Most network resources that I access with the Android applications that I build communicate over HTTPS. It isn’t often, but I sometimes access a resource over an unencrypted connection. This is usually the case for home automation and media control devices. One example of such an application is a Roku remote that I made for myself; the Roku accepts HTTP requests to simulate presses on the remote control. When I create something that needs to access resources over unencrypted HTTP, there’s a step I usually forget that leaves me wondering why I am receiving null responses back from my request.
When Android P was released, Google implemented a change to encourage developers to use encrypted HTTPS instead of unencrypted HTTP.
As part of a larger effort to move all network traffic away from cleartext (unencrypted HTTP) to TLS, we’re also changing the defaults for Network Security Configuration to block all cleartext traffic. You’ll now need to make connections over TLS, unless you explicitly opt-in to cleartext for specific domains.Android Developer Blog, Dave Burke, BP of Engineering for Android
The most recent time that I forgot to enable unencrypted communication was perplexing. I was communicating with a device over UDP and HTTP, and I saw that the device was responding to the UDP requests and was a bit confused before I remembered the step that I had missed.
To enable unencrypted clear text communication generally within an application, there is an additional attribute that must be added to the <application> element in the application’s manifest.
That is going to enable HTTP traffic for all domains. I used this option for communication over a local network since there isn’t a specific domain that I can target for someone’s home connection. When there is a specific domain that your application must communicate with, you can create a network security policy permitting unencrypted communication to that domain. Before doing this, consider what information that your application is sending. If there is any personally identifying or sensitive information in your messages, then this option is not acceptable. If for some reason you cannot enable HTTPS (such as the domain being controlled by another entity) and you’ve reviewed the risks and consider them acceptable, then you can move forward with allowing unencrypted communication with that domain. To do that, you will need to create a new XML file resource in res/xml, giving it the name of your choosing. The contents of the file will look like the following. You will need to place the domain(s) of interest in the configuration.
<?xml version="1.0" encoding="utf-8"?> <network-security-config> <domain-config cleartextTrafficPermitted="true"> <domain includeSubdomains="true">yourtargetdomain.net</domain> </domain-config> </network-security-config>
In the application’s manifest, add a reference to this policy. Assuming the above file is named “network_security_config.xml” the manifest entry would look like the following.
<application android:networkSecurityConfig="@xml/network_security_config" ... />
While using SSL/HTTPS is generally preferable and lower risks, there may be times when you must fallback on unencrypted clear text communication. When this happens, for Android-P and later your application must explicitly opt-in to clear text communication.