title: How to receive socket information if you don't know how much data is coming through?
body: <p>I am working on a GUI interface based on Python to interact with a robot running Python and an <a href="http://arduino.cc/en/Main/ArduinoBoardMega" rel="nofollow">Arduino Mega</a> as a motor controller and sensor controller.</p>
  
  <p>Originally, I was going to use a remote desktop to load my GUI from the robot. This turned out to be very slow because of the remote desktop.  I decided that a server and client would be better.</p>
  
  <p>I have a <a href="http://www.arduino.cc/en/Tutorial/Sketch" rel="nofollow">sketch</a> running on my Arduino, that catches motor commands, and performs them.  It also waits for a "Ping" command to come through, at which time it should check the ultrasonic sensor in three different positions, then write this information back to the server, which should catch this data and in turn pass it on to the client GUI.  I have gotten most all of it to work, but I can't seem to get the data from the server back to the client.  I had thought that a simple "client.recv()" would accomplish this, but it's not.</p>
  
  <p>How can I receive that data, if I don't know exactly how much data is coming back?</p>
  
  <p>The Arduino sends the data as "dist1,dist2,dist3 \n".</p>
  
  <p>Here is my Arduino code:</p>
  
  <pre><code>#include &lt;LiquidCrystal.h&gt;
  #include &lt;Ping.h&gt;
  #include &lt;Servo.h&gt;
  // Parallax Ping Unit for distance sensing.
  Ping sonic(22);
  
  // Setup LCD pins.
  LiquidCrystal lcd(7, 8, 9, 10, 11, 12);
  
  // Servo for Ping unit sweeping.
  Servo  PingServo;
  
  // Setup Ping distance setting variables.
  int pingDisCent;
  int pingDisLeft;
  int pingDisRight;
  
  // Variable to keep commands in.
  char MsgRcvd;
  
  // Motor setup information.
  
  int LF[] = {23,24};
  int LR[] = {25,26};
  int RF[] = {27,28};
  int RR[] = {29,30};
  
  // Set Debugging here
  // 1 - Debug on - Motors don't turn when commands are sent.
  // 0 - Debug off - Motors turn when commands are sent.
  int debug = 1;
  
  //Variables for speed
  int SpdPin = 22;
  int Speed = 255;
  
  void setup()
  {
    Serial.begin(9600);  // start serial communications
  
    // Setup motors for output.
    int i;
    for(i = 0; i &lt; 2; i++){
      pinMode(LF[i], OUTPUT);
      pinMode(LR[i], OUTPUT);
      pinMode(RF[i], OUTPUT);
      pinMode(RR[i], OUTPUT);
    }
  
    // Setup servo to sweep.
    PingServo.attach(6);
    PingServo.write(90);
  
    // Set up the LCD's number of rows and columns:
    lcd.begin(16, 2);
  
    // Print a message to the LCD.
    lcd.print("Waiting...");
  
    // Setup speed pin.
    pinMode(SpdPin, OUTPUT);
  }
  
  void loop()
  {
    if (Serial.available() &gt; 0)    //Check to see if a command is available.
    {
      MsgRcvd = Serial.read();    // If a command is there, see what it is.
      switch (MsgRcvd)
      {
        case '0':
          Stop();
          break;
        case '1':
          MoveForward();
          break;
        case '2':
          MoveLeft();
          break;
        case '3':
          MoveRight();
          break;
        case '4':
          MoveBackward();
          break;
        case '~':
          active_ir();
          break;
        case 'M':                    // Check to see if we have a connection from the GUI - if so spit out information to the LCD.
          lcd.clear();
          lcd.print("Connected");
          lcd.setCursor(0,1);
          lcd.print("waiting..");
          break;
        case 'D':
          lcd.setCursor(0,1);
          lcd.print("Disconnected"); // Client disconnected - spit out a disconnect to the LCD.
          break;
      }
    }
    delay(100);
  }
  
  //  ===================================
  //  =====    Ping Ultrasonic      =====
  //  ===================================
  void active_ir()
  {
    // Read to the right.
    PingServo.write(30);
    delay(300);
    pingDisRight = sonic.inch();
    delay(500);
  
    // Read to the front.
    PingServo.write(90);
    delay(300);
    pingDisCent = sonic.inch();
    delay(500);
    //  Read to the left.
    PingServo.write(150);
    delay(300);
    pingDisLeft = sonic.inch();
    delay(500);
    Serial.print(pingDisLeft);
    Serial.print(',');
    Serial.print(pingDisCent);
    Serial.print(',');
    Serial.println(pingDisRight);
    return;
  }
  
  
  
  //  ==========================================
  //  ======        MOTOR CONTROL      =========
  //  ==========================================
  
  void MoveForward()
  {
    lcd.clear();
    lcd.setCursor(0,0);
    lcd.print("Forward");
    if (debug == 0){
  
      digitalWrite(LF[0], HIGH);
      digitalWrite(LF[1], LOW);
      digitalWrite(LR[0], HIGH);
      digitalWrite(LR[1], LOW);
      digitalWrite(RF[0], HIGH);
      digitalWrite(RF[1], LOW);
      digitalWrite(RR[0], HIGH);
      digitalWrite(RR[1], LOW);
    }
  }
  
  void MoveBackward()
  {
    lcd.clear();
    lcd.setCursor(0,0);
    lcd.print("Reverse");
    if (debug == 0){
      analogWrite(SpdPin, Speed);
      digitalWrite(LF[0], LOW);
      digitalWrite(LF[1], HIGH);
      digitalWrite(LR[0], LOW);
      digitalWrite(LR[1], HIGH);
      digitalWrite(RF[0], LOW);
      digitalWrite(RF[1], HIGH);
      digitalWrite(RR[0], LOW);
      digitalWrite(RR[1], HIGH);
    }
  }
  
  void MoveLeft()
  {
    lcd.clear();
    lcd.setCursor(0,0);
    lcd.print("Left");
    if (debug == 0){
      analogWrite(SpdPin, Speed);
      digitalWrite(LF[0], LOW);
      digitalWrite(LF[1], HIGH);
      digitalWrite(LR[0], LOW);
      digitalWrite(LR[1], HIGH);
      digitalWrite(RF[0], HIGH);
      digitalWrite(RF[1], LOW);
      digitalWrite(RR[0], HIGH);
      digitalWrite(RR[1], LOW);
    }
  }
  
  void MoveRight()
  {
    lcd.clear();
    lcd.setCursor(0,0);
    lcd.print("Right");
    if (debug == 0) {
      analogWrite(SpdPin, Speed);
      digitalWrite(LF[0], HIGH);
      digitalWrite(LF[1], LOW);
      digitalWrite(LR[0], HIGH);
      digitalWrite(LR[1], LOW);
      digitalWrite(RF[0], LOW);
      digitalWrite(RF[1], HIGH);
      digitalWrite(RR[0], LOW);
      digitalWrite(RR[1], HIGH);
    }
  }
  
  void Stop()
  {
    lcd.clear();
    lcd.setCursor(0,0);
    lcd.print("Stopping");
    if (debug == 0){
      digitalWrite(LF[0], LOW);
      digitalWrite(LF[1], LOW);
      digitalWrite(LR[0], LOW);
      digitalWrite(LR[1], LOW);
      digitalWrite(RF[0], LOW);
      digitalWrite(RF[1], LOW);
      digitalWrite(RR[0], LOW);
      digitalWrite(RR[1], LOW);
    }
  }
  </code></pre>
  
  <p>Here is my Python server code:</p>
  
  <pre><code>import serial
  import socket
  
  Serv = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
  Serv.bind(('', 9000))
  Serv.listen(1)
  print "Listening on TCP 9000"
  motor = serial.Serial('/dev/ttyUSB0', 9600, timeout=1)
  print "Connected to Motor Controller: /dev/ttyUSB0"
  
  while(1):
      print "Waiting For Connection..."
      connection, addr = Serv.accept()
      connection.setblocking(0)
      print "Connected by", addr[0]
      while(1):
          try:
              Servdata = connection.recv(1)
              break
          except:
              pass
      if (Servdata == 'M'):
          print "Entering Manual Mode"
          motor.write(Servdata)
          while(Servdata != 'X'):
              Servdata = '9'
              try:
                  Servdata = connection.recv(1)
              except:
                  pass
              if Servdata == 'X':
                  print "Exiting"
                  break
              if Servdata == '0':
                  print "Stopping"
                  motor.write(Servdata)
              if Servdata == '1':
                  print "Forward"
                  motor.write(Servdata)
              if Servdata == '2':
                  print "Left"
                  motor.write(Servdata)
              if Servdata == '3':
                  print "Right"
                  motor.write(Servdata)
              if Servdata == '4':
                  motor.write(Servdata)
                  print "Backwards"
              if Servdata == '~':
                  motor.write(Servdata)
                  retval = motor.readline()
                  Serv.send(retval)
              else:
                  pass
          motor.write('0')
          connection.close()
          print addr[0], "Closed Manual Mode"
  </code></pre>
  
  <p>And last but not least, the client GUI code (and this is also where I think my problems lie...):</p>
  
  <pre><code>from socket import *
  from PythonCard import model
  HOST = ''
  PORT = 9000
  ADDR = (HOST,PORT)
  BUFSIZE = 4096
  Client = socket (AF_INET,SOCK_STREAM)
  Client.connect((ADDR))
  Client.send('M')
  class MainWindow(model.Background):
      def on_SetSpdBtn_mouseClick(self, event):
          spd = self.components.SpdSpn.value
      def on_FwdBtn_mouseClick(self, event):
          spd = self.components.SpdSpn.value
          Client.send('1')
      def on_LftBtn_mouseClick(self, event):
          spd = self.components.SpdSpn.value
          Client.send('2')
      def on_RitBtn_mouseClick(self, event):
          spd = self.components.SpdSpn.value
          Client.send('3')
      def on_RevBtn_mouseClick(self, event):
          spd = self.components.SpdSpn.value
          Client.send('4')
      def on_StpBtn_mouseClick(self, event):
          spd = self.components.SpdSpn.value
          Client.send('0')
      def on_GetPing_mouseClick(self, event):
          Client.send('~')
          retval = Client.recv()
          ping_data = retval.strip() # Strip out the newline, if you read an entire line.
          split_data = ping_data.split(',')
          L_Ping = split_data[0]
          R_Ping = split_data[1]
          self.components.PingLeft.text = str(L_Ping)
          self.components.PingRight.text = str(R_Ping)
  app = model.Application(MainWindow)
  app.MainLoop()
  </code></pre>