http4k-playground

📚 Learning and exploring http4.

The Functional toolkit for Kotlin HTTP applications

--https://www.http4k.org

Overview

http4k offers an ergonomic routing API for HTTP-based applications. This repository is me exploring it.

Instructions

Follow these instructions to build and run the demo program.

1. Pre-requisite: Java 21
2. Build the program distribution:

   • ./gradlew installDist

3. Start the server:

   • ./build/install/http4k-playground/bin/http4k-playground

4. Make a sample request:

   • curl http://localhost:8080

   • It should look like this:

     $ curl http://localhost:8080
     Hello from an http4k program!
     
     This server is powered by Apache HttpComponents. You made a request from an HTTP client with a user agent value of: curl/8.6.0
     

5. Try these other requests and see what you get:

   • curl http://localhost:8080/message/1

   • This will return a 404 response because there are no messages in the system. Let's create some messages.

   • curl -X POST -d 'Hello, world!' http://localhost:8080/messages
     curl -X POST -d 'Hello, world, again!' http://localhost:8080/messages
     curl -X POST -d 'Hello, world, one more time!' http://localhost:8080/messages

   • curl http://localhost:8080/messages

   • This will list all the messages. Now, let's limit the messages to just the first two.

   • curl http://localhost:8080/messages?limit=2

   • Now, let's just review the second message alone.

   • curl http://localhost:8080/message/2

6. Stop the server
   • Issue a SIGINT signal using the Ctrl + C keyboard shortcut from the same shell you started the program.
   • Altogether, it should look like this from start to stop:

     $ ./build/install/http4k-playground/bin/http4k-playground
     18:35:37 INFO main - Starting the server...
     18:35:37 INFO main - The server has started. Send an HTTP request to it!
     ^C18:36:08 INFO main - Shutting down the server...
     18:36:08 INFO main - The server is stopped. Goodbye.
     

Wish List

General clean-ups, TODOs and things I wish to implement for this project:

• DONE Do something with path variables, query parameters and content negotiation. These use-cases are why we want routing.
• SKIP (no. now we're in the business of control flow via runtime exceptions. This is no longer "functional". If I write my own handler code then I still get strong types, plus we get intentional error messaging) Look at the "lens" feature

Reference

• htt4pk website
• htt4pk GitHub repo
• GitHub issue #77 in the http4k repo
  • The conversation in this thread, although 5 years old, is still relevant. The http4k authors did not build the project for Java programs. As such, although you should be able to technically use http4k from a Java program, it might not be a pleasant experience. I have authored this playground repo in Kotlin for this reason.