无法读取套接字响应中的换行符/回车符

Question

I am sending setup commands to a TP-LINK wireless router through a telnet connection:

Trying 1.2.3.4...
Connected to 1.2.3.4.
Escape character is '^]'.
*HELLO*$$$
CMD
factory RESET
factory RESET

Set Factory Defaults
<4.00> set sys autoconn 0
set sys autoconn 0

AOK
<4.00>
...

I have a PHP code that performs the sending of commands and gets the response using sockets:

socket_write($socket, "factory RESET\r"); // send command
$response = socket_read($socket, 256); // get response

PHP works fine. The $response variable contains:

factory RESET

Set Factory Defaults

But using the Java I have problems. Using a BufferedReader object to read response, I can get the first line content. but I can not get the following lines:

BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
// ...
bw.write("factory RESET");
bw.newLine();
bw.flush();
// ...
StringBuilder sb = new StringBuilder();

String s;
while ((s = br.readLine()) != null) {
   sb.append(s);
}

I can get the first line content, but the second reading don't proceed and don't raise exception... If I use the read function, only the first row is returned:

char[] buffer = new char[256];
br.read(buffer, 0, 256);
String response = new String(buffer); // response is "factory RESET"

What is the problem?

Answer 1

1. Your PHP code execute two reads. Your Java code attempts to read until end of stream, which only happens when the peer closes the connection. Do a single read.

2. The line separator in the Telnet protocol is defined as \\r\\n , unless you're using binary mode, which you aren't. Not as \\r or whatever BufferedWriter may do on your platform.