ListTransactionsOfBlock RPC method

[shufps]

The method 'listtransactionsofblock' lists all transactions (from the wallet) which are in block with blockhash

It can be used this way: (pseudo-code)

ScanTransactions() {
  Database.TransactionBegin()

  long lastBlock = BitcoinRPC.getLastBlockNr()
  long lastScannedBlock = Database.getLastScannedBlock()

  while (lastBlock - lastScannedBlock > targetConfirms)  {
    lastScannedBlock++;
    string hash = BitcoinRPC.getHashOfBlock(lastScannedBlock)
    list<Transaction> list = BitcoinRPC.getTransactionsOfBlock(hash)
    for (Transaction t : list)
    {
      // do something
      // at this point, you can absolutely be sure to see only transactions 
      // with <targetconfirms> confirms.
      // and you only have to scan each block exactly once
    }
  }
  Database.saveLastScannedBlock()
  Database.TransactionCommit()
}

This is an easy example how payments can reliably be received.

Explained here: #2565

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[jgarzik]

Technical comment: is it better to iterate through one block, checking IsMine(), than all transactions in wallet?

Non-technical: is there a compelling use case? Ignored the solvable code objection, I'm tempted to close until a compelling need for this arises.

[shufps]

technical:

Iterating through the block would only give me txids of all transactions within a block. With IsMine() I could check if this transaction belongs to my addresses. Then, I would have to to query the wallet to give me all transaction details for every transaction which is mine in the block I currently processed.

I'm not sure if this would be more efficient because I thought json-rpc-calls are more expensive. So I thought, one single RPC-call would be better than lots of them ...

non-technical:

I tried to find a method for reliably receive confirmations about sent and received payments. I wanted to process every block exactly once and I'm working with a database which supports transactions, so everything happens within a single sql-transaction.

My solution is absolutely bullet-proof and repeatable in case an Exception in my java code occures. So I don't lose/oversee anything and I can easily debug my errors.

I invested almost a week and tried almost everything until I implemented it this way.

There is another method which is called 'listtransationssinceblock' but it mostly gives unconfirmed transactions over and over again (with each call) back to my java-class. I was not interested in unconfirmed transactions but the method couldn't be restricted to only give back confirmed txs.

I also tried what you suggested but there was the issue with lots and lots of rpc queries ...

[jgarzik]

That's not a compelling use case. If you are having problems with lots of RPC queries, then send a batch of them together as a JSON-RPC 2.0 batch.

The problem with this method is that it causes over-reliance on a broken assumption that block == totally confirmed transactions. This is not true. You might have a chain reorganization at any time, which would invalidate any queries based on a specific block height/hash, and move transactions from one block to another.