Develop Reference

Sniffing a LAN : Jpcap java program only seems to catch my packets

I have to create a program that sniff a local network for school. I chose to work with Java and found out that you can capture packets with jpcap.
So I wanted to follow one of the example provided in jpcap's github and it seems like I can only find my own packets.
Like I said, I've looked at the code and chose my wifi interface. The program is capturing packets and I put all the source ip addresses in a text file to run some tests. I have also created a hashmap the ip addresses I've finded when I did a arp -a. From what I've read online, this command shows you ip addresses in your network.I created a boolean set to false and I then proceeded to run a loop that goes through the textfile and looked if the ip address was in the hashMap : if one of the addresses appeared in the hashmap, the boolean would be change to true and it would mean that I've managed to catch something.
After running the test, the boolean came out false.
Here's the example code
``public class PacketCaptor {
private static final int INFINITE = -1;
private static final int PACKET_COUNT = INFINITE;
/*
private static final String HOST = "203.239.110.20";
private static final String FILTER =
"host " + HOST + " and proto TCP and port 23";
*/
private static final String FILTER =
// "port 23";
"";
public static void main(String[] args) {
try {
if(args.length == 1){
PacketCaptor sniffer = new PacketCaptor(args[0]);
} else {
System.out.println("Usage: java Sniffer [device name]");
System.out.println("Available network devices on your machine:");
String[] devs = PacketCapture.lookupDevices();
for(int i = 0; i < devs.length ; i++)
System.out.println("\t" + devs[i]);
}
} catch(Exception e) {
e.printStackTrace();
}
}
public PacketCaptor(String device) throws Exception {
// Initialize jpcap
PacketCapture pcap = new PacketCapture();
System.out.println("Using device '" + device + "'");
pcap.open(device, true);
//pcap.setFilter(FILTER, true);
pcap.addPacketListener(new PacketHandler());
System.out.println("Capturing packets...");
pcap.capture(PACKET_COUNT);
}
}
class PacketHandler implements PacketListener
{
WritingClass writing = new WritingClass();
public void packetArrived(Packet packet) {
try {
// only handle TCP packets
if(packet instanceof TCPPacket) {
TCPPacket tcpPacket = (TCPPacket)packet;
byte[] data = tcpPacket.getTCPData();
String srcHost = tcpPacket.getSourceAddress();
String dstHost = tcpPacket.getDestinationAddress();
String isoData = new String(data, "ISO-8859-1");
System.out.println(srcHost+" -> " + dstHost + ": " + isoData);
String datas = srcHost+"|"+dstHost+"|";
writing.write(datas, this.writing.getFileName());
}
} catch( Exception e ) {
e.printStackTrace();
}
}
Can anyone help me figure out why It doesn't work ?
Thank you so much for your help

The reason why you aren't able to capture more packets is because you need an interface in promisc or raw mode, I advice you to use a proper sniffer like wireshark to check if other packets that aren't addressed to you can be captured. If not, means you need apply a mitm method because you are in a commuted network. For use that code on wifi should be enough an interface in monitor mode (check aircrack-ng suite).
In GNU/Linux Debian based systems may use the command iw dev wlan0 interface add mon0 type monitor (from package wireless-tools)

Bitcoin protocol using socket (java)

I develop bitcoin protocol using socket, but met some issues. Firstly, when my code connects to bitcoin node, it doesn't give any response. I send version message, but another side node doesn't re-send anything. I think that problem could be that I implement protocol wrong, but I checked and think that it's fine. (2) Secondly, I think that could be impossible connect to bitcoin node using socket, but it's stupid idea. Yea?
One important thing, I coded only socket connection, version sending to bitcoin node, which I found on https://bitnodes.earn.com/nodes/ , and message receiving from node, but it always responses -1.
One more thing, I don't give response from node, but also don't give connection error. (I just say)
Please help me :)
What is wrong that I send version message, but then doesn't give another one from node?
Also, I attach output (connection phases and protocol structure) of console when try to connect to socket.
Connected
f9beb4d976657273696f6e0000000000000000660a75c8397f1101000100000000000000820b905c00000000010000000000000000000000000000000000ffff340e5966208d010000000000000000000000000000000000ffff7f000001208db910e81a17a5dd79102f417572696d61733a302e31362e332f0000000001
Magic:f9beb4d9
Command:76657273696f6e0000000000
Length:00000066
Checksum:0a75c839
Payload:7f1101000100000000000000820b905c00000000010000000000000000000000000000000000ffff340e5966208d010000000000000000000000000000000000ffff7f000001208db910e81a17a5dd79102f417572696d61733a302e31362e332f0000000001
Version:7f110100
Services:0100000000000000
timestamp:820b905c00000000
addr_recv:010000000000000000000000000000000000ffff340e5966208d
addr_from:010000000000000000000000000000000000ffff7f000001208d
nonce:b910e81a17a5dd79
user_agent:102f417572696d61733a302e31362e332f
start_height:00000000
relay:01
Connection end
Main class:
private static String address = "52.14.89.102";
private static int port = 8333;
public static void main(String [] args) throws IOException {
String line = "";
try {
socket = new Socket(address, port);
System.out.println("Connected");
input = new DataInputStream(socket.getInputStream());
out = new DataOutputStream(socket.getOutputStream());
VersionMessage message = new VersionMessage();
line = Hex.encodeHexString(message.getMessage());
System.out.println(line);
structure(message.getMessage());
out.writeBytes(line);;
} catch(UnknownHostException u) {
System.out.println(u);
} catch (IOException e) {
e.printStackTrace();
}
...
The part of VersionMessage class:
public VersionMessage() {
super();
this.version = 70015;
this.services = 1; // NODE_NETWORK
this.timestamp = System.currentTimeMillis() / 1000;
this.nonce = new Random().nextLong();
this.userAgent = "/Satoshi:0.16.3/";
this.startHeight = 0;
this.relay = true;
contructPayload();
contructMessage();
}
#Override
public void contructPayload() {
addByteArray(dataParser.toInt32(version));
addByteArray(dataParser.toInt64(services));
addByteArray(dataParser.toInt64(timestamp));
addAddr("52.14.89.102", 8333);
addAddr("127.0.0.1", 8333);
addByteArray(dataParser.toInt64(nonce));
addStr(userAgent);
addByteArray(dataParser.toInt32(startHeight));
addByteArray(dataParser.toInt8(relay ? (byte) 1 : (byte) 0));
payload = new byte[payloadBytes.size()];
IntStream.range(0, payloadBytes.size()).forEach(i -> payload[i] = payloadBytes.get(i).byteValue());
}
BitcoinMessage (parent of VersionMessage):
public BitcoinMessage() {
magic = 0xf9beb4d9;;
payloadBytes = new ArrayList<Integer>();
dataParser = new DataParser();
}
public void contructMessage() {
message = new byte[MAGIC_LENGTH + COMMAND_LENGTH + PAYLOAD_LENGTH_SIZE + CHECKSUM_LENGTH + payload.length];
length = payload.length;
byte[] doubleHashedPayload = MessageUtils.doubleHashWithSha256(payload);
MessageUtils.addToByteArray(MessageUtils.intToBytes(magic, MAGIC_LENGTH), 0, MAGIC_LENGTH, message);
MessageUtils.addToByteArray(getCommandName().getBytes(), MAGIC_LENGTH, COMMAND_LENGTH, message);
MessageUtils.addToByteArray(MessageUtils.intToBytes(length, PAYLOAD_LENGTH_SIZE), MAGIC_LENGTH + COMMAND_LENGTH, PAYLOAD_LENGTH_SIZE, message);
MessageUtils.addToByteArray(doubleHashedPayload, MAGIC_LENGTH + COMMAND_LENGTH + PAYLOAD_LENGTH_SIZE, CHECKSUM_LENGTH, message);
MessageUtils.addToByteArray(payload, MAGIC_LENGTH + COMMAND_LENGTH + PAYLOAD_LENGTH_SIZE + CHECKSUM_LENGTH, payload.length, message);
}

How to check if server is running a method in Java HttpServer; getting java.net.UnknownHostException

I am scheduling tasks on servers but I have no idea how to know if any server is currently doing the task. I am looping over servers like this:
for(int i = 0; i < tasksList.size(); i++){
for(URL url : serverURLsList){
if(InetAddress.getByName(url.toString()).isReachable(0)){ //this gives me exception
HttpURLConnection availableServer = (HttpURLConnection) url.openConnection();
availableServer.setDoOutput(true);
ObjectOutputStream oos = new ObjectOutputStream(availableServer.getOutputStream());
oos.writeObject(tasksList.get(i));
oos.close();
tasksList.remove(i);
break;
}
}
}
This is my server for task handling:
public class Serv{
public static void main(String[] args) throws IOException {
int port = 8080;
String host = "192.168.1.116";
System.out.println("Server 1 is up. Host: " + host + " port: " + port);
HttpServer s= HttpServer.create(new InetSocketAddress(host, port), 0);
s.createContext("/", new RootHandler());
s.setExecutor(null);
s.start();
}
}
class RootHandler implements HttpHandler{
private static int clientCounter = 1;
#Override
public void handle(HttpExchange exchange) throws IOException {
System.out.println("\nRoot handler; \n\tclient no. " + clientCounter++);
Task t;
ObjectInputStream ois = new ObjectInputStream(exchange.getRequestBody());
try {
System.out.println("Recieved object:");
t = (Task) ois.readObject();
ois.close();
System.out.println("Array not sorted:");
int[] arr = (int[]) t.getData();
for (int anArr : arr) {
System.out.print(anArr + " ");
}
TaskSolver.solve(t); // need to check if this is runned on the server or server is doing nothing
System.out.println("\nArray sorted!");
for (int anArr : (int[])t.getData()) {
System.out.print(anArr + " ");
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
String response = "<h1>Server up!</h1>";
exchange.sendResponseHeaders(200, response.getBytes().length);
OutputStream os = exchange.getResponseBody();
os.write(response.getBytes());
os.close();
}
}
What I really want to achieve is have the information if any server in the list is currently solving the task (the comment in the snippet above shows that place). No idea why getting the exception mentioned in the title because I can reach the server from the web browser. I suppose the method isReachable() is not good for that purpose (because it should tell if the host given is up or not while I want to know if the proper method on the server is currently running). Does somebody know a good solution to do so?
#Edit
According to the comment I need to say that each of my servers (I will have plenty of them) should be doing only one task, that is the purpose of my simulation.

InetAddress.getByName(url.toString()).isReachable(0)){ //this gives me exception
Of course it does. The argument to InetAddress.getByName() is not a URL. Check the Javadoc. It is a hostname.

Mulitple clients with a server and sockets? [duplicate]

I did some different tutorials but nothing works, can someone see what i'm doing wrong?
private volatile boolean keepRunning = true;
public FileSharedServer() {
}
#Override
public void run() {
try {
System.out.println("Binding to Port " + PORT + "...");
// Bind to PORT used by clients to request a socket connection to
// this server.
ServerSocket serverSocket = new ServerSocket(PORT);
System.out.println("\tBound.");
System.out.println("Waiting for Client...");
socket = serverSocket.accept();
System.out.println("\tClient Connected.\n\n");
if (socket.isConnected()) {
System.out.println("Writing to client serverId " + serverId
+ ".");
// Write the serverId plus the END character to the client thru
// the socket
// outStream
socket.getOutputStream().write(serverId.getBytes());
socket.getOutputStream().write(END);
}
while (keepRunning) {
System.out.println("Ready");
// Receive a command form the client
int command = socket.getInputStream().read();
// disconnect if class closes connection
if (command == -1) {
break;
}
System.out.println("Received command '" + (char) command + "'");
// decide what to do.
switch (command) {
case LIST_FILES:
sendFileList();
break;
case SEND_FILE:
sendFile();
break;
default:
break;
}
}
} catch (IOException e) {
System.out.println(e.getMessage());
} finally {
// Do not close the socket here because the readFromClient() method
// still needs to
// be called.
if (socket != null && !socket.isClosed()) {
try {
System.out.println("Closing socket.");
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
/**
* This method sends the names of all of the files in the share directory.
*
* #throws IOException
*/
private void sendFileList() throws IOException {
File serverFilesDir = new File("serverFiles/");
if (!serverFilesDir.exists() || serverFilesDir.isFile()) {
System.out.println("'serverfiles' is not an existing directory");
throw new IOException("'serverfiles' directory does not exist.");
}
File[] files = serverFilesDir.listFiles();
for (File file : files) {
socket.getOutputStream().write(file.getName().getBytes());
// Even the last one must end with END and then finally with
// END_OF_LIST.
socket.getOutputStream().write(END);
}
socket.getOutputStream().write(END_OF_LIST);
}
/**
* this methods sends a particular file to the client.
*
* #throws IOException
*/
private void sendFile() throws IOException {
StringBuilder filename = new StringBuilder();
int character = -1;
while ((character = socket.getInputStream().read()) > -1
&& character != END && (char) character != END_OF_LIST) {
filename.append((char) character);
}
System.out.println(filename);
File file = new File(System.getProperty("user.dir")
+ System.getProperty("file.separator") + "serverfiles",
filename.toString());
String totalLength = String.valueOf(file.length());
socket.getOutputStream().write(totalLength.getBytes());
socket.getOutputStream().write(END);
FileInputStream fileInputStream = new FileInputStream(file);
int nbrBytesRead = 0;
byte[] buffer = new byte[1024 * 2];
try {
while ((nbrBytesRead = fileInputStream.read(buffer)) > -1) {
socket.getOutputStream().write(buffer, 0, nbrBytesRead);
}
} finally {
fileInputStream.close();
}
}
public static void main(String[] args) throws InterruptedException {
// Create the server which waits for a client to request a connection.
FileSharedServer server = new FileSharedServer();
System.out.println("new thread");
Thread thread = new Thread(server);
thread.start();
}
}
Do I need another class or just a couple of lines in main? on the very bottom.
It's over a wifi network and all I need is two clients at once, or more :)

The problem here is that you are running only a single thread on the server. This thread accepts a connection, writes the server ID to the connection, then reads from the connection. The thread then continues to read from the connection until a -1 is received, at which point the thread exits. At no point does the thread try to accept a second connection; ServerSocket.accept() is called only once. As a result, you can only handle one client.
What you need is to split your class into two separate classes. In the first class, the run() method goes into a loop, calling ServerSocket.accept(), and each time that method returns a socket, creates an instance of the second class, hands it the socket, and starts it, after which it loops back to the ServerSocket.accept() call.
The second class is almost identical to the class you've already written, except that it doesn't contain the ServerSocket.accept() call. Instead, socket is a member variable which is initialized, by the first class, before it is started. It can do all the handling of the socket, sending the server ID, receiving and handling commands, etc., just as your existing code does.

How to create multiple peer-to-peer chats within client-server messaging program

I am trying to create a messenger program and have successfully set up client-server connections using sockets. However I am finding it difficult to code the process of having several clients communicating simultaneously. Shown in the code below is the methods for the chats that are held within a ClientThread class that regulates the interaction between client and server using threads stored in a shared ArrayList. How would you implement the code for multiple peer-to-peer chats here?
startChat method:
public void startChat()
{
// start the convo!
// first of all the user chooses who to speak to
// starts a loop until user enters a valid username or 'Group'
String line = "";
boolean validCommand = false;
while(validCommand == false)
{
try {
line = in.readLine();
} catch (IOException e) {
System.out.println("Problem reading reply about user chat");
}
if(line.equalsIgnoreCase("Group"))
{
validCommand = true;
chatAll(); // an integer of negative one starts a chat with everyone
}
else
{
synchronized(this){
// find user
for(int i = 0; i < threads.size(); i++)
{
if(threads.get(i) != null && threads.get(i).username != null)
{
if(threads.get(i).username.equals(line)) // means that we have found the index of the thread that the client wants to speak to
{
/*// START : BETWEEN THESE CAPITALISED COMMENTS IS MY ATTEMPT TO INITIATE TWO WAY CHAT
int thisIndex = -1;
for(int j = 0; j < threads.size(); j++) // gets the index of this thread object in the array
{
if(threads.get(j) == this)
{
thisIndex = j;
// out.println(j);
}
}
if(thisIndex != -1)
{
threads.get(i).out.println(username + " is trying to connect");
threads.get(i).processChat(thisIndex); // this is the line causing the problem!
}
// END : BETWEEN THESE CAPITALISED COMMENTS IS MY ATTEMPT TO INITIATE TWO WAY CHAT */
threads.get(i).out.println(username + " is trying to connect");
out.println("Chat with " + threads.get(i).username);
processChat(i);
validCommand = true;
}
// if the command is not group and not a username, it is not valid and we ask the user to re-enter
else if(i == threads.size() - 1)
{
out.println("This command is not valid, please re-enter");
}
}
}
} // end of synchronised bit
} // end of else statement
} // end of while loop
}
allChat method:
void chatAll()
//for the purpose of group chat
{
out.println("Group chat initiated");
boolean d = true;
while(d == true)
{
String message = "";
try {
message = in.readLine();
} catch (IOException e) {
System.out.println("Can't read line from client");
}
if(message.contains("goodbye") == true)
{
d = false;
}
else
{
synchronized(this)
{
for(int j = 0; j < threads.size(); j++)
{
if(threads.get(j) != null)
{
threads.get(j).out.println(username + ": " + message);
}
}
}
}
}
}
processChat method:
void processChat(int i)
//for the purpose of talking to pre-defined user
{
boolean d = true;
while(d == true)
{
String message = "";
try {
message = in.readLine();
} catch (IOException e) {
System.out.println("Can't read message from client");
}
if(message.contains("goodbye") == true)
{
d = false;
}
else {
if(threads.get(i) != null)
{
threads.get(i).out.println(username + ": " + message);
}
}
}
}
Just for good measure and a reference here is the overall client class (confusingly labelled ThreadedClient as opposed to ClientThread haha)
ThreadedClient class:
import java.net.*;
import java.io.*;
public class ThreadedClient implements Runnable {
// client socket
private static Socket clientSocket = null;
//I/O streams to and from the server
private static BufferedReader in = null;
private static PrintStream out = null;
// Input stream to read user input
private static BufferedReader inputReader = null;
private boolean open = true;
public ThreadedClient(String host, int port)
{
startConnection(host, port);
}
public void startConnection(String host, int port)
{
//open up the socket
try {
clientSocket = new Socket(host, port);
} catch (UnknownHostException e) {
System.out.println("The host name '" + host + "' isn't known");
} catch (IOException e) {
// TODO Auto-generated catch block
System.out.println("Cannot create socket");
}
// connect I/O streams
try {
in = new BufferedReader(new InputStreamReader(new DataInputStream(clientSocket.getInputStream())));
out = new PrintStream(clientSocket.getOutputStream());
inputReader = new BufferedReader(new InputStreamReader(System.in));
} catch (IOException e) {
System.out.println("Problem connecting streams");
}
// process the chat itself
// the thread deals with input coming in
Thread thread = new Thread(this);
thread.start();
// the loop deals with output
while(open == true)
{
String message;
try {
message = inputReader.readLine();
out.println(message);
if(message.contains("goodbye") == true)
{
open = false;
}
} catch (IOException e) {
System.out.println("Problem sending messages");
}
}
// chat is done, so we can close resources
try {
in.close();
inputReader.close();
out.close();
clientSocket.close();
} catch (IOException e) {
System.out.println("Problem closing resources");
}
}
// run method for sending input out. I imagine this will not be necessary in the GUI implemented version, as we can use
// an action listener for the send function, e.g. one that reads a text field into a output stream everytime the user clicks enter
public void run() {
while(open == true)
{
try {
String response = in.readLine();
if(response.contains("goodbye") == true)
{
open = false;
}
System.out.println(response);
} catch (IOException e) {
System.out.println("Problem recieving messages");
}
}
}
public static void main(String[] args)
{
ThreadedClient socket = new ThreadedClient("localhost", 50000);
}
}
I know that this code may not be as advanced as some others I have seen on this forum as well as DreamInCode and others but I was trying to build it from scratch and have been stuck here for what feels like a millennia. Trawling through the internet has not helped :(
Any suggestions and criticisms would be an absolute God send!
Thanks in advance guys.

OK.
You can do like this: Im focus on Console Application
- Define a class call Message:
class Message
{
public String username; // the sender that send this message to u.So you can reply back to this user
public boolean groupMessage; // this message is group message or not
public String message;
}
Define a global variable: ArrayList messages; to hold all incomming messages.
So when you start chat with a client --> create new Thread to read message from him.When you receive a message . You have to put that message to the array list: messages ( you have to remember to sync it. because it will be invoked by many thread)
synchorized(messages){
messages.add(....); // new message here
}
Then , you create a new Thread to show message & can reply back to the sender. In this read you will pop a message from array list messages & show it.
while(isrunning)
{
synchorized(messages){
if(messages.size()<=0) messages.wait(); // when you receive a new message you have to notify
}
synchorized(messages){
Message msg = messages.get(0);
messages.remove(0);
showmessage_to_ouput(msg); // something like this.
String s = read from input // to reply to this message.
Reply(....)// here you can check if this message is group message--> reply to all,..etc
}
}
P/S: That's a idea :) good luck

I can give you a solution , but you have to implement it
We have:
- Server A, Client B & C. B & C already connected to Server via TCP connection
- The first, client B want to chat with C. So B have to send a message by UDP to server
- 2nd, Server will receive a UDP messages from B ==> Server know which ip & port of B that B connected to Server by UDP. Then server send to C a message (TCP) that contains info about UDP ip:port of B .
- 3rd: Client C will receive that message from server via TCP . So C know ip:port that B is listenning .--> If C accept chat with B . C have to send a UDP message to Server to tell server that C accept to talk with B.
- 4th: Server will receive that message via UDP . So Server also know ip:port of C in UDP.
- 5th : The server will transfer UDP ip:port of C to B via TCP (or UDP if you want).
- 6th: Client B will receive it & know udp ip:port of C. So they can start to chat via UDP protocol now.
IT is call UDP/TCP Hole punching. You can research more about it to implement.
P/S: But this method doesnt work with Symetric NAT