上一篇文章我们介绍了目前go标准库存在的不足，以及新的slog库丰富的功能。
自定义日志处理程序(handler)
上一篇文章介绍，slog默认支持TextHandler和JSONHandler，但可以使用HandlerOptions类型进行自定义。前面学习了如何在日志属性之前调整最低级别和修改属性。另一个可以通过HandlerOptions完成的自定义是添加日志消息的来源:
func main() {
opts := slog.HandlerOptions{
AddSource: true,
Level: slog.LevelDebug,
}
logger := slog.New(opts.NewJSONHandler(os.Stdout))
logger.Debug("Debug message")
logger.Info("Info message")
logger.Warn("Warning message")
logger.Error("Error message")
}
output：
{"time":"2023-02-24T10:28:50.751111921+01:00","level":"DEBUG","source":"/home/betterstack/go-logging/main.go:55","msg":"Debug message"}
{"time":"2023-02-24T10:28:50.75120862+01:00","level":"INFO","source":"/home/betterstack/go-logging/main.go:56","msg":"Info message"}
{"time":"2023-02-24T10:28:50.751215229+01:00","level":"WARN","source":"/home/betterstack/go-logging/main.go:57","msg":"Warning message"}
{"time":"2023-02-24T10:28:50.751222025+01:00","level":"ERROR","source":"/home/betterstack/go-logging/main.go:60","msg":"Error message"}
根据应用程序环境切换处理程序也很容易。例如，你可能更喜欢使用TextHandler作为你的开发日志，因为它更容易阅读，然后在生产环境中切换到JSONHandler，以更好地兼容各种日志工具，你可以通过一个环境变量轻松地启用这种行为:
package main
import (
"os"
"golang.org/x/exp/slog"
)
var appEnv = os.Getenv("APP_ENV")
func main() {
opts := slog.HandlerOptions{
Level: slog.LevelDebug,
}
var handler slog.Handler = opts.NewTextHandler(os.Stdout)
if appEnv == "production" {
handler = opts.NewJSONHandler(os.Stdout)
}
logger := slog.New(handler)
logger.Info("Info message")
}
go run main.go
output:
time=2023-02-24T10:36:39.697+01:00 level=INFO msg="Info message"
APP_ENV=production go run main.go
output:
{"time":"2023-02-24T10:35:16.964821548+01:00","level":"INFO","msg":"Info message"}
创建自定义日志处理程序(handler)
由于Handler是一个接口，可以轻松地定义一个接口，以不同的方式格式化日志或将它们写入某个目的地。接口定义如下:
type Handler interface {
Enabled(context.Context, Level) bool
Handle(r Record) error
WithAttrs(attrs []Attr) Handler
WithGroup(name string) Handler
}
上面每个函数的作用如下：
- Enabled()用于决定是否应该根据日志记录的级别处理或丢弃日志记录。context也可以用来做决定。
- Handle()处理发送到处理程序的每条日志记录。只有当Enabled()返回true时才会调用它。
- WithAttrs()为处理程序设置配置项。
- 为处理程序添加group属性。
下面是一个使用log, json和color来实现为日志记录添加颜色美化输出效果的示例:
// NOTE: Not well tested, just an illustration of what's possible
package main
import (
"context"
"encoding/json"
"io"
"log"
"github.com/fatih/color"
"golang.org/x/exp/slog"
)
type PrettyHandlerOptions struct {
SlogOpts slog.HandlerOptions
}
type PrettyHandler struct {
opts PrettyHandlerOptions
slog.Handler
l *log.Logger
}
func (h *PrettyHandler) Handle(ctx context.Context, r slog.Record) error {
level := r.Level.String() + ":"
switch r.Level {
case slog.LevelDebug:
level = color.MagentaString(level)
case slog.LevelInfo:
level = color.BlueString(level)
case slog.LevelWarn:
level = color.YellowString(level)
case slog.LevelError:
level = color.RedString(level)
}
fields := make(map[string]interface{}, r.NumAttrs())
r.Attrs(func(a slog.Attr) {
fields[a.Key] = a.Value.Any()
})
b, err := json.MarshalIndent(fields, "", " ")
if err != nil {
return err
}
timeStr := r.Time.Format("[15:05:05.000]")
msg := color.CyanString(r.Message)
h.l.Println(timeStr, level, msg, color.WhiteString(string(b)))
return nil
}
func (opts PrettyHandlerOptions) NewPrettyHandler(
out io.Writer,
) *PrettyHandler {
h := &PrettyHandler{
Handler: opts.SlogOpts.NewJSONHandler(out),
l: log.New(out, "", 0),
}
return h
}
当你在代码中像这样使用PrettyHandler时:
package main
import (
"os"
"golang.org/x/exp/slog"
)
func main() {
opts := PrettyHandlerOptions{
SlogOpts: slog.HandlerOptions{
Level: slog.LevelDebug,
},
}
handler := opts.NewPrettyHandler(os.Stdout)
logger := slog.New(handler)
logger.Debug(
"executing database query",
slog.String("query", "SELECT * FROM users"),
)
logger.Info("image upload successful", slog.String("image_id", "39ud88"))
logger.Warn(
"storage is 90% full",
slog.String("available_space", "900.1 MB"),
)
logger.Error(
"An error occurred while processing the request",
slog.String("url", "https://example.com"),
)
}
你将看到以下彩色输出:
LogValue接口
LogValuer接口允许任何Go类型定义自身转换为日志格式。通过实现如下所示的LogValue()方法来记录日志的值:
type LogValuer interface {
LogValue() Value
}
你可以通过实现这个接口来定义各种类型的日志输出内容。下面看一个例子：
package main
import (
"os"
"golang.org/x/exp/slog"
)
// User does not implement `LogValuer`
type User struct {
ID string `json:"id"`
FirstName string `json:"first_name"`
LastName string `json:"last_name"`
Email string `json:"email"`
Password string `json:"password"`
}
func main() {
handler := slog.NewJSONHandler(os.Stdout)
logger := slog.New(handler)
u := &User{
ID: "user-12234",
FirstName: "Jan",
LastName: "Doe",
Email: "jan@example.com",
Password: "pass-12334",
}
logger.Info("info", "user", u)
}
output:
{
"time": "2023-02-26T22:11:30.080656774+01:00",
"level": "INFO",
"msg": "info",
"user": {
"id": "user-12234",
"first_name": "Jan",
"last_name": "Doe",
"email": "jan@example.com",
"password": "pass-12334"
}
}
如果不实现LogValuer接口，整个User类型将被添加到如上所示的日志中。如果类型包含不应该出现在日志中的敏感字段(比如密码)，这可能会产生问题，而且还会造成日志不必要地冗长。可以通过指定如何在日志中处理该类型来修复此问题。例如，你可以指定日志只记录User类型ID字段:
// implement the `LogValuer` interface
func (u *User) LogValue() slog.Value {
return slog.StringValue(u.ID)
}
你现在将看到以下输出:
{
"time": "2023-02-26T22:43:28.184363059+01:00",
"level": "INFO",
"msg": "info",
"user": "user-12234"
}
你也可以像这样把属性分组在一起:
func (u *User) LogValue() slog.Value {
return slog.GroupValue(
slog.String("id", u.ID),
slog.String("name", u.FirstName+" "+u.LastName),
)
}
output:
{
"time": "2023-03-15T14:44:24.223381036+01:00",
"level": "INFO",
"msg": "info",
"user": {
"id": "user-12234",
"name": "Jan Doe"
}
}
第三方日志库
- Zerolog
- Zap
- Logrus
