Explore creating robust HTTP services in Scala's functional programming paradigm. Gain insights into pure vs. impure implementations, their pros and cons, and effective tool usage.

scala-platform.tar.gz

Scala-Pure

Scala-Impure

Scala-Tapir

Scala-Impure-Test

Scala-Pure-Test

Scala-Tapir-Test

Test

Scala - Run Code Widget 

Scala-Pure-copy

Scala is one of the most popular general-purpose languages that supports both object-oriented and functional programming. In this course, you will learn how to create back-end HTTP services using Scala's functional programming paradigm.

You will also learn how to develop, test, and document the service using both pure and impure ways. You will be exposed to the differences between pure and impure implementation, their respective pros and cons, and how pure implementation can be more robust in terms of performance, understandability, testability, and type safeness. 

By the end of the course, you will have a clear idea of how functional programming works in Scala and how you can use the available tools more effectively.

Pure Functional HTTP APIs in Scala

# Broken JSON
Now that we have a proper streaming solution, we can try it out.

What do we get when we expect a list of products? 
> The `http` command is from the tool httpie19 for querying our service. 



% http :53248/products
HTTP/1.1 200 OK
Content-Type: application/json
Transfer-Encoding: chunked

{
  "id":"8773899b-fcfa-401f-af3e-b188ebb0c00c",
  "names":[
    {"lang":"de","name":"Erdbeere"}, 
    {"lang":"en","name":"Strawberry"}
  ]
}
{
  "id":"983aaf86-abe4-44af-9896-d8f2d2c5f82c",
  "names":[
    {"lang":"de","name":"Gurke"},
    {"lang":"en","name":"Cucumber"}
  ]
}

Well, whatever this is, it is not JSON! It might look like it, but it isn’t. However, quite often such things are seen in the wild (in production). 
So, how can we improve this? 

# Fixing JSON encoding issues

If we think about it, this looks like a bug in *http4s*. We find an [issue](https://github.com/http4s/http4s/issues/2371) for it because the underlying problem is not as trivial as it initially sounds.

Maybe we can try to work around the issue. The *fs2* API offers concatenation of streams and the nifty `intersperse` function to insert elements between emitted ones. Let’s give it a try. 





Learn how to implement the routes and find a workaround for the http4s error.

Introduction

Impure Implementation

Pure Implementation

Testing Impure Services

Testing Pure Services

Benchmarks

Documentation

Epilogue

JSON Trouble

Broken JSON