以太坊的智能合约是什么
以太坊的智能合约并非现实中常见的合同，而是存在区块链上，可以被触发执行的一段程序代码，这些代码实现了某种预定的规则，是存在于以太坊执行环境中的“自治代理”。以太坊的账户与合约如图 1 所示。
以太坊的账户与合约
图1：以太坊的账户与合约
以太坊的智能合约设计很简明。
- 任何人都可以在以太坊区块链上开发智能合约，这些智能合约的代码是存在于以太坊的账户中的，这类存有代码的账户叫合约账户。对应地，由密钥控制的账户可称为外部账户。
- 以太坊的智能合约程序，是在以太坊虚拟机（Ethereum Virtual Machine,EVM）上运行的。
- 合约账户不能自己启动运行自己的智能合约。要运行一个智能合约，需要由外部账户对合约账户发起交易，从而启动其中的代码的执行。
以太坊和比特币的一个重大不同是，前者提供了图灵完备的编程语言（Solidity）和相应的运行环境（EVM）。所谓图灵完备，指的是这个脚本编程语言可以运行所有可能的计算，而比特币的UTXO模型和脚本只能运行部分计算。
一、ABI（Application Binary Interface）
字面意思是应用程序二进制接口，简单的理解是合约的接口描述，描述了字段名称、字段类型、方法名称、参数名称、参数类型、方法返回值类型等。
当合约被编译后，对应的abi也就确定了。
二、为什么需要ABI
- 编写合约代码（一般使用solidity语言）
- 编译合约，将solidity编写的代码编译成EVM可识别的bytecode，同时生成abi
- 部署合约，将合约部署到区块链上，生成合约地址，将合约内容（即上一步生成的bytecode）作为input date输入。部署合约是一个交易过程，所以也会生成一个交易Hash
- 执行合约，获取合约地址，然后传入参数调用合约中的方法，获得执行结果
从上面的步骤可以看出，abi对于EVM来说，其实是不需要的。但是对于调用者来说，就需要知道合约有哪些方法，方法的参数是什么，返回值是什么，而这些信息就记录在智能合约的abi中。所以abi其实就相当于开发者的接口文档，方便开发者调用执行合约
三、怎么生成ABI:
- 使用remix
- 使用solidity(solcjs helloworld.sol --abi)
下面是helloworld.sol的合约代码
pragma solidity >=0.4.21 <0.6.0;
contract HelloWorld{
address payable creator;
string greeting;
constructor() public {
creator = msg.sender;
greeting = "hello world";
}
function greet() view public returns (string memory) {
return greeting;
}
function setGreeting(string memory _newgreeting) public {
greeting = _newgreeting;
}
function kill() public{
if (msg.sender == creator)
selfdestruct(creator); // kills this contract and sends remaining funds back to creator
}
}
使用remix生成ABI(我选择的solidity版本是0.5.11)，如下:
[
{
"constant": false,
"inputs": [],
"name": "kill",
"outputs": [],
"payable": false,
"stateMutability": "nonpayable",
"type": "function"
},
{
"constant": false,
"inputs": [
{
"internalType": "string",
"name": "_newgreeting",
"type": "string"
}
],
"name": "setGreeting",
"outputs": [],
"payable": false,
"stateMutability": "nonpayable",
"type": "function"
},
{
"constant": true,
"inputs": [],
"name": "greet",
"outputs": [
{
"internalType": "string",
"name": "",
"type": "string"
}
],
"payable": false,
"stateMutability": "view",
"type": "function"
},
{
"inputs": [],
"payable": false,
"stateMutability": "nonpayable",
"type": "constructor"
}
]
同时还得到bytecode:
{
"linkReferences": {},
"object": "608060405234801561001057600080fd5b50336000806101000a81548173ffffffffffffffffffffffffffffffffffffffff021916908373ffffffffffffffffffffffffffffffffffffffff1602179055506040518060400160405280600b81526020017f68656c6c6f20776f726c640000000000000000000000000000000000000000008152506001908051906020019061009c9291906100a2565b50610147565b828054600181600116156101000203166002900490600052602060002090601f016020900481019282601f106100e357805160ff1916838001178555610111565b82800160010185558215610111579182015b828111156101105782518255916020019190600101906100f5565b5b50905061011e9190610122565b5090565b61014491905b80821115610140576000816000905550600101610128565b5090565b90565b6103b5806101566000396000f3fe608060405234801561001057600080fd5b50600436106100415760003560e01c806341c0e1b514610046578063a413686214610050578063cfae32171461010b575b600080fd5b61004e61018e565b005b6101096004803603602081101561006657600080fd5b810190808035906020019064010000000081111561008357600080fd5b82018360208201111561009557600080fd5b803590602001918460018302840111640100000000831117156100b757600080fd5b91908080601f016020809104026020016040519081016040528093929190818152602001838380828437600081840152601f19601f82011690508083019250505050505050919291929050505061021f565b005b610113610239565b6040518080602001828103825283818151815260200191508051906020019080838360005b83811015610153578082015181840152602081019050610138565b50505050905090810190601f1680156101805780820380516001836020036101000a031916815260200191505b509250505060405180910390f35b6000809054906101000a900473ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff163373ffffffffffffffffffffffffffffffffffffffff16141561021d576000809054906101000a900473ffffffffffffffffffffffffffffffffffffffff1673ffffffffffffffffffffffffffffffffffffffff16ff5b565b80600190805190602001906102359291906102db565b5050565b606060018054600181600116156101000203166002900480601f0160208091040260200160405190810160405280929190818152602001828054600181600116156101000203166002900480156102d15780601f106102a6576101008083540402835291602001916102d1565b820191906000526020600020905b8154815290600101906020018083116102b457829003601f168201915b5050505050905090565b828054600181600116156101000203166002900490600052602060002090601f016020900481019282601f1061031c57805160ff191683800117855561034a565b8280016001018555821561034a579182015b8281111561034957825182559160200191906001019061032e565b5b509050610357919061035b565b5090565b61037d91905b80821115610379576000816000905550600101610361565b5090565b9056fea265627a7a723158206e85a5da055a6394a6dc80d00aff410d951095de857b24fd98f2f985659a2bd264736f6c634300050b0032",
"opcodes": "PUSH1 0x80 PUSH1 0x40 MSTORE CALLVALUE DUP1 ISZERO PUSH2 0x10 JUMPI PUSH1 0x0 DUP1 REVERT JUMPDEST POP CALLER PUSH1 0x0 DUP1 PUSH2 0x100 EXP DUP2 SLOAD DUP2 PUSH20 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF MUL NOT AND SWAP1 DUP4 PUSH20 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF AND MUL OR SWAP1 SSTORE POP PUSH1 0x40 MLOAD DUP1 PUSH1 0x40 ADD PUSH1 0x40 MSTORE DUP1 PUSH1 0xB DUP2 MSTORE PUSH1 0x20 ADD PUSH32 0x68656C6C6F20776F726C64000000000000000000000000000000000000000000 DUP2 MSTORE POP PUSH1 0x1 SWAP1 DUP1 MLOAD SWAP1 PUSH1 0x20 ADD SWAP1 PUSH2 0x9C SWAP3 SWAP2 SWAP1 PUSH2 0xA2 JUMP JUMPDEST POP PUSH2 0x147 JUMP JUMPDEST DUP3 DUP1 SLOAD PUSH1 0x1 DUP2 PUSH1 0x1 AND ISZERO PUSH2 0x100 MUL SUB AND PUSH1 0x2 SWAP1 DIV SWAP1 PUSH1 0x0 MSTORE PUSH1 0x20 PUSH1 0x0 KECCAK256 SWAP1 PUSH1 0x1F ADD PUSH1 0x20 SWAP1 DIV DUP2 ADD SWAP3 DUP3 PUSH1 0x1F LT PUSH2 0xE3 JUMPI DUP1 MLOAD PUSH1 0xFF NOT AND DUP4 DUP1 ADD OR DUP6 SSTORE PUSH2 0x111 JUMP JUMPDEST DUP3 DUP1 ADD PUSH1 0x1 ADD DUP6 SSTORE DUP3 ISZERO PUSH2 0x111 JUMPI SWAP2 DUP3 ADD JUMPDEST DUP3 DUP2 GT ISZERO PUSH2 0x110 JUMPI DUP3 MLOAD DUP3 SSTORE SWAP2 PUSH1 0x20 ADD SWAP2 SWAP1 PUSH1 0x1 ADD SWAP1 PUSH2 0xF5 JUMP JUMPDEST JUMPDEST POP SWAP1 POP PUSH2 0x11E SWAP2 SWAP1 PUSH2 0x122 JUMP JUMPDEST POP SWAP1 JUMP JUMPDEST PUSH2 0x144 SWAP2 SWAP1 JUMPDEST DUP1 DUP3 GT ISZERO PUSH2 0x140 JUMPI PUSH1 0x0 DUP2 PUSH1 0x0 SWAP1 SSTORE POP PUSH1 0x1 ADD PUSH2 0x128 JUMP JUMPDEST POP SWAP1 JUMP JUMPDEST SWAP1 JUMP JUMPDEST PUSH2 0x3B5 DUP1 PUSH2 0x156 PUSH1 0x0 CODECOPY PUSH1 0x0 RETURN INVALID PUSH1 0x80 PUSH1 0x40 MSTORE CALLVALUE DUP1 ISZERO PUSH2 0x10 JUMPI PUSH1 0x0 DUP1 REVERT JUMPDEST POP PUSH1 0x4 CALLDATASIZE LT PUSH2 0x41 JUMPI PUSH1 0x0 CALLDATALOAD PUSH1 0xE0 SHR DUP1 PUSH4 0x41C0E1B5 EQ PUSH2 0x46 JUMPI DUP1 PUSH4 0xA4136862 EQ PUSH2 0x50 JUMPI DUP1 PUSH4 0xCFAE3217 EQ PUSH2 0x10B JUMPI JUMPDEST PUSH1 0x0 DUP1 REVERT JUMPDEST PUSH2 0x4E PUSH2 0x18E JUMP JUMPDEST STOP JUMPDEST PUSH2 0x109 PUSH1 0x4 DUP1 CALLDATASIZE SUB PUSH1 0x20 DUP2 LT ISZERO PUSH2 0x66 JUMPI PUSH1 0x0 DUP1 REVERT JUMPDEST DUP2 ADD SWAP1 DUP1 DUP1 CALLDATALOAD SWAP1 PUSH1 0x20 ADD SWAP1 PUSH5 0x100000000 DUP2 GT ISZERO PUSH2 0x83 JUMPI PUSH1 0x0 DUP1 REVERT JUMPDEST DUP3 ADD DUP4 PUSH1 0x20 DUP3 ADD GT ISZERO PUSH2 0x95 JUMPI PUSH1 0x0 DUP1 REVERT JUMPDEST DUP1 CALLDATALOAD SWAP1 PUSH1 0x20 ADD SWAP2 DUP5 PUSH1 0x1 DUP4 MUL DUP5 ADD GT PUSH5 0x100000000 DUP4 GT OR ISZERO PUSH2 0xB7 JUMPI PUSH1 0x0 DUP1 REVERT JUMPDEST SWAP2 SWAP1 DUP1 DUP1 PUSH1 0x1F ADD PUSH1 0x20 DUP1 SWAP2 DIV MUL PUSH1 0x20 ADD PUSH1 0x40 MLOAD SWAP1 DUP2 ADD PUSH1 0x40 MSTORE DUP1 SWAP4 SWAP3 SWAP2 SWAP1 DUP2 DUP2 MSTORE PUSH1 0x20 ADD DUP4 DUP4 DUP1 DUP3 DUP5 CALLDATACOPY PUSH1 0x0 DUP2 DUP5 ADD MSTORE PUSH1 0x1F NOT PUSH1 0x1F DUP3 ADD AND SWAP1 POP DUP1 DUP4 ADD SWAP3 POP POP POP POP POP POP POP SWAP2 SWAP3 SWAP2 SWAP3 SWAP1 POP POP POP PUSH2 0x21F JUMP JUMPDEST STOP JUMPDEST PUSH2 0x113 PUSH2 0x239 JUMP JUMPDEST PUSH1 0x40 MLOAD DUP1 DUP1 PUSH1 0x20 ADD DUP3 DUP2 SUB DUP3 MSTORE DUP4 DUP2 DUP2 MLOAD DUP2 MSTORE PUSH1 0x20 ADD SWAP2 POP DUP1 MLOAD SWAP1 PUSH1 0x20 ADD SWAP1 DUP1 DUP4 DUP4 PUSH1 0x0 JUMPDEST DUP4 DUP2 LT ISZERO PUSH2 0x153 JUMPI DUP1 DUP3 ADD MLOAD DUP2 DUP5 ADD MSTORE PUSH1 0x20 DUP2 ADD SWAP1 POP PUSH2 0x138 JUMP JUMPDEST POP POP POP POP SWAP1 POP SWAP1 DUP2 ADD SWAP1 PUSH1 0x1F AND DUP1 ISZERO PUSH2 0x180 JUMPI DUP1 DUP3 SUB DUP1 MLOAD PUSH1 0x1 DUP4 PUSH1 0x20 SUB PUSH2 0x100 EXP SUB NOT AND DUP2 MSTORE PUSH1 0x20 ADD SWAP2 POP JUMPDEST POP SWAP3 POP POP POP PUSH1 0x40 MLOAD DUP1 SWAP2 SUB SWAP1 RETURN JUMPDEST PUSH1 0x0 DUP1 SWAP1 SLOAD SWAP1 PUSH2 0x100 EXP SWAP1 DIV PUSH20 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF AND PUSH20 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF AND CALLER PUSH20 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF AND EQ ISZERO PUSH2 0x21D JUMPI PUSH1 0x0 DUP1 SWAP1 SLOAD SWAP1 PUSH2 0x100 EXP SWAP1 DIV PUSH20 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF AND PUSH20 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF AND SELFDESTRUCT JUMPDEST JUMP JUMPDEST DUP1 PUSH1 0x1 SWAP1 DUP1 MLOAD SWAP1 PUSH1 0x20 ADD SWAP1 PUSH2 0x235 SWAP3 SWAP2 SWAP1 PUSH2 0x2DB JUMP JUMPDEST POP POP JUMP JUMPDEST PUSH1 0x60 PUSH1 0x1 DUP1 SLOAD PUSH1 0x1 DUP2 PUSH1 0x1 AND ISZERO PUSH2 0x100 MUL SUB AND PUSH1 0x2 SWAP1 DIV DUP1 PUSH1 0x1F ADD PUSH1 0x20 DUP1 SWAP2 DIV MUL PUSH1 0x20 ADD PUSH1 0x40 MLOAD SWAP1 DUP2 ADD PUSH1 0x40 MSTORE DUP1 SWAP3 SWAP2 SWAP1 DUP2 DUP2 MSTORE PUSH1 0x20 ADD DUP3 DUP1 SLOAD PUSH1 0x1 DUP2 PUSH1 0x1 AND ISZERO PUSH2 0x100 MUL SUB AND PUSH1 0x2 SWAP1 DIV DUP1 ISZERO PUSH2 0x2D1 JUMPI DUP1 PUSH1 0x1F LT PUSH2 0x2A6 JUMPI PUSH2 0x100 DUP1 DUP4 SLOAD DIV MUL DUP4 MSTORE SWAP2 PUSH1 0x20 ADD SWAP2 PUSH2 0x2D1 JUMP JUMPDEST DUP3 ADD SWAP2 SWAP1 PUSH1 0x0 MSTORE PUSH1 0x20 PUSH1 0x0 KECCAK256 SWAP1 JUMPDEST DUP2 SLOAD DUP2 MSTORE SWAP1 PUSH1 0x1 ADD SWAP1 PUSH1 0x20 ADD DUP1 DUP4 GT PUSH2 0x2B4 JUMPI DUP3 SWAP1 SUB PUSH1 0x1F AND DUP3 ADD SWAP2 JUMPDEST POP POP POP POP POP SWAP1 POP SWAP1 JUMP JUMPDEST DUP3 DUP1 SLOAD PUSH1 0x1 DUP2 PUSH1 0x1 AND ISZERO PUSH2 0x100 MUL SUB AND PUSH1 0x2 SWAP1 DIV SWAP1 PUSH1 0x0 MSTORE PUSH1 0x20 PUSH1 0x0 KECCAK256 SWAP1 PUSH1 0x1F ADD PUSH1 0x20 SWAP1 DIV DUP2 ADD SWAP3 DUP3 PUSH1 0x1F LT PUSH2 0x31C JUMPI DUP1 MLOAD PUSH1 0xFF NOT AND DUP4 DUP1 ADD OR DUP6 SSTORE PUSH2 0x34A JUMP JUMPDEST DUP3 DUP1 ADD PUSH1 0x1 ADD DUP6 SSTORE DUP3 ISZERO PUSH2 0x34A JUMPI SWAP2 DUP3 ADD JUMPDEST DUP3 DUP2 GT ISZERO PUSH2 0x349 JUMPI DUP3 MLOAD DUP3 SSTORE SWAP2 PUSH1 0x20 ADD SWAP2 SWAP1 PUSH1 0x1 ADD SWAP1 PUSH2 0x32E JUMP JUMPDEST JUMPDEST POP SWAP1 POP PUSH2 0x357 SWAP2 SWAP1 PUSH2 0x35B JUMP JUMPDEST POP SWAP1 JUMP JUMPDEST PUSH2 0x37D SWAP2 SWAP1 JUMPDEST DUP1 DUP3 GT ISZERO PUSH2 0x379 JUMPI PUSH1 0x0 DUP2 PUSH1 0x0 SWAP1 SSTORE POP PUSH1 0x1 ADD PUSH2 0x361 JUMP JUMPDEST POP SWAP1 JUMP JUMPDEST SWAP1 JUMP INVALID LOG2 PUSH6 0x627A7A723158 KECCAK256 PUSH15 0x85A5DA055A6394A6DC80D00AFF410D SWAP6 LT SWAP6 0xde DUP6 PUSH28 0x24FD98F2F985659A2BD264736F6C634300050B003200000000000000 ",
"sourceMap": "34:534:0:-;;;110:92;8:9:-1;5:2;;;30:1;27;20:12;5:2;110:92:0;151:10;141:7;;:20;;;;;;;;;;;;;;;;;;171:24;;;;;;;;;;;;;;;;;:8;:24;;;;;;;;;;;;:::i;:::-;;34:534;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;:::i;:::-;;;:::o;:::-;;;;;;;;;;;;;;;;;;;;;;;;;;;:::o;:::-;;;;;;;"
}
四、ABI各参数的含义
- name: 函数名称
- type：方法类型，包括function, constructor, fallback(缺省方法)可以缺省，默认为function
- constant：布尔值，如果为true指明方法不会修改合约字段的状态变量
- payable：布尔值，标明方法是否可以接收ether
- stateMutability：状态类型，包括pure (不读取区块链状态)，view (和constant类型，只能查看，不会修改合约字段)，nonpayable（和payable含义一样），payable（和payable含义一样）。其实保留payable和constant是为了向后兼容
- inputs：数组，描述参数的名称和类型
- name：参数名称
- type：参数类型
- outputs：和inputs一样，如果没有返回值，缺省是一个空数组
五、怎么使用ABI
使用ABI的细节请参考: 以太坊智能合约---helloworld
参考:
以太坊ABI介绍(一)
以太坊ABI介绍(二)
ABI编码外部方法调用的方式
深入以太坊智能合约ABI