
+func Strikeout(msg interface{}, styles ...string) string {
+	return global.Strikeout(msg, styles...)
+}

vendor/github.com/labstack/gommon/log/README.md

@@ -0,0 +1,5 @@
+## WORK IN PROGRESS
+
+### Usage
+
+[log_test.go](log_test.go)

vendor/github.com/labstack/gommon/log/color.go

@@ -0,0 +1,13 @@
+// +build !appengine
+
+package log
+
+import (
+	"io"
+
+	"github.com/mattn/go-colorable"
+)
+
+func output() io.Writer {
+	return colorable.NewColorableStdout()
+}

vendor/github.com/labstack/gommon/log/log.go

@@ -0,0 +1,416 @@
+package log
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"os"
+	"path"
+	"runtime"
+	"strconv"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"github.com/mattn/go-isatty"
+	"github.com/valyala/fasttemplate"
+
+	"github.com/labstack/gommon/color"
+)
+
+type (
+	Logger struct {
+		prefix     string
+		level      uint32
+		skip       int
+		output     io.Writer
+		template   *fasttemplate.Template
+		levels     []string
+		color      *color.Color
+		bufferPool sync.Pool
+		mutex      sync.Mutex
+	}
+
+	Lvl uint8
+
+	JSON map[string]interface{}
+)
+
+const (
+	DEBUG Lvl = iota + 1
+	INFO
+	WARN
+	ERROR
+	OFF
+	panicLevel
+	fatalLevel
+)
+
+var (
+	global        = New("-")
+	defaultHeader = `{"time":"${time_rfc3339_nano}","level":"${level}","prefix":"${prefix}",` +
+		`"file":"${short_file}","line":"${line}"}`
+)
+
+func init() {
+	global.skip = 3
+}
+
+func New(prefix string) (l *Logger) {
+	l = &Logger{
+		level:    uint32(INFO),
+		skip:     2,
+		prefix:   prefix,
+		template: l.newTemplate(defaultHeader),
+		color:    color.New(),
+		bufferPool: sync.Pool{
+			New: func() interface{} {
+				return bytes.NewBuffer(make([]byte, 256))
+			},
+		},
+	}
+	l.initLevels()
+	l.SetOutput(output())
+	return
+}
+
+func (l *Logger) initLevels() {
+	l.levels = []string{
+		"-",
+		l.color.Blue("DEBUG"),
+		l.color.Green("INFO"),
+		l.color.Yellow("WARN"),
+		l.color.Red("ERROR"),
+		"",
+		l.color.Yellow("PANIC", color.U),
+		l.color.Red("FATAL", color.U),
+	}
+}
+
+func (l *Logger) newTemplate(format string) *fasttemplate.Template {
+	return fasttemplate.New(format, "${", "}")
+}
+
+func (l *Logger) DisableColor() {
+	l.color.Disable()
+	l.initLevels()
+}
+
+func (l *Logger) EnableColor() {
+	l.color.Enable()
+	l.initLevels()
+}
+
+func (l *Logger) Prefix() string {
+	return l.prefix
+}
+
+func (l *Logger) SetPrefix(p string) {
+	l.prefix = p
+}
+
+func (l *Logger) Level() Lvl {
+	return Lvl(atomic.LoadUint32(&l.level))
+}
+
+func (l *Logger) SetLevel(level Lvl) {
+	atomic.StoreUint32(&l.level, uint32(level))
+}
+
+func (l *Logger) Output() io.Writer {
+	return l.output
+}
+
+func (l *Logger) SetOutput(w io.Writer) {
+	l.output = w
+	if w, ok := w.(*os.File); !ok || !isatty.IsTerminal(w.Fd()) {
+		l.DisableColor()
+	}
+}
+
+func (l *Logger) Color() *color.Color {
+	return l.color
+}
+
+func (l *Logger) SetHeader(h string) {
+	l.template = l.newTemplate(h)
+}
+
+func (l *Logger) Print(i ...interface{}) {
+	l.log(0, "", i...)
+	// fmt.Fprintln(l.output, i...)
+}
+
+func (l *Logger) Printf(format string, args ...interface{}) {
+	l.log(0, format, args...)
+}
+
+func (l *Logger) Printj(j JSON) {
+	l.log(0, "json", j)
+}
+
+func (l *Logger) Debug(i ...interface{}) {
+	l.log(DEBUG, "", i...)
+}
+
+func (l *Logger) Debugf(format string, args ...interface{}) {
+	l.log(DEBUG, format, args...)
+}
+
+func (l *Logger) Debugj(j JSON) {
+	l.log(DEBUG, "json", j)
+}
+
+func (l *Logger) Info(i ...interface{}) {
+	l.log(INFO, "", i...)
+}
+
+func (l *Logger) Infof(format string, args ...interface{}) {
+	l.log(INFO, format, args...)
+}
+
+func (l *Logger) Infoj(j JSON) {
+	l.log(INFO, "json", j)
+}
+
+func (l *Logger) Warn(i ...interface{}) {
+	l.log(WARN, "", i...)
+}
+
+func (l *Logger) Warnf(format string, args ...interface{}) {
+	l.log(WARN, format, args...)
+}
+
+func (l *Logger) Warnj(j JSON) {
+	l.log(WARN, "json", j)
+}
+
+func (l *Logger) Error(i ...interface{}) {
+	l.log(ERROR, "", i...)
+}
+
+func (l *Logger) Errorf(format string, args ...interface{}) {
+	l.log(ERROR, format, args...)
+}
+
+func (l *Logger) Errorj(j JSON) {
+	l.log(ERROR, "json", j)
+}
+
+func (l *Logger) Fatal(i ...interface{}) {
+	l.log(fatalLevel, "", i...)
+	os.Exit(1)
+}
+
+func (l *Logger) Fatalf(format string, args ...interface{}) {
+	l.log(fatalLevel, format, args...)
+	os.Exit(1)
+}
+
+func (l *Logger) Fatalj(j JSON) {
+	l.log(fatalLevel, "json", j)
+	os.Exit(1)
+}
+
+func (l *Logger) Panic(i ...interface{}) {
+	l.log(panicLevel, "", i...)
+	panic(fmt.Sprint(i...))
+}
+
+func (l *Logger) Panicf(format string, args ...interface{}) {
+	l.log(panicLevel, format, args...)
+	panic(fmt.Sprintf(format, args...))
+}
+
+func (l *Logger) Panicj(j JSON) {
+	l.log(panicLevel, "json", j)
+	panic(j)
+}
+
+func DisableColor() {
+	global.DisableColor()
+}
+
+func EnableColor() {
+	global.EnableColor()
+}
+
+func Prefix() string {
+	return global.Prefix()
+}
+
+func SetPrefix(p string) {
+	global.SetPrefix(p)
+}
+
+func Level() Lvl {
+	return global.Level()
+}
+
+func SetLevel(level Lvl) {
+	global.SetLevel(level)
+}
+
+func Output() io.Writer {
+	return global.Output()
+}
+
+func SetOutput(w io.Writer) {
+	global.SetOutput(w)
+}
+
+func SetHeader(h string) {
+	global.SetHeader(h)
+}
+
+func Print(i ...interface{}) {
+	global.Print(i...)
+}
+
+func Printf(format string, args ...interface{}) {
+	global.Printf(format, args...)
+}
+
+func Printj(j JSON) {
+	global.Printj(j)
+}
+
+func Debug(i ...interface{}) {
+	global.Debug(i...)
+}
+
+func Debugf(format string, args ...interface{}) {
+	global.Debugf(format, args...)
+}
+
+func Debugj(j JSON) {
+	global.Debugj(j)
+}
+
+func Info(i ...interface{}) {
+	global.Info(i...)
+}
+
+func Infof(format string, args ...interface{}) {
+	global.Infof(format, args...)
+}
+
+func Infoj(j JSON) {
+	global.Infoj(j)
+}
+
+func Warn(i ...interface{}) {
+	global.Warn(i...)
+}
+
+func Warnf(format string, args ...interface{}) {
+	global.Warnf(format, args...)
+}
+
+func Warnj(j JSON) {
+	global.Warnj(j)
+}
+
+func Error(i ...interface{}) {
+	global.Error(i...)
+}
+
+func Errorf(format string, args ...interface{}) {
+	global.Errorf(format, args...)
+}
+
+func Errorj(j JSON) {
+	global.Errorj(j)
+}
+
+func Fatal(i ...interface{}) {
+	global.Fatal(i...)
+}
+
+func Fatalf(format string, args ...interface{}) {
+	global.Fatalf(format, args...)
+}
+
+func Fatalj(j JSON) {
+	global.Fatalj(j)
+}
+
+func Panic(i ...interface{}) {
+	global.Panic(i...)
+}
+
+func Panicf(format string, args ...interface{}) {
+	global.Panicf(format, args...)
+}
+
+func Panicj(j JSON) {
+	global.Panicj(j)
+}
+
+func (l *Logger) log(level Lvl, format string, args ...interface{}) {
+	if level >= l.Level() || level == 0 {
+		buf := l.bufferPool.Get().(*bytes.Buffer)
+		buf.Reset()
+		defer l.bufferPool.Put(buf)
+		_, file, line, _ := runtime.Caller(l.skip)
+		message := ""
+
+		if format == "" {
+			message = fmt.Sprint(args...)
+		} else if format == "json" {
+			b, err := json.Marshal(args[0])
+			if err != nil {
+				panic(err)
+			}
+			message = string(b)
+		} else {
+			message = fmt.Sprintf(format, args...)
+		}
+
+		_, err := l.template.ExecuteFunc(buf, func(w io.Writer, tag string) (int, error) {
+			switch tag {
+			case "time_rfc3339":
+				return w.Write([]byte(time.Now().Format(time.RFC3339)))
+			case "time_rfc3339_nano":
+				return w.Write([]byte(time.Now().Format(time.RFC3339Nano)))
+			case "level":
+				return w.Write([]byte(l.levels[level]))
+			case "prefix":
+				return w.Write([]byte(l.prefix))
+			case "long_file":
+				return w.Write([]byte(file))
+			case "short_file":
+				return w.Write([]byte(path.Base(file)))
+			case "line":
+				return w.Write([]byte(strconv.Itoa(line)))
+			}
+			return 0, nil
+		})
+
+		if err == nil {
+			s := buf.String()
+			i := buf.Len() - 1
+			if s[i] == '}' {
+				// JSON header
+				buf.Truncate(i)
+				buf.WriteByte(',')
+				if format == "json" {
+					buf.WriteString(message[1:])
+				} else {
+					buf.WriteString(`"message":`)
+					buf.WriteString(strconv.Quote(message))
+					buf.WriteString(`}`)
+				}
+			} else {
+				// Text header
+				buf.WriteByte(' ')
+				buf.WriteString(message)
+			}
+			buf.WriteByte('\n')
+			l.mutex.Lock()
+			defer l.mutex.Unlock()
+			l.output.Write(buf.Bytes())
+		}
+	}
+}

vendor/github.com/labstack/gommon/log/white.go

@@ -0,0 +1,12 @@
+// +build appengine
+
+package log
+
+import (
+	"io"
+	"os"
+)
+
+func output() io.Writer {
+	return os.Stdout
+}