pyscript/core/src/fetch.js

import { FetchError, ErrorCode } from "./exceptions.js";

/**
 * @param {Response} response
 * @returns
 */
export const getText = (response) => response.text();

/**
 * This is a fetch wrapper that handles any non 200 responses and throws a
 * FetchError with the right ErrorCode. This is useful because our FetchError
 * will automatically create an alert banner.
 *
 * @param {string} url - URL to fetch
 * @param {Request} [options] - options to pass to fetch
 * @returns {Promise<Response>}
 */
export async function robustFetch(url, options) {
    let response;

    // Note: We need to wrap fetch into a try/catch block because fetch
    // throws a TypeError if the URL is invalid such as http://blah.blah
    try {
        response = await fetch(url, options);
    } catch (err) {
        const error = err;
        let errMsg;
        if (url.startsWith("http")) {
            errMsg =
                `Fetching from URL ${url} failed with error ` +
                `'${error.message}'. Are your filename and path correct?`;
        } else {
            errMsg = `Polyscript: Access to local files
        (using [[fetch]] configurations in &lt;py-config&gt;)
        is not available when directly opening a HTML file;
        you must use a webserver to serve the additional files.
        See <a style="text-decoration: underline;" href="https://github.com/pyscript/pyscript/issues/257#issuecomment-1119595062">this reference</a>
        on starting a simple webserver with Python.
            `;
        }
        throw new FetchError(ErrorCode.FETCH_ERROR, errMsg);
    }

    // Note that response.ok is true for 200-299 responses
    if (!response.ok) {
        const errorMsg = `Fetching from URL ${url} failed with error ${response.status} (${response.statusText}). Are your filename and path correct?`;
        switch (response.status) {
            case 404:
                throw new FetchError(ErrorCode.FETCH_NOT_FOUND_ERROR, errorMsg);
            case 401:
                throw new FetchError(
                    ErrorCode.FETCH_UNAUTHORIZED_ERROR,
                    errorMsg,
                );
            case 403:
                throw new FetchError(ErrorCode.FETCH_FORBIDDEN_ERROR, errorMsg);
            case 500:
                throw new FetchError(ErrorCode.FETCH_SERVER_ERROR, errorMsg);
            case 503:
                throw new FetchError(
                    ErrorCode.FETCH_UNAVAILABLE_ERROR,
                    errorMsg,
                );
            default:
                throw new FetchError(ErrorCode.FETCH_ERROR, errorMsg);
        }
    }
    return response;
}