Coin selection should include checks to avoid creating ambiguous transaction history. #178
Description
Describe the bug
In summary:
- Coin selection should not consider coins from transactions that are replacing other transactions.
- Coin selection should not consider coins from transactions that have been replaced.
Additional context
From Bitcoin Core:
// We should not consider coins from transactions that are replacing
// other transactions.
//
// Example: There is a transaction A which is replaced by bumpfee
// transaction B. In this case, we want to prevent creation of
// a transaction B' which spends an output of B.
//
// Reason: If transaction A were initially confirmed, transactions B
// and B' would no longer be valid, so the user would have to create
// a new transaction C to replace B'. However, in the case of a
// one-block reorg, transactions B' and C might BOTH be accepted,
// when the user only wanted one of them. Specifically, there could
// be a 1-block reorg away from the chain where transactions A and C
// were accepted to another chain where B, B', and C were all
// accepted.
if (nDepth == 0 && wtx.mapValue.count("replaces_txid")) {
safeTx = false;
}
// Similarly, we should not consider coins from transactions that
// have been replaced. In the example above, we would want to prevent
// creation of a transaction A' spending an output of A, because if
// transaction B were initially confirmed, conflicting with A and
// A', we wouldn't want to the user to create a transaction D
// intending to replace A', but potentially resulting in a scenario
// where A, A', and D could all be accepted (instead of just B and
// D, or just A and A' like the user would want).
if (nDepth == 0 && wtx.mapValue.count("replaced_by_txid")) {
safeTx = false;
}