Since you’re using the Netduino Plus’s built-in LED for this demo, there’s no need to wire up any components. This means you can move on to the code.

Create a new Netduino Plus app. Make sure that you select “Netduino Plus” instead of “Netduino,” so that the networking features are available to your app.

Inside your Main routine, start by typing in the following code:

// set up the LED and turn it off by default
OutputPort led = new OutputPort(Pins.ONBOARD_LED, false);

As before, this configures the onboard LED. You’ll turn this on and off via web requests.

Next, define a port for your Netduino to listen on. Port 80 is the default web server port, so use it here. If you want to connect to your Netduino over the Internet you may need to use a higher port number such as 8080—or use your router’s port forwarding feature—so that you can access your Netduino through a firewall:

// configure the port # (the standard web server port is 80)
int port = 80;

For this example, insert a five-second wait. This is so that the Netduino has time to request an IP address from the local router. Experienced C# programmers may want to write some code that waits only as long as it takes to get the address—or they may want to use a static IP address instead:

// wait a few seconds for the Netduino Plus to get a network address.
Thread.Sleep(5000);

Then, display the Netduino’s IP address in the Visual Studio programming environment. You need this so that you’ll know which address to use to talk to the Netduino Plus from your web browser:

// display the IP address
Microsoft.SPOT.Net.NetworkInformation.NetworkInterface 
  networkInterface =
    Microsoft.SPOT.Net.NetworkInformation.NetworkInterface.
      GetAllNetworkInterfaces()[0];

Debug.Print("my ip address: " + networkInterface.IPAddress.ToString());

The first line of code gets a reference to the first (and only) network interface on the Netduino Plus. The second line prints that address in the Output window of Visual Studio.

Now that you know the Netduino Plus’s IP address, you can have it start listening for incoming web page requests:

// create a socket to listen for incoming connections
Socket listenerSocket = new Socket(AddressFamily.InterNetwork, 
                                   SocketType.Stream, 
                                   ProtocolType.Tcp);
IPEndPoint listenerEndPoint = new IPEndPoint(IPAddress.Any, port);

// bind to the listening socket
listenerSocket.Bind(listenerEndPoint);
// and start listening for incoming connections
listenerSocket.Listen(1);

Now that the Netduino Plus is listening for incoming requests, create an infinite loop in which you watch for and then respond to those incoming requests.

Add the following loop:

// listen for and process incoming requests
while (true)
{

}

Inside this loop, you need to handle each individual request. First, wait for a connection:

// wait for a client to connect
Socket clientSocket = listenerSocket.Accept();

Then, wait up to five seconds for data to arrive:

// wait for data to arrive
bool dataReady = clientSocket.Poll(5000000, SelectMode.SelectRead);

Before you process that incoming data, make sure you received something. You will put all of this processing code inside of another subsection of code:

// if dataReady is true and there are bytes available to read,
// then you have a good connection.
if (dataReady && clientSocket.Available > 0)
{

}

As long as data is ready and there are more than zero bytes of a request available, you can process the data.

Inside the if statement’s curly braces, read all the incoming data:

byte[] buffer = new byte[clientSocket.Available];
int bytesRead = clientSocket.Receive(buffer);

Those lines of code first create a buffer, which will hold the incoming request. Then you receive that data into the buffer. The bytesRead value will hold the number of bytes that you actually read.

Now, turn the buffer into a string that you can process easily:

string request =
  new string(System.Text.Encoding.UTF8.GetChars(buffer));

The keyword that you’re looking for is the text “ON” (or “OFF”), in all upper case:

if (request.IndexOf("ON") >= 0) 
{
    led.Write(true);
}
else if (request.IndexOf("OFF") >= 0) 
{
    led.Write(false);
}

With this code, if the user requests a web page and adds the text “ON” in the request, the LED will turn on; if the user requests a web page and adds the text “OFF,” it will turn off.

Now that you’ve turned on/off the LED, write its status to a string that you can return to the user’s browser:

string statusText = "LED is " + (led.Read() ? "ON" : "OFF") + ".";

You haven’t seen the (led.Read() ? "ON" : "OFF") construct before. Here’s how it works: the statement before the ? is evaluated as true or false. If it is true (the LED is ON), then the value after the question mark (“ON”) is chosen. Otherwise, the value after the colon is chosen (“OFF”).

Now you can create a web page to return to the client:

// return a message to the client letting it
// know if the LED is now on or off.
string response =
  "HTTP/1.1 200 OK
" +
  "Content-Type: text/html; charset=utf-8

" +
  "<html><head><title>Netduino Plus LED Sample</title></head>" +
  "<body>" + statusText + "</body></html>";

This is a pretty basic web page. It will simply let the user know whether the LED is now ON or OFF, usually in response to their request. I’ve included the statusText variable from earlier.

Now send the response on its way:

clientSocket.Send(System.Text.Encoding.UTF8.GetBytes(response));

There’s one last piece of business to take care of. After the next curly brace (which ends the if block), you should close the client socket connection:

}

// important: close the client socket
clientSocket.Close();

Your full code will look like this:

public static void Main()
{
    // write your code here

    // setup the LED and turn it off by default
    OutputPort led = new OutputPort(Pins.ONBOARD_LED, false);

    // configure the port # (the standard web server port is 80)
    int port = 80;

    // wait a few seconds for the Netduino Plus to get a network address.
    Thread.Sleep(5000);

    // display the IP address
    Microsoft.SPOT.Net.NetworkInformation.NetworkInterface 
      networkInterface =
        Microsoft.SPOT.Net.NetworkInformation.NetworkInterface.
          GetAllNetworkInterfaces()[0];

    Debug.Print("my ip address: " + networkInterface.IPAddress.ToString());

    // create a socket to listen for incoming connections
    Socket listenerSocket = new Socket(AddressFamily.InterNetwork, 
                                       SocketType.Stream, 
                                       ProtocolType.Tcp);
    IPEndPoint listenerEndPoint = new IPEndPoint(IPAddress.Any, port);
    
    // bind to the listening socket
    listenerSocket.Bind(listenerEndPoint);
    // and start listening for incoming connections
    listenerSocket.Listen(1);

    // listen for and process incoming requests
    while (true)
    {
        // wait for a client to connect
        Socket clientSocket = listenerSocket.Accept();

        // wait for data to arrive
        bool dataReady = clientSocket.Poll(5000000, SelectMode.SelectRead);

        // if dataReady is true and there are bytes available to read,
        // then you have a good connection.
        if (dataReady && clientSocket.Available > 0)
        {
            byte[] buffer = new byte[clientSocket.Available];
            int bytesRead = clientSocket.Receive(buffer);

            string request =
              new string(System.Text.Encoding.UTF8.GetChars(buffer));
            if (request.IndexOf("ON") >= 0) 
            {
                led.Write(true);
            } 
            else if (request.IndexOf("OFF") >= 0)
            {
                led.Write(false);
            }

            string statusText = "LED is " + (led.Read() ? "ON" : "OFF") + ".";

            // return a message to the client letting it 
            // know if the LED is now on or off.
            string response =
              "HTTP/1.1 200 OK
" +
              "Content-Type: text/html; charset=utf-8

" +
              "<html><head><title>Netduino Plus LED Sample</title></head>" +
              "<body>" + statusText + "</body></html>";
            clientSocket.Send(System.Text.Encoding.UTF8.GetBytes(response));
        }

        // important: close the client socket
        clientSocket.Close();
    }
}

Now, go ahead and run your app.

After about five seconds, you should see the following text in Visual Studio’s Output window:

my ip address: 192.168.5.133

Using that address, use a web browser on your local network to open up a connection to your Netduino Plus. If you have a portable device (phone, tablet, etc.) connected to your WiFi network, that will work too.

Open up the following address in your browser, replacing 192.168.5.133 with your Netduino’s IP address (which is displayed in the Output window; to display this window, see Summoning the Output Window): http://192.168.5.133.

You will see a web page that says:

LED is OFF.

Now, change the web page request to include the word “ON.” Again, substitute your Netduino’s IP address:

http://192.168.5.133/ON

The LED on your Netduino Plus should turn on, as shown in Figure 8-1! And the response should read:

LED is ON.

Figure 8-1. Turning on and off the LED on the Netduino Plus—via the Internet

By changing the word ON in the web page request, you can also turn your Netduino Plus’s LED off again:

http://192.168.5.133/OFF