Is this the right topic for a quick code example?
I had need to find ownerOf on a private Ethereum test network. The library being using was missing the call. A workaround was far less complex than fixing the library. It's a quick hack but it may help others in the same situation. Plenty of other examples were found to modify to get here, thanks other random devs.
Needs - geth
First, you need to define an ABI. The Ethereum Application Binary Interface (ABI) lets you specify how to interact with a contract and return data in a format you’re expecting. I only care about ownerOf.
Add a new file, ownerof.abi :
abi = [{ "constant":true,"inputs":[{"name":"tokenId","type":"uint256"}],"name":"ownerOf","outputs":[{"name":"owner","type"
:"address"}], "type":"function" }]
Then a quick script with two passed arguments the NFT contract address and the tokenID of the NFT you are querying for ownership: NFTcheck.sh
!/bin/sh
/home/geth/geth -attach << EOF | grep "ADDRESS:" | sed "s/ADDRESS: //"
loadScript("/home/geth/ownerof.abi");
caddr = "$1";
c = web3.eth.contract(abi).at(caddr);
d = c.ownerOf.getData($2);
var addy = web3.eth.call({to: caddr, data: d});
console.log("ADDRESS: " + addy);
EOF
Then run this command like so ./NFTcheck.sh <contract> <tokenID>
You can run the script from any other language/script, for example PHP would use exec().
Note, the address returned is a byte32 and all lower case. You will need to slice the last 40 characters and use a checksum address to get the proper upper and lowercase of the actual address. For comparison against a known address it works fine.
The web3 that comes with geth is 0.20.1 so you can't use toChecksumAddress() on the return.
If there are better ways feel free to post.
