[3/?] Add ability to run code examples in the playground: Fetch tutorial snippet from URL by file name

[shaedrich]

See ponylang/pony-tutorial#340

Warning

Will only work, after #222 has been merged.

Example: https://playground.ponylang.io/?snippet=hello-world-main.pony

If we add .layer(CorsLayer::permissive()) here, we could even call the API from the tutorial and display the result below the code block (apparently, this had already been done in 2014, when the API was still written in Python: 02d0a98):

pony-playground/src/api.rs

Line 31 in 59b1ffd

.route("/evaluate.json", post(evaluate))

or, if we want to be a little more restrictive, it could look like this:

use http::HeaderValue;
use tower_http::cors::CorsLayer;

let layer = CorsLayer::new().allow_origin(
    "https://tutorial.ponylang.io".parse::<HeaderValue>().unwrap(),
);
let router = Router::new()
        .route(
            "/",
            get(|| async { static_html(include_bytes!("../static/web.html")) }),
        )
        .route("/evaluate.json", post(evaluate))
        .layer(layer)
        // ...

[mfelsche]

This looks good, just the little typo.

Always happy to accept PRs to allow calls from tutorial.ponylang.io. I am a bit hesitant to allow CORS requests from everywhere, unless we have proper monitoring and alerting and the ability to rate-limit/block clients.

[jemc]

If you're ready, feel free to convert to "ready for review" status and we can merge it. Thanks!

[jemc]

Looks like this has conflicts from merging #222 that need to be resolved. It wasn't straightforward enough for me to feel good about resolving it in the web editor without any testing.

[shaedrich]

@jemc Conflicts resolved

[jemc]

(Also it looks like the branch still has conflicts ❓ )

[shaedrich]

@jemc What gives you that impression? I don't see any pending conflicts

[jemc]

Hmmm... I guess it doesn't have conflicts. Maybe I misunderstood something I saw in the GitHub UI? But I'm not seeing it now.