zed-industries/zed · error

non-ASCII header value for {name}

Error message

non-ASCII header value for {name}

What it means

Guard in the wasm fetch header loop: HeaderValue::to_str() failed for a header, meaning the value contains non-ASCII/invalid bytes that a JS Headers object cannot store. The message names the offending header; HTTP/2-style binary header values are not representable in browser fetch.

Source

Thrown at crates/gpui_web/src/http_client.rs:142

                init.set_redirect(web_sys::RequestRedirect::Follow);
            }
        }
    }

    if let Some(ref bytes) = body_bytes {
        let uint8array = js_sys::Uint8Array::from(bytes.as_slice());
        init.set_body(uint8array.as_ref());
    }

    let url = parts.uri.to_string();
    let request = web_sys::Request::new_with_str_and_init(&url, &init)
        .map_err(|error| anyhow!("failed to create fetch Request: {error:?}"))?;

    let request_headers = request.headers();
    for (name, value) in &parts.headers {
        let value_str = value
            .to_str()
            .map_err(|_| anyhow!("non-ASCII header value for {name}"))?;
        request_headers
            .set(name.as_str(), value_str)
            .map_err(|error| anyhow!("failed to set header {name}: {error:?}"))?;
    }

    let promise =
        global_fetch(&request).map_err(|error| anyhow!("fetch threw an error: {error:?}"))?;
    let response_value = wasm_bindgen_futures::JsFuture::from(promise)
        .await
        .map_err(|error| anyhow!("fetch failed: {error:?}"))?;

    let web_response: web_sys::Response = response_value
        .dyn_into()
        .map_err(|error| anyhow!("fetch result is not a Response: {error:?}"))?;

    let status = web_response.status();
    let mut builder = http_client::http::Response::builder().status(status);

View on GitHub (pinned to f4178619ac)

Solutions

1. Encode binary header values as ASCII (e.g. base64) before sending from wasm
2. Reject or strip non-ASCII headers at the API boundary with a clear error
3. For protocols needing binary headers (HTTP/2), use a proxy that accepts them server-side

When it happens

Trigger: Thrown at crates/gpui_web/src/http_client.rs:142 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of zed-industries/zed@f4178619ac (2026-08-20). Data as JSON: /api/errors/31f7f0b9fb8810d3. Report an issue: GitHub.