Function http_call_with_retry

tests/common/mod.rs:533–549

Issues an idempotent HTTP request, retrying transient connection-level errors (the server racing its own readiness under parallel load) with a short bounded backoff. `send` performs one attempt; a `ureq::Error` that passes [`is_transient_connection_error`] is retried, any other error (or exhausted retries) panics with `label`.

(
    label: &str,
    send: impl Fn() -> Result<ureq::http::Response<ureq::Body>, ureq::Error>,
)

/// passes [`is_transient_connection_error`] is retried, any other error (or
/// exhausted retries) panics with `label`.
pub fn http_call_with_retry(
    label: &str,
    send: impl Fn() -> Result<ureq::http::Response<ureq::Body>, ureq::Error>,
) -> ureq::http::Response<ureq::Body> {
    let mut last_err: Option<ureq::Error> = None;
    for attempt in 0..12 {
        match send() {
            Ok(response) => return response,
            Err(err) if is_transient_connection_error(&err) => {
                last_err = Some(err);
                std::thread::sleep(Duration::from_millis(25 * (attempt + 1)));
            }
            Err(err) => panic!("{label} failed: {err}"),
        }
    }
    panic!("{label} failed after retries: {last_err:?}");
}

pub fn get_json(agent: &ureq::Agent, url: &str) -> (u16, Value) {
    let response = http_call_with_retry(&format!("GET {url}"), || agent.get(url).call());