Shrinking WhatsApp

Billions of people in over 180 countries use WhatsApp to stay in touch with friends and family. At WhatsApp we relentlessly work on shrinking our apk as much as possible given that many of our users live in regions with poor connectivity and we are committed to leave no one behind. In this session we will cover some of the wins, regressions, strategies and technologies that we use to tame WhatApp's apk size.

Conference: https://www.droidcon.sg
Video: coming soon

Transcript

1. Evelio Tarazona Cáceres Engineering Manager Shrinking
 WhatsApp
4. https://www.youtube.com/watch?v=8PW3O2mqTn8
5. We focus on building a simple, private and secure messaging service that works fast and reliably anywhere in the world.
6. https://www.youtube.com/watch?v=erDF7IoiHpo
7. Simple, Reliable, Secure Messaging WhatsApp is widely used on Android devices. 
 As we add new features to the product, 
 we must continue supporting it in older devices.
8. Simplicity
9. Keep it small
10. Fewer features
11. Keep the app size small
12. WhatsAppSize?
13. download apk universal build
14. https://www.reddit.com/r/MapPorn/comments/7gnuuk/world_map_of_average_internet_connection_speed/
15. download apk install universal build
16. keeping an eye on it
21. delivery
24. https://developer.android.com/platform/technology/app-bundle
25. Dynamic Delivery https://android-developers.googleblog.com/2018/05/io-2018-everything-new-in-google-play.html
26. End-to-end encryption
27. https://developer.android.com/platform/technology/app-bundle
28. If you are okay with giving your key to Google, you can use app bundles.
29. So what do we do?
30. Keep the apk size small
31. And do not share our signing key with anyone
32. apk splits
33. splits {
 density {
 enable true
 include "ldpi", "mdpi", "hdpi", "xhdpi", "xxhdpi", "xxxhdpi"
 }
 
 
 
 } // apk splits by density
34. Reduction of: ~1-2 MB per density split vs universal apk
35. splits {
 density {
 enable true
 include "ldpi", "mdpi", "hdpi", "xhdpi", "xxhdpi", "xxxhdpi"
 }
 abi { enable true include "armeabi-v7a", "arm64-v8a", "x86", "x86_64" } } // apk splits by density & abi
36. Reduction of: ~10-12 MB per abi split vs universal apk
37. At the cost of release management complexities
38. YMMV
39. Optimizations
40. WhatsAnAPK?
41. It's a zip file
42. Not all files in the apk are compressed
43. There is also zip metadata like timestamps
44. Repackaging and stripping metadata ~1MB reduction
45. ➜ unzip -v your.apk | grep -E ' 0%'
46. ➜ apksigner USAGE: apksigner <command> [options] apksigner --version apksigner --help EXAMPLE: apksigner sign --ks release.jks app.apk apksigner verify --verbose app.apk apksigner is a tool for signing Android APK files and for checking whether signatures of APK files will verify on Android devices. # built-in tooling
47. ➜ zipalign Zip alignment utility Copyright (C) 2009 The Android Open Source Project Usage: zipalign [-f] [-p] [-v] [-z] <align> infile.zip outfile.zip zipalign -c [-p] [-v] <align> infile.zip <align>: alignment in bytes, e.g. '4' provides 32-bit alig -c: check alignment only (does not modify file) -f: overwrite existing outfile.zip -p: memory page alignment for stored shared object files # built-in tooling
48. WhatsInAnAPK?
49. ➜ unzip whatsapp.apk
50. ➜ ls AndroidManifest.xml assets lib resources.arsc META-INF classes.dex res
51. remove stuff
53. configurations { packagingOptions { exclude 'META-INF/LICENSE.txt' exclude 'META-INF/NOTICE.txt' exclude 'com/google/android/search/verification/client/R.java' exclude 'third_party/java_src/error_prone/project/annotations/Annotations.gwt.xml' exclude 'third_party/java_src/error_prone/project/annotations/Google_internal.gwt.xml' exclude 'jsr305_annotations/Jsr305_annotations.gwt.xml' exclude 'error_prone/Annotations.gwt.xml' exclude 'protobuf.meta' exclude 'build-data.properties' exclude 'androidsupportmultidexversion.txt' // ... // This saved us ~300KB // packagingOptions - exclude
54. res
55. res/layout/preferences.xml: Warning: The resource R.layout.preferences appears to be unused [UnusedResources] # lint, enable UnusedResources
56. android {
 buildTypes {
 release { // ... shrinkResources true
 
 } 
 }
 } // built-in optimizations
57. aaptOptions { cruncherEnabled [false|true] } # optimize pngs
58. ➜ optipng ➜ pngcrush ➜ zopflipng ➜ advpng # zopflipng reduced png bloat by ~2MB # can't use webp because API level support, use it if you can # do use svg for some assets # vector drawable not used extensively enough # optimize pngs
59. android {
 defaultConfig {
 resConfigs "en", ”es", "fr”, // …
 }
 } // Removing strings for unsupported languages
 // saved us ~1MB. // remove unused configs
60. strings
61. String pool: "My App", "Hello", "Exit", "Settings", "Feature" Default config: string/myapp 0x00000001 string/hello 0x00000002 string/exit 0x00000003 string/settings 0x00000004 string/feature 0x00000005 ========== Config size: 20 bytes resources.arsc https://medium.com/androiddevelopers/smallerapk-part-3-removing-unused-resources-1511f9e3f761
62. String pool: "My App", "Hello", "Exit", "Settings", "Feature", "New feature" Default config: -v21 config: string/myapp 0x00000001 string/hello 0x00000002 string/exit 0x00000003 string/settings 0x00000004 string/feature 0x00000005 ========== Config size: 20 bytes resources.arsc https://medium.com/androiddevelopers/smallerapk-part-3-removing-unused-resources-1511f9e3f761
63. String pool: "My App", "Hello", "Exit", "Settings", "Feature", "New feature" Default config: -v21 config: string/myapp 0x00000001 NO_ENTRY string/hello 0x00000002 NO_ENTRY string/exit 0x00000003 NO_ENTRY string/settings 0x00000004 NO_ENTRY string/feature 0x00000005 0x00000006 ========== ========== Config size: 20 bytes 20 bytes! resources.arsc https://medium.com/androiddevelopers/smallerapk-part-3-removing-unused-resources-1511f9e3f761
64. 4 bytes * 3500 null entries * 50 languages = 700 kilobytes resources.arsc https://medium.com/androiddevelopers/smallerapk-part-3-removing-unused-resources-1511f9e3f761
65. alternatives: in code? other format? resources.arsc https://medium.com/androiddevelopers/smallerapk-part-3-removing-unused-resources-1511f9e3f761
68. stringpacks saved us ~8MB
69. bytecode
70. single dex app
71. ➜ ls AndroidManifest.xml assets lib resources.arsc META-INF classes.dex res
72. dependencies { implementation // ... debugImplementation // ... // ... // watch & limit your dependencies
73. android {
 buildTypes {
 release { // ... shrinkResources true
 minifyEnabled true
 } 
 }
 } // built-in optimizations
74. android {
 buildTypes {
 release { // ... shrinkResources true
 minifyEnabled true
 proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'config/proguard-rules-release.pro' } 
 }
 } // built-in optimizations
75. android {
 buildTypes {
 release { // ... shrinkResources true
 minifyEnabled true
 proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'config/proguard-rules-release.pro' } 
 }
 } // built-in optimizations
76. android {
 buildTypes {
 release { // ... shrinkResources true
 minifyEnabled true
 proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'config/proguard-rules-release.pro' } 
 }
 } // built-in optimizations
77. android.enableR8=true // we observed an increase of ~168KB // but a reduction on method reference count // and an improvement on cold start // some people on the community observed regressions R8
78. Method references count for consumer beta (pre-redex) 55000 81200 107400 133600 159800 186000 Debug Release/Proguard Release/R8 71,296 90,725 185,674 64K
79. redex
80. https://fbredex.com
81. ➜ redex your.apk -o your-optimized.apk -c config.json
82. { "redex" : { "passes" : [ "ReBindRefsPass", "BridgePass", "SynthPass", "FinalInlinePass", "DelSuperPass", "SingleImplPass", "MethodInlinePass", "StaticReloPass", "RemoveEmptyClassesPass", "ShortenSrcStringsPass" ] } } sample redex config
83. Method references count for consumer beta release 55000 81200 107400 133600 159800 186000 Unoptimized Proguard Proguard + Redex R8 R8 + Redex 61,640 71,296 66,778 90,725 185,674 64K
84. • Better Proguard/R8 configuration • Additional redex passes • Downloadable assets: emoji, stringpacks, other res. • Dynamic Features • Keyframes/VectorDrawables/WebP/basis universal • Work on install and download size • Native library optimizations: 
 noCompress vs. xz compress Future Work
85. Thanks!
86. Q&A @eveliotc 
 https://evel.io