Enabled proguard to reduce APK size and added the pertinent proguard rules to avoid removing too much code.

app/build.gradle

@@ -28,14 +28,13 @@ android {
     }
     buildTypes {
         release {
-            minifyEnabled false
+            minifyEnabled true
+            shrinkResources true
             proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
             // enable crashlytics
             ext.enableCrashlytics = true
         }
         debug {
-            minifyEnabled false
-            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
             resValue("string", "PORT_NUMBER", "8082")
             // disable crashlytics
             ext.enableCrashlytics = false

app/proguard-rules.pro

@@ -20,37 +20,76 @@
 # hide the original source file name.
 #-renamesourcefileattribute SourceFile
 
-###### itextpdf & opencsv
+-dontskipnonpubliclibraryclasses
--dontwarn java.awt.**
+# TODO enable optimization
--dontwarn javax.security.**
+-dontoptimize
+-dontpreverify
+# TODO enable obfuscation
+-dontobfuscate
+-verbose
+
+##--------------- proguard configuration for ITextPDF  ----------
+-dontwarn com.itextpdf.**
+
+
+##--------------- proguard configuration for openCSV  ----------
 -dontwarn java.beans.**
 
--dontwarn com.itextpdf.awt.**
--dontwarn javax.imageio.**
 
--keep class org.bouncycastle.**
+##--------------- proguard configuration for Gson  ----------
--dontwarn org.bouncycastle.**
+# Gson uses generic type information stored in a class file when working with fields. Proguard
+# removes such information by default, so configure it to keep all of it.
+-keepattributes Signature
 
--keep class org.spongycastle.** { *; }
+# For using GSON @Expose annotation
--dontwarn org.spongycastle.**
+-keepattributes *Annotation*
 
--keep class javax.xml.crypto.dsig.** { *; }
+# Gson specific classes
--dontwarn javax.xml.crypto.dsig.**
+-dontwarn sun.misc.**
+#-keep class com.google.gson.stream.** { *; }
 
--keep class org.apache.jcp.xml.dsig.internal.dom.** { *; }
+# Application classes that will be serialized/deserialized over Gson
--dontwarn org.apache.jcp.xml.dsig.internal.dom.**
+-keep class com.google.gson.examples.android.model.** { *; }
 
--keep class javax.xml.crypto.dom.** { *; }
+# Prevent proguard from stripping interface information from TypeAdapterFactory,
--dontwarn javax.xml.crypto.dom.**
+# JsonSerializer, JsonDeserializer instances (so they can be used in @JsonAdapter)
-
+-keep class * implements com.google.gson.TypeAdapterFactory
--keep class org.apache.xml.security.utils.** { *; }
+-keep class * implements com.google.gson.JsonSerializer
--dontwarn org.apache.xml.security.utils.**
+-keep class * implements com.google.gson.JsonDeserializer
-
--keep class javax.xml.crypto.XMLStructure
--dontwarn javax.xml.crypto.XMLStructure
 
 
-###### OkHttp
+##--------------- proguard configuration for Retrofit  ----------
+# Retrofit does reflection on generic parameters. InnerClasses is required to use Signature and
+# EnclosingMethod is required to use InnerClasses.
+-keepattributes Signature, InnerClasses, EnclosingMethod
+
+# Retrofit does reflection on method and parameter annotations.
+-keepattributes RuntimeVisibleAnnotations, RuntimeVisibleParameterAnnotations
+
+# Retain service method parameters when optimizing.
+-keepclassmembers,allowshrinking,allowobfuscation interface * {
+    @retrofit2.http.* <methods>;
+}
+
+# Ignore annotation used for build tooling.
+-dontwarn org.codehaus.mojo.animal_sniffer.IgnoreJRERequirement
+
+# Ignore JSR 305 annotations for embedding nullability information.
+-dontwarn javax.annotation.**
+
+# Guarded by a NoClassDefFoundError try/catch and only used when on the classpath.
+-dontwarn kotlin.Unit
+
+# Top-level functions that can only be used by Kotlin.
+-dontwarn retrofit2.KotlinExtensions
+
+# With R8 full mode, it sees no subtypes of Retrofit interfaces since they are created with a Proxy
+# and replaces all potential values with null. Explicitly keeping the interfaces prevents this.
+-if interface * { @retrofit2.http.* <methods>; }
+-keep,allowobfuscation interface <1>
+
+
+##--------------- proguard configuration for OkHttp  ----------
 # JSR 305 annotations are for embedding nullability information.
 -dontwarn javax.annotation.**
 
@@ -64,16 +103,38 @@
 -dontwarn okhttp3.internal.platform.ConscryptPlatform
 
 
-###### bitcoinj
+##--------------- proguard configuration for Okio  ----------
--dontwarn org.bitcoinj.store**
+# Animal Sniffer compileOnly dependency to ensure APIs are compatible with older versions of Java.
+-dontwarn org.codehaus.mojo.animal_sniffer.*
 
 
-###### ???
+##--------------- proguard configuration for bitcoinj  ----------
--keep class org.slf4j.** { *; }
+# source: https://github.com/bitcoin-wallet/bitcoin-wallet/blob/v7.07/wallet/proguard.cfg#L49
--dontwarn org.slf4j.**
+-keep,includedescriptorclasses class org.bitcoinj.wallet.Protos$** { *; }
+-keepclassmembers class org.bitcoinj.wallet.Protos { com.google.protobuf.Descriptors$FileDescriptor descriptor; }
+-keep,includedescriptorclasses class org.bitcoin.protocols.payments.Protos$** { *; }
+-keepclassmembers class org.bitcoin.protocols.payments.Protos { com.google.protobuf.Descriptors$FileDescriptor descriptor; }
+-dontwarn org.bitcoinj.store.WindowsMMapHack
+-dontwarn org.bitcoinj.store.LevelDBBlockStore
+-dontnote org.bitcoinj.crypto.DRMWorkaround
+-dontnote org.bitcoinj.crypto.TrustStoreLoader$DefaultTrustStoreLoader
+-dontnote com.subgraph.orchid.crypto.PRNGFixes
+-dontwarn okio.DeflaterSink
+-dontwarn okio.Okio
+-dontnote com.squareup.okhttp.internal.Platform
+-dontwarn org.bitcoinj.store.LevelDBFullPrunedBlockStore**
+-dontwarn org.bitcoinj.protocols.channels.PaymentChannelClient
 
 
-###### Firabase Crashlytics
+##--------------- proguard configuration for Crashlytics  ----------
--keepattributes *Annotation*
+# source https://stackoverflow.com/a/34751033/5428997
--keepattributes SourceFile,LineNumberTable
+-keep class com.crashlytics.** { *; }
--keep public class * extends java.lang.Exception
+-dontwarn com.crashlytics.**
+-keepattributes SourceFile,LineNumberTable,*Annotation*
+-keep class com.crashlytics.android.**
+
+
+##--------------- other  ----------
+-dontwarn org.slf4j.LoggerFactory
+-dontwarn org.slf4j.MDC
+-dontwarn org.slf4j.MarkerFactory