Project Middleware

Kotlin Ktor Server Ktor Client MongoDB Docker Fly.io GitHub Actions

Project Middleware is a backend API transformation service. You point it at any public API and define mapping rules (rename, nest, concatenate, exclude empty fields) — the service returns your custom shape. A /preview endpoint lets you test rules before persisting them as permanent mapped routes.

Architecture

The project is structured as a clean, multi-module Ktor server:

middleware/domain – use cases and repository interfaces
middleware/data – repository implementations and data models
middleware/mapper – field mapping engine
impl/ktor-server – HTTP routing and request handling
impl/ktor-client – outbound HTTP client
impl/mongo-database – MongoDB driver integration
common/shared & common/data – shared models and utilities
build-logic/ – custom convention plugins keeping build files lean

CI/CD

Three GitHub Actions workflows run on every PR:

Detekt – code style enforcement
JaCoCo – test coverage verification
Dokka – KDoc documentation generation on merge to main

Deployed on Fly.io (São Paulo region) via Docker.

Tech Stack

Layer	Technology
Language	Kotlin 1.9
Framework	Ktor Server 2.3
HTTP Client	Ktor Client
Database	MongoDB (kotlinx coroutine driver)
Serialization	kotlinx-serialization, Gson
Build	Gradle 7.5+, Shadow JAR
Quality	Detekt, JaCoCo, Dokka
Runtime	Docker (OpenJDK 17 Alpine)
Hosting	Fly.io