Stripping Log Statements using Proguard

This post describes how to use Proguard to strip log statements from your Android app; good for both the standard android.util.Log class as well as when using Timber.

Logging only on DEBUG Builds

Sometimes you want to remove all log statements from your app and it is as simple as not logging in your production releases.

You can wrap your calls to Log inside a check to ensure you are on a debug build.

if(BuildConfig.DEBUG) Log.i(TAG, "foo");

In Timber land, you’d only plant a DebugTree and not bother about planting anything else.

if(BuildConfig.DEBUG) Timber.plant(new Timber.DebugTree());

Logging in Production Too

However, if you need to sometimes log, it gets more complicated. Let’s say you use Timber and plant a debug tree which will handle your logging while in development, but you also want a logger which will log any messages which are a warning or greater when in production too.

Logging in Production? 😱

You probably shouldn’t actually log in production. So maybe you don’t actually log to logcat and instead send the most important logs to your crash reporting tool.

public class ProductionLogger extends Timber.Tree {
    @Override
    protected void log(int priority, String tag, String message, Throwable t) {
        if(priority >= Log.WARN) {
            // do your thing
        }
    }
}

Stripping Log Statements

In debug there is nothing to do; you want to see all logs statements. But in production, you want strip all logs except for warn and error. Proguard can help us here.

In build.gradle you can enable Proguard

minifyEnabled true
proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'

Note, that’s proguard-android-optimize.txt ☝️

Stripping Standard Log Statements

Modify the proguard-rules.pro file, which should live under your standard Android app directory:

proguard-rules.pro
==================

# This will strip `Log.v`, `Log.d`, and `Log.i` statements and will leave `Log.w` and `Log.e` statements intact.

-assumenosideeffects class android.util.Log {
    public static boolean isLoggable(java.lang.String, int);
    public static int v(...);
    public static int d(...);
    public static int i(...);
}

Stripping Timber Log Statements

Modify the proguard-rules.pro file:

-assumenosideeffects class timber.log.Timber* {
    public static *** v(...);
    public static *** d(...);
    public static *** i(...);
}

Testing it works

Add the following to a class you know will be executed (delete as appropriate depending on if you’re stripping standard Log statements or Timber logs)

Log.v(TAG, "verbose");
Log.d(TAG, "debug");
Log.i(TAG, "info");
Log.w(TAG, "warning");
Log.e(TAG, "error");

Timber.v("verbose");
Timber.d("debug");
Timber.i("info");
Timber.w("warning");
Timber.e("error");

When you run in debug mode, you should see all the statements in logcat.

When running the app after proguarding, however, you should only see the output from warning and error log statements.

Bonus Content: Using Proguard Only to Remove Logging

If you don’t really want to use Proguard, but do quite like the idea of it stripping out your logs for you, you can disable all proguarding except for the log stripping.

Add the following to your proguard-rules.pro to achieve this:

-dontwarn **
-target 1.7
-dontusemixedcaseclassnames
-dontskipnonpubliclibraryclasses
-dontpreverify
-verbose
-optimizations !code/simplification/arithmetic,!code/allocation/variable
-keep class **
-keepclassmembers class *{*;}
-keepattributes *

Attributions

• Cover photo by Malte Wingen on Unsplash
• StackOverflow — https://stackoverflow.com/a/15593061/1654145

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