Android

How to keep a Socket.IO client running in the background?

Long story short, you probably shouldn’t. The Socket.IO client is not meant to be used in a background service, as it will keep an open TCP connection to the server and quickly drain the battery of your users.

It is totally usable in the foreground though.

See also: https://developer.android.com/training/connectivity

How to reach an HTTP server?

Starting with Android 9 (API level 28) you need to explicitly allow cleartext traffic to be able to reach an HTTP server (e.g. a local server at http://192.168.0.10):

• either for all domains:

app/src/main/AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest>
    <uses-permission android:name="android.permission.INTERNET" />

    <application android:usesCleartextTraffic="true">
        ...
    </application>
</manifest>

• or for a restricted list of domains:

app/src/main/AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest>
    <uses-permission android:name="android.permission.INTERNET" />

    <application android:networkSecurityConfig="@xml/network_security_config">
        ...
    </application>
</manifest>

app/src/main/res/xml/network_security_config.xml

<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
    <domain-config cleartextTrafficPermitted="true">
        <domain includeSubdomains="true">localhost</domain>
        <domain includeSubdomains="true">192.168.0.10</domain>
    </domain-config>
</network-security-config>

Reference: https://developer.android.com/training/articles/security-config

How to run unit tests in Android Studio?

Local unit tests are tests that run on your machine’s local Java Virtual Machine.

Reference: https://developer.android.com/studio/test/test-in-android-studio

Since they run on your machine, the JSON library must be manually included for the tests (because it is not provided by the Android runtime):

build.gradle

dependencies {
    implementation ('io.socket:socket.io-client:2.0.1') {
        exclude group: 'org.json', module: 'json'
    }

    testImplementation 'org.json:json:20090211'

    ...
}

Note: we use this ancient version of org.json because it is compatible with the one bundled in Android.