Ktor

Ktor is an asynchronous framework for building connected applications in Kotlin. Developed by JetBrains, it supports server and client development and is designed for non-blocking I/O using Kotlin coroutines. It targets JVM and multiplatform projects, including Kotlin/JS and Kotlin/Native, enabling code sharing between client and server.

Core concepts in Ktor revolve around modular design and a lightweight programming model. Applications are composed from modules called features (plugins) that extend functionality. The routing DSL provides a type-safe way to define HTTP endpoints. A server engine runs the application, with common choices including Netty, CIO, Jetty, and Tomcat. The request handling pipeline is built by installing features and defining routes.

Server-side features include ContentNegotiation for formatting payloads (JSON, XML, and other formats via serializers such as kotlinx.serialization, Jackson, or Gson), Sessions, Authentication, CORS, Compression, Caching, and WebSockets. Ktor emphasizes a modular, extensible architecture and aims for clear, readable builder code.

Ktor also provides a multiplatform client library for HTTP requests. The Ktor client supports serialization, content negotiation, authentication, and WebSockets across Kotlin targets, enabling shared code between server and client in multiplatform projects.

License and history: Ktor is open source under the Apache 2.0 license and is maintained by JetBrains with community contributors. It debuted in the mid-2010s and has evolved into a versatile framework used for REST APIs, microservices, real-time applications, and other networked software written in Kotlin.