Trying to test write file from goroutines in Go - go

Question

Well, part of my code was working without a method approach, I'm trying to test
append text to a file and reading from goroutines, but I'm stuck here trying to
write it.
What is wrong? the file is created, but I can't append text to it, maybe something obvious, but seems I'm blind, maybe I'm failing understanding some language concepts...
package main
import (
"bufio"
"fmt"
"os"
"sync"
"time"
)
var w sync.WaitGroup
type Buffer struct {
F *os.File
}
func (buff *Buffer) Open(pathName string) (err error) {
buff.F, err = os.OpenFile(pathName, os.O_APPEND|os.O_CREATE, 0666)
if err != nil {
return
}
fmt.Println("Open() ok")
return nil
}
func (buff *Buffer) Close() (err error) {
err = buff.F.Close()
if err != nil {
return
}
fmt.Println("Close() ok")
return nil
}
func (buff *Buffer) Push(data string) (err error) {
w := bufio.NewWriter(buff.F)
_, err = fmt.Fprintf(w, "data=%s", data)
if err != nil {
return
}
w.Flush()
fmt.Println("Push() ok")
return nil
}
func checkErr(err error) {
if err != nil {
fmt.Println(err.Error())
}
}
func worker() {
var err error
buffer := new(Buffer)
err = buffer.Open("test")
checkErr(err)
err = buffer.Push("data\n")
checkErr(err)
time.Sleep(5 * time.Second)
err = buffer.Close()
checkErr(err)
w.Done()
}
func main() {
w.Add(2)
go worker()
go worker()
w.Wait()
}
Thanks

Answer 1

Open the file like this:
buff.F, err = os.OpenFile(pathName, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0666)
The write flag is required to write to the file.
You missed the write error because the return from bufio Flush is ignored. Change Push to:
func (buff *Buffer) Push(data string) (err error) {
w := bufio.NewWriter(buff.F)
_, err = fmt.Fprintf(w, "data=%s", data)
if err != nil {
return
}
err = w.Flush()
if err != nil {
return err
}
fmt.Println("Push() ok")
return nil
}
To cleanly append data without intermixing with other pushes, the data must be written with a single call to the file Write method. Use a bytes.Buffer instead of a bufio.Writer to ensure a single call to the file Write method:
func (buff *Buffer) Push(data string) (err error) {
var b bytes.Buffer
_, err = fmt.Fprintf(&b, "data=%s", data)
if err != nil {
return
}
_, err := buff.F.Write(b.Bytes())
if err != nil {
return err
}
fmt.Println("Push() ok")
return nil
}