Function build_request

modules/llrt_fetch/src/fetch.rs:488–569

(
    ctx: &Ctx<'js>,
    method: &hyper::Method,
    uri: &Uri,
    headers: Option<&Headers>,
    body: Option<&RequestBody<'js>>,
    prev_status: &u16,
    initial_uri: &Uri,
)

        *req = std::mem::take(req).header(ACCEPT_ENCODING, "zstd, br, gzip, deflate");
    }
    if !detected_headers.contains(ACCEPT_LANGUAGE.as_str()) {
        *req = std::mem::take(req).header(ACCEPT_LANGUAGE, "*");
    }
    if !detected_headers.contains(ACCEPT.as_str()) {
        *req = std::mem::take(req).header(ACCEPT, "*/*");
    }
}

fn parse_data_url<'js>(ctx: &Ctx<'js>, data_url: &str, method: &Method) -> Result<Response<'js>> {
    let (mime_type, data) = data_url
        .split_once(',')
        .ok_or_else(|| Exception::throw_type(ctx, "Invalid data URL format"))?;

    let mut is_base64 = false;
    let mut content_type = String::with_capacity(10);
    for (i, part) in mime_type.split(';').enumerate() {
        let part = part.trim();
        if i == 1 || i == 2 {
            if part == "base64" {
                is_base64 = true;
                break;
            }
            content_type.push(';');
        }
        content_type.push_str(part)
    }

    let content_type = if content_type.starts_with(';') {
        ["text/plain", &content_type].concat()
    } else if content_type.is_empty() {
        "text/plain;charset=US-ASCII".to_string()
    } else {
        content_type
    };

    let body = if method == Method::HEAD {
        vec![]
    } else if is_base64 {
        bytes_from_b64(data.as_bytes()).or_throw(ctx)?
    } else {
        let data = percent_decode_str(data).decode_utf8().or_throw(ctx)?;
        data.as_bytes().into()
    };

    let blob = Blob::from_bytes(ctx, body, Some(content_type.clone()))?.into_js(ctx)?;

    let headers = Object::new(ctx.clone())?;
    headers.set(CONTENT_TYPE.as_str(), content_type)?;

    let options = Object::new(ctx.clone())?;
    options.set("url", data_url)?;
    options.set("headers", headers)?;
    // data: URL spec requires "OK" reason phrase.
    options.set("statusText", "OK")?;

    Response::new(ctx.clone(), Opt(Some(blob)), Opt(Some(options)))
}