/**
* Pre-generate enough keys to reach the lookahead size. You can call this if you need to
* explicitly invoke the lookahead procedure, but it's normally unnecessary as it will be done
* automatically when needed.
*/
public void maybeLookAhead() {
lock.lock();
try {
List<DeterministicKey> keys = maybeLookAhead(externalKey, issuedExternalKeys);
keys.addAll(maybeLookAhead(internalKey, issuedInternalKeys));
// Batch add all keys at once so there's only one event listener invocation, as this will be
// listened to
// by the wallet and used to rebuild/broadcast the Bloom filter. That's expensive so we don't
// want to do
// it more often than necessary.
basicKeyChain.importKeys(keys);
} finally {
lock.unlock();
}
}
private void addToBasicChain(DeterministicKey key) {
basicKeyChain.importKeys(ImmutableList.of(key));
}
/** Returns freshly derived key/s that have not been returned by this method before. */
@Override
public List<DeterministicKey> getKeys(KeyPurpose purpose, int numberOfKeys) {
checkArgument(numberOfKeys > 0);
lock.lock();
try {
DeterministicKey parentKey;
int index;
switch (purpose) {
// Map both REFUND and RECEIVE_KEYS to the same branch for now. Refunds are a feature of
// the BIP 70
// payment protocol. Later we may wish to map it to a different branch (in a new wallet
// version?).
// This would allow a watching wallet to only be able to see inbound payments, but not
// change
// (i.e. spends) or refunds. Might be useful for auditing ...
case RECEIVE_FUNDS:
case REFUND:
issuedExternalKeys += numberOfKeys;
index = issuedExternalKeys;
parentKey = externalKey;
break;
case AUTHENTICATION:
case CHANGE:
issuedInternalKeys += numberOfKeys;
index = issuedInternalKeys;
parentKey = internalKey;
break;
default:
throw new UnsupportedOperationException();
}
// Optimization: potentially do a very quick key generation for just the number of keys we
// need if we
// didn't already create them, ignoring the configured lookahead size. This ensures we'll be
// able to
// retrieve the keys in the following loop, but if we're totally fresh and didn't get a chance
// to
// calculate the lookahead keys yet, this will not block waiting to calculate 100+ EC point
// multiplies.
// On slow/crappy Android phones looking ahead 100 keys can take ~5 seconds but the OS will
// kill us
// if we block for just one second on the UI thread. Because UI threads may need an address in
// order
// to render the screen, we need getKeys to be fast even if the wallet is totally brand new
// and lookahead
// didn't happen yet.
//
// It's safe to do this because when a network thread tries to calculate a Bloom filter, we'll
// go ahead
// and calculate the full lookahead zone there, so network requests will always use the right
// amount.
List<DeterministicKey> lookahead = maybeLookAhead(parentKey, index, 0, 0);
basicKeyChain.importKeys(lookahead);
List<DeterministicKey> keys = new ArrayList<DeterministicKey>(numberOfKeys);
for (int i = 0; i < numberOfKeys; i++) {
ImmutableList<ChildNumber> path =
HDUtils.append(parentKey.getPath(), new ChildNumber(index - numberOfKeys + i, false));
DeterministicKey k = hierarchy.get(path, false, false);
// Just a last minute sanity check before we hand the key out to the app for usage. This
// isn't inspired
// by any real problem reports from bitcoinj users, but I've heard of cases via the
// grapevine of
// places that lost money due to bitflips causing addresses to not match keys. Of course in
// an
// environment with flaky RAM there's no real way to always win: bitflips could be
// introduced at any
// other layer. But as we're potentially retrieving from long term storage here, check
// anyway.
checkForBitFlip(k);
keys.add(k);
}
return keys;
} finally {
lock.unlock();
}
}