How can I execute code locally at given address?

Question

What's the simplest way of executing piece of code at specific address of the main blockchain locally using the command-line interface?

In here it's demonstrated how to play mp3 file based on the input data using geth command, but how can you execute the actual code with its logic on your local machine for own testing purposes?

Answer 1

The JSON_RPC eth_call method allows you to simulate a transaction on the blockchain, including contract executions.

This method can be accessed in geth or web3.js as

eth.call({from: eth.accounts[0], to: myContract, gas: 1000000, value: web3.toWei(1,"ether")})

If you know the ABI for a contract, you can use

var myContract = eth.contract(myABI).at(contractAddress);
var result = myContract.myMethod.call(arg1,arg2,arg3,{from:myAddress, gas:1000000})

If you want to get a debugging trace of a transaction, you can send a transaction, then use debug_traceTransaction.