a-b-street/abstreet · error · anyhow::Error

HTTP

Error message

HTTP {}: {}

What it means

FileLoader fetches a remote file over HTTP in the browser and sends the downloaded bytes over a channel. When the fetch response's status is not OK (resp.ok() false), it formats 'HTTP <status>: <status_text>' and sends that as the error. It surfaces any non-2xx HTTP response from the server hosting the file.

Solutions

1. Verify the URL is correct and the file is reachable (curl -I the URL)
2. Check server logs for the status code's cause
3. Fix CORS headers (Access-Control-Allow-Origin) if the browser is blocking the response
4. Serve the file from the correct location or redeploy the asset

Example fix

// before
let url = "data/scenarios/map.bin";
// after: full, verified URL
let url = "https://example.com/abst/data/scenarios/map.bin";

// before loading, verify reachability and permissions
let resp = reqwest::blocking::head(url).send()?;
if !resp.status().is_success() {
    bail!("asset {} not available: {}", url, resp.status());
}

function is_ok_response(resp: Response): boolean { return resp.ok; }

match file_loader.response.recv() {
    Ok(Ok(bytes)) => use(bytes),
    Ok(Err(e)) => show_error(format!("Could not load file: {} — check the URL and server", e)),
    Err(_) => show_error("loader channel closed"),
}

When it happens

Trigger: Calling the load/new_state API with a URL that the server answers with a non-2xx status: 404 for a missing file, 403 for permissions, 500 for a server error, CORS-related 4xx, or a redirect that ends in an error page.

Common situations: Wrong or misspelled URL/path for the data file, file not deployed to the web server, missing CORS headers causing the browser to reject the response, server misconfiguration.

Understand the failure class

Background: "API error: {status}" and "HTTP 401/403/404/429/5xx" errors: non-2xx HTTP responses explained — this error's family across 27 libraries.

Related errors

• HTTP error
• {:?}
• Server error
• Failed to download stuff
• errors

AI-assisted analysis of a-b-street/abstreet@0964f29315 (2026-09-13). Data as JSON: /api/errors/54da5c611554005b. Report an issue: GitHub.

Appendix: source

Thrown at widgetry/src/tools/load.rs:191

                            let raw_body = resp.body().unwrap_throw();
                            let body = ReadableStream::from_raw(raw_body.dyn_into().unwrap_throw());
                            let mut stream = body.into_stream();
                            let mut buffer = Vec::new();
                            while let Some(Ok(chunk)) = stream.next().await {
                                let array = js_sys::Uint8Array::new(&chunk);
                                if let Err(err) =
                                    tx_read_bytes.try_send(array.byte_length() as usize)
                                {
                                    warn!("Couldn't send update on bytes: {}", err);
                                }
                                // TODO Can we avoid this clone?
                                buffer.extend(array.to_vec());
                            }
                            tx.send(Ok(buffer)).unwrap();
                        } else {
                            let status = resp.status();
                            let err = resp.status_text();
                            tx.send(Err(anyhow!("HTTP {}: {}", status, err))).unwrap();
                        }
                    }
                    Err(err) => {
                        tx.send(Err(anyhow!("{:?}", err))).unwrap();
                    }
                }
            });

            Box::new(FileLoader {
                response: rx,
                on_load: Some(on_load),
                panel: ctx.make_loading_screen(Text::from(format!("Loading {}...", url))),
                started: Instant::now(),
                url,
                total_bytes: None,
                read_bytes: 0,
                got_total_bytes,
                got_read_bytes,

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