Logging

Default implementation

Kitex defines several interfaces in the package pkg/klog: Logger, CtxLoggerKey and FormatLogger. And it provides a default logger that implements those interfaces and can be accessed by calling klog.DefaultLogger().

There are global functions in the package pkg/klog that expose the ability of the default logger, like klog.Info, klog.Errorf and so on.

Note that the default logger uses the log.Logger from the standard library as its underlying output. So the filename and line number shown in the log messages depend on the setting of call depth. Thus wrapping the implementation of klog.DefaultLogger may cause inaccuracies for these two values.

Inject your custom logger implementation

You can use klog.SetLogger to replace the default logger.

obs-opentelemetry provide logger implementation base on logrus and zap

Logrus

set logger impl

import (
    kitexlogrus "github.com/kitex-contrib/obs-opentelemetry/logging/logrus"
)

func init()  {
    klog.SetLogger(kitexlogrus.NewLogger())
    klog.SetLevel(klog.LevelDebug)
	...
}

log with context

// Echo implements the Echo interface.
func (s *EchoImpl) Echo(ctx context.Context, req *api.Request) (resp *api.Response, err error) {
	klog.CtxDebugf(ctx, "echo called: %s", req.GetMessage())
	return &api.Response{Message: req.Message}, nil
}

view log

{"level":"debug","msg":"echo called: my request","span_id":"056e0cf9a8b2cec3","time":"2022-03-09T02:47:28+08:00","trace_flags":"01","trace_id":"33bdd3c81c9eb6cbc0fbb59c57ce088b"}

Redirecting the Output of the Default Logger

The klog.SetOutput can be used to redirect the output of the default logger provided by the pkg/klog package.

For example, to redirect the output of the default logger to a file name ./output.log under the launch directory, a possible implementation might be:

package main
import (
    "os"
    "github.com/cloudwego/kitex/pkg/klog"
)
func main() {
    f, err := os.OpenFile("./output.log", os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
    if err != nil {
    	panic(err)
    }
    defer f.Close()
    klog.SetOutput(f)
    ... // continue to set up your server
}