Communication between 2 Android apps over GCM - php

Question

I have 2 Android apps on two different devices. App 1 is stationary and app 2 is mobile. I would like the app 1 to find the closest app 2 device and communicate like snapchat but I would like to update app 1 with app 2's current location. I am storing app 1's location in the server and retrieve app 2's location and calculate the distance between them and send the location of app 1 to app 2 over GCM. But this proved to be more complicated than I originally thought. I also tried to store the mobile app's location in the database and get the updated location once the stationary requests to communicate but that meant updating the database too much. Can someone give me a hint on how to accomplish this with efficiency? Following are code snippets to calculate distance between them and send location.
function distance_slc($lat1, $lon1, $lat2, $lon2) {
global $earth_radius;
global $delta_lat;
global $delta_lon;
$distance = sin(deg2rad($lat1)) * sin(deg2rad($lat2)) + cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * cos(deg2rad($delta_lon));
$distance = acos($distance);
$distance = rad2deg($distance);
$distance = $distance * 60 * 1.1515;
$distance = round($distance, 4);
return $distance;
}
function compute($id, $lat, $lon) {
$p = getPLocation();
$d = array($id, $lat, $lon);
foreach ($d as $index => $value) {
$d_pass_distance = distance_slc($p['latitude'], $p['longitude'], $d['1'], $d['2']);
$closest_d = 0;
if ($closest_d = min($d_pass_distance)) {
sendPLocation($d['0'], $p['latitude'], $p['longitude']);
}
}
}
function sendUserLocation($id, $lat, $lon) {
//request url
//$url = 'https://android.googleapis.com/gcm/send';
$url = 'gcm-preprod.googleapis.com:5236'; //this url is only for testing not production
//your api key
$apiKey = 'myserverapikeyhere';
$fields = array('id' => $id, 'latitude' => $lat, 'longitude' => $lon);
//http header
$headers = array('Authorization: key=' . $apiKey,
'Content-Type: application/json');
//curl connection
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($fields));
$result = curl_exec($ch);
curl_close($ch);
echo $result;
}

Answer 1

What comes to mind is when the app 1 client wants to communicate it sends a message to your app server. The app server then sends a GCM push message to all of the appropriate mobile devices, the app 2 client on each device receives the message, determines its current location, and uses an upstream message to send its location to the app server. The app server determines the closest device (probably waiting a few seconds to get all of the various responses), and then sends a push message to the closest app 2 client (and optionally the app 1 client) with the appropriate information.
EDIT: Include some example code for upstream and downstream messages. By and large I am excluding general messaging stuff. You can replace the "contents" and "username" fields with your own stuff, and will need to have different types of upstream messages
Downstream message (app server side - this is in Java)
public void actionPerformed(ActionEvent e) {
// who are we sending it to?
String toAddr = "zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz";
// create the message
Map<String, Object> message = new HashMap<String, Object>();
message.put("to", toAddr);
message.put("message_id", myNextMessageId());
HashMap<String, String> dataPayload = new HashMap<>();
dataPayload.put( "contents", dataInfo.getText() );
message.put("data", dataPayload);
// actually send the message
try {
Packet request = new GcmPacketExtension(JSONValue.toJSONString(message)).toPacket();
connection.sendPacket(request);
} catch ( NotConnectedException enc ) {
// quietly ignore the error
}
}
Downstream message (Android client)
public class MyGcmListenerService extends GcmListenerService {
public MyGcmListenerService() { }
public void onMessageReceived (String from, Bundle data) {
// get info ("data" stuff)
String contents = data.getString( "contents" );
... process contents
}
}
Upstream messages (Android client)
GoogleCloudMessaging gcm;
String SENDER_ID = "999999999999";
// send the registration to the back-end app server
private void sendUpstreamMessage( user ) {
// use upstream message to register with the app server
// app server uses the 'from' field of the message
String msg = "";
try {
Bundle data = new Bundle();
String user = getGoogleAccount();
// username is the user email
data.putString( "username", user );
// and note this is a registration request
data.putString("my_action", "edu.eku.styere.gcmpushclient.REGISTER");
String id = myNewMessageId();
// send the registration message
gcm.send(SENDER_ID + "#gcm.googleapis.com", id, data);
} catch (IOException ex) {
// for now ignore error
}
return;
}
Upstream message (app server - again in Java)
// assume we already know this is an upstream message and not an ACK or something else
protected void handleUpstreamMessage(Map<String, Object> jsonObject) {
// PackageName of the application that sent this message.
String category = (String) jsonObject.get("category");
String from = (String) jsonObject.get("from");
#SuppressWarnings("unchecked")
Map<String, String> payload = (Map<String, String>) jsonObject.get("data");
// what action do they want?
String my_action = (String) payload.get( "my_action" );
if ( my_action.equals( "edu.eku.styere.gcmpushclient.REGISTER" ) ) {
// registration request
String username = (String) payload.get( "username" );
registerUser( username, from );
return;
}
}