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FastEdge CDN applications run inside a CDN resource’s request pipeline and can inspect or modify requests and responses as they pass through the CDN. Complete the Rust (CDN / Proxy-Wasm) setup before proceeding. Once deployed, attach the application to a CDN resource to process live traffic — that step is in CDN applications.

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Write a handler

A CDN application consists of two parts: a root context that registers the filter factory, and a filter that implements the callbacks. Replace src/lib.rs with: 
use proxy_wasm::traits::*;
use proxy_wasm::types::*;

proxy_wasm::main! {{
    proxy_wasm::set_log_level(LogLevel::Info);
    proxy_wasm::set_root_context(|_| -> Box<dyn RootContext> {
        Box::new(Root)
    });
}}

struct Root;
impl Context for Root {}
impl RootContext for Root {
    fn create_http_context(&self, _: u32) -> Option<Box<dyn HttpContext>> {
        Some(Box::new(Filter))
    }
    fn get_type(&self) -> Option<ContextType> {
        Some(ContextType::HttpContext)
    }
}

struct Filter;
impl Context for Filter {}
impl HttpContext for Filter {
    fn on_http_request_headers(&mut self, _: usize, _: bool) -> Action {
        self.add_http_request_header("x-fastedge", "cdn");
        Action::Continue
    }
}
Root registers a new Filter for each incoming request via create_http_context. on_http_request_headers runs when the CDN receives request headers — this example adds a custom x-fastedge header and returns Action::Continue to pass the request downstream unchanged. To stop the request instead, return Action::Pause.

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Build

Compile the handler to a WebAssembly binary. The first build downloads dependencies and takes one to two minutes. 
cargo build --release --target wasm32-wasip1
The binary is at ./target/wasm32-wasip1/release/my_cdn_app.wasm. This file is uploaded to FastEdge in the next step.

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Deploy