Semyon Tikhonenko Semyon Tikhonenko - 1 year ago 159
Android Question

How to bind a socket to local wifi network address on Android?

I want to bind a socket to local wifi network address to make sure that requests are not running through 3g or other networks. I tried this code:

public static String getIpAddress(WifiManager wifiManager) {
WifiInfo wifiInfo = wifiManager.getConnectionInfo();
int ipAddress = wifiInfo.getIpAddress();
return String.format("%d.%d.%d.%d", (ipAddress & 0xff),(ipAddress >> 8 & 0xff),
(ipAddress >> 16 & 0xff),(ipAddress >> 24 & 0xff));

Socket socket = new Socket();
String localIpAddress = getIpAddress(wifiManager);
socket.bind(new InetSocketAddress(localIpAddress, 80));
socket.connect(new InetSocketAddress(serverHostname, serverPort), (int) timeoutMs);

And it throws: bind failed: EACCES (Permission denied)

I checked permissions in Manifest. Looks like all needed permissions are granted:

<!-- Uses: show 'disconnected' message when not connected to the internet -->
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>

<!-- Uses: record wifi network name when setting up a device -->
<!-- Uses: device wifi setup -->
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>

<!-- Uses: device wifi setup -->
<uses-permission android:name="android.permission.CHANGE_NETWORK_STATE"/>
<uses-permission android:name="android.permission.CHANGE_WIFI_STATE"/>
<uses-permission android:name="android.permission.INTERNET" />

Answer Source

You cannot bind to ports below 1024 without superuser access. So the Socket.bind() to port 80 is what is throwing an exception. Pick a custom port which is above 1024. For example, most user started web servers use port 8080.

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