Local Communication Example

Run one of the local servers, either ruby simple_server.rb or node simple_server.js.

###Quick Setup with Node.js

1. Install Node.js on Mac http://nodejs.org/download/

2. Once you're done, download the simple_server.js example from this repo.

3. Start the server from your command line with:

   node simple_server.js

4. Using Particle Build or Particle Dev, flash the firmware.cpp to your device (Core/Photon).

5. Run the following command where IPADDRESS is something like 192.168.1.123:

   curl https://api.particle.io/v1/devices/0123456789abcdef01234567/connect\ -d access_token=1234123412341234123412341234123412341234
   -d "args=IPADDRESS"

###In-depth Walkthrough

Let's imagine you want to control your device (Core/Photon) locally, so you build a simple server app to which the device will directly connect. One puzzle to solve is that you don't know in advance the IP address of your device or of the laptop that will run the server. How can the device and the server discover each other?

In this example, we will register a Particle function to pass the server IP address to the device. Once we've established the local connection, we'll be able to control the device without the data going through the Particle Cloud.

FYI: The following example code is located here: firmware.cpp

---

TCPClient client;

First, we construct the client that will connect to our local server.

---

void ipArrayFromString(byte ipArray[], String ipString) {
  int dot1 = ipString.indexOf('.');
  ipArray[0] = ipString.substring(0, dot1).toInt();
  int dot2 = ipString.indexOf('.', dot1 + 1);
  ipArray[1] = ipString.substring(dot1 + 1, dot2).toInt();
  dot1 = ipString.indexOf('.', dot2 + 1);
  ipArray[2] = ipString.substring(dot2 + 1, dot1).toInt();
  ipArray[3] = ipString.substring(dot1 + 1).toInt();
}

Then we need a function for translating the IP address String into the array of four bytes needed by the TCP client.

We work our way progressively through the string, saving the positions of the dots and the numeric substrings between them.

---

int connectToMyServer(String ip) {
  byte serverAddress[4];
  ipArrayFromString(serverAddress, ip);

  if (client.connect(serverAddress, 9000)) {
    return 1; // successfully connected
  } else {
    return -1; // failed to connect
  }
}

Here's the Particle function we're going to register. Like all Particle functions it takes a String parameter and returns an int. We allocate an array of 4 bytes for the IP address, then call ipArrayFromString() to convert the String into an array.

After that, we simply call client.connect() with the newly received address! Super simple!

---

void setup() {
  Particle.function("connect", connectToMyServer);

  for (int pin = D0; pin <= D7; ++pin) {
    pinMode(pin, OUTPUT);
  }
}

In setup() we only have two jobs:

• Register the Particle function
• Set D0–D7 as output pins

---

void loop() {
  if (client.connected()) {
    if (client.available()) {
      char pin = client.read() - '0' + D0;
      char level = client.read();
      if ('h' == level) {
        digitalWrite(pin, HIGH);
      } else {
        digitalWrite(pin, LOW);
      }
    }
  }
}

In loop() we first check whether the client is connected to the server. If not, we don't do anything.

If the client is connected, then we ask whether any commands have been received over local communication. If not, again, we don't do anything.

However, if we are connected and have received a command then we use the command to perform a digitalWrite().

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