maintenance-mode.ts

const RETRY_DELAY_KEY = Symbol('retryDelay')

export const onError = axios => async (error) => {
	const { config, response, request } = error
	const responseURL = request?.responseURL
	const status = response?.status
	const headers = response?.headers

	/**
	 * Retry requests if they failed due to maintenance mode
	 *
	 * The delay is exponential. It starts at 2s and then doubles
	 * until a final retry after 32s. This results in roughly 1m of
	 * retries until we give up and throw the axios error towards
	 * the caller.
	 */
	if (status === 503
		&& headers['x-nextcloud-maintenance-mode'] === '1'
		&& config.retryIfMaintenanceMode
		&& (!config[RETRY_DELAY_KEY] || config[RETRY_DELAY_KEY] <= 32)) {
		const retryDelay = (config[RETRY_DELAY_KEY] ?? 1) * 2
		console.warn(`Request to ${responseURL} failed because of maintenance mode. Retrying in ${retryDelay}s`)
		await new Promise((resolve, _) => {
			setTimeout(resolve, retryDelay*1000)
		})

		return axios({
			...config,
			[RETRY_DELAY_KEY]: retryDelay,
		})
	}

	return Promise.reject(error)
}