Develop Reference

Java proxy https implementation

I try to make my own proxy server and already implemented the http support for my proxy server. The proxy server works fine.
Now I want to have https as well (only with sockets). I looked up what I have to do at https://www.rfc-editor.org/rfc/rfc2817.
In my function I try to establish a TLS tunnel.
With my approach I only get a method not allowed as response. I also check some source in the internet, but didn't find anything which can help me with my problem.
Here is my function.
private Socket openTLSTunnel(String host) throws IOException {
String raw_request = "CONNECT " + host + ":80 HTTP/1.1\n"
+ "Host: " + host + ":80"
+ "\r\n\r\n";
// Make a connection to the website.
Socket tunnel = new Socket();
int timeout = 10000;
var server = new InetSocketAddress(host, 80);
tunnel.connect(server, timeout);
// Write the request to server.
OutputStream out = tunnel.getOutputStream();
byte[] msg = raw_request.getBytes(StandardCharsets.UTF_8);
out.write(msg);
out.flush();
// TODO send error to client.
// Get the response from server.
InputStream in = tunnel.getInputStream();
byte reply[] = new byte[200];
int replyLen = 0;
int newlinesSeen = 0;
boolean headerDone = false;
while (newlinesSeen < 2) {
int i = in.read();
if (i < 0) {
throw new IOException("Unexpected EOF from proxy");
}
if (i == '\n') {
headerDone = true;
++newlinesSeen;
}
else if (i != '\r') {
newlinesSeen = 0;
if (!headerDone && replyLen < reply.length) {
reply[replyLen++] = (byte) i;
}
}
}
String replyStr = new String(reply, 0, replyLen, "ASCII7");
// Check if connection established.
if(!replyStr.toLowerCase().contains("200 connection established")) {
System.out.println("No TLS connection established!");
throw new AccessDeniedException(replyStr);
}
else{
System.out.println("Connection established!");
}
return tunnel;
}
Thanks in advance!

Newbie getting nullPointers all over the place [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 3 years ago.
So I'm trying to create an smtp from scratch, (assignment) and I'm trying to connect classes together but miserably failing and trying everything out. The compiler doesn't throw up any errors but when I run it I don't get very far. I tried calling the other classes with the .start thread but still, failure
If you could help me or give tips, I would really appreciate it
//Problem seems to be here: I have no idea how to correct it
socketManager soketManager = null;
DataInputStream clientDataIn = new DataInputStream(soketManager.getInputStream());
socketManager clientReaderSocket = soketManager;```
public class socketManager {
public Socket soc = null;`
`
//socketManager.java
public DataInputStream input = null;
public DataOutputStream output = null;
public socketManager(Socket socket) throws IOException {
soc = socket;
input = new DataInputStream(soc.getInputStream());
output = new DataOutputStream(soc.getOutputStream());
}
public InputStream getInputStream() throws IOException {
input = new DataInputStream(soc.getInputStream());
return null;
}
public OutputStream getOutputStream() throws IOException {
output = new DataOutputStream(soc.getOutputStream());
return null;
}
}
Exception in thread "Thread-1" java.lang.NullPointerException at
me.censored.loopback.SMTPclient.Client$ClientSocketManager.run(Client.java:117)
at java.base/java.lang.Thread.run(Thread.java:834)
// Main Method:- called when running the class file.
public static void main(String[] args) throws UnknownHostException, IOException {
Port Declaration & Checks.
String serverIP = "loopback";
int defaultServerPort = 25;
PortManager portManage = new PortManager();
Thread portManagerThread = new Thread(portManage);
portManagerThread.start();
}// End of main
static public class PortManager implements Runnable {
Scanner userInput = new Scanner(System.in);
int serverPort = 25;
// Will accept only tcp/udp ports as of (2019) After several attempts the port
// will be auto selected to default 25,
// Should we accept parsed HEX?
boolean portCompletion = false;
short portTriesCounter = 1;
public void run() {
try {
do {
// Asks user for server's port at the start up of the client.
System.out.println("Please enter the port the server is on.");
String userEntry = userInput.nextLine();
userInput.close();
try {
serverPort = Integer.parseInt(userEntry);
if (portTriesCounter != 5) { // Partial tries timeout.
if (serverPort != 0) { // "Port Zero" does not officially exist. It is defined as an invalid
// port
// number. But valid Internet packets can be formed and sent "over
// the
// wire"
// to and from "port 0" just as with any other ports.
if ((serverPort > 0 && serverPort <= 1023)
|| (serverPort >= 1024 && serverPort <= 49151)
|| (serverPort >= 49152 && serverPort <= 65535)) // Check for ports inside the
// tcp/udp
// range
portCompletion = true;
else {
System.out.println(
"Wrong input! Make sure you are using correct numbers and port range! ");
portCompletion = false;
portTriesCounter++;
}
// End Check for ports inside the tcp/udp range
} else {
System.out.print("Wrong input! ");
portCompletion = false;
portTriesCounter++;
}
// End Check for zero
}
// End Too many attempts
else {
portTriesCounter = 5;
portCompletion = true;
System.out.print("Many wrong attemps. Selecting and trying the default port (25)... ");
try {
System.out.print("Success");
portCompletion = true;
serverPort = 25; // For SSL connections use port 465.
} catch (Exception except) {
portCompletion = false;
}
}
} catch (Exception except) {
portCompletion = false;
portTriesCounter++;
} finally {
userInput.close();
}
} while (!portCompletion);
ClientSocketManager clientSocketManage = new ClientSocketManager();
Thread clientSocketManagerThread = new Thread(clientSocketManage);
clientSocketManagerThread.start();
System.out.println("DEBUG 0");
} catch (Exception except) { // Any Failure will send 421 Error to client
System.out.println("\t 421 \t Service not available, closing transmission channel.\n" + except);
}
}
}
static class ClientSocketManager implements Runnable {
public void run() {
try {
String CRLF = "\r\n";
String LF = "\n";
boolean SocketInitiation = false;
socketManager soketManager = null;
DataInputStream clientDataIn = new DataInputStream(soketManager.getInputStream());
socketManager clientReaderSocket = soketManager;
DataOutputStream clientDataOut;
clientDataOut = new DataOutputStream(soketManager.getOutputStream());
String sendSocketMessage = (CRLF);
clientDataOut.writeUTF(sendSocketMessage);// Sends string to output stream using UTF-8
clientDataOut.flush();
System.out.println("DEBUG 1");
String socketReplyIn = clientDataIn.readUTF();
PortManager portInstance = new PortManager();
int portNumber = portInstance.serverPort;
Socket soket = new Socket("loopback", portNumber);
ClientWriter clientWrite = new ClientWriter(soket);
Thread clientWriteThread = new Thread(clientWrite);
ClientReader clientRead = new ClientReader(soket);
Thread clientReadThread = new Thread(clientRead);
System.out.println("DEBUG 2");
// Cleans stream from any write buffer method.
System.out.println("Connection to server using TCP...");
if (socketReplyIn.contains("220")) {
System.out.println("\t 220 \t Service ready"); // Connection established successfully
clientReadThread.start();
clientWriteThread.start();
SocketInitiation = true;
} else {
System.out.println("\t 421 \t Service not available, closing transmission channel");
SocketInitiation = false;
}
} catch (IOException e) {
System.out.println("\t 421 \t Service not available, closing transmission channel");
System.out.println("TCP connection error: " + e);
}
}
}

you have defined socketManager soketManager = null; in ClientSocketManager.
but you never assigned a value to it, so it is still null.
The code after that is trying to access streams from it, which is throwing NullPointerException:
DataInputStream clientDataIn = new DataInputStream(soketManager.getInputStream());
socketManager clientReaderSocket = soketManager;
DataOutputStream clientDataOut;
clientDataOut = new DataOutputStream(soketManager.getOutputStream());
String sendSocketMessage = (CRLF);
clientDataOut.writeUTF(sendSocketMessage);// Sends string to output stream using UTF-8
clientDataOut.flush();
System.out.println("DEBUG 1");
just create a new instance of the socketManager and assign it to soketManager before using it.
PortManager portInstance = new PortManager();
int portNumber = portInstance.serverPort;
Socket soket = new Socket("loopback", portNumber);
socketManager soketManager = new sockerManager(soket);

What is the problem of this code...? Java socket programming

I am coding client-server multithread calculator using java, socket programming.
There's any syntax error, but msgs cannot be received from server.
I think
receiveString = inFromServer.readLine()
does not works. This code is in Client program, in the while(true) loop.
What is the problem?
Here is my full code.
SERVER
import java.io.*;
import java.net.*;
public class Server implements Runnable
{
static int max = 5; //maximum thread's number
static int i = 0, count = 0; //i for for-loop, count for count number of threads
public static void main(String args[]) throws IOException
{
ServerSocket serverSocket = new ServerSocket(6789); //open new socket
File file = new File("src/serverinfo.dat"); //make data file to save server info.
System.out.println("Maximum 5 users can be supported.\nWaiting...");
for(i=0; i <= max; i++) { new Connection(serverSocket); } //make sockets - loop for max(=5) times
try //server information file writing
{
String dataString = "Max thread = 5\nServer IP = 127.0.0.1\nServer socket = 6789\n";
#SuppressWarnings("resource")
FileWriter dataFile = new FileWriter(file);
dataFile.write(dataString);
}
catch(FileNotFoundException e) { e.printStackTrace(); }
catch(IOException e) { e.printStackTrace(); }
}
static class Connection extends Thread
{
private ServerSocket serverSocket;
public Connection(ServerSocket serverSock)
{
this.serverSocket = serverSock;
start();
}
public void run()
{
Socket acceptSocket = null;
BufferedReader inFromClient = null;
DataOutputStream msgToClient = null;
String receiveString = null;
String result = "", sys_msg = "";
try
{
while(true)
{
acceptSocket = serverSocket.accept(); // 접속수락 소켓
count++;
inFromClient = new BufferedReader(new InputStreamReader(acceptSocket.getInputStream()));
msgToClient = new DataOutputStream(acceptSocket.getOutputStream());
System.out.println(count + "th client connected: " + acceptSocket.getInetAddress().getHostName() + " " + count + "/" + max);
System.out.println("Waiting response...");
while(true)
{
if (count >= max+1) // if 6th client tries to access
{
System.out.println("Server is too busy. " + max + " clients are already connected. Client access denied.");
sys_msg = "DENIED";
msgToClient.writeBytes(sys_msg);
acceptSocket.close();
count--;
break;
}
try{ msgToClient.writeBytes(result); }
catch(Exception e) {}
try{ receiveString = inFromClient.readLine(); }
catch(Exception e) // if receiveString = null
{
System.out.println("Connection Close");
count--;
break;
}
System.out.println("Input from client : " + receiveString);
try
{
if(receiveString.indexOf("+") != -1) { result = cal("+", receiveString); }
else if(receiveString.indexOf("-") != -1) { result = cal("-", receiveString); }
else if(receiveString.indexOf("/") != -1) { result = cal("/", receiveString); }
else if(receiveString.indexOf("*") != -1) { result = cal("*", receiveString); }
else if(receiveString.indexOf("+") == -1 || receiveString.indexOf("-") == -1 || receiveString.indexOf("*") == -1 || receiveString.indexOf("/") == -1) { result = "No INPUT or Invalid operation"; }
}
catch(Exception e){ result = "Wrong INPUT"; }
try{ msgToClient.writeBytes(result); }
catch(Exception e) {}
}
}
}
catch(IOException e) { e.printStackTrace(); }
}
}
private static String cal(String op, String recv) //function for calculating
{
double digit1, digit2; //first number, second number
String result = null;
digit1 = Integer.parseInt(recv.substring(0, recv.indexOf(op)).trim());
digit2 = Integer.parseInt(recv.substring(recv.indexOf(op)+1, recv.length()).trim());
if(op.equals("+")) { result = digit1 + " + " + digit2 + " = " + (digit1 + digit2); }
else if(op.equals("-")) { result = digit1 + " - " + digit2 + " = " + (digit1 - digit2); }
else if(op.equals("*")) { result = digit1 + " * " + digit2 + " = " + (digit1 * digit2); }
else if(op.equals("/"))
{
if(digit2 == 0){ result = "ERROR OCCURRED: Cannot be divided by ZERO"; }
else{ result = digit1 + " / " + digit2 + " = " + (digit1 / digit2); }
}
return result;
}
#Override
public void run() {
// TODO Auto-generated method stub
}
}
-----------------------------------------------------------------
CLIENT
import java.io.*;
import java.net.*;
public class Client {
public static void main(String args[]) throws IOException
{
Socket clientSocket = null;
BufferedReader userInput = new BufferedReader(new InputStreamReader(System.in));
BufferedReader inFromServer = null;
DataOutputStream msgToServer = null;
String sendString = "", receiveString = "";
try
{
clientSocket = new Socket("127.0.0.1", 6789); //make new clientSocket
inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
msgToServer = new DataOutputStream(clientSocket.getOutputStream());
System.out.println("Input exit to terminate");
System.out.println("Connection Success... Waiting for permission");
while(true)
{
receiveString = inFromServer.readLine();
if(receiveString.equals("DENIED"))
{
System.out.println("Server is full. Try again later.");
break;
}
else { System.out.println("Connection permitted."); }
System.out.print("Input an expression to calculate(ex. 3+1): ");
sendString = userInput.readLine();
if(sendString.equalsIgnoreCase("exit")) //when user input is "exit" -> terminate
{
clientSocket.close();
System.out.println("Program terminated.");
break;
}
try { msgToServer.writeBytes(sendString); }
catch(Exception e) {}
try { receiveString = userInput.readLine(); }
catch(Exception e) {}
System.out.println("Result: " + receiveString); //print result
}
}
catch(IOException e)
{
e.printStackTrace();
}
}
}

You've set up your server socket stack wrong.
Your code will make 5 threads, each calling accept on a serversocket.
The idea is to have a single ServerSocket (and not 5, as in your example). Then, this single serversocket (running in a single thread that handles incoming sockets flowing out of this serversocket) will call .accept which will block (freeze the thread) until a connection is made, and will then return a Socket object. You'd then spin off a thread to handle the socket object, and go right back to the accept call. If you want to 'pool' (which is not a bad idea), then disassociate the notion of 'handles connections' from 'extends Thread'. For example, implement Runnable instead. Then pre-create the entire pool (for example, 10 threads), have some code that lets you 'grab a thread' from the pool and 'return a thread' to the pool, and now the serversocket thread will, upon accept returning a socket object, grab a thread from the pool (which will block, thus also blocking any incoming clients, if every thread in the pool is already taken out and busy handling a connection), until a thread returns to the pool. Alternatively, the serversocket code checks if the pool is completely drained and if so, will put on a final thread the job of responding to that client 'no can do, we are full right now'.
I'm not sure if you actually want that; just.. make 1 thread per incoming socket is a lot simpler. I wouldn't dive into pool concepts until you really need them, and if you do, I'd look for libraries that help manage them. I think further advice on that goes beyond the scope of this question, so I'll leave the first paragraph as an outlay of how ServerSocket code ought to work, for context.

How to check if client has disconnected? [duplicate]

This question already has answers here:
Java detect lost connection [duplicate]
(9 answers)
Java socket API: How to tell if a connection has been closed?
(9 answers)
Closed 9 years ago.
I have a java program with Socket. I need to check if client has disconnected. I need a example how to do that. I have researched but I don't understand. So can someone make example code and explane everything.
sorry for bad English
my code:
package proov_server;
//SERVER 2
import java.io.*;
import java.net.*;
class server2 {
InetAddress[] kasutaja_aadress = new InetAddress[1000];
String newLine = System.getProperty("line.separator");
int kliendiNr = 0;
int kilene_kokku;
server2(int port) {
try {
ServerSocket severi_pistik = new ServerSocket(port);
System.out.println("Server töötab ja kuulab porti " + port + ".");
while (true) {
Socket pistik = severi_pistik.accept();
kliendiNr++;
kasutaja_aadress[kliendiNr] = pistik.getInetAddress();
System.out.println(newLine+"Klient " + kliendiNr + " masinast "
+ kasutaja_aadress[kliendiNr].getHostName() + " (IP:"
+ kasutaja_aadress[kliendiNr].getHostAddress() + ")");
// uue kliendi lõime loomine
KliendiLoim klient = new KliendiLoim(pistik,kliendiNr);
// kliendi lõime käivitamine
klient.start();
}
}
catch (Exception e) {
System.out.println("Serveri erind: " + e);
}
}
DataOutputStream[] väljund = new DataOutputStream[1000];
DataInputStream[] sisend = new DataInputStream[1000];
int klient = 0;
int nr;
// sisemine klass ühendusega tegelemiseks
class KliendiLoim extends Thread {
// kliendi pistik
Socket pistik;
// kliendi number
KliendiLoim(Socket pistik2,int kliendiNr) {
nr = kliendiNr;
this.pistik = pistik2;
}
public boolean kontroll(){
try{
System.out.println("con "+pistik.isConnected());
System.out.println("close "+pistik.isClosed());
if(pistik.isConnected() && !pistik.isClosed()){
//System.out.print(con_klient);
return true;
}
}catch(NullPointerException a){
System.out.println("Sihukest klienti pole!!!");
}
kliendiNr --;
return false;
}
public void run() {
try {
sisend[nr] = new DataInputStream(pistik.getInputStream()); //sisend
väljund[nr] = new DataOutputStream(pistik.getOutputStream()); //väljund
}catch (Exception ea) {
System.out.println(" Tekkis erind: " + ea);
}
while(true){
try{
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
System.out.print("Sisesta k2sk: ");
String k2sk = null;
k2sk = br.readLine();
/*
String command;
if(k2sk.indexOf(" ") < 0){
command = k2sk;
}else{
command = k2sk.substring(0, k2sk.indexOf(" "));
}
*/
String[] words = k2sk.split("\\s+");
for (int i = 0; i < words.length; i++) {
words[i] = words[i].replaceAll(" ", "");
}
switch(words[0]){
case "suhtle":
if(väljund.length > klient && väljund[klient] != null)
{
väljund[klient].writeUTF("1");
}else{
väljund[klient] = null;
sisend[klient] = null;
System.out.println("Sihukest klienti pole");
}
break;
case "vaheta":
try{
int klinetnr = Integer.parseInt(words[1]);
//if(kontroll(klinetnr) ){
klient = Integer.parseInt(words[1]);
//}
}
catch(NumberFormatException e){
System.out.println("See pole number!!! ");
}
break;
case "kliendid":
if(kliendiNr != 0){
for(int i=1;i <= kliendiNr;i++){
if(kontroll()){
System.out.println("Klient:"+i+" ip: " + kasutaja_aadress[i] );
}else{
System.out.println("Pisi");
väljund[klient] = null;
sisend[klient] = null;
}
}
System.out.println(newLine);
}else{
System.out.println("Kiente pole");
}
break;
}
System.out.println(kliendiNr);
}catch(SocketException a){
System.out.println("Klient kadus");
}
catch(Exception e){
System.out.println(" Viga: " + e);
}
}
}
}
public static void main(String[] args) {
new server2(4321);
}
}

If the client has disconnected properly:
read() will return -1
readLine() returns null
readXXX() for any other X throws EOFException.
The only really reliable way to detect a lost TCP connection is to write to it. Eventually this will throw an IOException: connection reset, but it takes at least two writes due to buffering.

A related thread on Stackoverflow here along with the solution. Basically, the solution says that the best way to detect a client-server disconnect is to attempt to read from the socket. If the read is successfully, then the connection is active.If an exception is thrown during the read there is no connection between the client and the server. Alternatively it may happen that the socket is configured with a timeout value for the read operation to complete. In case, this timeout is exceeded a socket timeout exception will be thrown which can be considered as either the client is disconnected or the network is down.
The post also talks about using the isReachable method - refer InetAddress documentation. However, this method only tells us whether a remote host is reachable or not. This may just one of the reasons for the client to disconnect from the server. You wont be able to detect disconnection due to client crash or termination using this technique.

Java NIO multiple socket connections failing

I have a program that attempts to connect to port 80 on different machines and reports if there is a server running. I am using NIO which therefore uses sockets to do the connection. I do a connect and then poll using finishConnect().
I am getting inconsistent behaviour. Sometimes the program correctly reports that there are web servers running on the various machines that I am scanning. However at other times the connections do not get reported even though there are webservers running on the target machines.
I would understand this if I was using UDP sockets as these are not reliable but I am using a TCP connection that should be reliable i.e no dropped packets.
I need to be able to scan many machines but this inconsistent behaviour exhibits it self even when testing the program with just 4 target IP addresses that all have webservers on port 80.
TIA
Rod
class SiteFinder {
private static final long TIMEOUT = 500;
public void findSites() {
int numSocketChannels = 100;
int socketChannelCounter = 0;
long ipAddressCounter = 0;
boolean done = false;
List<String> allIpAddresses =
IPAddressGenerator.getIPAddresses(170);
SocketChannel[] socketChannelArray =
new SocketChannel[numSocketChannels];
Iterator<String> itr = allIpAddresses.iterator();
while(itr.hasNext()) {
int k;
for (k = 0; k < numSocketChannels && itr.hasNext(); k++) {
String ipAddress = itr.next();
ipAddressCounter++;
if (ipAddressCounter % 50000 == 0)
System.out.println(ipAddressCounter + " at " + new Date());
try {
socketChannelArray[k] = SocketChannel.open();
socketChannelArray[k].configureBlocking(false);
if (socketChannelArray[k].connect(
new InetSocketAddress(ipAddress,80))) {
System.out.println(
"connection established after connect() "
+ ipAddress);
socketChannelArray[k].close();
socketChannelArray[k] = null;
}
} catch (IOException ioe) {
System.out.println(
"error opening/connecting socket channel " + ioe);
socketChannelArray[k] = null;
}
}
while (k < numSocketChannels) {
socketChannelArray[k++] = null;
}
long startTime = System.currentTimeMillis();
long timeout = startTime + TIMEOUT;
connect:
while (System.currentTimeMillis() < timeout) {
//System.out.println("passing");
socketChannelCounter = 0;
for(int j = 0; j < socketChannelArray.length; j++) {
//System.out.println("calling finish connect");
if (socketChannelArray[j] == null) {
++socketChannelCounter;
if (socketChannelCounter == numSocketChannels) {
System.out.println("terminating connection loop");
break connect;
}
continue;
}
try {
if (socketChannelArray[j].finishConnect()) {
/*try {
out.write("connection established after " +
finishConnect()" +
clientChannelVector.elementAt(j).socket().
getInetAddress() + '\n');
out.flush();
} catch (IOException ioe) {
System.out.println(
"error writing to site-list "
+ ioe.getMessage());
}*/
System.out.println(
"connection established after finishConnect()"
+ socketChannelArray[j].socket().
getInetAddress());
socketChannelArray[j].close();
socketChannelArray[j] = null;
}
} catch (IOException ioe) {
System.out.println(
"error connecting from "
+ "clientChannel.finishConnect()");
try {
socketChannelArray[j].close();
} catch (IOException e) {
System.out.println("error closing socket channel");
} finally {
//System.out.println("removing socket channel");
//System.out.println(clientChannelVector.size());
socketChannelArray[j] = null;
}
}
}
}
closeConnections(socketChannelArray);
}
}
private void closeConnections(SocketChannel[] socketChannelArray) {
for (int i = 0; i < socketChannelArray.length; i++) {
if (socketChannelArray[i] == null) {
continue;
}
try {
socketChannelArray[i].close();
//System.out.println(
//"TIME OUT WAITING FOR RESPONSE CLOSING CONNECTION");
} catch (IOException ioe) {
System.out.println(
"error closing socket channel " + ioe.getMessage());
}
}
}
}