Updated the example demos

[rodkeys]

Fixed issue where recent changes caused subscription demo to fail. Also added a simple chat message demo.

[hoffmabc]

Thanks for the submission. I’ll take a look soon.

[rmisio]

@rodkeys I found that, given the same peerID, the subscription key in this example generated via generateSubscriptionKey does not match the one generated by the go code.

Here's a tweaked generateSubscriptionKey function which will make the keys match.

(FWIW, the keys matching is critical to messages being routed properly)

import {
  fromB58String,
  toB58String,
  decode,
  encode
} from 'multihashes';
import BufferShift from 'buffershift';

export async function generateSubscriptionKey(peerID) {
  const mh = fromB58String(peerID);
  const decodedMh = decode(mh);
  const digest = decodedMh.digest;
  const prefix = new Buffer(new Uint8Array(digest.slice(0, 8)));

  const shifted = new Buffer(prefix.length);
  prefix.copy(shifted);
  BufferShift.shr(shifted, 48);

  const checksum = await crypto.subtle.digest('SHA-256', shifted);
  const subscriptionKey = encode(Buffer.from(checksum), 'sha2-256');
  return toB58String(subscriptionKey);
}