go-ethereum/ethlog/README.md

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## Features
- packages use tagged logger sending log messages to shared (process-wide) logging engine
- log writers (interface ethlog.LogSystem) can be added to the logging engine by wrappers/guis/clients
- shared logging engine dispatching to multiple log systems
- log level can be set separately per log system
- async logging thread: logging IO does not block main thread
- log messages are synchronously stringified to avoid incorrectly logging of changed states
## Usage
In an ethereum component package:
import "github.com/ethereum/eth-go/ethlog"
// package-wide logger using tag
var logger = ethlog.NewLogger("TAG")
logger.Infoln("this is info") # > [TAG] This is info
Ethereum wrappers should register log systems conforming to ethlog.LogSystem
import "github.com/ethereum/eth-go/ethlog"
type CustomLogWriter struct {
logLevel ethlog.LogLevel
}
func (t *TestLogSystem) SetLogLevel(i LogLevel) {
t.level = i
}
func (t *TestLogSystem) GetLogLevel() LogLevel {
return t.level
}
func (c *CustomLogWriter) Printf(format string, v...interface{}) {
//....
}
func (c *CustomLogWriter) Println(v...interface{}) {
//....
}
ethlog.AddLogWriter(&CustomLogWriter{})
ethlog also provides constructors for that wrap io.Writers into a standard logger with a settable level:
filename := "test.log"
file, _ := os.OpenFile(filename, os.O_RDWR|os.O_CREATE, os.ModePerm)
fileLogSystem := NewStdLogSystem(file, 0, WarnLevel)
AddLogSystem(fileLogSystem)
stdOutLogSystem := NewStdLogSystem(os.Stdout, 0, WarnLevel)
AddLogSystem(stdOutLogSystem)