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Kotlin to Javascript

In my opinion, one of the most interesting Kotlin features is the ability to transpile into Javascript. I’m a huge fan of GWT (Java -> Javascript), a lot of my projects are working in the web with GWT (like http://chess.mobialia.com or http://12chess.com), and I need to know if Kotlin is going to be able to replace Java+GWT in the near future.

So I tried to compile the Carballo Kotlin code to JS (as a NodeJS app) in the “js” branch: https://github.com/albertoruibal/karballo/tree/js, and I couldn’t make it work yet. I found some problems that I will detail in this post.

GWT includes a reduced version of the JRE, without some classes and methods, but Kotlin is much more radical: To compile a Kotlin code to JS, it cannot reference any java.* class, so forget about java.lang.*, java.util.* or java.io.*.

No basic java types

Integer, Character, Boolean… are a Java classes and they cannot be used, so a lot of common operations must be done the “Kotlin way”, i.e.:

Integer.parseInt(myString) -> myString.toInt()
Character.toLowerCase(myChar) -> myChar.toLowerCase()
Integer.MAX_VALUE -> Int.MAX_VALUE

Emulating Java classes: System, Math, Random, Arrays, Date

These classes are not available when building to JS. To avoid changing the original code and migrate seamless from JVM to JS, I created auxiliar classes with the methods used in the code:

  • System: I implemented currentTimeMillis() (calling the JS Date object), exit(), arraycopy(), and an empty gc()
  • Math: When building for JS, the java.lang.Math class must be replaced by kotlin.js.Math, using this class avoids to change a lot of code
  • Random: Using kotlin.js.Math.random()
  • Arrays: Implementing some variants of the fill() method
  • Date: partial implementation to get the current date

Other problems

  • IntelliJ does not allow to mix the Java and the JS Kotlin stdlib in the same project, so I hat to create a different branch “js”
  • No Threads nor Coroutines support in JS jet
  • Kotlin’s readLine() (to read lines from stdin) is only available in the JVM stdlib
  • String.toBoolean() is only available in the JVM stdlib, I fixed it defining a extension function in the same package: 
    inline fun String.toBoolean(): Boolean = "true".equals(this.toLowerCase())
  • No support for asserts in the JS compiler
  • Some annotations aren’t available @JvmOverloads, @Throws…
  • No LinkedList
  • No StringBuffer, but in this case it’s better to use Kotlin’s StringBuilder
  • Missing StringBuilder.setLength() method (I sent a pull request to Kotlin implementing setLength() and substring())
  • It does not allow returns into synchronized blocks
  • No printStackTrace() on exceptions
  • No JUnit tests in JS, so I removed the tests in the “js” branch

Overall conclusion

After solving all these problems, the Kotlin2JS compiler is introducing bugs that don’t allow the karballo engine to work.

Kotlin2JS isn’t production ready, and years behind GWT.


Converting Carballo to Kotlin

Kotlin is a JVM language developed by JetBrains: http://kotlinlang.org gaining momentum among Android developers. Kotlin has interesting features like:

  • It can be compiled to bytecode compatible with Java >=6, allowing to use a lot of Java 7-8 features (lambdas…)  in Java 6 bytecode (=Android)
  • It can be transpiled to Javascript (like Java with GWT)

So I decided to migrate the Carballo Chess Engine code to Kotlin (and his name is Karballo) to make some experiments and having some “fun” :)… but it became a non-trivial task, the converted code is at: https://github.com/albertoruibal/karballo.

Converting the code

To start working with Kotlin I installed the Kotlin plugin for Android Studio (=IntelliJ) from:

File->Settings->Plugins->Install JetBrains Plugin

Once the Kotlin plugin is installed, it’s quite easy to convert java source files to Kotlin with: CTRL + SHIFT + ALT + K

Conversion problems

The Java to Kotlin code conversion does not work perfectly, the Carballo conversion arose these errors:

  • Kotlin is strong typed, you cannot compare a long against the literal ‘0’, you must use ‘0L’… I had hundreds of this comparisons
  • A Long cannot be initialized with an unsigned hex literal if the value does not fit in the signed type, it gives a “Value out of range” compilation error ,  so you cannot do:
    var variable = 0xffffffffffffffffL

    The solution is to convert the literals to a signed decimal:

    var variable = -1
  • Error “Property must be initialized or be abstract” with attributes not initialized in the constructor, solved adding the “lateinit” modifier to the declaration of the attributes (yes, Kotlin knows if you are initializing the attribute in the constructor)
  • Strange toInt() insertions:
    pieceNames.indexOf(pieceChar.toInt())

    should be:

    pieceNames.indexOf(pieceChar)
  • Variables of type Byte cannot be used as array indices, I had to manually change many vars from Byte to Int
  • Kotlin does not allow assignments in expressions, so it’s impossible to do:
    while ((node.move = node.moveIterator.next()) != Move.NONE) { 

    I manually had to change some cases to the more verbose:

    while (true) {
        node.move = node.moveIterator.next()
        if (node.move == Move.NONE) {
           break
        }
  • The binary operators do not work in multi line if they are placed at the beginning of the second line, only if they are at the end of the first, so:
    var myLong : Long = long1
        or long2

    does not compile, it must be:

    var myLong : Long = long1 or
        long2
  • It didn’t recognize some custom getters and I had to merge them manually, I like a lot how they look in Kotlin (notice the use of the special word “field” to avoid calling the getter recursively):
    var lastMoveSee: Int = SEE_NOT_CALCULATED
        get() {
            if (field == SEE_NOT_CALCULATED) {
                field = board.see(move, ai)
            }
            return field
        }
  • The conversion process got hung with two complex classes: CompleteEvaluator and ExperimentalEvaluator… I had to kill IntelliJ. I converted the CompleteEvaluator class copying to a new class small chunks of code.
  • Kotlin’s when() statement do not work like the Java’s switch->case, as it hasn’t breaks, you cannot jump from one option to the next excluding the break: the conversion duplicated a lot of the MoveIterator code and I fixed it manually.
  • Some other strange errors like wrong expressions and missing parenthesis…

Some things of Kotlin that I don’t like (yet)

Some are part of the claimed Kotlin “features”:

  • Kotlin does not has primitive types, but it seems to not affect the performance…
  • There is no ternary operator in Kotlin, it’s replaced with “if (…) … else …” expressions: This increases a lot the verbosity, al least in my code
  • Kotlin’s crusade against NullPointerExcepcions: It a type allows null, it must be explicitly indicated appending a question mark to the type:
    var myString : String? = null

    To convert a nullable var/val to a non-nullable, you should use the !! operator, this forces a NullPointerException if the value is null (and it seems that you are shouting to the IDE…):

    var myString : String? = "hello"
    var myStringNotNull : String = myString!!
  • Static fields and methods are grouped in a “Companion Object”
  • Compilation is slower than pure Java
  • Many bugs running from Android Studio non-android projects (IntelliJ worked better for me)
  • Couldn’t get the JS compilation working yet

And other things that I like

  • The full interoperability with Java
  • Type inference, normally I continue to specify the types, but in some cases it saves a bit of code
  • Data classes, they will save you hundreds of lines of boilerplate code https://kotlinlang.org/docs/reference/data-classes.html
  • Array initialization with lambdas
    nodes = Array(MAX_DEPTH, {i->Node(this, i)})
  • The singleton pattern is embedded in the language: using “object” instead “class” assumes that the class is a singleton
  • Visibility is “public” by default, with the access modifier “internal” it can be accessed only from the same module
  • Implicit getters / setters
  • No need for “new” to call constructors
  • And much more…

Performance

I’m my first tests, I’m not noticing any performance downgrade (or upgrade) over the Carballo Java version.


Improving Carballo Chess Engine the hard way  

torneo_ajedrezOne year ago my Carballo Chess Engine (https://github.com/albertoruibal/carballo) was stuck: all the improvements that I was trying were not working, and I detected the main problem: I am a poor chess player so I will never be a good chess engine developer. I thought that the main chess programming skill was statistical analysis and not chess knowledge, but I was wrong.

So, I took the decision of starting to learn and play chess. I joined the local chess club Xadrez Ramiro Sabell (http://www.xadrezramirosabell.com) and I was so lucky that in this club teaches chess the International Master Yudania Hernández Estevez. It’s quite curious the amazing people that you can find in a small city like Ponteareas. I also try to help the club in the tournaments organization and with a small Mobialia sponsorship. Now I am playing the Galician Chess League (in third division) and all the tournaments that I can.

My chess level is improving fast (ok, I’m under 1600 ELO yet: http://ratings.fide.com/card.phtml?event=24597015), but the real deal is that the Carballo Chess Engine strength is improving much faster, climbing positions in the CCRL list (http://www.computerchess.org.uk/ccrl/4040/). Learning chess helps me to diagnose the flaws and to understand better what’s going on under the hood.

Finally,  playing chess also helps me to detect the chess player needs, so I realized the main missing feature from Mobialia Chess: a chess database to review historic games and to analyze your own games searching statistics for each position. This year I worked to implement this feature and starting today you can access a Beta version of the database in Mobialia Chess Web (http://chess.mobialia.com).


Benchmarking Java to native compilers

Java DukeJava to native compilers have been around for some years, and I was curious about if one of this solutions could improve the performance of my Carballo Chess Engine.

I ran a tournament between binaries of the Carballo development version (1.5) compiled with different solutions to compare the performance. I used cutechess-cli to run a 3000 game tournament with time control 5″ + 0.1″ per move by side and with the Noomen Test Suite as the starting positions.

The compared binaries

  • The Pure Java Version: This is the carballo-1.5.jar ran with the Oracle JDK 1.8.0_73 VM under my 64bit linux (Debian Sid).
  • GCJ: The GNU’s Java compiler, incomplete and unfinished, but it works for Carballo. This binary was compiled with this script.
  • Excelsior Jet: A classic proprietary Java to native converter at http://www.excelsiorjet.com. I used Excelsior Jet 11 32bit for Linux (evaluation) to generate this binary. The 64bit version had worse results.
  • RoboVM: (https://robovm.com) A solution to run Java apps on iOS. Recently it was bought by Xamarin, and after the Microsoft acquisition of Xamarin, RoboVM was discontinued. RoboVM also has the option to compile Java apps to desktop binaries. I built this binary with the last RoboVM free version (1.8). Now RoboVM is forked in BugVM, but I was not able to build the binary with BugVM.
  • C# compiled with Mono: There is a C# version of Carballo converted with the Sharpen tool. I compiled this binary with MonoDevelop 5.10. The converted code is sub-optimal but it is a good solution if you need a native version (or if you need to integrate Java code in a C# project).

Test results

Rank Name                          ELO   Games   Score   Draws
   1 carballo-1.5-gcj               89    1200     62%     28%
   2 carballo-1.5                   37    1200     55%     27%
   3 carballo-1.5-mono              -5    1200     49%     30%
   4 carballo-1.5-jet              -33    1200     45%     28%
   5 carballo-1.5-robovm           -88    1200     38%     27%

Conclusion

The JVM performance is very good, better than almost all the Java to native solutions.

The exception is GCJ, but it’s incomplete and it will not work for all the Java apps.

I expected better results from Excelsior Jet, as some time ago Carballo Jet binaries where available an used for testing.

The C# version is a bit worse but acceptable.


Vender en Google Play desde España

Por aclamación popular os cuento los requisitos legales para vender aplicaciones en Google Play desde España. Me centraré en el caso de vender como trabajador autónomo, que es como estoy facturando en Mobialia.

CONSIDERACIONES SOBRE GOOGLE WALLET

En el Google Play los pagos se hacen a través de la plataforma Google Wallet. En Google Wallet no tenemos facturas, sólo tenemos las órdenes de venta, que son una especie de albaranes y los pagos mensuales que nos manda.

La entidad gestora de Google Wallet, Google Payment Limited (GPL) es una entidad intermediadora en el pago que no cuenta para nada (bueno sí, para enviarte el dinero).

ALTA EN HACIENDA

Para poder facturar hay que darse de alta en hacienda (modelo 036). Yo me puse en el epígrafe IAE 213 Ingenieros de Telecomunicación, cada caso personal tendréis que estudiarlo. En este formulario también escogí la modalidad de estimación directa simplificada.

Suele ser útil darse de alta en el registro de operadores de IVA intracomunitario, que necesitaréis si vais a emitir facturas a empresas europeas sin IVA.

ALTA EN SEGURIDAD SOCIAL

También es necesario darse da alta en la Seguridad Social como autónomo (modelo TA.0521) escogiendo una base de cotización según la que pagarás una cuota mensual.  Yo estoy pagando a la seguridad social 267,03 euros mensuales con la base de cotización mínima. Aunque tengas otro trabajo en el que ya estés cotizando a la seguridad social, este trámite es obligatorio.

Teóricamente si tu actividad no se considera “habitual” no tendrías que pagar esta cuota, y según la jurisprudencia vigente la actividad es habitual si generas más que el salario mínimo interprofesional. De todas formas podrías meterte en un lío si no la pagas…

TRÁMITES PERIÓDICOS

Al estar dado de alta con el 036, tenéis la obligación de presentar trimestralmente el formulario 303 de autoliquidación de IVA (pones facturas de compra, facturas de venta y pagas la diferencia de IVA entre las ventas y las compras. Anualmente también hay que presentar el formulario 390 (que es un resumen recapitulativo del IVA).

Si tenéis operaciones de IVA intracomunitarias (si se cobran anuncios de Admob o Adsense, por ejemplo) también hay que presentar trimestralmente el modelo 349, que es un modelo informativo en el que se detallan estas operaciones (además de ir su total reflejado en el 303).

También se está obligado a presentar trimestalmente el formulario 130 de pago fraccionado del IRPF, en el cual anticiparemos a la AEAT un 20% del beneficio trimestral para la próxima declaración de la renta.

En la declaración de la renta, en la sección de ingresos por estimación directa, pones los ingresos, gastos, pagos a la seguridad social como autónomo y pagas por los beneficios dependiendo del tramo de renta en el que estés.

IVA DE LAS VENTAS EN GOOGLE PLAY

En un post anterior comentaba los Cambios a partir del 1 de enero de 2015.

Desde 2015 es Google quien vende las apps directamente a los usuarios, y el desarrollador factura a Google, de forma similar a como se facturan las ventas en Amazon Appstore. La diferencia es que en este caso se le factura todo a Google Inc. USA. como se entiende al leer las Condiciones de Servicio de Google Play.

FACTURA DE COMPRA A GOOGLE POR LAS COMISIONES DEL 30%

Google no te manda ninguna factura, sólo tienes las órdenes de Google Wallet y los informes financieros de Google Play. Yo mensualmente introduzco una factura de compra a Google Inc USA pagándole las comisiones que me descuenta de las ventas (30%). Esta factura está exenta de IVA, y Google debería mandármela, pero como no me la manda, me la “invento”, ya que me la está cobrando implícitamente.

FACTURAS DE VENTA A ADMOB O ADSENSE

Si monetizáis aplicaciones a través de Admob o webs a través de Adsense, los ingresos se le facturan a Google Ireland, por lo que necesitaréis ser operador de IVA intracomunitario, ya que las facturas son también sin IVA, y trimestralemente tenéis que informar de estas facturas en el modelo 349.

Recordad que yo no soy un experto fiscal, simplemente os estoy contando mi experiencia, por lo que agradeceré comentarios y correcciones.


Cambios en el IVA para las ventas en Google Play

euroA partir del 1 de enero de 2015 entran en vigor nuevas reglas de IVA para la prestación de servicios TRE (Telecomunicaciones, Radiodifusión y TV, y Electrónicos) en la Unión Europea y afecta a las ventas de apps en Google Play. Anteriormente a las apps se les aplicaba en Europa el IVA del país desde el que eran vendidas, pero ahora se les va a tener que apicar el IVA de cada uno de los países en los que se vendan.

Hasta ahora éramos los desarrolladores europeos los que nos encargábamos de recaudar el IVA y pagarlo a la agencia tributaria de nuestro país, y con este cambio habría que pagar el IVA recaudado en cada país a cada una de sus agencias tributarias. Para simplificar este proceso se va a poner el marcha la ventanilla única (Mini-One-Stop-Shop o MOSS) que, aunque simplificaría algo el proceso, seguiría siendo complejo….

Google al rescate

Afortunadamente Google acaba de anunciar que a partir del 1 de enero se va a encargar de recaudar el IVA y presentarlo ante las agencias tributarias de los países europeos, liberando a los desarrolladores de esta responsabilidad:

https://support.google.com/googleplay/android-developer/answer/138000

Por lo tanto a partir de ahora es Google quien vende las apps directamente a los usuarios, y luego el desarrollador facturará a Google, de forma similar a como se facturan las ventas en Amazon Appstore. La diferencia es que en este caso se le factura todo a Google Inc. USA. como se entiende al leer las Condiciones de Servicio de Google Play.

También se cambiará la forma de incluir el IVA en los precios: hasta ahora se le sumaba el IVA al precio especificado por el desarrollador, ahora el precio final pasará a llevar incluído el IVA (Tax-Incusive-Pricing).

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Filmon: Free IPTV service

filmonIPTV is in a great momentum. In Spain we saw the rise of a lot of platforms: Yomvi, MovistarTV, OrangeTV, Nubeox… mainly paid platforms, but I am only interested in channels in English and Filmon is a great (and legal) option to watch some of them for free.

Filmon offers more than 600 live channels. There are lots of crap, but others are quite interesting:

  • UK TV channels: BBC One, BBC Two, BBC Three, BBC News, ITV1, ITV2, ITV3, ITV4…
  • News channels: Al Jazeera, Bloomberg, Euronews, France24, Russia Today…

Filmon is free for SD resolution, if you want to watch it in HD and access to program recording you must pay a 15€/month fee.

You can can watch Filmon directly from their web page http://filmon.tv, or from their Android and iOS apps.

There is also an unofficial Kodi plugin (previously called XBMC) at SuperRepo.


Running Android apps inside Chrome

I couldn’t believe it when somebody told me: Google is running Android apps in ChromeBooks and some selected apps can be installed from the Chrome Webstore. It works with a Chrome extension that implements an Android virtual machine running over the Native Client (NaCL is a sandbox for running compiled C and C++ code inside Chrome).

Based on this Google work, Vlad Filippov released an unofficial Chrome extension called ARChon (https://github.com/vladikoff/chromeos-apk/blob/master/archon.md) to allow this for all the desktop Chromes (Linux, Mac & Windows). This ARChon extension is a 100MB zip that must be unzipped and loaded into Chrome as an unpacked extension.

Then each Android APK must be converted to an unpacked extension with a Node-JS based tool, chromeos-apk (https://github.com/vladikoff/chromeos-apk) and loaded into Chrome. The generated extension contains the APK and some support files. Once installed, it appears as a regular Chrome app.

I tested all my Android apps and I was very surprised with the results, they load fast and run smooth. Some of my apps did not work because:

  • It does not support Google Play Services
  • It does not support apps using the Android NDK
  • It does not support GL_TEXTURE_CUBE_MAP in OpenGL ES (and my app crashes)

But I consider it SPECTACULAR. This opens a lot of new possibilities for Android, now running inside browsers like Flash, … and confirms my “theory” that Android is only a virtual machine (IMHO, the underlying SO is Linux :P).

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chromeos-apk


Facturar en España las ventas de apps en Amazon Appstore

amazon_appstoreEl caso de Amazon Appstore es algo diferente al de Google Play (que analizaba en este otro post) y bastante más sencillo, porque es Amazon quien vende las apps directamente al usuario y luego efectúa el pago de royalties al desarrollador.

Amazon separa las ventas realizadas en Amazon.com y las de cada uno de sus portales europeos (Amazon.co.uk, Amazon.de, Amazon.es, Amazon.fr y Amazon.it), enviando una transferencia mensual por cada uno de dichos portales. Se pueden ver fácilmente estos pagos desde la Developer Console en Reporting->Payments.

Los royalties de las ventas a través de Amazon.com se deben facturar a:

Amazon Digital Services Inc.
410 Terry Avenue North
Seattle, WA 98109
US

Es una exportación (IVA 0%) y por lo tanto irá en la casilla 60 del modelo 303 de IVA (exportaciones y operaciones asimiladas).

Los royalties del resto de portales europeos se facturan desde Luxemburgo:

Amazon EU Sarl
5 rue Plaetis
L-2338 Luxembourg
Luxembourg
VAT Registration Number: LU20260743

Yo las agrupo en una factura por mes con una línea por cada uno de los portales. En este caso es una venta intracomunitaria (también IVA 0%) que irá en la casilla 59 del modelo 303 (entregas intracomunitarias de bienes y servicios) y que se debe hacer constar en el modelo 349 con la clave “S” (prestaciones intracomunitarias de servicios).

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ACTUALIZACIÓN

Desde el 1 de noviembre de 2014 las ventas en Europa se pasan a facturar por Amazon Media EU:

Amazon Media EU S.à r.l.
5 Rue Plaetis
L-2338 Luxembourg
Luxembourg
VAT Registration Number: LU20944528


Chromecast vs a HDMI cable (with a MHL adapter)

chromecast_vs_hdmi_cableIt’s been some time since Chromecast was launched in Europe and, despite the hype, I cannot find too much advantages over using a simple HDMI cable with a MHL adapter that you plug in your phone’s MicroUSB (mirroring your phone/tablet screen to the TV screen). Here is my comparative, you will decide if is Chromecast worth it.

Chromecast HDMI cable with a MHL adapter
Price 35€ 12€
Wireless Yes No, it’s a wire 😉 you need to be near your TV (or a long cable)
Router needed Needs a router with Wifi No
Additional development Apps need to implement specific features to use Chromecast You can view in your TV all that you see in your phone screen
Multi-User Yes You need to unplug the cable and plug it to the another device
Phone charging while streaming Needs to plug a charger to the phone Needs to plug a charger to the MHL adapter
Stream your own content from your phone Yes, but normally with paid applications Yes
You can use your phone/tablet while viewing content Yes No, you see in the TV what you are doing in the phone
Play/pause From your phone From your phone
Screen mirroring With lag With almost no lag

Ok, I didn’t bought a Chromecast yet…