fetch-dht/routes/fetch.js

const Router = require('express-promise-router');
const bencode = require('bencode');
const qs = require('querystring');

const peerListFormatters = require('../lib/peerListFormatters');
const bqs = require('../lib/binaryQuerystring');

const INFO_HASH_REGEX = new RegExp('^[0-9a-f]{40}$', 'i');

module.exports = ({ dht }) => {
  const app = Router();
  app.get(
    '/',
    async (
      {
        log,
        originalUrl,
        query: { info_hash: infoHash, compact, json, event = '' },
      },
      res,
    ) => {
      // worst case if every character is percent encoded, or best case if every _is_ decoded
      if (!infoHash || infoHash.length > 60 || infoHash < 20) {
        res
          .status(400)
          .end(bencode.encode({ 'failure reason': 'invalid arguments' }));
        return;
      }

      if (infoHash.length !== 20) {
        infoHash = bqs.fromUrl(originalUrl).info_hash;

        if (!infoHash || infoHash.length !== 20) {
          res
            .status(400)
            .end(bencode.encode({ 'failure reason': 'invalid arguments' }));
          log({ status: 'refused', type: 'dhtGateway' });
          return;
        }
      }

      infoHash = Buffer.from(infoHash, 'latin1').toString('hex');
      if (!infoHash.match(INFO_HASH_REGEX)) {
        res
          .status(400)
          .end(bencode.encode({ 'failure reason': 'invalid arguments' }));
        log({ status: 'refused', type: 'dhtGateway' });
        return;
      }

      let format = 'bencoded';
      if (compact === '1') {
        format = 'compact';
      } else if (json === '1') {
        format = 'json';
      }

      try {
        let peers = [];
        // a completed or stopped torrent does not need peers
        if (event !== 'completed' && event !== 'stopped') {
          peers = await dht.lookup(infoHash);
        }
        // this sends the response as well as formatting it
        peerListFormatters(peers, res, format);
        log({
          status: 'served',
          type: 'dhtGateway',
          format,
          count: peers.length,
        });
      } catch (e) {
        res
          .status(500)
          .end(bencode.encode({ 'failure reason': 'internal error' }));
        log({
          status: 'failed',
          type: 'dhtGateway',
          format,
          error: e.message,
          stack: e.stack,
        });
      }
    },
  );
  return app;
};