JetBrains has announced the release of Ktor 3.1.0, a minor update to its Kotlin-based framework for building asynchronous server-side and client-side applications. The new version introduces a command-line tool for creating projects, enhances server-sent events with serialization, reconnection, and heartbeat features, and brings several other improvements to the table.

The Ktor CLI tool is a significant addition to the framework, offering an easy-to-use interface for generating project templates with preferred features. This reduces boilerplate code and setup times, making it easier for developers to get started with Ktor. By running the `ktor new` command, users can enter an interactive mode where they can choose plugins and configure their project using the same options available in the Ktor Project Generator at start.ktor.io.

Server-sent events (SSE) have also received a significant boost in Ktor 3.1.0. The update brings built-in serialization for both client and server, enabling them to handle SSE streams with automatic serialization and deserialization. Additionally, SSE support now includes the ability to specify a heartbeat event to keep a session active, as well as a reconnection feature that can be enabled by setting the `maxReconnectionAttempts` property to a value greater than zero. If the client's connection to the server is lost, it will wait for a specified `reconnectionTime` and then make `maxReconnectionAttempts` to reestablish the connection.

Beyond the CLI tool and SSE enhancements, Ktor 3.1.0 brings several other notable improvements. The CIO engine has been expanded to support `wasm-js` and `js` targets for both server and client-side development, making it the first server-side JavaScript engine for Ktor. The `HttpClient` has also been improved to support multipart requests, making it easier to upload files and handle complex request bodies across different engines.

Other updates in Ktor 3.1.0 include the addition of a "Report a Problem" link for every API symbol, available both in the IDE's help section and on api.ktor.io. This aims to improve the API and documentation process. The Compression plugin can now be disabled for specific requests, and Ktor supports Unix domain sockets on native targets, enabling inter-process communication without relying on TCP. The Curl client engine is now statically linked, eliminating the need to install third-party dependencies, and Arm architecture support has been added, including for macOS.

In a move to further engage with the community, JetBrains has introduced Ktor Library Improvement Proposals (KLIP), an initiative that allows developers to propose, discuss, and collaborate on new features and improvements for Ktor. The KLIP repository is open for contributions, and everyone can participate in discussions or submit new proposals. Approved KLIPs will be merged into the repository and implemented in the framework by the JetBrains team.

Ktor 3.1.0 follows the October 2024 release of Ktor 3.0, which introduced support for SSE, brought WebAssembly support to the Ktor client, and switched to the kotlinx.io library. With this latest update, JetBrains continues to demonstrate its commitment to enhancing the Ktor framework and providing developers with a robust and feature-rich toolset for building asynchronous applications.