Golang segment stdin stream to file

instead of writing a pipe to a huge file i want to segment the stream in chunks on signal USR1. i think i got the basics working but the app just hangs and nothing happens, any clues or best practices when handling with an uncontrollable input stream and byte perfect segmentation?

package main
import (
"bufio"
"fmt"
"io"
"os"
"os/signal"
"syscall"
"time"
)
var done bool
func handle(c chan os.Signal) {
for {
sig := <-c
switch sig {
case syscall.SIGUSR1:
fmt.Println("###Sink temporarily_closed###")
done = true
case syscall.SIGUSR2:
fmt.Println("###Sink closed###")
done = true
case syscall.SIGHUP:
fmt.Println("###Sink running###")
}
}
}
func check(e error) {
if e != nil {
panic(e)
}
}
func main() {
c := make(chan os.Signal, 1)
signal.Notify(c, syscall.SIGUSR1, syscall.SIGUSR2, syscall.SIGHUP)
go handle(c)
reader := bufio.NewReaderSize(os.Stdin,1024*10)
for true {
if done {
file, err := os.Create("./temp.file")
check(err)
writer := bufio.NewWriter(file)
written, err := io.Copy(writer,reader)
check(err)
fmt.Println(written)
writer.Flush()
file.Close()
reader.Reset(os.Stdin)
done = false
}
time.Sleep(time.Millisecond)
}
}

So you need to io.CopyN(dst, src, 4096) in the loop and rotate the file once in a while. See example. I made rotation by size but it is easy to add signal handling.

package main
import (
"fmt"
"io"
"log"
"os"
"time"
)
var count int
var f *os.File
func rotate() *os.File {
if f != nil {
if err := f.Close(); err != nil {
log.Fatal(err)
}
}
fname := fmt.Sprintf("./dump-%d.bin", count)
count++
f, err := os.Create(fname)
if err != nil {
log.Fatal(err)
}
log.Println("rotated:", fname)
return f
}
func main() {
var n, written int
reader := os.Stdin
for {
if written == 0 || written >= 4096*10 {
f = rotate()
written = 0
}
n, err := io.CopyN(f, reader, 4096)
if err != nil {
log.Fatal(err)
}
written += n
log.Println("written:", written)
time.Sleep(time.Millisecond * 500)
}
}