plugin.js

/*
 * Copyright (c) 2021 RethinkDNS and its authors.
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

import { services } from "./svc.js";
import * as bufutil from "../commons/bufutil.js";
import * as dnsutil from "../commons/dnsutil.js";
import * as envutil from "../commons/envutil.js";
import * as util from "../commons/util.js";

export default class RethinkPlugin {
  /**
   * @param {{request: Request}} event
   */
  constructor(event) {
    if (!services.ready) throw new Error("services not ready");
    /**
     * Parameters of RethinkPlugin which may be used by individual plugins.
     */
    this.parameter = new Map();

    const rxid = util.rxidFromHeader(event.request.headers) || util.xid();
    this.registerParameter("rxid", "[rx." + rxid + "]");

    // works on fly.io and cloudflare
    this.registerParameter("region", getRegion(event.request) || "");

    // caution: event isn't an event on nodejs, but event.request is a request
    this.registerParameter("request", event.request);
    // TODO: a more generic way for plugins to queue events on all platforms
    // dispatcher fn when called, fails with 'illegal invocation' if not
    // bound explicitly to 'event' (since it then executes in the context
    // of which-ever obj calls it): stackoverflow.com/a/9678166
    this.registerParameter("dispatcher", event.waitUntil.bind(event));

    this.log = log.withTags("RethinkPlugin");

    this.plugin = [];

    this.registerPlugin(
      "userOp",
      services.userOp,
      ["rxid", "request", "isDnsMsg"],
      this.userOpCallback,
      false
    );

    this.registerPlugin(
      "cacheOnlyResolver",
      services.dnsCacheHandler,
      ["rxid", "userBlocklistInfo", "requestDecodedDnsPacket", "isDnsMsg"],
      this.dnsCacheCallBack,
      false
    );

    this.registerPlugin(
      "commandControl",
      services.commandControl,
      ["rxid", "request", "isDnsMsg"],
      this.commandControlCallBack,
      false
    );

    this.registerPlugin(
      "dnsResolver",
      services.dnsResolver,
      [
        "rxid",
        "dispatcher",
        "request",
        // resolver-url overriden by user-op
        "userDnsResolverUrl",
        "userBlocklistInfo",
        "domainBlockstamp",
        "requestDecodedDnsPacket",
        "requestBodyBuffer",
      ],
      this.dnsResolverCallBack,
      false
    );
  }

  registerParameter(k, v) {
    this.parameter.set(k, v);
  }

  registerPlugin(
    pluginName,
    module,
    parameter,
    callBack,
    continueOnStopProcess
  ) {
    this.plugin.push({
      name: pluginName,
      module: module,
      param: parameter,
      callBack: callBack,
      continueOnStopProcess: continueOnStopProcess,
    });
  }

  async execute() {
    const io = this.io;
    const rxid = this.parameter.get("rxid");

    const t = this.log.startTime("exec-plugin-" + rxid);

    for (const p of this.plugin) {
      if (io.stopProcessing && !p.continueOnStopProcess) {
        continue;
      }

      this.log.lapTime(t, rxid, p.name, "send-io");

      const res = await p.module.RethinkModule(
        generateParam(this.parameter, p.param)
      );

      this.log.lapTime(t, rxid, p.name, "got-res");

      if (typeof p.callBack === "function") {
        await p.callBack.call(this, res, io);
      }

      this.log.lapTime(t, rxid, p.name, "post-callback");
    }
    this.log.endTime(t);
  }

  /**
   * params
   * @param {*} response
   * @param {*} io
   */
  async commandControlCallBack(response, io) {
    const rxid = this.parameter.get("rxid");
    const r = response.data;
    this.log.d(rxid, "command-control response");

    if (!util.emptyObj(r) && r.stopProcessing) {
      this.log.d(rxid, "command-control reply", r);
      io.hResponse(r.httpResponse);
    }
  }

  /**
   * Adds "userBlocklistInfo" and "dnsResolverUrl" to RethinkPlugin params
   * @param {*} response - Contains `data` which is `userBlocklistInfo`
   * @param {*} io
   */
  async userOpCallback(response, io) {
    const rxid = this.parameter.get("rxid");
    const r = response.data;
    this.log.d(rxid, "user-op response");

    if (response.isException) {
      this.log.w(rxid, "unexpected err userOp", r);
      this.loadException(rxid, response, io);
    } else if (!util.emptyObj(r)) {
      // r.userBlocklistInfo and r.dnsResolverUrl may be "null"
      const bi = r.userBlocklistInfo;
      const rr = r.dnsResolverUrl;
      this.log.d(rxid, "set user:blockInfo/resolver", bi, rr);
      this.registerParameter("userBlocklistInfo", bi);
      this.registerParameter("userDnsResolverUrl", rr);
    } else {
      this.log.i(rxid, "user-op is a no-op, possibly a command-control req");
    }
  }

  dnsCacheCallBack(response, io) {
    const rxid = this.parameter.get("rxid");
    const r = response.data;
    const deny = r.isBlocked;
    const isAns = dnsutil.isAnswer(r.dnsPacket);
    const noErr = dnsutil.rcodeNoError(r.dnsPacket);

    this.log.d(rxid, "crr: block?", deny, "ans?", isAns, "noerr", noErr);

    if (response.isException) {
      this.loadException(rxid, response, io);
    } else if (deny) {
      // TODO: create block packets/buffers in dnsBlocker.js
      io.dnsBlockResponse(r.flag);
    } else if (isAns) {
      this.registerParameter("responseBodyBuffer", r.dnsBuffer);
      this.registerParameter("responseDecodedDnsPacket", r.dnsPacket);
      io.dnsResponse(r.dnsBuffer, r.dnsPacket, r.flag);
    } else {
      this.registerParameter("domainBlockstamp", r.stamps);
      this.log.d(rxid, "resolve query; no response from cache-handler");
    }
  }

  /**
   * Adds "responseBodyBuffer" (arrayBuffer of dns response from upstream
   * resolver) to RethinkPlugin params
   * @param {*} response
   * @param {*} io
   */
  dnsResolverCallBack(response, io) {
    const rxid = this.parameter.get("rxid");
    const r = response.data;
    const deny = r.isBlocked;
    // dns packets may have no answers, but still be a valid response
    // for example, servfail do not contain any answers, whereas
    // nxdomain has an authority-section (but no answers).
    const isAns = dnsutil.isAnswer(r.dnsPacket);
    const noErr = dnsutil.rcodeNoError(r.dnsPacket);
    this.log.d(rxid, "rr: block?", deny, "ans?", isAns, "noerr?", noErr);

    if (deny) {
      // TODO: create block packets/buffers in dnsBlocker.js?
      io.dnsBlockResponse(r.flag);
    } else if (response.isException || !isAns) {
      // if not blocked, but then, no-ans or is-exception, then:
      this.loadException(rxid, response, io);
    } else {
      this.registerParameter("responseBodyBuffer", r.dnsBuffer);
      this.registerParameter("responseDecodedDnsPacket", r.dnsPacket);
      io.dnsResponse(r.dnsBuffer, r.dnsPacket, r.flag);
    }
  }

  loadException(rxid, response, io) {
    this.log.e(rxid, "exception", JSON.stringify(response));
    io.dnsExceptionResponse(response);
  }

  async initIoState(io) {
    this.io = io;

    const request = this.parameter.get("request");
    const rxid = this.parameter.get("rxid");
    const region = this.parameter.get("region");
    const isDnsMsg = util.isDnsMsg(request);
    const isGwReq = util.isGatewayRequest(request);
    let question = null;

    io.id(rxid, region);

    this.registerParameter("isDnsMsg", isDnsMsg);
    // nothing to do if the current request isn't a dns question
    if (!isDnsMsg) {
      // throw away any request that is not a dns-msg since cc.js
      // processes non-dns msgs only via GET, while rest of the
      // plugins process only dns-msgs via GET and POST.
      if (!util.isGetRequest(request)) {
        this.log.i(rxid, "not a dns-msg, not a GET req either", request);
        io.hResponse(util.respond405());
        return;
      }
    }

    // else: treat doh as if it was a dns-msg iff "dns" query-string is set
    question = await extractDnsQuestion(request);

    // not a dns request
    if (bufutil.emptyBuf(question)) return;

    if (isGwReq) io.gatewayAnswersOnly(envutil.gwip4(), envutil.gwip6());

    try {
      const questionPacket = dnsutil.decode(question);
      this.registerParameter("isDnsMsg", true);
      this.log.d(rxid, "cur-ques", JSON.stringify(questionPacket.questions));
      io.decodedDnsPacket = questionPacket;

      this.registerParameter("requestDecodedDnsPacket", questionPacket);
      this.registerParameter("requestBodyBuffer", question);
    } catch (e) {
      // err if question is not a valid dns-packet
      this.log.d(rxid, "cannot decode dns query; may be cc GET req?");
      // TODO: io.hResponse(util.respond400()) instead?
      // at this point: req is GET and has "dns" in its url-string
      // but: is not a valid dns request
      return;
    }
  }
}

/**
 * Retrieves parameters of a plugin
 * @param {String[]} list - Parameters of a plugin
 * @returns - Object of plugin parameters
 */
function generateParam(parameter, list) {
  const out = {};
  for (const key of list) {
    out[key] = parameter.get(key) || null;
  }
  return out;
}

async function extractDnsQuestion(request) {
  if (util.isPostRequest(request)) {
    return await request.arrayBuffer();
  } else {
    // TODO: okay to assume GET request?
    const queryString = new URL(request.url).searchParams;
    const dnsQuery = queryString.get("dns");
    return bufutil.base64ToBytes(dnsQuery);
  }
}

function getRegion(request) {
  if (envutil.onCloudflare()) {
    return util.regionFromCf(request);
  } else if (envutil.onFly()) {
    return envutil.region();
  }
  return "";
}