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I would like to send data to my server from a Raspberry.

The Raspberry is connected by Wi-Fi to a network, and by Ethernet to my server.

When I try to ping my server (at 198.168.1.30) I must specify the interface :

ping -I eth0 198.168.1.30 otherwise, I have an error message : Network unreachable.

In my Android Things App, I have the same error. I think I have to "say" to my raspberry to send the request on eth0.

Is it possible to specify on which interface we want to contact an address on Android Things App ?

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As far as I can tell, you want to use the ConnectivityManager. It has a method called [requestNetwork](https://developer.android.com/reference/android/net/ConnectivityManager.html#requestNetwork(android.net.NetworkRequest, android.net.ConnectivityManager.NetworkCallback)) which lets you select the type of network you want based on a NetworkRequest object which lets you filter available interfaces based on properties like TRANSPORT_ETHERNET.

You will get a callback with your Network object, which you can then use to create a URLConnection. You will probably get back an HttpURLConnection (or an HttpsURLConnection) and then you can follow the code snippets there to see how to make a basic request to a server.

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  • Thank you ! By the way, don't you know how to make an Android Thing answer to ping requests please ?
    – Maskim
    Jan 30 '18 at 8:33
  • I don't know for ping. It does not connect over normal ssh.
    – Nick Felker
    Jan 30 '18 at 18:31
  • I used ConnectivityManager.getActiveNetworkInfo(); and displayed the result in my app log, to know more about the current network. It appears that my ActiveNetwork is : [type: Ethernet[], state: CONNECTED/CONNECTED, reason: (unspecified), extra: b8:27:eb:b3:07:30, failover: false, available: true, roaming: false, metered: false] Do I need to use requestNetwork() ?
    – Maskim
    Jan 31 '18 at 10:10
  • I'm sorry to unpick your answer but it doesn't change anything to use ConnectivityManager.requestNetwork. Moreover, I need to use UDP and URLConnection works only with HTTP
    – Maskim
    Jan 31 '18 at 11:32
  • There's both HttpURLConnection and HttpsURLConnection for either protocol type.
    – Nick Felker
    Jan 31 '18 at 17:57
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So I found the problem : The OS, Android things, cannot hanlde two interfaces at the same time. The problem is not comming from the app.

Android Things needs to get its IP address from a DHCP server : you can try to assign a static address with ifconfig conmmand, but Android Things won't use the interface anyway.
Android will use : the first interface connected who had its IP through a DHCP service. If both Ethernet and Wi-Fi are available at boot, Wi-Fi gets the priority.
Lastly, if you connect Wi-Fi (with DHCP) after Ethernet, the Android Things device will use the Wi-Fi but only for answering ...

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