Replacement for *os.File of Go default log - go

Question

I'm trying to write a wrapper for Go's built-in logger.
This is to have compatibility.
package main
import (
"log"
"os"
)
var(
mylog *log.Logger
)
func main() {
mylog = log.New(os.Stdout, "", 0)
mylog.Printf("test")
}
Instead of using os.Stdout, I want to create one something. Similar to os.Stdout but prints with prefix like below.
package main
import(
"log"
"mylibrary"
)
var(
mylog *log.Logger
)
func main() {
mylog = log.New(mylibrary.Prefix, "", 0)
mylog.Printf("test")
}
Basically, I still want to have *log.Logger while having custom log. Can someone give me a hint how I can make this works?
Currently, I'm using following to do that. But I bet there's a better way.
func NewIoWriter(f func(string)) *io.PipeWriter {
r, w := io.Pipe()
go func() {
scanner := bufio.NewScanner(r)
for scanner.Scan() {
f(scanner.Text())
}
if err := scanner.Err(); err != nil {
f(err.Error())
}
r.Close()
}()
runtime.SetFinalizer(w, (*io.PipeWriter).Close)
return w
}
What would be the better way to make it work?
Thank you

Answer 1

How about something like this:
type myLogWriter struct {
logFunc func(string)
line string
}
func (w *myLogWriter) Write(b []byte) (int, error) {
l := len(b)
for len(b) != 0 {
i := bytes.Index(b, []byte{'\n'})
if i == -1 {
w.line += string(b)
break
} else {
w.logFunc(w.line + string(b[:i]))
b = b[i+1:]
w.line = ""
}
}
return l, nil
}
func NewLogWriter(f func(string)) *myLogWriter {
return &myLogWriter{
logFunc: f,
}
}
See https://play.golang.org/p/L6PG1gCK1er.