How to read all data from a TCP socket server and execute an operation afterwards - sockets

Question

After spending many hours on this. I can't find a way to read all the data coming from a TCP socket server and then make an operation, as I can't find a way to break the loop.
The socket server sends texts containing a lot of lines finishing with "\n". The client should be able to read all those lines and make a POST request with all the data but the loop always hangs out and there is not a way to break it. Then, it will continue waiting for more data, so a stop condition could be a three seconds timeout.
I have tried different solutions (Scanner, ReadString, ReadLine, ReadAll) but it always hangs out and the loop won't ever finish.
The last line in the code is never printed.
conn, err := net.Dial("tcp", "127.0.0.1:15000")
reader := bufio.NewReader(conn)
message := ""
for {
line, err := reader.ReadString('\n')
if err == io.EOF {
break
}
message += line
}
log.Println(message)

Answer 1

If your only option is to read lines until a timeout, you can set a read deadline on the connection after the first read completes. You can then intercept the timeout error, and convert it to an EOF for the buffered reader to correctly interpret your intent.
type timeoutReader struct {
net.Conn
once sync.Once
}
func (r *timeoutReader) Read(b []byte) (int, error) {
n, err := r.Conn.Read(b)
// Set a read deadline only after the first Read completes
r.once.Do(func() {
r.Conn.SetReadDeadline(time.Now().Add(3 * time.Second))
})
// If we got a timeout, treat it as an io.EOF so the bufio.Scanner handles
// the error as if it was the normal end of the stream.
var netErr net.Error
if errors.As(err, &netErr) && netErr.Timeout() {
return n, io.EOF
}
return n, err
}
func main() {
conn, err := net.Dial("tcp", "127.0.0.1:15000")
if err != nil {
log.Fatal(err)
}
scanner := bufio.NewScanner(&timeoutReader{Conn: conn})
message := ""
for scanner.Scan() {
message += scanner.Text()
}
if err := scanner.Err(); err != nil {
log.Fatal(err)
}
log.Println(message)
}

Answer 2

If the criteria is a timeout of 3 seconds after the first line is received, the solution is to close the socket 3 seconds after the first line is received.
var firstLineReceived bool
conn, err := net.Dial("tcp", "127.0.0.1:15000")
reader := bufio.NewReader(conn)
message := ""
for {
line, err := reader.ReadString('\n')
if err == io.EOF {
break
}
message += line
if !firstLineReceived {
firstLineReceived = true
go func(){
time.Sleep(3*time.Second)
conn.Close()
}()
}
}
log.Println(message)