Principles, Models, and Applications for Distributed Systems M

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Università degli Studi di Bologna Facoltà di Ingegneria Principles, Models, and Applications for Distributed Systems M Exercitation 3 Connected Java Sockets Jacopo De Benedetto Distributed

1 Università degli Studi di Bologna Facoltà di Ingegneria Principles, Models, and Applications for Distributed Systems M Exercitation 3 Connected Java Sockets Jacopo De Benedetto Distributed architecture for the file transfer: Sequential Server Std Input file name client put file network put file server file - Connection usage for coordination and communication: send file name and file content Std Output 1

2 Distributed architecture for the file transfer: Concurrent Server file name 1 client serverthread1 serverthread2 file name 2 client put file2 Network rete server file name 3 client serverthread3 Implementation details Develop a C/S application to transfer a binary file from client to server (put). The Client asks the user the file name of the file to transfer; then, it connects to the server (using stream sockets: java.net.socket), builds an output stream over the socket connection, and sends the file name and the file content. Finally, it waits and prints the server reply (success/failure) and prepares to receive other user requests until the end of the program. The Server listens for connection requests (using java.net. ServerSocket class), accepts incoming connection request (java.net.socket), and builds an input stream on the connected socket, that it uses to read the file name and the file content, by saving the file in its local file system (current working directory). Then, it sends a reply and closes the connection. There are two possible responses: file overwriting (if the file already exists) and file creation (if it has been created) and each of them can be either successful or not. 2

3 Filter A filter is an application thate consumes the input stream and writes on the output stream Input Filter Output Filters can be combined to build a pipeline. For example a filter could read until the End Of File (EOF) an input stream and copy read input data to its output stream (see the following slides). Many filter types: character/line/byte/ oriented. In the following we use a simple line-oriented filter: SimpleFilter then, we use a byte-oriented filter: byte_file_transfer Line-Oriented Filter This filter reads lines from standard input, and writes to the standard output only those lines that contain the a character : public class SimpleFilter { public static void main(string[] args) { String line; BufferedReader input = new BufferedReader(new InputStreamReader(System.in)); BufferedWriter output = new BufferedWriter(new OutputStreamWriter(System.out)); System.err.println("\nSimpleFilter message:"); try { while ((line = input.readline())!= null) if (line.lastindexof('a') > 0) output.write(line + "\n"); output.flush(); // flush buffer catch (IOException e) { System.out.println("Error: "); e.printstacktrace(); 3

4 Filters and Streams Input/output streams as filters Examples of input/output streams wrapping a socket: DataInputStream insock = new DataInputStream(socket.getInputStream()); DataOutputStream outsock = new DataOutputStream(socket.getOutputStream()); Examples of input/output streams wrapping a binary file: DataInputStream insock = new DataInputStream(new FileInputStream(filename)); DataOutputStream outsock = new DataOutputStream(new FileOutputStream(filename)); FileUtility: Byte-oriented filter for file transfer // Static method: byte_file_transfer static protected void byte_file_transfer (DataInputStream src, DataOutputStream dest) throws IOException { // loop: read from src and write to dest int buffer = 0; try { // break from loop if we read // a negative value -> EOF while ( (buffer = src.read()) >= 0) dest.write(buffer); dest.flush(); catch (EOFException e) { System.out.println("Error: "); e.printstacktrace(); 4

5 Solution sketch: Client (1) 1. Create a socket with implicit bind (and set options, if needed): socket = new Socket(addr, port); socket.setxxx( ); 2. User interaction: BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in)); System.out.print("Insert a file name: "); String filename = null; while( filename=stdin.readline() )!=null) 3. Wrap socket output stream: outsock = new DataOutputStream(socket.getOutputStream()); Solution sketch: Client (2) 4. Wrap binary file in a input stream: infile = new DataInputStream(new FileInputStream(filename)); 5. Send data to server: outsock.writeutf(filename); FileUtility.byte_file_transfer(inFile, outsock); 6. Graceful socket close and receive response: socket.shutdownoutput();... response = insock.readutf(); socket.shutdowninput(); 5

6 Solution sketch: Server (1) 1. Create a socket with explicit bind (and set options, if needed): serversocket = new ServerSocket(port); serversocket.setreuseaddress(true); 2. Wait for a connection request and accept it: clientsocket = serversocket.accept(); 3. Wrap socket input stream: insock = new DataInputStream(clientSocket.getInputStream()); 4. Wrap binary file in an output stream: filename=insock.readutf(); outfile = new DataOutputStream( new FileOutputStream(filename)); Solution sketch: Server (2) 5. Receive data from client and write to output file: FileUtility.byte_file_transfer(inSock,outFile); 6. Close file and socket, send response: outfile.close(); socket.shutdowninput();... outsock.writeutf(response); socket.shutdownoutput(); Remember to close always all sockets and files no longer in use! 6

7 PutFileClient for binary files 1/3 public class PutFileClient { public static void main(string[] args) throws IOException { InetAddress addr = null; int port = -1; try{ // check invocation arguments if(args.length == 2){ addr = InetAddress.getByName(args[0]); port = Integer.parseInt(args[1]); else{ System.out.println("Usage:..."); System.exit(1); //try catch(exception e){... // objects for network communication and file access Socket socket = null; FileInputStream infile = null; String filename = null; DataInputStream insock = null; DataOutputStream outsock = null; BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in)); System.out.print("\n^D(Unix)/^Z(Win)+enter. File name?"); PutFileClient for binary files2/3 try{ while ((filename=stdin.readline())!=null){ if(new File(filename).exists()){ try{ // socket creation socket = new Socket(addr, port); socket.setsotimeout(30000); insock = new DataInputStream(socket.getInputStream()); outsock = new DataOutputStream(socket.getOutputStream()); catch(exception e){... continue; else{system.out.println("file " + filename + " does not exist"); System.out.print("\n^D(Unix)/^Z(Win)..."); continue; // Send file try{ infile = new FileInputStream(filename); catch(filenotfoundexception e){ 7

8 PutFileClient for binary files 3/3 try{ outsock.writeutf(filename); FileUtility.byte_file_transfer( new DataInputStream(inFile), outsock); infile.close(); // close file socket.shutdownoutput(); // close socket output stream, i.e., send EOF catch (SocketTimeoutException te) {... continue; catch(exception e){... continue; String response; // read reply try{ response = insock.readutf(); socket.shutdowninput(); // close socket input stream catch (SocketTimeoutException te) {... continue; catch(exception e){... continue; System.out.print("\n^D(Unix)/^Z(Win)..."); // new request // while // try catch(exception e){... System.exit(3); // main // class PutFileServerSeq for binary files1/3 public class PutFileServerSeq { public static final int PORT = 54321; // default port public static void main(string[] args) throws IOException { int port = -1; try // check arguments { if (args.length == 1) { port = Integer.parseInt(args[0]); else if (args.length == 0) { port = PORT; else { // Msg errore... //try catch (Exception e) {... ServerSocket serversocket = null; // build socket and in/out streams try { serversocket = new ServerSocket(port); serversocket.setreuseaddress(true); catch (Exception e) {... try { while (true) // server endless loop { Socket clientsocket = null; DataInputStream insock = null; DataOutputStream outsock = null; 8

9 PutFileServerSeq for binary files 2/3 try { clientsocket = serversocket.accept(); clientsocket.setsotimeout(30000); catch (Exception e) {... continue; String filename; try // build I/O streams { insock =new DataInputStream(clientSocket.getInputStream()); outsock =new DataOutputStream(clientSocket.getOutputStream()); filename = insock.readutf(); catch (SocketTimeoutException te) {... continue; catch (IOException e) {... continue; FileOutputStream outfile = null; String response; // receive file if (filename == null) { clientsocket.close(); continue; else { File curfile = new File(filename); if (curfile.exists()) { try { response = "File overwritten"; curfile.delete(); // delete the file catch (Exception e) {... continue; PutFileServerSeq for binary files 3/3 else response = "New file created"; outfile = new FileOutputStream(filename); try // receive file { FileUtility.byte_file_trasfer( insock, new DataOutputStream(outFile)); // Note: the function above consumes the EOF outfile.close(); // close file clientsocket.shutdowninput(); outsock.writeutf(response+", file saved on server"); clientsocket.shutdownoutput(); catch (SocketTimeoutException te) {... continue; catch (Exception e) {...continue; catch (Exception e) {... System.exit(3); 9

10 PutFileServerCon for binary files 1/4 class PutFileServerThread extends Thread { private Socket clientsocket = null; public PutFileServerThread(Socket clientsocket) { this.clientsocket = clientsocket; public void run() // Child process that manages a connection { DataInputStream insock; DataOutputStream outsock; try { String filename; try // build stream { insock = new DataInputStream(clientSocket.getInputStream()); outsock = new DataOutputStream(clientSocket.getOutputStream()); filename = insock.readutf(); catch (SocketTimeoutException te) {... catch (IOException ioe) {... catch (Exception e) {... FileOutputStream outfile = null; String response; // receive file: error if (filename == null) {clientsocket.close(); return; PutFileServerCon for binary files 2/4 else { // checks if file exsists File curfile = new File(filename); if (curfile.exists()) { try // delete old file { response = "File overwritten"; curfile.delete(); catch (Exception e) {... return; else response = "New file created"; outfile = new FileOutputStream(filename); try { FileUtility.byte_file_transfer (insock, new DataOutputStream(outFile)); outfile.close(); // close file and socket // IMPORTANT: socket closed by child process clientsocket.shutdowninput(); outsock.writeutf(response + ", file saved"); clientsocket.shutdownoutput(); catch (Exception e) {... catch (Exception e) {... System.exit(3); // run // PutFileServerThread 10

11 PutFileServerCon for binary files 3/4 public class PutFileServerCon { public static final int PORT = 1050; public static void main (String[] args) throws IOException { int port = -1; try // check arguments { if (args.length == 1) {port = Integer.parseInt(args[0]); else if (args.length == 0) {port = PORT; else { System.out.println("Usage:..."); System.exit(1); //try catch (Exception e) {... System.exit(1); ServerSocket serversocket = null; Socket clientsocket = null; try { serversocket = new ServerSocket(port); serversocket.setreuseaddress(true); catch (Exception e) {... System.exit(1); try { while (true) { try { clientsocket = serversocket.accept(); clientsocket.setsotimeout(30000); catch (Exception e) {... continue; PutFileServerCon for binary files 4/4 try { // service delegated to a new thread new PutFileServerThread(clientSocket).start(); /* IMPORTANT!!! The socket is closed ONLY by the child process. If the father tries to close the socket you could incur in race conditions (due to shared memory). */ catch (Exception e) {... continue; // while catch (Exception e) {... System.exit(2); // main // PutFileServerCon 11

12 Proposed Exercise Develop a C/S application that manages the transfer of all the files in a specific directory from the server to the client (multiple get). Specification: Client The client asks the user the name of the directory, relative to the working directory of the server, connects to the server (using java.net.socket), builds an output stream to send the request and an input stream to receive the files or a negative response, if the directory does not exist. Requested files are saved in the working directory, overwriting existing files having the same name. 12

13 Specification: Server Server listens for client connection requests (using java.net.serversocket), then uses the resulting connected socket (java.net.socket) to build an input stream to receive a request and an output stream to send requested files or a negative response, then closes the connection. Server must use the same socket to send all the files. Server must be concurrent and parallel. For each request received by the father process, it must activate a child that manages the service completion. Implementation Hints To correctly send files, it is necessary to design a protocol to handle multiple file transfers. For example the server, before sending the first file, could send the file name and its size in bytes, then sends the byte stream. The server follows this protocol for each file and uses the same socket for all transfers. All these steps are repeated until the server has sent all the files in the requested directory, then the server closes the connection to notify the end of transmission. Client File1 File2 File3 Server filename1 length1 File1 filename2 length2 File2 filename3 length3 File3 13

14 Implementation Hints To open a directory use a File object: File dir = new File(dirName); To verify if a file (or a directory) exists: dir.exists(); //return true or false To verify if the File object is a directory: dir.isdirectory(); //return true or false To get all the files in the directory: File[] files = dir.listfiles(); Implementation Hints n_byte_file_transfer() function: protected static void n_byte_file_transfer(datainputstream src, DataOutputStream dest, long nbytes) throws IOException { int cont = 0; // loop: read from source and write to dest int buffer = 0; try { // exit the cycle after reading nbytes bytes while (cont < nbytes) { buffer = src.read(); dest.write(buffer); cont++; dest.flush(); System.out.println("Transferred bytes: " + cont); catch (EOFException e) { System.out.println("Error: "); e.printstacktrace(); 14

Principles, Models, and Applications for Distributed Systems M

Università degli Studi di Bologna Facoltà di Ingegneria Principles, Models, and Applications for Distributed Systems M Lab assignment 4 (worked-out) Connection-oriented Java Sockets Luca Foschini Winter