urllib/src/HttpAgent.ts

Help in opening URLs (mostly HTTP) in a complex world — basic and digest authentication, redirections, cookies and more. Base undici fetch API.

import dns from 'dns';
import { LookupFunction, isIP } from 'net';
import {
  Agent,
} from 'undici';
import { DispatchHandlers } from 'undici/types/dispatcher';
import { BuildOptions } from 'undici/types/connector';

export type CheckAddressFunction = (ip: string, family: number | string) => boolean;

export type HttpAgentOptions = {
  lookup?: LookupFunction;
  checkAddress?: CheckAddressFunction;
  connect?: BuildOptions,
};

class IllegalAddressError extends Error {
  hostname: string;
  ip: string;
  family: number;

  constructor(hostname: string, ip: string, family: number) {
    const message = 'illegal address';
    super(message);
    this.name = this.constructor.name;
    this.hostname = hostname;
    this.ip = ip;
    this.family = family;
    Error.captureStackTrace(this, this.constructor);
  }
}

export class HttpAgent extends Agent {
  #checkAddress?: CheckAddressFunction;

  constructor(options: HttpAgentOptions) {
    /* eslint node/prefer-promises/dns: off*/
    const _lookup = options.lookup ?? dns.lookup;
    const lookup: LookupFunction = (hostname, dnsOptions, callback) => {
      _lookup(hostname, dnsOptions, (err, address, family) => {
        if (err) return callback(err, address, family);
        if (options.checkAddress && !options.checkAddress(address, family)) {
          err = new IllegalAddressError(hostname, address, family);
        }
        callback(err, address, family);
      });
    };
    super({
      connect: { ...options.connect, lookup },
    });
    this.#checkAddress = options.checkAddress;
  }

  dispatch(options: Agent.DispatchOptions, handler: DispatchHandlers): boolean {
    if (this.#checkAddress && options.origin) {
      const originUrl = typeof options.origin === 'string' ? new URL(options.origin) : options.origin;
      let hostname = originUrl.hostname;
      // [2001:db8:2de::e13] => 2001:db8:2de::e13
      if (hostname.startsWith('[') && hostname.endsWith(']')) {
        hostname = hostname.substring(1, hostname.length - 1);
      }
      const family = isIP(hostname);
      if (family === 4 || family === 6) {
        // if request hostname is ip, custom lookup won't excute
        if (!this.#checkAddress(hostname, family)) {
          throw new IllegalAddressError(hostname, hostname, family);
        }
      }
    }
    return super.dispatch(options, handler);
  }
}