@httpland/nel-middleware/esm/middleware.js

HTTP network error logging(NEL) middleware

// Copyright 2023-latest the httpland authors. All rights reserved. MIT license.
// This module is browser compatible.
import { stringifyJfv, withHeader } from "./deps.js";
import { assertValidNELPolicy } from "./utils.js";
import { Header } from "./constants.js";
/** Create `NEL` header field middleware.
 *
 * @example
 * ```ts
 * import {
 *   type Handler,
 *   nel,
 * } from "https://deno.land/x/nel_middleware@$VERSION/mod.ts";
 * import { assert } from "https://deno.land/std/testing/asserts.ts";
 *
 * declare const request: Request;
 * declare const handler: Handler;
 *
 * const middleware = nel({ report_to: "default", max_age: 86400 });
 * const response = await middleware(request, handler);
 *
 * assert(response.headers.has("nel"));
 * ```
 *
 * @throws {Error} If the endpoints include invalid member.
 */
export function nel(policy) {
    assertValidNELPolicy(policy);
    const fieldValue = stringifyJfv([policy]);
    return async (request, next) => {
        const response = await next(request);
        if (response.headers.has(Header.NEL))
            return response;
        return withHeader(response, Header.NEL, fieldValue);
    };
}