Ethereum: Smart Contract

Aug. 23, 2016

Core Concepts:

MPT state and storage
Turing-Complete VM

New features:

Gas Limit and NO Free Transactions
Uncle blocks strengthen
Turing Complete Script
State Storage mounted

Motivations:

color-ed coins ( compare later)
SPV (skipped)

Limit on color-ed coins of bitcoin

colored

From UTXOs to State Database

Bitcoin blockchain is a database of UTXOs, in fact.
Smart Contract need more states be recorded in blockchains.

APIs of ethereum

Command line options:
- https://github.com/ethereum/go-ethereum/wiki/Command-Line-Options

Web3:
- https://github.com/ethereum/wiki/wiki/JavaScript-API

Console or RPC
- http://ethdocs.org/en/latest/contracts-and-transactions/contracts.html

Experiment: new account

$ geth --datadir ./node1 account new
> Address: {ed0340bb8ac2d79aec6156d2c383a8f89ce13686}

$ geth --datadir ./node1 init genesis.json

Experiment: genesis.json

{
    "nonce": "0x0000000000000042",     
    "timestamp": "0x0",
    "parentHash": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "extraData": "0x0",     
    "gasLimit": "0x8000000",     
    "difficulty": "0x400",
    "mixhash": "0x0000000000000000000000000000000000000000000000000000000000000000",
    "coinbase": "0x3333333333333333333333333333333333333333",    
    "alloc": {
        "0xffffffffffffffffffff" : {
            "balance" : "10000000000000000000"
        }
    }
}

Experiment: mining with low difficulty

lowdiff

Experiment: basic transfer

Ref:
- https://ethereum.gitbooks.io/frontier-guide/content/sending_ether.html

> var sender = eth.accounts[0];
> var receiver = eth.accounts[1];
> var amount = web3.toWei(0.01, "ether")
> eth.sendTransaction({from:sender, to:receiver, value: amount})

Experiment: compile a contract with solidity

sample: multiply

contract test { 
    function multiply(uint a) returns(uint d) 
    { return a * 7; }
 }

compile:

var test_Contract = eth.compile.solidity(source);

TODO:
more inspections on test_Contract;

Experiment: Burn gas to deploy contract

Essentialy deploying a contract is to sendTransaction
- to : <must absent>
- code: byte code of compiled contract
- from: address of contract creator

Note:
To deploy a contract requires payment to miners, so remeber to personal.unlockAccout().
- http://ethereum.stackexchange.com/questions/6870/create-a-new-contract-by-json-rpc-of-cpp-ethereum

Note:
This is very like the P2SH, and ehtereum is evolved from this feature of bitcoin.

Experiment: call contract

Prerequisites to call a contract:

Contract address
ABI

sample:

>eth.getTransactionReceipt('0xb31cc6169ceb2db952749eb89f1a965eee0ca8de8f656633d9c6195fa01f2f59').contractAddress 
>var contract_address = "0xb63897f156cef728279b461663286c11c8866ff1".
>var abi = [{constant: false, inputs: [{name: 'a', type: 'unit256'}]}];
> var c = web3.eth.contract(constract_abi);
> var obj = c.at(contract_address);
> var arg1 = 3;
> var my_acccount_address = '0x2773ffb039ded4bd86c3c96bf136e9f2bf510114';
> obj.multiply.sendTransaction(arg1, {from: my_account_address});

Experiment: a contract instance with constructor

Construct a contract instance with parameters and deploy this instance on the blockchain.

https://www.ethereum.org/greeter

Note:
1) deploy the contract code.
2) invoke the Constructor with initialization paramters list.

TODO:

MPT state & storage tree
gas estimate
Web3 API Impl.
Inside contract lifetime
contract global registration

on reading this snap text from the book: data insertion in bitcoin’s blockchain:

It is common knowledge that extrinsic data can be stored in the Blockchain, and there are
numerous websites that provide access to a subset of that data,51–53 and some excellent sleuthing
has uncovered a variety of interesting historical artifacts that have previously been stored.54
Nevertheless, there remains confusion and misinformation about the variety of different methods
by which data can be (and has been) stored. For instance, a recent comprehensive textbook on
Bitcoin included the following:
“There’s no good way to prevent people from writing arbitrary data into the Bitcoin
block chain [sic]. One possible countermeasure is to only accept Pay-to-Script-Hash
transactions. This would make it a bit more expensive to write in arbitrary data, but it
still wouldn’t prevent it.”55
The first claim, that one cannot prevent arbitrary data insertion, is correct, since there is no
general way to distinguish between legitimate address hashes and arbitrary binary data. However,
the second claim is false, as P2SH (Pay-to-Script-Hash) transactions actually provide the least
expensive and most efficient method for storing large amounts of arbitrary data (see section 5).

while reading the second claim, i feel very superised, but then the author say about “least expensive”, i get relaxed.

【比特币】 From P2SH of bitcoin to Smart Contract of ethereum