Rust Handler Template

Verified status as of March 28, 2026. Runtime note: FastFN auto-installs function-local dependencies from requirements.txt / package.json; host runtimes are required in fastfn dev --native, while fastfn dev depends on a running Docker daemon. Rust runtime is implemented. Use this template for handler.rs.

rust-handler.rs

use serde_json::{json, Value};

pub fn handler(event: Value) -> Value {
    let name = event
        .get("query")
        .and_then(|q| q.get("name"))
        .and_then(|n| n.as_str())
        .unwrap_or("world");

    json!({
        "status": 200,
        "headers": { "Content-Type": "application/json" },
        "body": json!({ "runtime": "rust", "hello": name }).to_string()
    })
}

Contract

Defines expected request/response shape, configuration fields, and behavioral guarantees.

End-to-End Example

Use the examples in this page as canonical templates for implementation and testing.

Edge Cases

• Missing configuration fallbacks
• Route conflicts and precedence
• Runtime-specific nuances

See also

• Function Specification
• HTTP API Reference
• Run and Test Checklist

Last reviewed: March 28, 2026 · Docs on fastfn.dev