(based on this question: Uber Zap Logger: how to prepend every log entry with a string)
I replaced the Encoder of my uber-zap logger with a custom one to prepend every log entry with a SystemD-friendly error level (<LEVEL>
), but now after I use the logger with additional fields (With(fields ...Field)
), the custom prepending is gone:
package main
import (
"os"
"go.uber.org/zap"
"go.uber.org/zap/buffer"
"go.uber.org/zap/zapcore"
)
func getConfig() zap.Config {
// your current config options
return zap.NewProductionConfig()
}
type prependEncoder struct {
// embed a zapcore encoder
// this makes prependEncoder implement the interface without extra work
zapcore.Encoder
// zap buffer pool
pool buffer.Pool
}
// EncodeEntry implementing only EncodeEntry
func (e *prependEncoder) EncodeEntry(entry zapcore.Entry, fields []zapcore.Field) (*buffer.Buffer, error) {
// new log buffer
buf := e.pool.Get()
// prepend the JournalD prefix based on the entry level
buf.AppendString(e.toJournaldPrefix(entry.Level))
buf.AppendString(" ")
// calling the embedded encoder's EncodeEntry to keep the original encoding format
consolebuf, err := e.Encoder.EncodeEntry(entry, fields)
if err != nil {
return nil, err
}
// just write the output into your own buffer
_, err = buf.Write(consolebuf.Bytes())
if err != nil {
return nil, err
}
return buf, nil
}
// some mapper function
func (e *prependEncoder) toJournaldPrefix(lvl zapcore.Level) string {
switch lvl {
case zapcore.DebugLevel:
return "<7>"
case zapcore.InfoLevel:
return "<6>"
case zapcore.WarnLevel:
return "<4>"
}
return ""
}
func main() {
cfg := getConfig()
// constructing our prependEncoder with a ConsoleEncoder using your original configs
enc := &prependEncoder{
Encoder: zapcore.NewConsoleEncoder(cfg.EncoderConfig),
pool: buffer.NewPool(),
}
logger := zap.New(
zapcore.NewCore(
enc,
os.Stdout,
zapcore.DebugLevel,
),
// this mimics the behavior of NewProductionConfig.Build
zap.ErrorOutput(os.Stderr),
)
logger.Info("this is info")
logger.Debug("this is debug")
logger.Warn("this is warn")
logger = logger.With(zap.String("foo", "bar"))
logger.With(zap.String("foo", "bar")).Info("this does not have the prefix :(")
}
The output I get is:
<6> 1.640656130756576e 09 info this is info
<7> 1.640656130756611e 09 debug this is debug
<4> 1.640656130756615e 09 warn this is warn
1.6406561307566311e 09 info this does not have the prefix :( {"foo": "bar"}
What am I doing wrong?
CodePudding user response:
You have to also implement Clone()
from the zapcore.Encoder
interface. If you wish to keep the parent logger unaltered, you have to construct an actual clone — possibly with the same config, so you might want to store it as a field:
type prependEncoder struct {
zapcore.Encoder
pool buffer.Pool
cfg zapcore.EncoderConfig
}
func (e *prependEncoder) Clone() zapcore.Encoder {
return &prependEncoder{
// cloning the encoder with the base config
Encoder: zapcore.NewConsoleEncoder(e.cfg),
pool: buffer.NewPool(),
cfg: e.cfg,
}
}
If you don't implement it, the method that runs is the next shallowest one when calling logger.Clone()
, which is the Clone()
declared on the embedded zapcore.Encoder
. That one then doesn't have your custom EncodeEntry
anymore.
Now running the following:
logger.Info("this is info")
logger.Debug("this is debug")
logger.Warn("this is warn")
child := logger.With(zap.String("foo", "bar"))
logger.Warn("original")
child.Info("new one")
Outputs:
<6> INFO this is info
<7> DEBUG this is debug
<4> WARN this is warn
cloning...
<4> WARN original
<6> INFO new one {"foo": "bar"}