I have a Java application that consists of a client and a server. The client sends encrypted commands to the server, and the server executes them.
The problem that I am having right now is that, with my encryption algorithm, sometimes the encrypted command contains "\n" or "\r" characters, which mess up my server code. This is because I am using the readLine() method, which stops when it finds a line terminator. What I need is a way to read all the characters the client sends into one string.
Here is my code:
public void run(){
System.out.println("Accepted Client!");
try{
in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream(), "ISO8859_1"));
out = new PrintWriter(new OutputStreamWriter(clientSocket.getOutputStream(), "ISO8859_1"));
String clientCommand = null;
while(RunThread){
// read incoming stream
do{
clientCommand = in.readLine();
}while(clientCommand == null);
//decrypt the data
System.out.println("Client: " + clientCommand);
if(clientCommand.equalsIgnoreCase("quit")){
RunThread = false;
}else{
//do something
out.flush();
}
}
}catch(Exception e){
e.printStackTrace();
}
}
Everything I've tried (various forms of nested loops using the read() function) hasn't worked. I would welcome any help or suggestions. Thanks, everyone!
I don't see encryption in the code you posted, but usually it's not a good idea to rely on separator characters.
When sending binary data, you should prepend the length of the data to the stream, and then you know exactly how many bytes to expect (and when the message will end.) It's more efficient to do things that way too instead of looking for a newline character.
// read incoming stream
do{
clientCommand = in.readLine();
}while(clientCommand == null);
That == null seems wrong
Try
String line = null;
do {
line = in.readLine ();
clientCommand += line
} while (line != null);
One thing you must do, when working with TCP/IP, is to send the message length before the actual message. The application level cannot foresee the package size the TCP level is delivering to the destiny. So, before your message, you have to send a header with the message size and the destiny would read just these bytes.
About readLine(), I think it's better use another approaches like streams. Shortly, one suggestion:
Socket oSocket = new Socket(sAddress, iPort);
PrintWriter out = new PrintWriter(oSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(new InputStreamReader(oSocket.getInputStream()));
do{
clientCommand = in.readLine();
} while(clientCommand == null);
This makes no sense. readLine() only returns null at end of stream, so you are telling Java to loop infinitely at end of stream. I don't even understand why there is a loop at all. You don't want to ignore any input from the client, you want to process it all. You should read one line from the client, execute it, and read another line. Repeat until null, then close the socket.
Related
readLine() works fine in many cases but few times, the line I read in by BufferedReader.readLine() is incomplete line. This question talks about similar issue. However the solutions are not satisfactory. A solution there says that it maybe because of EOF character. But in my case I am not sending any EOF character at all. Below are my codes:
/*Sending Code*/
public void sendToLocalDaemon(String msg){/*msg have no New line or \r*/
localMachineWriter.println(msg);
}
/*Receiving Code*/
public int receiveFromCoordinator(){
String response = "";
while(true){/*Each message separated from new line will have its independent meaning.*/
try{
coordinator.setSoTimeout(1);
try{
response = coordinatorReader.readLine();
}
catch(java.net.SocketTimeoutException e){
response = null;
}
if(response == null){
return coordinatorsMessage.size();
}
coordinatorsMessage.add(response);
}
catch(IOException e){
log(e.getMessage());
//System.exit(0);
}
}
}
/*This is how I set reader and writer*/
public void setReaderWriter() throws IOException{
this.coordinatorWriter = new PrintWriter(coordinator.getOutputStream(),true);
this.coordinatorReader = new BufferedReader(new InputStreamReader(coordinator.getInputStream()));
}
Please either suggest me someway to make this work correctly. Or suggest me some other way by which I can read whole message, with 100% guarantee.
The problem is your read timeout. If it happens, you can lose data. If readLine() times out in the middle of a line, the part read so far is lost. If you set it too short, you will lose a lot of data, and you're setting it much too short. You should set it much higher, or not use one at all.
I am currently interfacing a GUI to an UCI chess engine. For this purpose i am creating the engine process using:
try {
process = Runtime.getRuntime().exec(enginePath);
} catch (IOException e) {
System.err.println("ENGINE NOT FOUND");
e.printStackTrace();
}
and i am sure that i am able to open the engine.
When engine is opened, there is no significant stream outputted from engine. In order to initiate communication, I have to send specific commands to the engine. The engine will respond then... Therefore it is working in a command/response approach(not immediately streaming data when opened or talking without spoken to). In order to communicate i have a send message block. In this block write a message to the engine using its outputstream and get input using its standart input stream as in the following send method:
private String sendCommand(String command) {
stdin = new PrintWriter(new OutputStreamWriter(process.getOutputStream()));
BufferedReader inputReader = new BufferedReader(new InputStreamReader(process.getInputStream()));
BufferedReader errReader = new BufferedReader(newInputStreamReader(process.getErrorStream()));
String answer = "";
stdin.println(command);
stdin.flush();
stdin.close();
try {
String line = "";
while ((line = inputReader.readLine()) != null) {
System.out.println(line);
answer = line;
}
inputReader.close();
} catch (IOException ioe) {
System.err.println("READ ERROR");
ioe.printStackTrace();
}
try {
String line = "";
while ((line = errReader.readLine()) != null) {
System.err.println(line);
}
errReader.close();
} catch (IOException ioe) {
System.err.println("READ ERROR");
ioe.printStackTrace();
}
return answer;
}
By the way the whole engine is working in a single seperate thread other than the main GUI thread. Therefore no overloading for the GUI. However i didnot seperate the stdin stderr and output methods in individual threads since i suppose there will be only stdin and the one that i will write to the engine. For the time being i assume they will not collide.
With these codes i am able to communicate with the engine and i can see the outputs in the console. However due to stdin.close(); i can only use this method once (In the seconds time i have a STREAM CLOSED error). The chess engine is needed to be communicated in command/response approach many times when opened, without restarting the exe in each time. The problem is that if i remove the line : stdin.close(); yes the communication continues, but my console is blocked by this communication. I.e. i cannot println to the console for debugging purposes anymore. Which is very critical because my main debugging weapon is system.out.println. If i do not remove stdin.close(); i have to restart executable each time i want to send message and i do not want that. **The strange part is that i can see the messages coming from the engine in my console due to "System.out.println(line);" line in the send method; however i cannot print anything on the console once the code exits the method. **
EDIT: Actually after this block:
while ((line = inputReader.readLine()) != null) {
System.out.println(line);
answer = line;
}
System.out.println starts not to work.
EDIT: The problem seems not to be with println but any statement after while loop.
Why statements after while loop is not getting executed?
according to this, it seems that since the stream is never closed, "while loop" is stuck(?). Actually when printing inside while loop, at some point(after a stream is finished), the prints stop, which must indicate while loop is finished. Therefore if it is finished, it should continue on the next statements, shouldn't it? Anyway, the messages from the engine had a set of strings at end of each stream; therefore when i encounter one of them i am breaking the while loop.
Note: it is also interesting that : accumulating data as: "receivedString += line"; doesnot work,i.e. data is not accumulated. In order to fix it i luckily made it "receivedString = receivedString + line + "\n""; and it worked.. I dont know why.
You're reading the input until end of stream, so it won't stop reading until end of stream occurs. End of stream means that the peer has closed the connection in this case. That won't happen for a process's output or error stream until the process exits. You'll have to find some other loop termination condition, or else consume the stdout and stderr in separate threads.
I am reading a streaming data from an TCP streaming software. I'm currently using while loop to read continuously. But I am not sure that if this is the best technique to read streaming data.
Following is the code i'm currently using:
Socket client=new Socket("169.254.99.2",1234);
System.out.println("Client connected ");
//getting the o/p stream of that connection
PrintStream out=new PrintStream(client.getOutputStream());
out.print("Hello from client\n");
out.flush();
//reading the response using input stream
BufferedReader in= new BufferedReader(new InputStreamReader(client.getInputStream()));
int a = 1;
int b= 1;
//
while(a==b){
// I'm just printing it out.
System.out.println("Response" + in.read());
}
Suggestions plz???
That loop would be the same as while(true), which is continuous. Also, I suggest running this in a thread.
After you init your socket and streams, I suggest calling a method like this:
Thread messageThread;
public void chatWithServer() {
messageThread = new Thread(new Runnable() {
public void run() {
String serverInput;
while((serverInput = in.readLine()) != null) {
//do code here
}
}
};
messageThread.start();
}
We put it in a thread so the loop doesn't hold up the rest of the client's code. (does not progress after loop)
The while loop initilizes serverInput within the parameters, so each time it loops, it re-inits serverInput so it doesn't constantly loop with the very first sent piece of data.
You gotta put it in parenthesis, because of course, while loops only accept boolean parameters (true/false). So, in pseudocode, if the InputStream always returns something, continue with the new recieved data.
I'm currently using while loop to read continuously.
That is the best technique for reading streaming data. However your loop must test for end of stream, which is signalled by read() retuning -1 in Java. Your 'a==b' test is pointless. There are several possible loop tests:
while (true) // with a break when you detect EOS
Or
while ((c = in.read()) != -1)
where 'c' is an 'int'.
But I am not sure that if this is the best technique to read streaming data.
Why not?
I am trying to connect to the POP server through Sockets in Java. I did the following code to run a LIST command to list all the emails from the server. But I don't know why on the second readLine() to read the second line and onwards, my application hangs at there.
popSock = new Socket(mailHost, pop_PORT);
inn = popSock.getInputStream();
outt = popSock.getOutputStream();
in = new BufferedReader(new InputStreamReader(inn));
out = new PrintWriter(new OutputStreamWriter(outt), true);
//USER and PASS commands to auth the server are ok
out.println("LIST");
String response = in.readLine();
System.out.println(response);
//Attempt to read the second line from the buffer but it hangs at here.
response = in.readLine();
System.out.println(response);
On the second in.readLine(), the application gets stuck at here and doesn't proceed from here. When I run the LIST command on telnet, I get the whole list of emails. So I should get the same response from the socket but I am not. How should I read the whole response line by line from the server?
readLine() won't return until it's read a carriage return or a line feed, which is what you normally get when you read from a terminal or a text file.
I wouldn't be surprised if the POP server doesn't actually tack \r\n on the end of its messages. Try read() instead.
You should be sending \r\n after each command, also, try not using a BufferedInputStream, try reading directly from the InputStream byte by byte to see at which point it actually hangs. The BufferedInputStream may be hanging waiting to read more before returning what it has already read.
Try reading it one character at a time using in.read and printing it. Perhaps, there's an issue with the newline character that the server is sending.
You can try following--
try {
String line = inn.readLine();
while(***input.ready()***)
{
System.out.println(line);
line=inn.readLine();
}
inn.close();
} catch (IOException e) {
e.printStackTrace();
}
where inn is your bufferedReader object whih stores the inputstreamdata
On the one side of the socket I know the data is going into the socket correctly.
I set up a connection:
Connection sr = new Connection();
Server server = new Server("NAME", Interger.parseInt(port));
server.setIp(ip);
sr.setServer(server);
//I know my server connection code is correct because I can send and receive data in
//other areas of my program just fine
InputStream is = null;
try
{
is = sr.getChannel().socket().getInputStream();
BufferedReader br = new BufferedReader(new InputStreamReader(is));
StringBuffer text = new StringBuffer();
int k =0;
while(k != -1)
{
k = br.read();
text.append((char) k);
}
}
catch(Exception e)
{
//no errors ever get thrown
}
And then I only get about half my data, 10989 bytes out of a total 21398 that I send. The amount of bytes it reads varies but the data always ends with ..., "values": [" which in the data I send over looks like , ..., "values": ["", ""].
Keep reading until you have all the data. This question has been showing up about once a week lately. There's no guarantee that the network is going to have all your data show up at once.
You need to keep reading until you have all your data. How do you know how much data was sent? You should probably build a little protocol between the client/server that defines how much data is going to be sent, the server reads that little header and continues to read until the full message has been received.
Don't know if this could help you :
int k =0;
while((k = br.read()) != -1){
text.append((char) k);
}
1) In your case it is making the check on the next iteration, which may lead to appending of non-representable character(char of -1) to the end of text.
2) Never leave catch block empty, may be there is some execption.
So because my sending side of the socket was in c++ I was accidentally passing in a null ASCII value into the socket. And it is undocumented on the java side of the socket that if the read encounters a null value it treats it as an end of file. So it was prematurely ending the stream because it hit the null.