Is it possible to generate(mine) a block with specific transaction via bitcoin-cli on regtest?

Question

I want to generate a block with specific transaction via bitcoin-cli on regtest.

The "generate" command does not have the option. It collects transactions in mempool by the default rule.

I guess I can do it with some code change like the following way but I don't want to change it if possible.

TestChain100Setup::CreateAndProcessBlock(const std::vector<CMutableTransaction>& txns, const CScript& scriptPubKey)
{
    const CChainParams& chainparams = Params();
    std::unique_ptr<CBlockTemplate> pblocktemplate = BlockAssembler(chainparams).CreateNewBlock(scriptPubKey);
    CBlock& block = pblocktemplate->block;

    // Replace mempool-selected txns with just coinbase plus passed-in txns:
    block.vtx.resize(1);
    for (const CMutableTransaction& tx : txns)
        block.vtx.push_back(MakeTransactionRef(tx));

https://github.com/bitcoin/bitcoin/blob/v0.17.1/src/miner.cpp#L147 https://github.com/bitcoin/bitcoin/blob/v0.17.1/src/test/test_bitcoin.cpp#L155 https://bitcoincore.org/en/doc/0.17.0/rpc/generating/generate/

Answer 1

When you run generate, it mines a block with the transactions in the mempool:

generate nblocks ( maxtries )

Mine up to nblocks blocks immediately (before the RPC call returns) to an address in the wallet.

If you want those new coins to be mined to a specific address, you can use generatetoaddress

You can create transactions and submit them to the mempool either using the wallet RPC, e.g. sendtoaddress or using the rawtransactions RPC: e.g.

1. createrawtransaction
2. signrawtransaction
3. sendrawtransaction

sendrawtransaction will put the transaction in the mempool, which can then be included in the next block using generate

Answer 2

In the addPackageTxs func https://github.com/bitcoin/bitcoin/blob/ef70f9b52b851c7997a9f1a0834714e3eebc1fd8/src/miner.cpp#L306

while (mi != mempool.mapTx.get<ancestor_score>().end() || !mapModifiedTx.empty())
{
    // First try to find a new transaction in mapTx to evaluate.
    if (mi != mempool.mapTx.get<ancestor_score>().end() &&
            SkipMapTxEntry(mempool.mapTx.project<0>(mi), mapModifiedTx, failedTx)) {
        ++mi;
        continue;
    }

you can modify the while loop and select which transation index should you include in block.

ex: you can skip transactions which are in mempool within 2 seconds before current time

while (mi != mempool.mapTx.get<entry_time>().end() || !mapModifiedTx.empty())
{
    CTxMemPool::txiter iter = mempool.mapTx.project<0>(mi);
    auto time_now = GetTime();

    if (time_now - iter->GetTime() < 2){
       continue;
    }

}