Serialize browser fetch Request

serializeRequest.js

// @ts-check
"use strict";

/** @param {*} value @returns {value is string} */
const isString = value => typeof value === "string";
/** @param {*} value @returns {value is RegExp} */
const isRegExp = value => value instanceof RegExp;

class Santinizer {
    #redactStr;
    #redactRe;

    /** @param {{ redact: Array<string | RegExp> }} _ */
    constructor({ redact }) {
        this.#redactStr = new Set(redact.filter(isString));
        this.#redactRe = redact.filter(isRegExp);
    }

    /**
     * @template {URLSearchParams | Headers | object} T
     * @param {T} target
     * @returns {Promise<T>}
     */
    async redact(target) {
        if (target instanceof URLSearchParams) {
            target.forEach((value, key, dict) => {
                if (this.#redactStr.has(key) || this.#redactRe.some(re => re.test(key))) {
                    dict.set(key, "--REDACTED--");
                }
            });
            return target;
        }
        if (target instanceof Headers) {
            target.forEach((value, key, dict) => {
                if (this.#redactStr.has(key) || this.#redactRe.some(re => re.test(key))) {
                    dict.set(key, "--REDACTED--");
                }
            });
            return target;
        }
        return this.#redactObject(target);
    }

    #redactObject(target) {
        if (target && typeof target === "object") {
            Object.keys(target).forEach(key => {
                if (this.#redactStr.has(key) || this.#redactRe.some(re => re.test(key))) {
                    target[key] = "--REDACTED--";
                } else {
                    this.#redactObject(target[key]);
                }
            });
        }
        return target;
    }
}

/** @param {Request} request @param {{ redact?: Array<string | RegExp> }} _ @returns {Promise<object>} */
async function serializeRequest(request, { redact = [] } = {}) {
    const santinizer = new Santinizer({ redact });

    const url = new URL(request.url);
    santinizer.redact(url.searchParams);

    const headers = new Headers(request.headers);
    santinizer.redact(headers);

    let body = "--UNKNOWN--";
    if (request.headers.get("content-type") === "application/json") {
        body = await request.clone().json();
        santinizer.redact(body);
    }

    return {
        method: request.method,
        url: url.toString(),
        headers: Array.from(headers.entries()),
        body,
    };
}

module.exports = {
    serializeRequest,
};