JetBrains has rolled out Ktor 3.1.0, the latest iteration of its Kotlin-based framework designed for both server-side and client-side asynchronous applications. This update introduces a command-line interface (CLI) to streamline project initialization and brings key enhancements to server-sent events (SSE), optimizing serialization, automatic reconnections, and heartbeat mechanisms.

Streamlined Project Setup with Ktor CLI

A significant addition in this release is the Ktor CLI tool, simplifying project creation by reducing the time spent on boilerplate configuration. By executing the ktor new command, developers can access an interactive setup mode that guides them through plugin selection and configuration, mirroring the experience available via the web-based Ktor Project Generator at start.ktor.io.

Enhancements to Server-Sent Events

With Ktor 3.1.0, SSE support has been refined to include built-in serialization on both the client and server sides. This means that SSE streams now benefit from automatic serialization and deserialization, making it easier to manage event-driven interactions. Additionally, developers can define heartbeat events to maintain active sessions and configure reconnection settings by adjusting the maxReconnectionAttempts property. If a connection drops, the client will attempt reconnection based on a predetermined wait time and retry limit.

Additional Improvements in Ktor 3.1.0

Beyond the CLI tool and SSE refinements, this update introduces several other enhancements:

• Expanded CIO Engine Support: The CIO engine now supports wasm-js and js targets for both server and client applications, positioning it as the first server-side JavaScript engine within Ktor.
• Multipart Request Handling: The HttpClient now offers improved support for multipart requests, facilitating file uploads and handling complex request bodies more efficiently across different engines.
• Documentation and API Enhancements: A new “Report a Problem” feature has been integrated into the IDE’s help section and the API documentation site (api.ktor.io), allowing developers to quickly provide feedback on API symbols.
• Compression Plugin Flexibility: Developers can now disable the Compression plugin for specific requests, offering greater control over performance tuning.
• Unix Domain Socket Support: Native targets now support Unix domain sockets, enabling inter-process communication without relying on TCP.
• Improved Curl Client Engine: The Curl client engine is now statically linked, removing the need for third-party dependencies. This update also extends support to Arm architecture, including macOS compatibility.

Community Collaboration via KLIP

JetBrains has also launched Ktor Library Improvement Proposals (KLIP), an initiative that invites the developer community to contribute ideas and participate in discussions about potential improvements. The KLIP repository is open for proposals, ensuring that community-approved features are integrated into future Ktor updates.

Looking Ahead

Ktor 3.1.0 builds upon the advancements introduced in Ktor 3.0, which debuted in October 2024. That version brought initial SSE support, WebAssembly capabilities for Ktor’s client, and a shift to the kotlinx.io library. With this latest update, JetBrains continues to refine Ktor, making it an even more powerful tool for building Kotlin-based web applications.