In this previous post we’ve seen that before using Scala’s Future it might be worth taking some time to think of the use cases (especially error cases), the execution model we need, … as it might be more advantageous to choose a solution like Monix’s Task (although not available in standard library) to gain finer control over the execution. However some might not be able to make a decision at this stage and like to keep their options open. Let’s see how we can revisit our product repository in such way that we don’t have to make a decision too early.
Continue reading “Introduction to Tagless final”
Scala Futures vs Monix Tasks
In this previous post we saw how Scala Futures work and why they need an implicit ExecutionContext to run their computation. While there is some trick to pass the ExecutionContext, it’s usually cumbersome and clutter the code.
So the question really is: Do you need an ExecutionContext everywhere? Well, you do as long as you use Futures, but is there any alternatives? Continue reading “Scala Futures vs Monix Tasks”
Understanding Scala Futures and Execution Contexts
Viktor Klang recently published a set of useful tips on Scala Futures. While being widespread and heavily used, people (especially newcomers) are still experiencing problems working with Scala Futures.
In my opinion many of the problems come from a misunderstanding or misconception on how Futures work. (e.g. the strict nature of Futures and the way they interact with Execution Contexts to name a few).
That’s enough of an excuse to dive into the Scala Future and ExecutionContext implementation. Continue reading “Understanding Scala Futures and Execution Contexts”
gRPC in Scala
As many might think, gRPC doesn’t stand for “google Remote Procedure Call” but is a recursive acronym meaning “gRPC Remote Procedure Call”. I don’t know if you buy it but the truth is that is was originally developed by Google and then open-sourced.
If you’ve been in the IT for a while RPC doesn’t necessarily bring back happy memories. On the JVM it all started with RMI in the 90s. RMI was inspired by CORBA and suffered from a lack of interoperability as both the client and the server had to be implemented in Java. RMI was also particularly slow as Java serialisation is not a very efficient protocol.
Later in the 2000s came XML based RPC with XML-RPC and especially SOAP. Both of these formats address the interoperability as it no longer matters how the client/server are implemented. They only need to speak XML. However XML is still not an efficient protocol and communications remain slow.
SOAP provides an interesting definition language (WSDL – Web Service Definition Language) that can be used to generate service implementations.
gRPC addresses all these drawbacks. By default, it uses protobuf (Protocol buffers) for the service definitions and as its serialisation mechanism, which allows it to interoperate with many different languages while providing an efficient serialisation protocol. gRPC also takes advantage of HTTP/2 to add streaming capabilities.
gRPC generates all the boilerplate code for you, so that you only have to implement the business logic inside your services. It supports a number of different languages out of the box: C++, Java (Netty), Python, Go, Ruby, C#, Javascript (Node.JS), Android, Objective-C and PHP.
Unfortunately Scala is not in the list! … but we have scalaPB (and sbt-protoc) to save the day! Continue reading “gRPC in Scala”
Generating protobuf formats with scala.meta macros
Today’s focus is on scalameta. In this introduction post we’re going to see how to create a macro annotation to generate protobuf formats for case classes.
The idea is to be able to serialise any case classes to protobuf just by adding a @PBSerializable annotation to the case class declaration.
Then behind the scene the macro will generate implicit formats in the companion object. These implicit formats can then be used to serialise the case class to/from protobuf binary format.
This is quite similar to Json formats of play-json.
In this post we’re going to cover the main principles of scalameta and how to apply them to create our own macros. Continue reading “Generating protobuf formats with scala.meta macros”
Building anti-corruption layers with Akka
Akka actors fits nicely with DDD (Domain Driven Design) to design an application. E.g. It’s quite natural to model entities as individual actors who can be persisted, …
One of the key aspect in DDD is the notion of bounded context. A bounded context is simply a “self-content” component. It can interact with other components but it is coherent on its own. Each bounded context has its own domain model which belongs only to itself and should not leaked or be influenced by other bounded context.
Anti-corruption layers (aka translation layers or adapter layers) are used to enforce this principle. Basically their role is to translate the core domain objects into/from another domain that is used for communication or persistence.
In this blog post we’re going to try to follow the DDD principles to build a small (contrived) application using Akka and try to figure out the best way to build efficient anticorruption layers. Continue reading “Building anti-corruption layers with Akka”
PBDirect – Protobuf without the .proto files
Protocol Buffer (aka Protobuf) is an efficient and fast way to serialise data into a binary format. It is much more compact than Java serialisation or any text-based format (Json, XML, CSV, …).
Protobuf is schema based – it needs a description (in a .proto file) of the data structures to be serialised/deserialised.
On the JVM, protoc (the Protobuf compiler) reads the .proto description files and generates corresponding classes.
For Scala there is a very good sbt plugin “scalaPB” that follows the same process and generates case classes corresponding to the .proto files definitions.
The .proto files are an easy way to describe a protocol between 2 components (e.g. services). However there are some cases (e.g. writing to persistent storage) where the .proto files definition are just unnecessary and add superfluous complexity. (Who likes to read auto-generated code?).
In such cases it would be much easier to serialise an object directly into protobuf (using its class definition as a schema). Afterall this is what the protobuf java binding does: it serialises (auto-generated) java classes into protobuf binary format.
To that matter, let me introduce – PBDirect – a scala library to directly encode scala objects into protobuf. Continue reading “PBDirect – Protobuf without the .proto files”
Rethinking logging on the JVM with Logoon
Logging has been around on the JVM for a while now. It all started with Log4J back in 2001. Log4J was the first logging framework and it is still around today (in its version 2). It provides a simple and efficient API (compare to System.out.println that was in use before).
- Get a logger for a class
- Use that logger to log messages
val logger = Logger.getLogger(classOf[MyClass])
...
logger.log(Level.DEBUG, "I am doing something right now")
...
logger.error("Oops, something went wrong", theException)
...
Today there are a few more frameworks on the JVM but they all provide similar APIs as Log4J:
- JUL(2002): java.util.logging provides a standardisation of Log4J and of course provides a similar API
- Commons-logging (2002): Apache project providing a façade over Log4J, JUL, … still the same API
- SLF4J (2005): Another façade over Log4J (1&2), JUL, JCL, … no much changes in the API
- Logback (2006): Brings structured logging with an API compatible (and similar) to SLF4J (and Log4J)
- Log4J2 (2012): Rewrite of Log4J inspired by Log4J and Logback with improved performances. The API does not change much though.
As you can see the logging APIs available on the JVM haven’t changed much over the last 15 years. The most interesting additions are structured logging and the Mapped Dependent Context (MDC) as we shall see later.
In this post I am going to look at the current limitations of these APIs and see how we can overcome them while still relying on this frameworks to actually write the logs. Continue reading “Rethinking logging on the JVM with Logoon”
Fluent – A deep dive into Shapeless and implicit resolution
As promised in my previous post we’re going to explore to internal of Fluent and how it uses Shapeless and implicit resolution to transform case classes.
Fluent started as an experiment (and still is), the code is rather small (about 300 lines of code) and yet I am still impressed by the variety of cases it can handle.
Before working with Shapeless I’ve often heard that is pure magic and I got the impression that most people (including me) don’t really know how it works. It turns out that the principles used in Shapeless are not really difficult to understand – especially if you read the well-written Type Astronaut’s guide to Shapeless.
Understanding how Shapeless works doesn’t mean it’s easy to work with. Actually Shapeless makes a heavy use of implicits and working with implicits is hard. Remember that implicits resolution is performed at compile time so when it fails, there is nothing to debug, no log messages or stack trace. We are just left with rather blunt messages like could not find implicit value for parameter ...
In this post I am going to explain the concept used in Fluent, the problem I faced during implementation and hopefully by the end of the post, you’ll know enough to understand and edit the code (Pull requests welcomed!). Continue reading “Fluent – A deep dive into Shapeless and implicit resolution”
Introducing Fluent – the seamless translation layer
In Domain Driven Design (DDD) it is recommended to introduce a translation layer (aka anticorruption layer) between 2 bounded contexts. The role of the anticorruption layer is to avoid any concepts to leak from one domain into the other.
This is a sound idea as it keeps the domains isolated from each other ensuring they can evolve independently. After having implemented several anticorruption layers I realised that, although useful, they also introduced a lot of boilerplate code that doesn’t add much value to the business.
To this extent, let me introduce Fluent, a library that aims at getting rid of this boilerplate code by leveraging all the power of Shapeless and its generic programming. Continue reading “Introducing Fluent – the seamless translation layer”