Solidity Syntax – Calling Contract State Changing Methods

Here's your function slightly modified by adding public to numbers so we can peek at the data:

contract C {    
     uint[] public numbers;

     function initNumbers() {
         numbers.push(1);
         numbers.push(2);
     }

     function stateChanger(uint a) {
         numbers.push(a);
     }    
}

Using the stripCrLf script in How to load Solidity source file into geth, I've flattened the source code using the following command:

user@Kumquat:~$ echo "var cSource='`stripCrLf C.sol`'"
var cSource='contract C { uint[] public numbers; function initNumbers() { numbers.push(1); numbers.push(2); } function stateChanger(uint a) { numbers.push(a); }      }'

I'm running a dev network using the following command (I have my password in passwordfile):

user@Kumquat:~$ geth --datadir ~/devdata --dev --mine --minerthreads 1 --unlock 0 --password ~/passwordfile console

I paste the flattened code in the geth command line:

> var cSource='contract C { uint[] public numbers; function initNumbers() { numbers.push(1); numbers.push(2); } function stateChanger(uint a) { numbers.push(a); }      }'
undefined

And compile the code using the following command:

> var cCompiled = web3.eth.compile.solidity(cSource);
Version: 0.3.5-0/RelWithDebInfo-Linux/g++/Interpreter

path: /usr/bin/solc
undefined

Here is the Application Binary Interface:

> cCompiled.C.info.abiDefinition
[{
    constant: false,
    inputs: [],
    name: "initNumbers",
    outputs: [],
    type: "function"
}, {
    constant: false,
    inputs: [{
        name: "a",
        type: "uint256"
    }],
    name: "stateChanger",
    outputs: [],
    type: "function"
}, {
    constant: true,
    inputs: [{
        name: "",
        type: "uint256"
    }],
    name: "numbers",
    outputs: [{
        name: "",
        type: "uint256"
    }],
    type: "function"
}]

Deploy the contract on the blockchain:

> var cContract = web3.eth.contract(cCompiled.C.info.abiDefinition);
undefined
> var c = cContract.new({
    from:web3.eth.accounts[0], 
    data: cCompiled.C.code, gas: 400000}, 
    function(e, contract) {
      if (!e) {
        if (!contract.address) {
          console.log("Contract transaction send: TransactionHash: " + 
            contract.transactionHash + " waiting to be mined...");
        } else {
          console.log("Contract mined! Address: " + contract.address);
          console.log(contract);
        }
    }
})
Contract mined! Address: 0x672807a8c0f72a52d759942e86cfe33264e73934

Call your initNumbers():

> c.initNumbers({from:eth.accounts[0], gas: 400000})
"0x3f21e1cdb636a2cf291cd9296282a4e9c4f4ed57c65a13fedc937a97203c3a75"
...
> c.numbers(0)
1
> c.numbers(1)
2
> c.numbers(2)
0

Calling stateChanger(...) - Method 1

> c.stateChanger(3, {from:eth.accounts[0], gas: 400000})
"0x3ecf3aa6464f93d5b062ad01b76b5dbc4302c190baf70d157a4d7607d4c7c749"
...
> c.numbers(2)
3
> c.numbers(3)
0

Calling stateChanger(...) - Method 2

> c.stateChanger.sendTransaction(4, {from: eth.accounts[0], gas: 400000})
"0xe1d9c57ca55dbdf446e55602570888ff5efce97a91ddc5c9575d10c7c9a1f0c8"
...
> c.numbers(3)
4
> c.numbers(4)
0

Calling stateChanger(...) - Method 3

And following is how to use the raw data sendTransaction(...) format.

Find the function signature. Note that the uint parameter is actually a uint256 (see the ABI format above):

> web3.sha3('stateChanger(uint256)').substr(0, 10)
"0x65060775"

Here is 5 encoded in hex and padded to 32 bytes:

0x0000000000000000000000000000000000000000000000000000000000000005

Join the data together, removing the 0x from the hex(5) string:

0x650607750000000000000000000000000000000000000000000000000000000000000005

Here's how to sendTransaction(...). The to: parameter is the address of the mined contract:

> var result = web3.eth.sendTransaction({
    from: eth.accounts[0], 
    to: "0x672807a8c0f72a52d759942e86cfe33264e73934", 
    data: "0x650607750000000000000000000000000000000000000000000000000000000000000005", 
    gas: 400000}
)
undefined
> result
"0x420d4256718b4326967677da2e460a1d361a62f3ceee386e1313d25b12c0f610"
...
> c.numbers(4)
5
> c.numbers(5)
0

Bonus 1 - estimateGas(...)

Since we have worked out the data to send with sendTransaction(...) above.

Here is the gas used by the sendTransaction(...) call above:

> eth.getTransactionReceipt(result).gasUsed
46888

You can use the same data format to estimate the gas using the estimateGas(...) call:

var result = web3.eth.estimateGas({
    from: eth.accounts[0], 
    to: "0x672807a8c0f72a52d759942e86cfe33264e73934", 
    data: "0x650607750000000000000000000000000000000000000000000000000000000000000005", 
    gas: 400000}
)
undefined
> result
46888

Bonus 2 - The Transaction Data

Set debug.verbosity(7) and watch the transaction get removed from the transaction pool after it is executed:

> debug.verbosity(7)
...
I0730 00:13:43.918828 core/tx_pool.go:547] removed tx (
    TX(07c3c717c87ce1e2b31ba144b6b751d66c90a8a69375478a5ef4e60a6f42996c)
    Contract: false
    From:     a7857047907d53a2e494d5f311b4b586dc6a96d2
    To:       672807a8c0f72a52d759942e86cfe33264e73934
    Nonce:    35
    GasPrice: 20000000000
    GasLimit  400000
    Value:    0
    Data:     0x650607750000000000000000000000000000000000000000000000000000000000000004
    V:        0x1c
    R:        0x75ff67a969670a0f35ae415f2fa541446a71fa9b7d8ad6247ad12fd7ae3986a
    S:        0x7150424ed1698792cdcf1253a79f2474e4df411610db97e36240bab50af6c80c
    Hex:      f889238504a817c80083061a8094672807a8c0f72a52d759942e86cfe33264e7393480a46506077500000000000000000000000000000000000000000000000000000000000000041ca0075ff67a969670a0f35ae415f2fa541446a71fa9b7d8ad6247ad12fd7ae3986aa07150424ed1698792cdcf1253a79f2474e4df411610db97e36240bab50af6c80c
) from pool: low tx nonce or out of funds

The different methods of calling (c.stateChanger(3, {from:eth.accounts[0], gas: 400000}) and c.stateChanger.sendTransaction(4, {from: eth.accounts[0], gas: 400000})) are converted to the sendTransaction(...) format.