Certain features, such as HTTP/2, HTTPS, or compression might not be needed. When Kvarn is deployed to an IOT device controlled from within the network, these features aren’t needed. Disabling them cuts down on compilation time, memory requirements, and space requirements.

To view the dependencies used by each feature, see the Cargo.toml file.

These can be enabled in your Cargo.toml:

[dependencies]
kvarn = { version = "0.5", default-features = false, features = ["base", "https", "http2", "all-compression"] }

See the official Cargo guide on the matter.

Which Cargo features are required for certain items are also shown in the docs (e.g. the Host::new function).

Please always enable base (see below for more details).

• https: Enables HTTPS, the secure HTTP protocol. This is strongly recommended if you’re doing anything that’s not resource constrained and local.
• http2: Enables HTTP/2. This is strongly recommended as it’s considerably faster and less resource intensive than HTTP/1.1, which is always supported. This also reduces latency due to implementation details.
• br: Brotli compression
• gzip: Gzip compression
• graceful-shutdown: Enables graceful shutdown and handover. This means you can upgrade the Kvarn server without ANY downtime - using UNIX socket magic we bind the new server on the same sockets, then tell the old instance to shut down. All pending and current requests are waited for.
• auto-hostname: Populates the host name and alternative names automatically. This uses the info stored in the certificate.
• nonce: enables usage of nonce on inline <script> and <style> elements.
• websocket: enables the websocket module in Kvarn which allows easy and fast WebSockets from you web application.
• async-networking: use Tokio’s async networking primitives instead of the blocking std::net variants. Recommended for every application that can enable it. See embedded for more details.

There are additionally several feature sets:

• full: enables all the features above.
• base: enables async-networking, a feature considered critical for all platforms except embedded (e.g. ESP32-IDF)
• all-http: enables all HTTP standards and versions available - https & http2
• all-compression: enables all compression features - br & gzip

Embedded

Some embedded platforms have std support (e.g. ESP32-IDF) but don’t support mio. Disabling the feature async-networking causes Kvarn to block on every request, but removes the dependency on mio. It’s very useful for IOT devices which don’t need large throughput nor sub-ms responsiveness (which the embedded controllers doesn’t have computing power to achieve anyway).