non-standard tx finder

This is a quick-and-dirty tool to find transactions in the blockchain that are non-standard according to Bitcoin Core's default mempool policy.

This tool requires two Bitcoin Core nodes: a data-node and a test-node. The data-node only provides blocks (in theory, a block explorer API could be used too, however, that's not implemented). The test-node is used to test if it accepts the transactions in the block to its mempool. This requires the node to not be aware of the block with the transaction yet. This can be accomplished by syncing the node with -stopatheight=X. Once synced and stopped, the node can be restarted with -maxconnections=0 to stop if from further synchronizing with other nodes.

Then, for each block the data-node knows about, but the test-node doesn't, each transaction is added to the test-node's mempool while recording any failures and failure reasons. This uses the testmempoolaccept RPC to see if the transaction would be accepted and then the sendrawtransaction RPC to actually submit the transaction. Once all transactions are submitted, the full block is submitted with the submitblock RPC. This cleans the mempool and allows us to move on to the next block with transactions to test.

sequenceDiagram
    app->>test-node: getblockcount
    test-node->>app: block count
    Note left of app: X = block count + 1
    loop while test-node not at tip
        app->>data-node: getblock X
        data-node->>app: blockX
        loop for tx in blockX
            app->>test-node: testmempoolaccept tx
            test-node->>app: mempool accept result
            Note left of app: if tx rejected, <br> write to CSV file
            app->>test-node: sendrawtransaction tx
        end
        app->>test-node: submitblock X
        Note left of app: increment X
    end

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Known limitations:

• Transactions depending on a rejected transaction are rejected as missing-inputs
• Transactions might be rejected for multiple reasons. However, only one reason is returned
• Transactions rejected due to mempool limits (e.g. too-long-mempool-chain) can't be analyzed statically without the mempool state
• Does not report full-RBF replacements mined

Setup

1. Fully synchronize a data-node.
2. Start a test-node with -stopatheight=X where X+1 is the height you want to test from.
3. Once the test-node is synchronized and has stopped, restart it with -maxconnections=0.
4. Copy the config.toml.example file to config.toml and fill in the RPC credentials for both nodes.
5. Run the rust application (e.g. cargo run).
6. Wait while the application submits each transaction and block to the test-node. Check progress in the test-node's debug.log
7. Done. The application wrote a CSV file with information about each non-standard transaction.