https://getmonero.org/resources/developer-guides/daemon-rpc.html
Using the monerod json rpc, we can get the blob data for a specific block.
curl -X POST http://127.0.0.1:18081/json_rpc -d '{"jsonrpc":"2.0","id":"0","method":"getblock","params":{"height":912345}}' -H 'Content-Type: application/json'
blob data returned for that block:
"blob": "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",
block hash for that block:
"hash": "e22cf75f39ae720e8b71b3d120a5ac03f0db50bba6379e2850975b4859190bc6"
I think the blob is made up of the blockheader, nonce, merketMerkle root hash,size and size of transactions.
Using get_block_longhash from https://github.com/monero-project/monero/blob/960886aa04f0b50265884c0d4338031a93b1bc5d/src/cryptonote_basic/cryptonote_format_utils.cpp#L883
Can we hash that blob manually, which should yield its block hash?
Also whatswhat's the difference between the getblock method blob and the getblocktemplate method blocktemplate_blob ?