Trying to find the raw genesis transaction length

Question

I see that many different altcoins have different lengths for the initial genesis tx. How would I go about finding the length of the initial genesis tx? I saw another answer but I have no need of making it as complicated; I just need the length and nothing else.

For example, Bitcoin's is

01000000010000000000000000000000000000000000000000000000000000000000000000ffffffff4d04ffff001d0104455468652054696d65732030332f4a616e2f32303039204368616e63656c6c6f72206f6e206272696e6b206f66207365636f6e64206261696c6f757420666f722062616e6b73ffffffff0100f2052a01000000434104678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5fac00000000.

However, altcoins have different lengths. Is there an identifier I can use to determine the length of the genesis tx and nothing else?

EDIT: I am making a block explorer so I cannot use a block explorer to help me in getting info.

Answer 1

Unfortunately, the genesis block is not indexed in most altcoins (because they forked from bitcoin and kept the same bug), so you can't really get access to it via the RPC methods.

What you could do instead:

• Use a block explorer that will tell you the size of the transaction. For example, blockchain.info makes this information available (204 bytes).
• Find the parameters file and put a print the size of the genesis block to stdout.

The second option basically entails putting the following lines at the end of CMainParams() and then compiling.

CDataStream ssBlock(SER_NETWORK, PROTOCOL_VERSION);
ssBlock << genesis;
printf("block: %s\n", HexStr(ssBlock.begin(), ssBlock.end()).c_str());
printf("block size: %i\n", (int)::GetSerializeSize(genesis, SER_NETWORK, PROTOCOL_VERSION));
printf("tx size: %i\n", (int)::GetSerializeSize(genesis.vtx[0], SER_NETWORK, PROTOCOL_VERSION));

This will print the raw block data, it's size, and the transaction's size. (Note, this is untested, but something along these lines should work)

NOTE: It's possible, although not the norm, to put multiple transactions in a genesis block. Just check that your assumption is correct.