Proguard And Netty 5 On Android

I've seen a couple questions regarding this issue, but they are for older versions of Netty. I have tried their answers, switching org.jboss.netty out with io.netty, but the same e

Solution 1:

I have fixed this issue with some carefully* applied Proguard rules after reading through parts of the rather huge Netty sources:

-keepattributes Signature,InnerClasses
-keepclasseswithmembers class io.netty.** {
    *;
}
-keepnames class io.netty.** {
    *;
}

My original exception was caused by the type variables being removed from the bytecode, which Netty uses via reflection. Signature in -keepattributes keeps this information.

You get a slightly different exception if you only do Signature on -keepattributes - adding InnerClasses fixes this one by bringing back even more information in the class files.

Later, I got java.lang.NoSuchFieldException: ctl; that's what -keepnames is for. This way, the field is still called ctl like Netty expects.

Finally, some members (like ctl, seen earlier) were being removed by Proguard because Netty only uses them via reflection. The final rule, -keepclasseswithmembers, makes sure Proguard doesn't remove them.

If you take this approach, I strongly recommend you use only the Netty jars you need, instead of the -all jar. Switching from -all to just the required Netty jars brought my method count way down after I had gone past the 65k limit. Reducing your jars requires bit of trial-and-error though as the separation is unclear and there's not really any resources saying what's what.

_{* not carefully at all, I just slapped rules into the file and removed them if they did nothing. There's probably a better way to do this that doesn't keep this information in the entire program, but instead just Netty.}

Solution 2:

Una's answer keep too many class, which makes my app 1MB larger than usual. So I use the rules below:

# netty
-keepclassmembernames class io.netty.buffer.AbstractByteBufAllocator {
    *;
}

-keepclassmembernames class io.netty.buffer.AdvancedLeakAwareByteBuf {
    *;
}

-keep public class io.netty.util.ReferenceCountUtil {
    *;
}

I have tested these rules on Netty 4.1.63.Final