Hi
I'm using TelnetClient to send and receive commands from a server, each
command consisting of character data followed by a newline. However, at
seemingly random times the response obtained from TelnetClient's
InputStream appears to have bytes missing, or sometimes includes extra
bytes.
I was able to reproduce the problem on Ubuntu, Windows and OSX and I am
using commons-net version 3.1 and Oracle's 1.6 JDK.
I'm not sure if this is a bug or whether I'm just not using TelnetClient
correctly, as I was unable to find any previous reports of similar
problems. I've attached the simple test program I used to recreate the
issue. The program connects to a basic socket server in a loop until the
message echoed back is not the same as the one sent, which I've seen
happen anywhere between 2-400 iterations.
Can anybody confirm the problem or else point out what mistake I've made?
Many thanks,
Mark
package telnetbug.telnetbug;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import org.apache.commons.net.telnet.TelnetClient;
public class Test
{
static class EchoServer extends Thread {
boolean stop = false;
ServerSocket ss;
Socket cs;
public void run(){
try{
ss = new ServerSocket(4444);
while(!stop){
cs = ss.accept();
InputStream is = cs.getInputStream();
OutputStream os = cs.getOutputStream();
while(!stop){
try{
String msg = read(is);
if(msg==null) break;
write(os,msg);
}catch(IOException e){
break;
}
}
}
}catch(IOException e){
throw new RuntimeException(e);
}
finally{
shutdown();
}
}
public void shutdown(){
stop = true;
if(cs!=null) try{ cs.close(); }catch(IOException e){}
if(ss!=null) try{ ss.close(); }catch(IOException e){}
}
}
static String read(InputStream is) throws IOException {
String s = "";
while(true){
int c = is.read();
if(c==-1) return null;
if(c==(int)'\n') break;
s += (char)c;
}
return s;
}
static void write(OutputStream os, String msg) throws IOException {
os.write((msg+"\n").getBytes("US-ASCII"));
os.flush();
}
public static void main(String[] args) throws Exception {
String testString = "abcdefghijklmnopqrstuvwxyz";
EchoServer s = new EchoServer();
try{
s.start();
int i=0;
while(true){
TelnetClient c = null;
try{
c = new TelnetClient();
c.connect("127.0.0.1",4444);
InputStream is = c.getInputStream();
OutputStream os = c.getOutputStream();
write(os,testString);
String received = read(is);
if(!received.equals(testString)){
System.out.println(String.format("Failed on iteration %d:\n"+
"sent\t\"%s\"\ngot\t\"%s\"",i,testString,received));
break;
}
i++;
try{ Thread.sleep(50); }catch(InterruptedException e){}
System.out.print(".");
}finally{
if(c!=null) c.disconnect();
}
}
}finally{
s.shutdown();
}
}
}
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