Function validateLastMessages

src/server/chat.js:9–38

(pending, lastSeen, lastRejected)

class VerificationError extends Error {}
function validateLastMessages (pending, lastSeen, lastRejected) {
  if (lastRejected) {
    const rejectedTime = pending.get(lastRejected.sender, lastRejected.signature)
    if (rejectedTime) pending.acknowledge(lastRejected.sender, lastRejected.signature)
    else throw new VerificationError(`Client rejected a message we never sent from '${lastRejected.sender}'`)
  }

  let lastTimestamp
  const seenSenders = new Set()

  for (const { messageSender, messageSignature } of lastSeen) {
    if (pending.previouslyAcknowledged(messageSender, messageSignature)) continue

    const ts = pending.get(messageSender)(messageSignature)
    if (!ts) {
      throw new VerificationError(`Client saw a message that we never sent from '${messageSender}'`)
    } else if (lastTimestamp && (ts < lastTimestamp)) {
      throw new VerificationError(`Received messages out of order: Last acknowledged timestamp was at ${lastTimestamp}, now reading older message at ${ts}`)
    } else if (seenSenders.has(messageSender)) {
      // in the lastSeen array, last 5 messages from different players are stored, not just last 5 messages
      throw new VerificationError(`Two last seen entries from same player not allowed: ${messageSender}`)
    } else {
      lastTimestamp = ts
      seenSenders.add(messageSender)
      pending.acknowledgePrior(messageSender, messageSignature)
    }
  }

  pending.setPreviouslyAcknowledged(lastSeen, lastRejected)
}

module.exports = function (client, server, options) {
  const mojangPubKey = crypto.createPublicKey(mojangPublicKeyPem)