DRAFT: TV Casting App - Add size-optimized Android build variant

examples/tv-casting-app/android/App/app/build.gradle

@@ -2,6 +2,10 @@ plugins {
     id 'com.android.application'
 }
 
+// Read the size optimization flag passed from the build system.
+// When true, enables R8 shrinking and allows .so stripping in debug builds.
+def optimizeApkSize = project.hasProperty('optimizeApkSize') && project.property('optimizeApkSize') == 'true'
+
 android {
     // Namespace (required for AGP 8.0+)
     namespace 'com.chip.casting'
@@ -28,13 +32,22 @@ android {
 
     buildTypes {
         release {
-            minifyEnabled false
+            minifyEnabled true
             proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
         }
 
         debug {
-            packagingOptions{
-                doNotStrip "**/*.so"
+            if (optimizeApkSize) {
+                // Size-optimized debug: enable R8 to remove unused Java/Kotlin code
+                minifyEnabled true
+                proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
+                // Do NOT add doNotStrip — let the build system strip .so files
+            } else {
+                // Normal debug: keep everything for debugging
+                minifyEnabled false
+                packagingOptions {
+                    doNotStrip "**/*.so"
+                }
             }
         }
     }
@@ -73,7 +86,17 @@ android {
 }
 
 dependencies {
-    implementation fileTree(dir: "libs", include: ["*.jar","*.so"])
+    if (optimizeApkSize) {
+        // When R8 is enabled, the compat source files (src/compat/jni) are compiled
+        // by Gradle AND also present in TvCastingApp.jar from the GN build.
+        // Exclude the JAR to avoid "defined multiple times" R8 errors; the Gradle-
+        // compiled classes are identical and sufficient.
+        implementation fileTree(dir: "libs", include: ["*.so"])
+        implementation fileTree(dir: "libs", include: ["*.jar"], exclude: ["TvCastingApp.jar"])
+        compileOnly files("libs/TvCastingApp.jar")
+    } else {
+        implementation fileTree(dir: "libs", include: ["*.jar","*.so"])
+    }
     implementation 'androidx.appcompat:appcompat:1.6.1'
     implementation 'com.google.android.material:material:1.11.0'
     implementation 'androidx.constraintlayout:constraintlayout:2.1.4'

examples/tv-casting-app/android/App/app/proguard-rules.pro

@@ -1,21 +1,76 @@
-# Add project specific ProGuard rules here.
-# You can control the set of applied configuration files using the
-# proguardFiles setting in build.gradle.
+# ProGuard / R8 rules for the Matter TV Casting App
 #
-# For more details, see
-#   http://developer.android.com/guide/developing/tools/proguard.html
-
-# If your project uses WebView with JS, uncomment the following
-# and specify the fully qualified class name to the JavaScript interface
-# class:
-#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
-#   public *;
-#}
-
-# Uncomment this to preserve the line number information for
-# debugging stack traces.
-#-keepattributes SourceFile,LineNumberTable
-
-# If you keep the line number information, uncomment this to
-# hide the original source file name.
-#-renamesourcefileattribute SourceFile
+# The native library (libTvCastingApp.so) calls back into Java via JNI.
+# R8 cannot trace these references, so we must explicitly keep all classes
+# and members that are accessed from native code.
+
+# ============================================================================
+# 1. App-level JNI classes (called from libTvCastingApp.so via FindClass/GetMethodID)
+# ============================================================================
+
+# Casting core classes — constructed and field-accessed from native code
+-keep class com.matter.casting.core.** { *; }
+
+# Casting support classes — fields read/written from native code
+-keep class com.matter.casting.support.** { *; }
+
+# Compat JNI layer — legacy API surface also called from native code
+-keep class com.chip.casting.** { *; }
+
+# ============================================================================
+# 2. CHIP SDK classes (from dependency JARs, called via JNI from libTvCastingApp.so
+#    and the CHIP platform native code)
+# ============================================================================
+
+# Platform layer — JNI bridge between native CHIP stack and Android
+-keep class chip.platform.** { *; }
+
+# App server — CHIP application server Java bindings
+-keep class chip.appserver.** { *; }
+
+# Interaction model — cluster/command/attribute Java bindings
+-keep class chip.clusterinfo.** { *; }
+
+# Device controller — used by the interaction model layer
+-keep class chip.devicecontroller.** { *; }
+
+# Setup payload (QR code / manual pairing code parsing)
+-keep class chip.setuppayload.** { *; }
+
+# TLV codec — used by interaction model serialization
+-keep class chip.tlv.** { *; }
+
+# ============================================================================
+# 3. Keep native method declarations so the JNI linkage works
+# ============================================================================
+-keepclasseswithmembernames class * {
+    native <methods>;
+}
+
+# ============================================================================
+# 4. Keep the Android Application subclass (entry point)
+# ============================================================================
+-keep class com.matter.casting.ChipTvCastingApplication { *; }
+
+# ============================================================================
+# 5. Standard Android keep rules
+# ============================================================================
+
+# Keep Parcelable implementations
+-keepclassmembers class * implements android.os.Parcelable {
+    public static final ** CREATOR;
+}
+
+# Keep enum values (used by reflection in some Android APIs)
+-keepclassmembers enum * {
+    public static **[] values();
+    public static ** valueOf(java.lang.String);
+}
+
+# ============================================================================
+# 6. Suppress warnings for annotations not present at runtime
+# ============================================================================
+
+# javax.annotation.* annotations (Nonnull, Nullable) are compile-time only
+# and not included in the Android runtime. They are safe to ignore.
+-dontwarn javax.annotation.**

examples/tv-casting-app/android/App/app/src/main/jni/cpp/core/CastingApp-JNI.cpp

@@ -38,12 +38,12 @@ using namespace chip;
 
 #define JNI_METHOD(RETURN, METHOD_NAME) extern "C" JNIEXPORT RETURN JNICALL Java_com_matter_casting_core_CastingApp_##METHOD_NAME
 
-jint JNI_OnLoad(JavaVM * jvm, void * reserved)
+jint JNIEXPORT JNI_OnLoad(JavaVM * jvm, void * reserved)
 {
     return AndroidAppServerJNI_OnLoad(jvm, reserved);
 }
 
-void JNI_OnUnload(JavaVM * jvm, void * reserved)
+void JNIEXPORT JNI_OnUnload(JavaVM * jvm, void * reserved)
 {
     return AndroidAppServerJNI_OnUnload(jvm, reserved);
 }

examples/tv-casting-app/android/BUILD.gn

@@ -18,6 +18,7 @@ import("//build_overrides/chip.gni")
 import("${build_root}/config/android_abi.gni")
 import("${chip_root}/build/chip/java/rules.gni")
 import("${chip_root}/build/chip/tools.gni")
+import("${chip_root}/examples/tv-casting-app/tv-casting-common/tv-casting-common.gni")
 
 shared_library("jni") {
   output_name = "libTvCastingApp"
@@ -58,6 +59,21 @@ shared_library("jni") {
   output_dir = "${root_out_dir}/lib/jni/${android_abi}"
 
   ldflags = [ "-Wl,--gc-sections" ]
+
+  if (optimize_apk_size) {
+    # Identical Code Folding: merge functions with identical machine code.
+    ldflags += [ "-Wl,--icf=safe" ]
+
+    # Thin LTO at link time (must match cflags).
+    ldflags += [ "-flto=thin" ]
+
+    # Static libc++: fold libc++ into libTvCastingApp.so so we don't ship
+    # the 7.5 MB libc++_shared.so as a separate file. The linker's
+    # --gc-sections + LTO will strip unused libc++ code.
+    if (use_static_libcxx) {
+      ldflags += [ "-static-libstdc++" ]
+    }
+  }
 }
 
 android_library("java") {
@@ -73,9 +89,13 @@ android_library("java") {
 
   data_deps = [
     ":jni",
-    "${chip_root}/build/chip/java:shared_cpplib",
   ]
 
+  # When using static libc++, we don't need the shared libc++ library.
+  if (!use_static_libcxx) {
+    data_deps += [ "${chip_root}/build/chip/java:shared_cpplib" ]
+  }
+
   sources = [
     "App/app/src/compat/jni/com/chip/casting/AppParameters.java",
     "App/app/src/compat/jni/com/chip/casting/CommissioningCallbacks.java",

examples/tv-casting-app/android/args.gni

@@ -24,7 +24,7 @@ chip_project_config_include_dirs =
     [ "${chip_root}/examples/tv-casting-app/tv-casting-common/include" ]
 chip_project_config_include_dirs += [ "${chip_root}/config/standalone" ]
 
-chip_build_libshell = true
+import("${chip_root}/examples/tv-casting-app/tv-casting-common/tv-casting-common.gni")
 
 chip_enable_additional_data_advertising = true
 
@@ -36,12 +36,20 @@ chip_max_discovered_ip_addresses = 20
 
 enable_rtti = true
 
-# Build Configuration: Fast Development Mode
-optimize_for_size = false  # -O2 (speed) vs -Os (size) - faster compilation
-symbol_level =
-    0  # -g0 (no debug symbols) - fastest compilation, no stack traces
-
-#is_debug = false            # Release mode: faster execution, removes safety checks
+if (optimize_apk_size) {
+  # Size-optimized build: smaller APK, fewer debug features
+  # NOTE: matter_enable_tracing_support and matter_trace_config are
+  # passed as GN build args from android.py to properly override
+  # their declare_args() defaults in tracing_args.gni.
+  chip_build_libshell = false
+  optimize_for_size = true   # -Os (size) instead of -O2 (speed)
+  symbol_level = 0           # -g0: no debug symbols
+} else {
+  # Default development build: full debug features, fast compilation
+  chip_build_libshell = true
+  optimize_for_size = false  # -O2 (speed) - faster compilation
+  symbol_level = 0           # -g0 (no debug symbols) - fastest compilation
+}
 
 # Symbol Level Options:
 # 0 = No debug symbols (-g0): Fastest build, smallest binary, no crash stack traces
@@ -53,5 +61,5 @@ symbol_level =
 # false = Release mode: Removes assert() checks, bounds checking, extra logging
 # true = Debug mode: Keeps all safety checks, slower execution but catches bugs
 # Default: true (if not specified, GN defaults to debug mode)
-
-# For Release Builds: Use optimize_for_size=true, symbol_level=1
+# Note: In size-optimized builds, is_debug=false is set by android.py as a
+# GN build arg to properly override the declare_args() default.

examples/tv-casting-app/darwin/args.gni

@@ -24,6 +24,11 @@ chip_project_config_include_dirs = [
   "${chip_root}/examples/tv-casting-app/tv-casting-common",
 ]
 
+import("${chip_root}/examples/tv-casting-app/tv-casting-common/tv-casting-common.gni")
+
+# Use slim cluster-objects: only the ~36 clusters a casting client needs.
+chip_cluster_objects_source_override = "${chip_root}/examples/tv-casting-app/tv-casting-common/casting-cluster-objects.cpp"
+
 chip_build_libshell = true
 
 # Example Credentials like ExampleDAC.h/cpp are not required for the tv-casting-app

examples/tv-casting-app/linux/args.gni

@@ -24,6 +24,11 @@ chip_project_config_include_dirs =
     [ "${chip_root}/examples/tv-casting-app/tv-casting-common/include" ]
 chip_project_config_include_dirs += [ "${chip_root}/config/standalone" ]
 
+import("${chip_root}/examples/tv-casting-app/tv-casting-common/tv-casting-common.gni")
+
+# Use slim cluster-objects: only the ~36 clusters a casting client needs.
+chip_cluster_objects_source_override = "${chip_root}/examples/tv-casting-app/tv-casting-common/casting-cluster-objects.cpp"
+
 chip_build_libshell = true
 
 chip_enable_additional_data_advertising = true