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  • How to implement a bidirectional "mailbox service" over tcp?

    - by igorgatis
    The idea is to allow to peer processes to exchange messages (packets) over tcp as much asynchronously as possible. The way I'd like it to work is each process to have an outbox and an inbox. The send operation is just a push on the outbox. The receive operation is just a pop on the inbox. Underlying protocol would take care of the communication details. Is there a way to implement such mechanism using a single TCP connection? How would that be implemented using BSD sockets and modern OO Socket APIs (like Java or C# socket API)?

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  • Information on Rojiani's Numerical methods C textbook

    - by yCalleecharan
    Hi, having taken a look at a few textbooks that discuss numerical methods and C programming, I was gladly surprised when browsing through "programming in C with numerical methods for engineers" by Rojiani. I understand of course it's important that one need to have a solid background in numerical methods prior to try implementing them on a computer. I would like to know if someone here has been using this book and if possible point out strengths and weaknesses of this textbook. Thanks a lot...

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  • How to save image drawn on a JPanel?

    - by swift
    I have a panel with transparent background which i use to draw an image. now problem here is when i draw anything on panel and save the image as a JPEG file its saving the image with black background but i want it to be saved as same, as i draw on the panel. what should be done for this? plz guide me j Client.java public class Client extends Thread { static DatagramSocket datasocket; static DatagramSocket socket; Point point; Whiteboard board; Virtualboard virtualboard; JLayeredPane layerpane; BufferedImage image; public Client(DatagramSocket datasocket) { Client.datasocket=datasocket; } //This function is responsible to connect to the server public static void connect() { try { socket=new DatagramSocket (9000); //client connection socket port= 9000 datasocket=new DatagramSocket (9005); //client data socket port= 9002 ByteArrayOutputStream baos=new ByteArrayOutputStream(); DataOutputStream dos=new DataOutputStream(baos); //this is to tell server that this is a connection request dos.writeChar('c'); dos.close(); byte[]data=baos.toByteArray(); //Server IP address InetAddress ip=InetAddress.getByName("10.123.97.154"); //create the UDP packet DatagramPacket packet=new DatagramPacket(data, data.length,ip , 8000); socket.send(packet); Client client=new Client(datasocket); client.createFrame(); client.run(); } catch(Exception e) { e.printStackTrace(); } } //This function is to create the JFrame public void createFrame() { JFrame frame=new JFrame("Whiteboard"); frame.setVisible(true); frame.setBackground(Color.black); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setSize(680,501); frame.addWindowListener(new WindowAdapter() { public void windowOpened(WindowEvent e) {} public void windowClosing(WindowEvent e) { close(); } }); layerpane=frame.getLayeredPane(); board= new Whiteboard(datasocket); image = new BufferedImage(590,463, BufferedImage.TYPE_INT_ARGB); board.setBounds(74,2,590,463); board.setImage(image); virtualboard=new Virtualboard(); virtualboard.setImage(image); virtualboard.setBounds(74,2,590,463); layerpane.add(virtualboard,new Integer(2));//Panel where remote user draws layerpane.add(board,new Integer(3)); layerpane.add(board.colourButtons(),new Integer(1)); layerpane.add(board.shapeButtons(),new Integer(0)); //frame.add(paper.addButtons(),BorderLayout.WEST); } /* * This function is overridden from the thread class * This function listens for incoming packets from the server * which contains the points drawn by the other client */ public void run () { while (true) { try { byte[] buffer = new byte[512]; DatagramPacket packet = new DatagramPacket(buffer, buffer.length); datasocket.receive(packet); InputStream in=new ByteArrayInputStream(packet.getData(), packet.getOffset(),packet.getLength()); DataInputStream din=new DataInputStream(in); int x=din.readInt(); int y=din.readInt(); String varname=din.readLine(); String var[]=varname.split("-",4); point=new Point(x,y); virtualboard.addPoint(point, var[0], var[1],var[2],var[3]); } catch (IOException ex) { ex.printStackTrace(); } } } //This function is to broadcast the newly drawn point to the server public void broadcast (Point p,String varname,String shape,String event, String color) { try { ByteArrayOutputStream baos=new ByteArrayOutputStream(); DataOutputStream dos=new DataOutputStream(baos); dos.writeInt(p.x); dos.writeInt(p.y); dos.writeBytes(varname); dos.writeBytes("-"); dos.writeBytes(shape); dos.writeBytes("-"); dos.writeBytes(event); dos.writeBytes("-"); dos.writeBytes(color); dos.close(); byte[]data=baos.toByteArray(); InetAddress ip=InetAddress.getByName("10.123.97.154"); DatagramPacket packet=new DatagramPacket(data, data.length,ip , 8002); datasocket.send(packet); } catch (Exception e) { e.printStackTrace(); } } //This function is to close the client's connection with the server public void close() { try { ByteArrayOutputStream baos=new ByteArrayOutputStream(); DataOutputStream dos=new DataOutputStream(baos); //This is to tell server that this is request to remove the client dos.writeChar('r'); dos.close(); byte[]data=baos.toByteArray(); //Server IP address InetAddress ip=InetAddress.getByName("10.123.97.154"); DatagramPacket packet=new DatagramPacket(data, data.length,ip , 8000); socket.send(packet); System.out.println("closed"); } catch(Exception e) { e.printStackTrace(); } } public static void main(String[] args) throws Exception { connect(); } } Whiteboard.java class Whiteboard extends JPanel implements MouseListener,MouseMotionListener,ActionListener,KeyListener { BufferedImage image; Boolean tooltip=false; int post; String shape; String selectedcolor="black"; Color color=Color.black; //Color color=Color.white; Point start; Point end; Point mp; Point tip; int keycode; String fillshape; Point fillstart=new Point(); Point fillend=new Point(); int noofside; Button r=new Button("rect"); Button rectangle=new Button("rect"); Button line=new Button("line"); Button roundrect=new Button("roundrect"); Button polygon=new Button("poly"); Button text=new Button("text"); JButton save=new JButton("Save"); Button elipse=new Button("elipse"); ImageIcon fillicon=new ImageIcon("images/fill.jpg"); JButton fill=new JButton(fillicon); ImageIcon erasericon=new ImageIcon("images/eraser.gif"); JButton erase=new JButton(erasericon); JButton[] colourbutton=new JButton[28]; String selected; Point label; String key=""; int ex,ey;//eraser DatagramSocket dataSocket; JButton button = new JButton("test"); Client client; Boolean first; int w,h; public Whiteboard(DatagramSocket dataSocket) { try { UIManager.setLookAndFeel( UIManager.getCrossPlatformLookAndFeelClassName()); } catch (Exception e) { e.printStackTrace(); } setLayout(null); setOpaque(false); setBackground(new Color(237,237,237)); this.dataSocket=dataSocket; client=new Client(dataSocket); addKeyListener(this); addMouseListener(this); addMouseMotionListener(this); setBorder(BorderFactory.createLineBorder(Color.black)); } public void paintComponent(Graphics g) { try { super.paintComponent(g); g.drawImage(image, 0, 0, this); Graphics2D g2 = (Graphics2D)g; if(color!=null) g2.setPaint(color); if(start!=null && end!=null) { if(selected==("elipse")) g2.drawOval(start.x, start.y,(end.x-start.x),(end.y-start.y)); else if(selected==("rect")) g2.drawRect(start.x, start.y, (end.x-start.x),(end.y-start.y)); else if(selected==("rrect")) g2.drawRoundRect(start.x, start.y, (end.x-start.x),(end.y-start.y),11,11); else if(selected==("line")) g2.drawLine(start.x,start.y,end.x,end.y); else if(selected==("poly")) { g2.drawLine(start.x,start.y,end.x,end.y); client.broadcast(start, "start", "poly", "drag", selectedcolor); client.broadcast(end, "end", "poly", "drag", selectedcolor); } } if(tooltip==true) { System.out.println(selected); if(selected=="text") { g2.drawString("|", tip.x, tip.y-5); g2.drawString("Click to add text", tip.x+10, tip.y+23); g2.drawString("__", label.x+post, label.y); } if(selected=="erase") { g2.setPaint(new Color(237,237,237)); g2.fillRect(tip.x-10,tip.y-10,10,10); g2.setPaint(color); g2.drawRect(tip.x-10,tip.y-10,10,10); } } } catch(Exception e) {} } //Function to draw the shape on image public void draw() { Graphics2D g2 = (Graphics2D) image.createGraphics(); Font font=new Font("Times New Roman",Font.PLAIN,14); g2.setFont(font); g2.setPaint(color); if(start!=null && end!=null) { if(selected=="line") g2.drawLine(start.x, start.y, end.x, end.y); else if(selected=="elipse") g2.drawOval(start.x, start.y, (end.x-start.x),(end.y-start.y)); else if(selected=="rect") g2.drawRect(start.x, start.y, (end.x-start.x),(end.y-start.y)); else if(selected==("rrect")) g2.drawRoundRect(start.x, start.y, (end.x-start.x),(end.y-start.y),11,11); else if(selected==("poly")) { g2.drawLine(start.x,start.y,end.x,end.y); client.broadcast(start, "start", "poly", "release", selectedcolor); client.broadcast(end, "end", "poly", "release", selectedcolor); } fillstart=start; fillend=end; fillshape=selected; } if(selected!="poly") { start=null; end=null; } if(label!=null) { if(selected==("text")) { g2.drawString(key,label.x,label.y); client.broadcast(label, key, "text", "release", selectedcolor); } } repaint(); g2.dispose(); } //Function which provides the erase functionality public void erase() { Graphics2D pic=(Graphics2D) image.createGraphics(); Color erasecolor=new Color(237,237,237); pic.setPaint(erasecolor); if(start!=null) pic.fillRect(start.x-10, start.y-10, 10, 10); } //To set the size of the image public void setImage(BufferedImage image) { this.image = image; } //Function to add buttons into the panel, calling this function returns a panel public JPanel shapeButtons() { JPanel shape=new JPanel(); shape.setBackground(new Color(181, 197, 210)); shape.setLayout(new GridLayout(5,2,2,4)); shape.setBounds(0, 2, 74, 166); rectangle.addActionListener(this); rectangle.setToolTipText("Rectangle"); line.addActionListener( this); line.setToolTipText("Line"); erase.addActionListener(this); erase.setToolTipText("Eraser"); roundrect.addActionListener(this); roundrect.setToolTipText("Round edge Rectangle"); polygon.addActionListener(this); polygon.setToolTipText("Polygon"); text.addActionListener(this); text.setToolTipText("Text"); fill.addActionListener(this); fill.setToolTipText("Fill with colour"); elipse.addActionListener(this); elipse.setToolTipText("Elipse"); save.addActionListener(this); shape.add(elipse); shape.add(rectangle); shape.add(roundrect); shape.add(polygon); shape.add(line); shape.add(text); shape.add(fill); shape.add(erase); shape.add(save); return shape; } public JPanel colourButtons() { JPanel colourbox=new JPanel(); colourbox.setBackground(new Color(181, 197, 210)); colourbox.setLayout(new GridLayout(8,2,8,8)); colourbox.setBounds(0,323,70,140); //colourbox.add(empty); for(int i=0;i<16;i++) { colourbutton[i]=new JButton(); colourbox.add(colourbutton[i]); if(i==0) colourbutton[0].setBackground(Color.black); else if(i==1) colourbutton[1].setBackground(Color.white); else if(i==2) colourbutton[2].setBackground(Color.red); else if(i==3) colourbutton[3].setBackground(Color.orange); else if(i==4) colourbutton[4].setBackground(Color.blue); else if(i==5) colourbutton[5].setBackground(Color.green); else if(i==6) colourbutton[6].setBackground(Color.pink); else if(i==7) colourbutton[7].setBackground(Color.magenta); else if(i==8) colourbutton[8].setBackground(Color.cyan); else if(i==9) colourbutton[9].setBackground(Color.black); else if(i==10) colourbutton[10].setBackground(Color.yellow); else if(i==11) colourbutton[11].setBackground(new Color(131,168,43)); else if(i==12) colourbutton[12].setBackground(new Color(132,0,210)); else if(i==13) colourbutton[13].setBackground(new Color(193,17,92)); else if(i==14) colourbutton[14].setBackground(new Color(129,82,50)); else if(i==15) colourbutton[15].setBackground(new Color(64,128,128)); colourbutton[i].addActionListener(this); } return colourbox; } public void fill() { if(selected=="fill") { Graphics2D g2 = (Graphics2D) image.getGraphics(); g2.setPaint(color); System.out.println("Fill"); if(fillshape=="elipse") g2.fillOval(fillstart.x, fillstart.y, (fillend.x-fillstart.x),(fillend.y-fillstart.y)); else if(fillshape=="rect") g2.fillRect(fillstart.x, fillstart.y, (fillend.x-fillstart.x),(fillend.y-fillstart.y)); else if(fillshape==("rrect")) g2.fillRoundRect(fillstart.x, fillstart.y, (fillend.x-fillstart.x),(fillend.y-fillstart.y),11,11); // else if(fillshape==("poly")) // g2.drawPolygon(x,y,2); } repaint(); } //To save the image drawn public void save() { try { ByteArrayOutputStream bos = new ByteArrayOutputStream(); JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(bos); JFileChooser fc = new JFileChooser(); fc.showSaveDialog(this); encoder.encode(image); byte[] jpgData = bos.toByteArray(); FileOutputStream fos = new FileOutputStream(fc.getSelectedFile()+".jpeg"); fos.write(jpgData); fos.close(); //add replce confirmation here } catch (IOException e) { System.out.println(e); } } public void mouseClicked(MouseEvent e) { } @Override public void mouseEntered(MouseEvent e) { } public void mouseExited(MouseEvent arg0) { } public void mousePressed(MouseEvent e) { if(selected=="line"||selected=="text") { start=e.getPoint(); client.broadcast(start,"start", selected,"press", selectedcolor); } else if(selected=="elipse"||selected=="rect"||selected=="rrect") mp = e.getPoint(); else if(selected=="poly") { if(first==true) { start=e.getPoint(); //client.broadcast(start,"start", selected,"press", selectedcolor); } else if(first==false) { end=e.getPoint(); repaint(); //client.broadcast(end,"end", selected,"press", selectedcolor); } } else if(selected=="erase") { start=e.getPoint(); erase(); } } public void mouseReleased(MouseEvent e) { if(selected=="text") { System.out.println("Reset"); key=""; post=0; label=new Point(); label=e.getPoint(); grabFocus(); } if(start!=null && end!=null) { if(selected=="line") { end=e.getPoint(); client.broadcast(end,"end", selected,"release", selectedcolor); draw(); } else if(selected=="elipse"||selected=="rect"||selected=="rrect") { end.x = Math.max(mp.x,e.getX()); end.y = Math.max(mp.y,e.getY()); client.broadcast(end,"end", selected,"release", selectedcolor); draw(); } else if(selected=="poly") { draw(); first=false; start=end; end=null; } } } public void mouseDragged(MouseEvent e) { if(end==null) end = new Point(); if(start==null) start = new Point(); if(selected=="line") { end=e.getPoint(); client.broadcast(end,"end", selected,"drag", selectedcolor); } else if(selected=="erase") { start=e.getPoint(); erase(); client.broadcast(start,"start", selected,"drag", selectedcolor); } else if(selected=="elipse"||selected=="rect"||selected=="rrect") { start.x = Math.min(mp.x,e.getX()); start.y = Math.min(mp.y,e.getY()); end.x = Math.max(mp.x,e.getX()); end.y = Math.max(mp.y,e.getY()); client.broadcast(start,"start", selected,"drag", selectedcolor); client.broadcast(end,"end", selected,"drag", selectedcolor); } else if(selected=="poly") end=e.getPoint(); System.out.println(tooltip); if(tooltip==true) { if(selected=="erase") { Graphics2D g2=(Graphics2D) getGraphics(); tip=e.getPoint(); g2.drawRect(tip.x-10,tip.y-10,10,10); } } repaint(); } public void mouseMoved(MouseEvent e) { if(selected=="text" ||selected=="erase") { tip=new Point(); tip=e.getPoint(); tooltip=true; repaint(); } } public void actionPerformed(ActionEvent e) { if(e.getSource()==elipse) selected="elipse"; else if(e.getSource()==line) selected="line"; else if(e.getSource()==rectangle) selected="rect"; else if(e.getSource()==erase) { selected="erase"; tooltip=true; System.out.println(selected); erase(); } else if(e.getSource()==roundrect) selected="rrect"; else if(e.getSource()==polygon) { selected="poly"; first=true; start=null; } else if(e.getSource()==text) { selected="text"; tooltip=true; } else if(e.getSource()==fill) { selected="fill"; fill(); } else if(e.getSource()==save) save(); if(e.getSource()==colourbutton[0]) { color=Color.black; selectedcolor="black"; } else if(e.getSource()==colourbutton[1]) { color=Color.white; selectedcolor="white"; } else if(e.getSource()==colourbutton[2]) { color=Color.red; selectedcolor="red"; } else if(e.getSource()==colourbutton[3]) { color=Color.orange; selectedcolor="orange"; } else if(e.getSource()==colourbutton[4]) { selectedcolor="blue"; color=Color.blue; } else if(e.getSource()==colourbutton[5]) { selectedcolor="green"; color=Color.green; } else if(e.getSource()==colourbutton[6]) { selectedcolor="pink"; color=Color.pink; } else if(e.getSource()==colourbutton[7]) { selectedcolor="magenta"; color=Color.magenta; } else if(e.getSource()==colourbutton[8]) { selectedcolor="cyan"; color=Color.cyan; } } @Override public void keyPressed(KeyEvent e) { //System.out.println(e.getKeyChar()+" : "+e.getKeyCode()); if(label!=null) { if(e.getKeyCode()==10) //Check for Enter key { label.y=label.y+14; key=""; post=0; repaint(); } else if(e.getKeyCode()==8) //Backspace { try{ Graphics2D g2 = (Graphics2D) image.getGraphics(); g2.setPaint(new Color(237,237,237)); g2.fillRect(label.x+post-7, label.y-13, 14, 17); if(post>0) post=post-6; keycode=0; key=key.substring(0, key.length()-1); System.out.println(key.substring(0, key.length())); repaint(); Point broadcastlabel=new Point(); broadcastlabel.x=label.x+post-7; broadcastlabel.y=label.y-13; client.broadcast(broadcastlabel, key, "text", "backspace", selectedcolor); } catch(Exception ex) {} } //Block invalid keys else if(!(e.getKeyCode()>=16 && e.getKeyCode()<=20 || e.getKeyCode()>=112 && e.getKeyCode()<=123 || e.getKeyCode()>=33 && e.getKeyCode()<=40 || e.getKeyCode()>=144 && e.getKeyCode()<=145 || e.getKeyCode()>=524 && e.getKeyCode()<=525 ||e.getKeyCode()==27||e.getKeyCode()==155 ||e.getKeyCode()==127)) { key=key+e.getKeyChar(); post=post+6; draw(); } } } @Override public void keyReleased(KeyEvent e) { } @Override public void keyTyped(KeyEvent e) { } } class Button extends JButton { String name; int i; public Button(String name) { this.name=name; try { UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel"); } catch (Exception e) { e.printStackTrace(); } } public Button(int i) { this.i=i; } public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2 = (Graphics2D)g; g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); //g2.setStroke(new BasicStroke(1.2f)); if (name == "line") g.drawLine(5,5,30,30); if (name == "elipse") g.drawOval(5,7,25,20); if (name== "rect") g.drawRect(5,5,25,23); if (name== "roundrect") g.drawRoundRect(5,5,25,23,10,10); int a[]=new int[]{20,9,20,23,20}; int b[]=new int[]{9,23,25,20,9}; if (name== "poly") g.drawPolyline(a, b, 5); if (name== "text") g.drawString("Text",8, 24); } }

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  • client side application not working as intended while using AsyncSocket

    - by Miraaj
    Hi All, I am using AsyncSocket class in a simple client-server application. As a first step I want that - as soon as connection is established between client and server, client transmit a welcome message - "connected to xyz server" to server and server displays it in textview. //The code in ClientController class is: -(void)awakeFromNib{ NSError *error = nil; if (![connectSocket connectToHost:@"192.168.0.32" onPort:25242 error:&error]) { NSLog(@"Error starting client: %@", error); return; } NSLog(@"xyz chat client started on port %hu",[connectSocket localPort]); } - (void)onSocket:(AsyncSocket *)sock didConnectToHost:(NSString *)host port:(UInt16)port{ [sock writeData:[@"connected to xyz server" dataUsingEncoding:NSUTF8StringEncoding] withTimeout:30.0 tag:0]; } - (void)onSocket:(AsyncSocket *)sock didReadData:(NSData *)data withTag:(long)tag{ // some relevant code goes here } - (void)onSocket:(AsyncSocket *)sock didWriteDataWithTag:(long)tag{ NSLog(@"within didWriteDataWithTag:"); // getting this message, means it should have written something to remote socket but // delegate- onSocket:didReadData:withTag: at server side is not getting invoked } // The code in ServerController class is: - (IBAction)startStop:(id)sender{ NSLog(@"startStopAction"); if(!isRunning) { NSError *error = nil; if(![listenSocket acceptOnPort:INPUT_PORT error:&error]) { NSLog(@"Error starting server: %@", error); return; } NSLog(@"Echo server started on port %hu",[listenSocket localPort]); isRunning = YES; [sender setTitle:@"Stop"]; } else { // Stop accepting connections [listenSocket disconnect]; // Stop any client connections int i; for(i = 0; i < [connectedSockets count]; i++) { // Call disconnect on the socket, // which will invoke the onSocketDidDisconnect: method, // which will remove the socket from the list. [[connectedSockets objectAtIndex:i] disconnect]; } NSLog(@"Stopped Echo server"); isRunning = false; [sender setTitle:@"Start"]; } } - (void)onSocket:(AsyncSocket *)sock didAcceptNewSocket:(AsyncSocket *)newSocket{ [connectedSockets addObject:newSocket]; } - (void)onSocket:(AsyncSocket *)sock didConnectToHost:(NSString *)host port:(UInt16)port{ NSLog(@"Accepted client %@:%hu", host, port); // it is getting displayed [sock readDataToData:[AsyncSocket CRLFData] withTimeout:READ_TIMEOUT tag:0]; } - (void)onSocket:(AsyncSocket *)sock didReadData:(NSData *)data withTag:(long)tag{ NSString *msgReceived = [[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding] autorelease]; NSLog(@"msgReceived in didReadData- %@",msgReceived); // it is not getting displayed [outputView insertText:msgReceived]; [sock readDataToData:[AsyncSocket CRLFData] withTimeout:READ_TIMEOUT tag:0]; } Can anyone suggest me where I may be wrong?? Thanks in advance...... Miraaj

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  • how do i make my own P2P software ?

    - by wefwgeweg
    how can i make my own napster ? which library are these p2p programs using ? i am not too familiar with the concept of socket programming. could you make p2p program using Qt4 ? i've been wondering about this question since the Napster days. how would you also go about creating the next "bitorrent" ? is this by using similar socket libraries ? what's the latest in p2p technology ? are there any news sites? what's the future hold for p2p ?

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  • drawing images and lines over UIScrollView

    - by Jorge
    I'm programming an app in which one of the ViewControllers is showing an UIScrollView that shows an image. I'd like to load an image (pushpin in png format) and draw it (and delete it) in some points of the UIScrollView image. I'd also would like to draw bezier paths in that image (and deleting them). I've programmed several apps but this is the first time I face graphic programming and don't know where to start from. Any suggestions? Thanks!

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  • how to specify which port to use using INET in perl

    - by alex
    Hi: I am using perl INET to create inter-process communication in my program. I need to use a specific port number in my TCP client. I was following the example in Perl doc, but it doesn't work. Here is my code: old code(working): tx_socket = new IO::Socket::INET-new('127.0.0.1:8001') || die "Can't connect to 127.0.0.1:8001 : $!\n"; new code(not working): tx_socket = new IO::Socket::INET-new('127.0.0.1:8001', LocalPort=9000 ) || die "Can't connect to 127.0.0.1:8001 : $!\n"; Does anyone know what's wrong? Thanks

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  • Does a multithreaded crawler in Python really speed things up?

    - by beagleguy
    Was looking to write a little web crawler in python. I was starting to investigate writing it as a multithreaded script, one pool of threads downloading and one pool processing results. Due to the GIL would it actually do simultaneous downloading? How does the GIL affect a web crawler? Would each thread pick some data off the socket, then move on to the next thread, let it pick some data off the socket, etc..? Basically I'm asking is doing a multi-threaded crawler in python really going to buy me much performance vs single threaded? thanks!

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  • Software Engineering Papers

    - by kunjaan
    Please recommend me software engineering/methodology/practices paper. So far I have enjoyed: 1968 Dijkstra : Go To Statement Considered Harmful Nikalus Wirth : Program Development by Stepwise Refinement 1971 David Parnas : Information Distribution Aspects of Design Methodology 1972 Liskov : Design Methodology for Reliable Software Systems Extensible Language : Schuman and P Jourrand R. Balzer Structured Programming : Dahl - Hierarchical Program StructuresImplementation Patterns 1971 Jim Morris Protection in Programming Languages 1973 Bill Wulf and Mary Shaw Global Variable Considered Harmful 1974 : Lisko and Zilles ADTs

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  • django sending emails

    - by dotty
    Hay, i can't seem to send emails using send_mail(), and I'm not sure why. Here's my details settins.py EMAIL_HOST = 'localhost', EMAIL_PORT = 25 My view from django.core.mail import send_mail send_mail('Subject here', 'Here is the message.', '[email protected]', ['[email protected]'], fail_silently=False) This fails with the error getaddrinfo() argument 1 must be string or None Anyone have any ideas? I'm developing on OS X Leopard Heres the last traceback /System/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/smtplib.py in connect for res in socket.getaddrinfo(host, port, 0, socket.SOCK_STREAM): ... ? Local vars Variable Value host ('localhost',) msg 'getaddrinfo returns an empty list' port 25 self <smtplib.SMTP instance at 0x153b1e8>

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  • Reading Source Code Aloud

    - by Jon Purdy
    After seeing this question, I got to thinking about the various challenges that blind programmers face, and how some of them are applicable even to sighted programmers. Particularly, the problem of reading source code aloud gives me pause. I have been programming for most of my life, and I frequently tutor fellow students in programming, most often in C++ or Java. It is uniquely aggravating to try to verbally convey the essential syntax of a C++ expression. The speaker must give either an idiomatic translation into English, or a full specification of the code in verbal longhand, using explicit yet slow terms such as "opening parenthesis", "bitwise and", et cetera. Neither of these solutions is optimal. On the one hand, an idiomatic translation is only useful to a programmer who can de-translate back into the relevant programming code—which is not usually the case when tutoring a student. In turn, education (or simply getting someone up to speed on a project) is the most common situation in which source is read aloud, and there is a very small margin for error. On the other hand, a literal specification is aggravatingly slow. It takes far far longer to say "pound, include, left angle bracket, iostream, right angle bracket, newline" than it does to simply type #include <iostream>. Indeed, most experienced C++ programmers would read this merely as "include iostream", but again, inexperienced programmers abound and literal specifications are sometimes necessary. So I've had an idea for a potential solution to this problem. In C++, there is a finite set of keywords—63—and operators—54, discounting named operators and treating compound assignment operators and prefix versus postfix auto-increment and decrement as distinct. There are just a few types of literal, a similar number of grouping symbols, and the semicolon. Unless I'm utterly mistaken, that's about it. So would it not then be feasible to simply ascribe a concise, unique pronunciation to each of these distinct concepts (including one for whitespace, where it is required) and go from there? Programming languages are far more regular than natural languages, so the pronunciation could be standardised. Speakers of any language would be able to verbally convey C++ code, and due to the regularity and fixity of the language, speech-to-text software could be optimised to accept C++ speech with a high degree of accuracy. So my question is twofold: first, is my solution feasible; and second, does anyone else have other potential solutions? I intend to take suggestions from here and use them to produce a formal paper with an example implementation of my solution.

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  • Hackers as CS Majors - Easy?

    - by Marcus Pink
    Just curious. For those of you who had extensive experience programming before school (or who got really, really good at programming during school) did you're CS classes became very easy? Almost like trivial side work?

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  • How Can I create different selectors for accepting new connection in java NIO

    - by Deepak
    I want to write java tcp socket programming using java NIO. Its working fine. But I am using the same selector for accepting reading from and writing to the clients. How Can I create different selectors for accepting new connection in java NIO, reading and writing. Is there any online help. Actually when I am busy in reading or writing my selector uses more iterator. So If more number of clients are connected then performance of accepting new coneection became slow. But I donot want the accepting clients to be slow // Create a selector and register two socket channels Selector selector = null; try { // Create the selector selector = Selector.open(); // Create two non-blocking sockets. This method is implemented in // e173 Creating a Non-Blocking Socket. SocketChannel sChannel1 = createSocketChannel("hostname.com", 80); SocketChannel sChannel2 = createSocketChannel("hostname.com", 80); // Register the channel with selector, listening for all events sChannel1.register(selector, sChannel1.validOps()); sChannel2.register(selector, sChannel1.validOps()); } catch (IOException e) { } // Wait for events while (true) { try { // Wait for an event selector.select(); } catch (IOException e) { // Handle error with selector break; } // Get list of selection keys with pending events Iterator it = selector.selectedKeys().iterator(); // Process each key at a time while (it.hasNext()) { // Get the selection key SelectionKey selKey = (SelectionKey)it.next(); // Remove it from the list to indicate that it is being processed it.remove(); try { processSelectionKey(selKey); } catch (IOException e) { // Handle error with channel and unregister selKey.cancel(); } } } public void processSelectionKey(SelectionKey selKey) throws IOException { // Since the ready operations are cumulative, // need to check readiness for each operation if (selKey.isValid() && selKey.isConnectable()) { // Get channel with connection request SocketChannel sChannel = (SocketChannel)selKey.channel(); boolean success = sChannel.finishConnect(); if (!success) { // An error occurred; handle it // Unregister the channel with this selector selKey.cancel(); } } if (selKey.isValid() && selKey.isReadable()) { // Get channel with bytes to read SocketChannel sChannel = (SocketChannel)selKey.channel(); // See e174 Reading from a SocketChannel } if (selKey.isValid() && selKey.isWritable()) { // Get channel that's ready for more bytes SocketChannel sChannel = (SocketChannel)selKey.channel(); } } Thanks Deepak

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  • java share data between thread

    - by ayush
    i have a java process that reads data from a socket server. Thus i have a BufferedReader and a PrintWriter object corresponding to that socket. Now in the same java process i have a multithreaded java server that accepts client connections. I want to achieve a functionality where all these clients that i accept can read data from the BufferedReader object that i mentioned above.(so that they can multiplex the data) How do i make these individual client threads read the data from BuffereReader single object? Sorry for the confusion.

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  • how to serialize / deserialize classes defined in .proto (protobuf)

    - by make
    Hi, Could someone please help me with serialization/deserialization classes defined in .proto (protobuf). here is an exp that I am trying to build: file.proto message Data{ required string x1 = 1; required uint32 x2 = 2; required float x3 = 3; } message DataExge { repeated Data data = 1; } client.cpp ... void serialize(const DataExge &data_snd){ try { ofstream ofs("DataExge"); data_snd.SerializeToOstream(&ofs); } catch(exception &e) { cerr << "serialize/exception: " << e.what() << endl; exit(1); } } void deserialize(DataExge &data_rec){ try { ifstream ifs("DataExge"); data_rec.ParseFromIstream(&ifs); } catch(exception& e) { cerr << "deserialize/exception: " << e.what() << endl; exit(1); } } int main(){ ... DataExge dataexge; Data *dat = dataexge.add_data(); char *y1 = "operation1"; uint32_t y2 = 123 ; float y3 = 3.14; // assigning data to send() dat->set_set_x1(y1); dat->set_set_x2(y2); dat->set_set_x3(y3); //sending data to the client serialize(dataexge); if (send(socket, &dataexge, sizeof(dataexge), 0) < 0) { cerr << "send() failed" ; exit(1); } //receiving data from the server deserialize(dataexge); if (recv(socket, &dataexge, sizeof(dataexge), 0) < 0) { cerr << "recv() failed"; exit(1); } //printing received data cout << dat->x1() << "\n"; cout << dat->x2() << "\n"; cout << dat->x3() << "\n"; ... } server.cpp ... void serialize(const DataExge &data_snd){ try { ofstream ofs("DataExge"); data_snd.SerializeToOstream(&ofs); } catch(exception &e) { cerr << "serialize/exception: " << e.what() << endl; exit(1); } } void deserialize(DataExge &data_rec){ try { ifstream ifs("DataExge"); data_rec.ParseFromIstream(&ifs); } catch(exception& e) { cerr << "deserialize/exception: " << e.what() << endl; exit(1); } } int main(){ ... DataExge dataexge; Data *dat = dataexge.add_data(); //receiving data from the client deserialize(dataexge); if (recv(socket, &dataexge, sizeof(dataexge), 0) < 0) { cerr << "recv() failed"; exit(1); } //printing received data cout << dat->x1() << "\n"; cout << dat->x2() << "\n"; cout << dat->x3() << "\n"; // assigning data to send() dat->set_set_x1("operation2"); dat->set_set_x2(dat->x2() + 1); dat->set_set_x3(dat->x3() + 1.1); //sending data to the client serialize(dataexge); //error// I am getting error at this line ... if (send(socket, &dataexge, sizeof(dataexge), 0) < 0) { cerr << "send() failed" ; exit(1); } ... } Thanks for your help and replies -

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  • How can one connect to an RFCOMM device other than another phone in Android?

    - by Charles Duffy
    The Android API provides examples of using listenUsingRfcommWithServiceRecord() to set up a socket and createRfcommSocketToServiceRecord() to connect to that socket. I'm trying to connect to an embedded device with a BlueSMiRF Gold chip. My working Python code (using the PyBluez library), which I'd like to port to Android, is as follows: sock = bluetooth.BluetoothSocket(proto=bluetooth.RFCOMM) sock.connect((device_addr, 1)) return sock.makefile() ...so the service to connect to is simply defined as channel 1, without any SDP lookup. As the only documented mechanism I see in the Android API does SDP lookup of a UUID, I'm slightly at a loss.

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  • questions about multi threading for sockets/tcp-connections.

    - by Fantastic Fourier
    I have a server that connects to multiple clients using TCP/IP connections, using C in Unix. Since it won't have more than 20 connections at a time, I figured I would use a thread per connection/socket. But the problem is writing to the sockets as I'll be sending user prompted msgs to clients. Once each socket is handled by a thread, how do I interact with the created thread to write to the sockets? Should each thread just read from the sockets and I'll write to sockets in the main program? Not sure if that's a good way to go about it.

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  • adding SSL to microchip Generic TCP server application

    - by Surjya Narayana Padhi
    Hi, Has anybody upgraded the code of generic tcp server application provided by Microchip to SSL? I added new listener port to existing server socket. But then also its not TCPPutIsReady state. When I tried to connect through ssh client Tera Term its asking for username and password. But does it required for client to provide username and password? I a bit new to SSL. So please let me know the steps to connect to any ssl server using Tera Term. Another doubt is that can i use a TCP server socket without using http or ftp or telnet session?

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  • How do I recieve byteArray sent from a Server and read 4 single bytes at a time.

    - by k80sg
    I need to receive 320 bytes of data from a server which consist of 80 4 byte int fields. How do I receive them in bytes of 4 and display their respective int values? Thanks. Not sure if this is right for the receiving part: //for reading the data from the socket BufferedInputStream bufferinput=new BufferedInputStream(NewSocket.getInputStream()); DataInputStream datainput=new DataInputStream(bufferinput); byte[] handsize=new byte[32]; // The control will halt at the below statement till all the 32 bytes are not read from the socket. datainput.readFully(handsize);

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  • Scala actors: receive vs react

    - by jqno
    Let me first say that I have quite a lot of Java experience, but have only recently become interested in functional languages. Recently I've started looking at Scala, which seems like a very nice language. However, I've been reading about Scala's Actor framework in Programming in Scala, and there's one thing I don't understand. In chapter 30.4 it says that using react instead of receive makes it possible to re-use threads, which is good for performance, since threads are expensive in the JVM. Does this mean that, as long as I remember to call react instead of receive, I can start as many Actors as I like? Before discovering Scala, I've been playing with Erlang, and the author of Programming Erlang boasts about spawning over 200,000 processes without breaking a sweat. I'd hate to do that with Java threads. What kind of limits am I looking at in Scala as compared to Erlang (and Java)? Also, how does this thread re-use work in Scala? Let's assume, for simplicity, that I have only one thread. Will all the actors that I start run sequentially in this thread, or will some sort of task-switching take place? For example, if I start two actors that ping-pong messages to each other, will I risk deadlock if they're started in the same thread? According to Programming in Scala, writing actors to use react is more difficult than with receive. This sounds plausible, since react doesn't return. However, the book goes on to show how you can put a react inside a loop using Actor.loop. As a result, you get loop { react { ... } } which, to me, seems pretty similar to while (true) { receive { ... } } which is used earlier in the book. Still, the book says that "in practice, programs will need at least a few receive's". So what am I missing here? What can receive do that react cannot, besides return? And why do I care? Finally, coming to the core of what I don't understand: the book keeps mentioning how using react makes it possible to discard the call stack to re-use the thread. How does that work? Why is it necessary to discard the call stack? And why can the call stack be discarded when a function terminates by throwing an exception (react), but not when it terminates by returning (receive)? I have the impression that Programming in Scala has been glossing over some of the key issues here, which is a shame, because otherwise it's a truly excellent book.

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  • Problem requesting a HTTPS with TCL

    - by Javier
    Hi Everybody, I'm trying to do the following request using TCL (OpenACS) http::register https 443 tls::socket set url "https://encrypted.google.com" set token [http::geturl $url -timeout 30000] set status [http::status $token] set answer [http::data $token] http::cleanup $token http::unregister https The problem is that when I read the $status variable I get "eof" and the $answer variable becomes empty. I tried enabling tls V.1 http::register https 443 [list tls::socket -tls1 1] and it works only for the site https://www.galileo.edu, but not for https://encrypted.google.com. The site what I'm trying to connect is https://graph.facebook.com/me/feed?access_token=... but it doesn't work. I used curl to retrieve the contents of the pages in HTTPS and it works, I have installed OpenSSL, so I can't see the problem, there is another way to do HTTPS connections with TCL?. I can't see if this is a problem of coding (maybe I'm registered wrong the https protocol) or maybe It is a bad configuration of my server. Hope somebody helps!! Thanks!

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  • How to set timeout with python-mechanize?

    - by Michal Cihar
    I'm using python-mechanize to scrape some web sites, which sometime simply don't respond to requests and these requests stay open too long, so I need to limit timeout for these requests. While using urlopen method, the timeout can be set using timeout parameter, but I have not found easy way for doing it with high level API such as submit or click methods. Ideally the timeout would be set just once for whole browser class and all calls would honor that. It would be probably possible to customize this by passing custom request_class to every click and submit call, but this would just pollute the code, so I'm looking for nicer solution for setting timeout for mechanize's browser class (and no, I don't want to change default socket timeout using socket.setdefaulttimeout).

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  • Why can't I get Python's urlopen() method to work?

    - by froadie
    Why isn't this simple Python code working? import urllib file = urllib.urlopen('http://www.google.com') print file.read() This is the error that I get: Traceback (most recent call last): File "C:\workspace\GarchUpdate\src\Practice.py", line 26, in <module> file = urllib.urlopen('http://www.google.com') File "C:\Python26\lib\urllib.py", line 87, in urlopen return opener.open(url) File "C:\Python26\lib\urllib.py", line 206, in open return getattr(self, name)(url) File "C:\Python26\lib\urllib.py", line 345, in open_http h.endheaders() File "C:\Python26\lib\httplib.py", line 892, in endheaders self._send_output() File "C:\Python26\lib\httplib.py", line 764, in _send_output self.send(msg) File "C:\Python26\lib\httplib.py", line 723, in send self.connect() File "C:\Python26\lib\httplib.py", line 704, in connect self.timeout) File "C:\Python26\lib\socket.py", line 514, in create_connection raise error, msg IOError: [Errno socket error] [Errno 10060] A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond I've tried it with several different pages but I can never get the urlopen method to execute correctly.

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