Solidity ABI 编码解码

ABI编码

Solidity中，ABI编码有4个函数：abi.encode, abi.encodePacked, abi.encodeWithSignature, abi.encodeWithSelector。

我们将用编码4个变量，他们的类型分别是uint256, address, string, uint256[2]：

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

1. abi.encode

将给定参数利用ABI规则编码。ABI被设计出来跟智能合约交互，他将每个参数转填充为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。

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

编码的结果为

0x000000000000000000000000000000000000000000000000000000000000000a0000000000000000000000007a58c0be72be218b41c608b7fe7c5bb630736c7100000000000000000000000000000000000000000000000000000000000000a00000000000000000000000000000000000000000000000000000000000000005000000000000000000000000000000000000000000000000000000000000000600000000000000000000000000000000000000000000000000000000000000043078414100000000000000000000000000000000000000000000000000000000

由于abi.encode将每个数据都填充为32字节，中间有很多0。

2. abi.encodePacked

将给定参数根据其所需最低空间编码。它类似 abi.encode，但是会把其中填充的很多0省略。比如，只用1字节来编码uint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。

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

编码的结果为

0x000000000000000000000000000000000000000000000000000000000000000a7a58c0be72be218b41c608b7fe7c5bb630736c713078414100000000000000000000000000000000000000000000000000000000000000050000000000000000000000000000000000000000000000000000000000000006

由于abi.encodePacked对编码进行了压缩，长度比abi.encode短很多。

3. abi.encodeWithSignature

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

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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

0xe87082f1000000000000000000000000000000000000000000000000000000000000000a0000000000000000000000007a58c0be72be218b41c608b7fe7c5bb630736c7100000000000000000000000000000000000000000000000000000000000000a00000000000000000000000000000000000000000000000000000000000000005000000000000000000000000000000000000000000000000000000000000000600000000000000000000000000000000000000000000000000000000000000043078414100000000000000000000000000000000000000000000000000000000

等同于在abi.encode编码结果前加上了4字节的函数选择器。

4. abi.encodeWithSelector

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。

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

编码的结果为

0xe87082f1000000000000000000000000000000000000000000000000000000000000000a0000000000000000000000007a58c0be72be218b41c608b7fe7c5bb630736c7100000000000000000000000000000000000000000000000000000000000000a00000000000000000000000000000000000000000000000000000000000000005000000000000000000000000000000000000000000000000000000000000000600000000000000000000000000000000000000000000000000000000000000043078414100000000000000000000000000000000000000000000000000000000

与abi.encodeWithSignature结果一样。

ABI解码

abi.decode

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。

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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