ABI(Application Binary Interface,应用二进制接口)是与以太坊智能合约交互的标准。数据基于他们的类型编码；并且由于编码后不包含类型信息，解码时需要注明它们的类型。

Solidity中ABI编码有4个函数：abi.encode，abi.encodePacked，abi.encodeWithSignature，abi.encodeWithSelector。而ABI编码有一个函数：abi.decode，用于解码abi.encode的数据。

我们将编码4个变量，他们的类型分别是uint256（别名 uint）, address, string, uint256[2]：

    uint x = 10;
    address addr = 0x7A58c0Be72BE218B41C608b7Fe7C5bB630736C71;
    string name = "0xAA";
    uint[2] array = [5, 6]; 

将给定参数利用ABI规则编码。ABI被设计出来跟只能合约交互，它将每个参数填充为32字节的数据，并拼接在一起。如果你要和合约交互，你要用的就是abi.encode。

    function encode() public view returns(bytes memory result) {
        result = abi.encode(x, addr, name, array);
    }

编码结果为0x000000000000000000000000000000000000000000000000000000000000000a0000000000000000000000005b38da6a701c568545dcfcb03fcb875f56beddc400000000000000000000000000000000000000000000000000000000000000a00000000000000000000000000000000000000000000000000000000000000005000000000000000000000000000000000000000000000000000000000000000600000000000000000000000000000000000000000000000000000000000000043078414100000000000000000000000000000000000000000000000000000000，由于abi.encode将每个数据都填充为32字节，中间有很多0。

将给定参数根据所需最低空间编码。它类似abi.encode，但是会把其中填充的很多0省略。比如，只有一个字节来编码uint8类型。当你想省空间，并且不与合约交互的时候，可以使用abi.encodePacked，例如算一些数据的hash时。

    function encodePacked() public view returns(bytes memory result) {
        result = abi.encodePacked(x, addr, name, array);
    }

编码结果为0x000000000000000000000000000000000000000000000000000000000000000a5b38da6a701c568545dcfcb03fcb875f56beddc43078414100000000000000000000000000000000000000000000000000000000000000050000000000000000000000000000000000000000000000000000000000000006，由于abi.encodePacked对编码进行了压缩，长度比abi.encode短很多。

与abi.encode功能类似，只不过第一个参数为函数名，比如"foo(uint256,address,string,uint256[2])"。当调用其他合约的时候可以使用。

    function encodeWithSignature() public view returns(bytes memory result) {
        result = abi.encodeWithSignature("foo(uint256,address,string,uint256[2])", x, addr, name, array);
    }

编码的结果为0xe87082f1000000000000000000000000000000000000000000000000000000000000000a0000000000000000000000005b38da6a701c568545dcfcb03fcb875f56beddc400000000000000000000000000000000000000000000000000000000000000a00000000000000000000000000000000000000000000000000000000000000005000000000000000000000000000000000000000000000000000000000000000600000000000000000000000000000000000000000000000000000000000000043078414100000000000000000000000000000000000000000000000000000000，等同于在abi.encode编码结果前加上4字节的函数选择器。

与abi.encodeWithSIgnature功能类似，只不过第一个参数为函数选择器，为函数签名Keccak哈希的前4个字节。

    function encodeWithSelector() public view returns(bytes memory result) {
        result = abi.encodeWithSelector(bytes4(keccak256("foo(uint256,address,string,uint256[2])")), x, addr, name, array);
    }

编码结果为0xe87082f1000000000000000000000000000000000000000000000000000000000000000a0000000000000000000000005b38da6a701c568545dcfcb03fcb875f56beddc400000000000000000000000000000000000000000000000000000000000000a00000000000000000000000000000000000000000000000000000000000000005000000000000000000000000000000000000000000000000000000000000000600000000000000000000000000000000000000000000000000000000000000043078414100000000000000000000000000000000000000000000000000000000，与abi.encodeWithSignature结果一样。

abi.decode用于解码abi.encode生成的二进制编码，将它还原成原本的参数。

    function decode(bytes memory data) public pure returns(uint dx, address daddr, string memory dname, uint[2] memory darray) {
        (dx, daddr, dname, darray) = abi.decode(data, (uint, address, string, uint[2]));
    }

我们将abi.encode的二进制编码输入给decode，将解码出原来的参数：

部署ABIEncode合约，验证各种编码

1. 在合约开发中，ABI长配合call来实现对合约的底层调用

    bytes4 selector = contract.getValue.selector;

    bytes memory data = abi.encodeWithSelector(selector, _x);
    (bool success, bytes memory returnedData) = address(contract).staticcall(data);
    require(success);

    return abi.decode(returnedData, (uint256));

1. ethers.js中常用ABI实现合约的导入和函数调用。

    const wavePortalContract = new ethers.Contract(contractAddress, contractABI, signer);
    /*
        * Call the getAllWaves method from your Smart Contract
        */
    const waves = await wavePortalContract.getAllWaves();

1. 对不开源合约进行反编译后，某些函数无法查到函数签名，可通过ABI进行调用。

• 0x533ba33a() 是一个反编译后显示的函数，只有函数编码后的结果，并且无法查到函数签名

• 这种情况无法通过构造interface接口或contract来进行调用

这种情况下，就可以通过ABI函数选择器来调用

    bytes memory data = abi.encodeWithSelector(bytes4(0x533ba33a));

    (bool success, bytes memory returnedData) = address(contract).staticcall(data);
    require(success);

    return abi.decode(returnedData, (uint256));