netwatcher

netwatcher is a cross-platform Rust library for enumerating network interfaces and their IP addresses, featuring the ability to watch for changes to those interfaces efficiently. It uses platform-specific methods to detect when interface changes have occurred instead of polling, which means that you find out about changes more quickly and there is no CPU or wakeup overhead when nothing is happening.

Current platform support

Usage

Listing interfaces

/// Returns a HashMap from ifindex (a `u32`) to an `Interface` struct
let interfaces = netwatcher::list_interfaces().unwrap();
for i in interfaces.values() {
    println!("interface {} has {} IPs", i.name, i.ips.len());
}

Watching for changes to interfaces

let handle = netwatcher::watch_interfaces(|update| {
    // This callback will fire once immediately with the existing state

    // Update includes the latest snapshot of all interfaces
    println!("Current interface map: {:#?}", update.interfaces);

    // The `UpdateDiff` describes changes since previous callback
    // You can choose whether to use the snapshot, diff, or both
    println!("ifindexes added: {:?}", update.diff.added);
    println!("ifindexes removed: {:?}", update.diff.removed);
    for (ifindex, if_diff) in update.diff.modified {
        println!("Interface index {} has changed", ifindex);
        println!("Added IPs: {:?}", if_diff.addrs_added);
        println!("Removed IPs: {:?}", if_diff.addrs_removed);
    }
});
// keep `handle` alive as long as you want callbacks
// ...
drop(handle);

Android Setup

Security/privacy restrictions in Android mean that we can't use the standard Linux approach when watching for network interface changes. Unfortunately, the way we are allowed to do this is inaccessible to native code. Even using JNI it is not possible to directly construct the types required to work with Android's connectivity API. All is not lost, however: I have published some support code on Maven Central which netwatcher can hook into in order to get the information it needs.

Add the Java support library with the matching version to your app's build.gradle.kts. The following snippet will work but probably you will want to follow the libs.versions.toml pattern.

dependencies {
    implementation("net.octet-stream.netwatcher:netwatcher-android:0.2.0")
}

Ensure the app module which is going to end up running netwatcher has these permissions:

    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.INTERNET" />

Finally, you will need to make sure that netwatcher gets access to the android context. There is built-in support for the ndk-context crate. What this means is that if you're using certain frameworks for building all-Rust Android apps then it will be able to pick up the context automatically. In other situations, the Rust code in your app will have to call netwatcher::set_android_context.

There is a test app included in the repo that provides a full example. MainActivity.kt is an activity with some methods defined in Rust. app-native/src/lib.rs provides the native implementations of those methods. This includes an example of calling set_android_context, and using the netwatcher library to watch for interface changes, passing the results back to the Java GUI.

Licence

MIT