Whitepaper - Ethereum Classic With Cover

Ethereum Classic Documentation, Release 0.1
was included and how much gas was used by the EVM. If a transaction creates a contract it will also contain the
contract address. We can retrieve the receipt with the eth_getTransactionReceipt RPC method.
> curl --data '{"jsonrpc":"2.0","method": "eth_getTransactionReceipt", "params": ["0x3a90b5face52c
{"id":7,"jsonrpc":"2.0","result":{"transactionHash":"0x3a90b5face52c4c5f30d507ccf51b0209ca628c6824
We can see that our contract was created on 0x6ff93b4b46b41c0c3c9baee01c255d3b4675963d. If
you got null instead of a receipt the transaction has not been included in a block yet. Wait for a moment and check
if your miner is running and retry it.
Interacting with smart contracts
Now that our contract is deployed we can interact with it. There are 2 methods for this, sending a transaction or
using call as previously explained. In this example we will be sending a transaction to the multiply method of the
contract.
If we look at the documentation for the eth_sendTransaction we can see that we need to supply several arguments.
In our case we need to specify the from, to and data arguments. From is the public address of our account
and to the contract address. The data argument is a bit harder. It contains a payload that defines which method
must be called and with which arguments. This is were the ABI comes into play. The ABI defines how to define
and encode data for the EVM. You can read all the details about the ABI here.
The bytes of the payload is the function selector and defines which method is called. This is done by taking the
first 4 bytes from the Keccak hash over the function name and its argument types and hex encode it. The multiply
function accepts an uint which is an alias for uint256. This leaves us with:
> web3.sha3("multiply(uint256)").substring(0, 8)
"c6888fa1"
See for details this page.
The next step is to encode the arguments. We only have one uint256, lets assume we supply the value 6. The ABI
has a section which specifies how to encode uint256 types.
int: enc(X) is the big-endian two’s complement encoding of X, padded on the higher-oder (left)
side with 0xff for negative X and with zero bytes for positive X such that the length is a multiple of 32
bytes.
This encodes to 0000000000000000000000000000000000000000000000000000000000000006.
Combining the function selector and the encoded argument our data will be
0xc6888fa10000000000000000000000000000000000000000000000000000000000000006.
Lets try it:
> curl --data '{"jsonrpc":"2.0","method": "eth_sendTransaction", "params": [{"from": "0xeb85a5557e
{"id":8,"jsonrpc":"2.0","result":"0x759cf065cbc22e9d779748dc53763854e5376eea07409e590c990eafc0869d
Since we sent a transaction we got the transaction hash returned. If we retrieve the receipt we can see something
new:
{
blockHash: "0xbf0a347307b8c63dd8c1d3d7cbdc0b463e6e7c9bf0a35be40393588242f01d55",
blockNumber: 268,
contractAddress: null,
cumulativeGasUsed: 22631,
gasUsed: 22631,
logs: [{
address: "0x6ff93b4b46b41c0c3c9baee01c255d3b4675963d",
blockHash: "0xbf0a347307b8c63dd8c1d3d7cbdc0b463e6e7c9bf0a35be40393588242f01d55",
blockNumber: 268,
data: "0x000000000000000000000000000000000000000000000000000000000000002a",
logIndex: 0,
topics: ["0x24abdb5865df5079dcc5ac590ff6f01d5c16edbc5fab4e195d9febd1114503da"],
1.7. Contracts and Transactions 87