# esi
A streaming Edge Side Includes parser and executor designed for Fastly Compute@Edge.
The implementation is currently a subset of the [ESI Language Specification 1.0](https://www.w3.org/TR/esi-lang/), supporting the following tags:
- `<esi:include>` (+ `alt`, `onerror="continue"`)
- `<esi:comment>`
- `<esi:remove>`
Other tags will be ignored.
## Example Usage
```rust,no_run
use fastly::{http::StatusCode, mime, Error, Request, Response};
fn main() {
if let Err(err) = handle_request(Request::from_client()) {
println!("returning error response");
Response::from_status(StatusCode::INTERNAL_SERVER_ERROR)
.with_body(err.to_string())
.send_to_client();
}
}
fn handle_request(req: Request) -> Result<(), Error> {
// Fetch ESI document from backend.
let mut beresp = req.clone_without_body().send("origin_0")?;
// If the response is HTML, we can parse it for ESI tags.
if beresp
.get_content_type()
.map(|c| c.subtype() == mime::HTML)
.unwrap_or(false)
{
let processor = esi::Processor::new(
// The original client request.
Some(req),
// Optionally provide a template for the client response.
Some(Response::from_status(StatusCode::OK).with_content_type(mime::TEXT_HTML)),
// Use the default ESI configuration.
esi::Configuration::default()
);
processor.process_response(
// The ESI source document. Note that the body will be consumed.
&mut beresp,
// Provide logic for sending fragment requests, otherwise the hostname
// of the request URL will be used as the backend name.
Some(&|req| {
println!("Sending request {} {}", req.get_method(), req.get_path());
Ok(Some(req.with_ttl(120).send_async("mock-s3")?))
}),
// Optionally provide a method to process fragment responses before they
// are streamed to the client.
Some(&|req, resp| {
println!(
"Received response for {} {}",
req.get_method(),
req.get_path()
);
Ok(resp)
}),
)?;
Ok(())
} else {
// Otherwise, we can just return the response.
beresp.send_to_client();
Ok(())
}
}
```
See a full example app in the [`esi_example_app`](./esi_example_app/src/main.rs) subdirectory, or read the hosted documentation at [docs.rs/esi](https://docs.rs/esi).
## License
The source and documentation for this project are released under the [MIT License](LICENSE).