bufio: preemptive Flush() inside Write*() methods #20943
Description
Hello!
While digging the sources of bufio.Writer I had a question:
Inside Writer.ReadFrom() method exists a "preemptive" Flush(). I think this is made to deal with src.Read() deadlines in subsequent calls of ReadFrom – to not spent time on buffer flush before read attempt.
Could it be useful to make the same "preemptive" flushes inside other Writer.Write*() methods?
I mean that in current implementation test like this will fail:
type snoozeWriter struct {
delay time.Duration
}
func (w snoozeWriter) Write(p []byte) (int, error) {
time.Sleep(w.delay)
return len(p), nil
}
type deadlineReader struct {
deadline time.Time
}
func (r deadlineReader) Read(p []byte) (int, error) {
if time.Since(r.deadline) > 0 {
return 0, fmt.Errorf("deadline exceeded")
}
return len(p), io.EOF
}
func TestWriterReadFromTimeout(t *testing.T) {
const size = 10
bw := bufio.NewWriterSize(snoozeWriter{time.Second}, 10)
// Fill buffer, without Flush().
bw.WriteString("0123456789")
// Emulate some reader with read deadline set.
r := deadlineReader{time.Now().Add(500 * time.Millisecond)}
if n, err := bw.ReadFrom(r); n != size || err != nil {
t.Fatalf("ReadFrom() = (%v, %v); want (10, nil)", n, err)
}
}