Cryptocurrency: check if transaction is viable masternode output

Question

I'm developing a tool for masternode automization similar to https://gincoin.io .

I'm trying to figure out how to decode if transaction is viable for a masternode.

From what I know the transaction must meet the following criteria to be a viable masternode candidate:

• The send amount must be exactly as required for a masternode per coin specification (for example exactly 1000.0 coins)
• None of those coins should be spent
• The transaction must be verified by enough peers
• Send and return address must match (must be a transaction to yourself)

From what I have gather getrawtransaction call with txindex enabled client is the only tool that provide accurate info on transaction, as gettransaction is for wallet's internal use only.

So for example

I made the following transaction to myself at yPNYZoqKHMM49z1JzvCFAzrSTJpKmVmMio receive address:

When I execute

$ dash-cli -testnet getrawtransaction dd4011a1892a49d9109c299cad6a902ea60aff5a76f49c7d43f1a28861d0a8d3 1

Returns the following info on the transaction details:

{
  "hex": "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",
  "txid": "dd4011a1892a49d9109c299cad6a902ea60aff5a76f49c7d43f1a28861d0a8d3",
  "size": 372,
  "version": 1,
  "locktime": 211929,
  "vin": [
    {
      "txid": "afb84848ed58d4c3baddec4ea4eec3070376641c760d848f972bdc68a011057d",
      "vout": 0,
      "scriptSig": {
        "asm": "304402206d040ff0825fa11af1fa497f9e9ca52218b7576e61679ce73475a899d1d005420220572d6104cab20d1abc77eec0e8d50b78f20ad0aaa5d7720878664a38af90a0c0[ALL] 030613391de767cf19d8dd1fd3275ce661f5ff1e341e0130d7ade004b4a37c0607",
        "hex": "47304402206d040ff0825fa11af1fa497f9e9ca52218b7576e61679ce73475a899d1d005420220572d6104cab20d1abc77eec0e8d50b78f20ad0aaa5d7720878664a38af90a0c00121030613391de767cf19d8dd1fd3275ce661f5ff1e341e0130d7ade004b4a37c0607"
      },
      "sequence": 4294967294
    }, 
    {
      "txid": "afb84848ed58d4c3baddec4ea4eec3070376641c760d848f972bdc68a011057d",
      "vout": 1,
      "scriptSig": {
        "asm": "30440220296f0c7f8a8a538613e10644454c2146cc978509963a5bfe2211c8126c19c03502207c3310582e08585a2e9329cd14687589da58c3ff730ad75a0bba06a846de0caf[ALL] 0393b4249c1d422cda439e9629ecb80c23aa0586082c5473ae509c94b395d0d061",
        "hex": "4730440220296f0c7f8a8a538613e10644454c2146cc978509963a5bfe2211c8126c19c03502207c3310582e08585a2e9329cd14687589da58c3ff730ad75a0bba06a846de0caf01210393b4249c1d422cda439e9629ecb80c23aa0586082c5473ae509c94b395d0d061"
      },
      "sequence": 4294967294
    }
  ],
  "vout": [
    {
      "value": 13.66859403,
      "valueSat": 1366859403,
      "n": 0,
      "scriptPubKey": {
        "asm": "OP_DUP OP_HASH160 6be245a75e9e2b49f3392d260a06249de2396d33 OP_EQUALVERIFY OP_CHECKSIG",
        "hex": "76a9146be245a75e9e2b49f3392d260a06249de2396d3388ac",
        "reqSigs": 1,
        "type": "pubkeyhash",
        "addresses": [
          "yW9tDPWry4F4Yoh2ejVpdvMtjawBpNq2jV"
        ]
      }
    }, 
    {
      "value": 1000.00000000,
      "valueSat": 100000000000,
      "n": 1,
      "scriptPubKey": {
        "asm": "OP_DUP OP_HASH160 217e65d7d68fc632e1ae63b7536c900021fa9272 OP_EQUALVERIFY OP_CHECKSIG",
        "hex": "76a914217e65d7d68fc632e1ae63b7536c900021fa927288ac",
        "reqSigs": 1,
        "type": "pubkeyhash",
        "addresses": [
          "yPNYZoqKHMM49z1JzvCFAzrSTJpKmVmMio"
        ]
      }
    }
  ]
}

This vout portion in particular confirms that exactly 1000.0 coins is sent to the address as requested yPNYZoqKHMM49z1JzvCFAzrSTJpKmVmMio:

    {
      "value": 1000.00000000,
      "valueSat": 100000000000,
      "n": 1,
      "scriptPubKey": {
        "asm": "OP_DUP OP_HASH160 217e65d7d68fc632e1ae63b7536c900021fa9272 OP_EQUALVERIFY OP_CHECKSIG",
        "hex": "76a914217e65d7d68fc632e1ae63b7536c900021fa927288ac",
        "reqSigs": 1,
        "type": "pubkeyhash",
        "addresses": [
          "yPNYZoqKHMM49z1JzvCFAzrSTJpKmVmMio"
        ]
      }
    }

But how do I check if that's a transaction yourself, and that none of those 1000 coins were spent?

NOTE This is not a specific cryptocurrency related, and should work on any generic rpc wallet client that's masternode enabled.

Answer 1

Each project may have different specific requirements for what is deemed a valid transaction, but generally an unspent transaction must be checked against all previous transactions in the blockchain to make sure it has not been referenced as an input (vin) to another tx. Bitcoin stores a database of unspent transaction outputs (UTXO), to do this check more efficiently.

This check is done in Bitcoin before the transaction enters the mempool of a node (prior to being mined), and if it fails, the transaction will be rejected.

Update: You can get a specific utxo by txid using $ bitcoin-cli gettxout, you just can't query by address, per @PieterWuille's comment below.