Android

How to keep a Socket.IO client running in the background?
How to reach an HTTP server?

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.

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