Develop Reference

Receiving byte packets by TCP

i have some problem with receive byte packets by TCP in JAVA.
My TCPServer class sending 207 - byte packets. When I send one packet, program display in console "Read 207 byte packet." and stops. With next packet it continue execution, display "Multiple Measurement" and
"Read 1868767867 byte packet.". After that receiving is stopped forever. I don't know why 1868767867 bytes it receive. I check it in wireshark and server sending always 207 bytes.
This is my TCPClient class:
public class TCPClient extends Thread {
private ServerSocket serverSocket;
private Socket connectionSocket;
private InputStream inputStream;
private DataInputStream dataInputStream;
public TCPClient() throws IOException {
try {
serverSocket = new ServerSocket(Config.TCP_PORT);
} catch (IOException e) {
e.printStackTrace();
}
}
#Override
public void run() {
try {
connectionSocket = serverSocket.accept();
inputStream = connectionSocket.getInputStream();
dataInputStream = new DataInputStream(inputStream);
} catch (IOException e) {
e.printStackTrace();
}
while(true) {
try {
JsonObject json = getJsonFromTcp();
if (json != null) {
String command = json.getAsJsonPrimitive("command").getAsString();
if(command.equals("multipleMeasurement")) {
executeMultipleMeasurement();
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
private JsonObject getJsonFromTcp() throws IOException {
byte[] buff = new byte[4];
for(int i = 0; i < 4; i++) {
buff[i] = dataInputStream.readByte();
}
int len = (((buff[3] & 0xff) << 24) | ((buff[2] & 0xff) << 16) | ((buff[1] & 0xff) << 8) | (buff[0] & 0xff));
if(len > 0) {
System.out.println("Read " + len + " byte packet.");
byte[] data = new byte[len];
dataInputStream.readFully(data);
String jsonString = new String(data, "UTF-8");
JsonParser jsonParser = new JsonParser();
JsonObject json = jsonParser.parse(jsonString).getAsJsonObject();
return json;
}
return null;
}
private void executeMultipleMeasurement() {
System.out.println("Multiple Measurement");
}
}
Anyone know solution?

Looking at the number 1868767867, its bytes are
"%c%c%c%c" % (0x7b,0x22,0x63,0x6f)
'{"co'
So you could be reading the first four bytes of the next message as the length of the message. The most likely explanation given the claim that the server sends exactly 207 bytes each time is that the server includes the length of the length prefix (4 bytes) in the total message length. Depending on the intended protocol, it might be appropriate to read (length - 4) bytes as the body of the packet.
// Account for the length of the header
len -= 4;
if(len > 0) {
System.out.println("Read " + len + " byte packet.");
byte[] data = new byte[len];
dataInputStream.readFully(data);
A second possibility is that the server is measuring the number of characters in a string and then using that length as the length of the utf-8 converted byte buffer that it will send, including some non-ascii characters that cause the resulting buffer to be longer.
Without seeing the server code, it's impossible to be certain which is happening here.

Reliable UDP in java

I am working on my assignment to make UDP reliable using java. How can i add Timeout and re-transmission to handle data-grams that are discarded and add Sequence numbers so the client can verify that a reply is for the appropriate request ??
this is client code
import java.net.*;
import java.io.*;
public class EchoClient {
// UDP port to which service is bound
public static final int SERVICE_PORT = 7;
// Max size of packet
public static final int BUFSIZE = 256;
public static void main(String args[]){
if (args.length != 1)
{
System.err.println ("Syntax - java EchoClient hostname");
return;
}
String hostname = args[0];
// Get an InetAddress for the specified hostname
InetAddress addr = null;
try
{
// Resolve the hostname to an InetAddr
addr = InetAddress.getByName(hostname);
}
catch (UnknownHostException uhe)
{
System.err.println ("Unable to resolve host");
return;
}
try
{
// Bind to any free port
DatagramSocket socket = new DatagramSocket();
// Set a timeout value of two seconds
socket.setSoTimeout (2 * 1000);
for (int i = 1 ; i <= 10; i++)
{
// Copy some data to our packet
String message = "Packet number " + i ;
char[] cArray = message.toCharArray();
byte[] sendbuf = new byte[cArray.length];
for (int offset = 0; offset < cArray.length ; offset++)
{
sendbuf[offset] = (byte) cArray[offset];
}
// Create a packet to send to the UDP server
DatagramPacket sendPacket = new DatagramPacket(sendbuf, cArray.length, addr, SERVICE_PORT);
System.out.println ("Sending packet to " + hostname);
// Send the packet
socket.send (sendPacket);
System.out.print ("Waiting for packet.... ");
// Create a small packet for receiving UDP packets
byte[] recbuf = new byte[BUFSIZE];
DatagramPacket receivePacket = new DatagramPacket(recbuf, BUFSIZE);
// Declare a timeout flag
boolean timeout = false;
// Catch any InterruptedIOException that is thrown
// while waiting to receive a UDP packet
try
{
socket.receive (receivePacket);
}
catch (InterruptedIOException ioe)
{
timeout = true;
}
if (!timeout)
{
System.out.println ("packet received!");
System.out.println ("Details : " + receivePacket.getAddress() );
// Obtain a byte input stream to read the UDP packet
ByteArrayInputStream bin = new ByteArrayInputStream (
receivePacket.getData(), 0, receivePacket.getLength() );
// Connect a reader for easier access
BufferedReader reader = new BufferedReader (
new InputStreamReader ( bin ) );
// Loop indefinitely
for (;;)
{
String line = reader.readLine();
// Check for end of data
if (line == null)
break;
else
System.out.println (line);
}
}
else
{
System.out.println ("packet lost!");
}
// Sleep for a second, to allow user to see packet
try
{
Thread.sleep(1000);
}catch (InterruptedException ie) {}
}
}
catch (IOException ioe)
{
System.err.println ("Socket error " + ioe);
}
}
}

What you can do is adding import TCP headers like sequence number, windows into the UDP message body to make it more like TCP. Here is the a solution that might help you.

How to read all of Inputstream in Server Socket JAVA

I am using Java.net at one of my project.
and I wrote a App Server that gets inputStream from a client.
But some times my (buffered)InputStream can not get all of OutputStream that client sent to my server.
How can I write a wait or some thing like that, that my InputStream gets all of the OutputStream of client?
(My InputStream is not a String)
private Socket clientSocket;
private ServerSocket server;
private BufferedOutputStream outputS;
private BufferedInputStream inputS;
private InputStream inBS;
private OutputStream outBS;
server = new ServerSocket(30501, 100);
clientSocket = server.accept();
public void getStreamFromClient() {
try {
outBS = clientSocket.getOutputStream();
outputS = new BufferedOutputStream( outBS);
outputS.flush();
inBS = clientSocket.getInputStream();
inputS = new BufferedInputStream( inBS );
} catch (Exception e) {
e.printStackTrace();
}
}
Thanks.

The problem you have is related to TCP streaming nature.
The fact that you sent 100 Bytes (for example) from the server doesn't mean you will read 100 Bytes in the client the first time you read. Maybe the bytes sent from the server arrive in several TCP segments to the client.
You need to implement a loop in which you read until the whole message was received.
Let me provide an example with DataInputStream instead of BufferedinputStream. Something very simple to give you just an example.
Let's suppose you know beforehand the server is to send 100 Bytes of data.
In client you need to write:
byte[] messageByte = new byte[1000];
boolean end = false;
String dataString = "";
try
{
DataInputStream in = new DataInputStream(clientSocket.getInputStream());
while(!end)
{
int bytesRead = in.read(messageByte);
dataString += new String(messageByte, 0, bytesRead);
if (dataString.length == 100)
{
end = true;
}
}
System.out.println("MESSAGE: " + dataString);
}
catch (Exception e)
{
e.printStackTrace();
}
Now, typically the data size sent by one node (the server here) is not known beforehand. Then you need to define your own small protocol for the communication between server and client (or any two nodes) communicating with TCP.
The most common and simple is to define TLV: Type, Length, Value. So you define that every message sent form server to client comes with:
1 Byte indicating type (For example, it could also be 2 or whatever).
1 Byte (or whatever) for length of message
N Bytes for the value (N is indicated in length).
So you know you have to receive a minimum of 2 Bytes and with the second Byte you know how many following Bytes you need to read.
This is just a suggestion of a possible protocol. You could also get rid of "Type".
So it would be something like:
byte[] messageByte = new byte[1000];
boolean end = false;
String dataString = "";
try
{
DataInputStream in = new DataInputStream(clientSocket.getInputStream());
int bytesRead = 0;
messageByte[0] = in.readByte();
messageByte[1] = in.readByte();
int bytesToRead = messageByte[1];
while(!end)
{
bytesRead = in.read(messageByte);
dataString += new String(messageByte, 0, bytesRead);
if (dataString.length == bytesToRead )
{
end = true;
}
}
System.out.println("MESSAGE: " + dataString);
}
catch (Exception e)
{
e.printStackTrace();
}
The following code compiles and looks better. It assumes the first two bytes providing the length arrive in binary format, in network endianship (big endian). No focus on different encoding types for the rest of the message.
import java.nio.ByteBuffer;
import java.io.DataInputStream;
import java.net.ServerSocket;
import java.net.Socket;
class Test
{
public static void main(String[] args)
{
byte[] messageByte = new byte[1000];
boolean end = false;
String dataString = "";
try
{
Socket clientSocket;
ServerSocket server;
server = new ServerSocket(30501, 100);
clientSocket = server.accept();
DataInputStream in = new DataInputStream(clientSocket.getInputStream());
int bytesRead = 0;
messageByte[0] = in.readByte();
messageByte[1] = in.readByte();
ByteBuffer byteBuffer = ByteBuffer.wrap(messageByte, 0, 2);
int bytesToRead = byteBuffer.getShort();
System.out.println("About to read " + bytesToRead + " octets");
//The following code shows in detail how to read from a TCP socket
while(!end)
{
bytesRead = in.read(messageByte);
dataString += new String(messageByte, 0, bytesRead);
if (dataString.length() == bytesToRead )
{
end = true;
}
}
//All the code in the loop can be replaced by these two lines
//in.readFully(messageByte, 0, bytesToRead);
//dataString = new String(messageByte, 0, bytesToRead);
System.out.println("MESSAGE: " + dataString);
}
catch (Exception e)
{
e.printStackTrace();
}
}
}

You can read your BufferedInputStream like this. It will read data till it reaches end of stream which is indicated by -1.
inputS = new BufferedInputStream(inBS);
byte[] buffer = new byte[1024]; //If you handle larger data use a bigger buffer size
int read;
while((read = inputS.read(buffer)) != -1) {
System.out.println(read);
// Your code to handle the data
}

int c;
String raw = "";
do {
c = inputstream.read();
raw+=(char)c;
} while(inputstream.available()>0);
InputStream.available() shows the available bytes only after one byte is read, hence do .. while

Trouble receiving data to Java socket client from C socket server

I'm having a problem trying to send strings back and forth between a simple Java socket client and a simple C socket server.
It works as follows:
Java client sends msg to C server
out.writeBytes(msg);
C server receives the msg and puts into buf
if ((numbytes = recv(new_fd, buf, MAXDATASIZE-1, 0)) == -1) {
perror("recv");
exit(1);
}
C server sends the messsage back to the Java client
if ((len = send(new_fd, buf, numbytes, 0)) == -1)
perror("send");
However the Java client cannot receive the msg from the C server, I've tried using DataInputStream, BufferedReader, reading into char[], byte[], converting to string but cannot get the received message. When trying to read into an array on the client side I sometimes get only the first character which leads me to believe it's a blocking problem?
Any help would be appreciated
Code:
C server main loop
while(1) { // main accept() loop
sin_size = sizeof their_addr;
new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size);
if (new_fd == -1) {
perror("accept");
continue;
}
inet_ntop(their_addr.ss_family,
get_in_addr((struct sockaddr *)&their_addr),
s, sizeof s);
printf("server: got connection from %s\n", s);
if ((numbytes = recv(new_fd, buf, MAXDATASIZE-1, 0)) == -1) {
perror("recv");
exit(1);
}
buf[numbytes] = '\0';
printf("msg size: '%d' bytes\n",numbytes);
printf("received msg: %s\n",buf);
char* array = (char*)buf;
printf("as char array: %s\n", array);
if (!fork()) { // this is the child process
close(sockfd); // child doesn't need the listener
int len = 0;
if ((len = send(new_fd, buf, numbytes, 0)) == -1)
perror("send");
printf("sent %d bytes\n", len);
close(new_fd);
exit(0);
}
close(new_fd); // parent doesn't need this
}
Java client
public void send(String text){
Socket sock = null;
DataInputStream in = null;
DataOutputStream out = null;
BufferedReader inReader = null;
try {
sock = new Socket(HOST, PORT);
System.out.println("Connected");
in = new DataInputStream(sock.getInputStream());
out = new DataOutputStream(sock.getOutputStream());
out.writeBytes(text + "\n");
String res = "";
//get msg from c server and store into res
System.out.println("Response: " + res);
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
sock.close();
//in.close();
out.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}

Java stream socket can only send once

I'm writing a simple download accelerator. The problem is I can send and receive messages once. The next time I try to send and receive message, I get no response froms server. I'm not even sure if I am able to send the second message.
The first message is something like;
*HEAD /TIPS/LAWLER/PANOHOW2.PDF HTTP/1.0\r\n
HTTP/1.0\r\n
Connection: close\r\n
\r\n*
and response is;
*HTTP/1.1 200 OK
Date: Mon, 24 Jan 2011 10:53:38 GMT
Server: Apache
Last-Modified: Tue,
22 Sep 1998 13:19:52 GMT
ETag: "1968013-2b4f4-3386e15b6ee00"
Accept-Ranges: bytes
Content-Length: 177396
Connection: close
Content-Type: application/pdf*
When i attemp to sen message;
GET /TIPS/LAWLER/hedeh/PANOHOW2.PDF HTTP/1.0\r\n
Range: bytes=0-44349\r\n
Connection: close\r\n
\r\n
I get nothing.
What is wrong with my code?
public class Main {
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
//Parse URL
String cmd = "http://www.imaging-resource.com"; //Host Name
if (cmd.contains("http://"))
{
cmd = cmd.substring(7); //
if (cmd.contains("/"))
{
int index = cmd.indexOf("/");
cmd = cmd.substring(0, index);
System.out.println(cmd);
}
}
String str = "HEAD /TIPS/LAWLER/PANOHOW2.PDF HTTP/1.0\r\nConnection: close\r\n\r\n"; //First message to send
//Create socket, connect, initialize read and write handlers
//in, out
Socket socket = null; //Create a client socket
SocketAddress sockaddr = null;
InetAddress address = null;
InputStream input = null; //Input handler
OutputStream output = null; //Output handler
try
{
address = InetAddress.getByName(cmd); //Get ip using host name
socket = new Socket(); //Contrusct Socket
sockaddr = new InetSocketAddress(address, 80);
//socket.setTcpNoDelay(false);
socket.connect(sockaddr, 2000); //Connect to server set and timeout to 2 sec
} //End of try Block
catch (Exception ex)
{
Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
System.out.println(ex);
} //End of catch Block
if (!socket.isConnected())
{
System.out.println("not connected");
System.exit(-1);
}
//Sending package here
try
{
int c;
byte[] buf = new byte[65535];
char[] chr = new char[65535];
input = socket.getInputStream(); //Input handler is created
output = socket.getOutputStream(); //Output handler is created
buf = str.getBytes(); //HEAD message converted into byte array
output.write(buf); //Sending message to server
output.flush();
int counter = 0;
while ((c = input.read()) != -1) //Reading received package
chr[counter++]=(char)c;
//input.reset();
str = new String(chr); //For better manipulation, server message is converted to string
System.out.println(str);
} catch (IOException e)
{
System.err.print(e);
} //End of catch
int index = str.indexOf("Content-Length"); //Look for "Content-Length" in response
str = str.substring(index); //Using its beginning index create an substring
index = str.indexOf("\r\n"); //Search for end of line
str = str.substring(0, index); //Erase end if line chars - \r\n
str = str.substring(16, str.length()); //"Content-Length: " 16 chars
int fileSize = Integer.parseInt(str); //Lentgh of file is converted to Integer
int[][] parts = new int[4][2]; //Beginning and en of jobs for threads will be stored here
int remainder = fileSize; //Bytes left to split for rest of the threads will be stored here
int start = 0;
int finish = 0;
for (int i = 0; i < 4; i++) //Number of threads many times
{
parts[i][0] = start; //*******Each threads job Interval(eg. 0-108)
//System.out.print(parts[i][0] + "-"); //******
finish += remainder / 4 - i; //*****
parts[i][1] = finish; //****
start = finish + 1; //***
if (i + 1 == 4)
parts[i][1] = fileSize; //*
}
str = "GET /TIPS/LAWLER/hedeh/PANOHOW2.PDF HTTP/1.0\r\nRange: bytes=" + parts[0][0] + "-" + parts[0][1] + "\r\nConnection: close\r\n\r\n";
//System.out.println(str);
if(!socket.isConnected())
{
System.out.println("closed");
try
{
socket.connect(sockaddr, 2000);
}//End od try
catch(Exception e){
System.err.print(e);
}//End of catch
}//End of If
System.out.println("Is Outputhandler closed :"+socket.isOutputShutdown());
System.out.println("Is Inputhandler closed :"+socket.isInputShutdown());
try
{
int c;
byte[] buf = new byte[65535];
char[] chr = new char[65535];
buf = str.getBytes(); //Output handler is created
output.write(buf); //Sending message to server
output.flush();
int counter = 0;
if((c = input.read()) != -1)
{
chr[counter++] = (char) c;
while ((c = input.read()) != -1) //Reading received package
{
System.out.println("response is not -1");
chr[counter++]=(char)c;
}
str = new String(chr); //For better manipulation, serve message is converted to string
System.out.println("Response "+str);
}//End of If
else System.out.println("No Response!");
}catch(Exception e)
{System.err.print(e);}
//Closing open stuff
try {
output.close();
input.close();
socket.close();
} catch (Exception e) {
System.out.println(e);
}
}// End of main method
}//End of class definition

The first message is something like;
HTTP/1.0\r\n
You have to use HTTP version 1.1 to use multiple requests on a single TCP connection.
From the Wikipedia article on HTTP:
In HTTP/0.9 and 1.0, the connection is closed after a single request/response pair. In HTTP/1.1 a keep-alive-mechanism was introduced, where a connection could be reused for more than one request.
Also, as #Joachim Sauer points out in the comments, you're explicitly saying Connection: close in your header. :-)

I think that the problem is that you are trying to connect to HTTP server using plain TCP socket. Yes, HTTP is on top of TCP but it is complicated protocol that requires a lot of things to know. I'd suggest you to work with higher level API that implements HTTP protocol and provides you more convenient API.
The simplest example is URL+URLConnection from JDK. Probably better is HttpClient from Jakarta.