zed-industries/zed · error

failed to set header {name}: {error:?}

Error message

failed to set header {name}: {error:?}

What it means

Guard in the wasm fetch header loop: the JS Headers.set() call rejected a header pair — {name} with {error:?}. Usually a forbidden header name the browser controls (Host, Content-Length, User-Agent, etc.) or an invalid header syntax.

Source

Thrown at crates/gpui_web/src/http_client.rs:145

    }

    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);

    // `Headers` is a JS iterable yielding `[name, value]` pairs.
    // `js_sys::Array::from` calls `Array.from()` which accepts any iterable.
    let header_pairs = js_sys::Array::from(&web_response.headers());

View on GitHub (pinned to f4178619ac)

Solutions

1. Filter browser-forbidden headers before calling set(); let fetch add its own
2. Validate header names/values with the Headers spec rules before setting
3. Move headers that browsers forbid into query params or a proxy when they must reach the server

When it happens

Trigger: Thrown at crates/gpui_web/src/http_client.rs:145 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/25889b77079af273. Report an issue: GitHub.