Function esp_idf_svc::sys::esp_http_client_fetch_headers

pub unsafe extern "C" fn esp_http_client_fetch_headers(
    client: *mut esp_http_client,
) -> i64

@brief This function need to call after esp_http_client_open, it will read from http stream, process all receive headers

@param[in] client The esp_http_client handle

@return - (0) if stream doesn’t contain content-length header, or chunked encoding (checked by esp_http_client_is_chunked response) - (-1: ESP_FAIL) if any errors - (-ESP_ERR_HTTP_EAGAIN = -0x7007) if call is timed-out before any data was ready - Download data length defined by content-length header