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There is no way in solidity to check if an address is a contract. One of the goals of Ethereum is for humans and smart contracts to both be treated equally.' O' ^0 {% @9 K) l$ }
https://stackoverflow.com/a/37670490/7218912
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有时候确实有需要向智能合约转账:
但是大多数 smart contract 的 token 是不能转出的,只要合约里没写转出的逻辑,就不能转出。以太坊将智能合约看做是独立的个体,没人知道它的私钥,给不支持转出的智能合约转 token 就等于销毁了。8 H: R" w- M+ ^( q8 N
当我们要转账时,会转到交易方的地址,不会闲着没事给智能合约转 token。但是这种事情仍然会发生,不断有人给 EOSTokenContract 转 EOS(见下图),EOSTokenContract 账户下现在有 154,834 EOS,价值 $1,176,738.4(价格 $7.6)。类似的,QtumTokenContract 账户下现在有 22,293 QTUM,价值 $158,280.3(价格 $7.1)。
这些 token 都都都都销毁了 (⊙?⊙) F: i5 P# x1 I6 i
Dexaran 认识到了这个问题,
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Contracts that are not designed to work with tokens must reject incoming token transactions. Otherwise, each token becomes a potential token trap.- F- k2 l$ g# K' k
ERC20 token standard issues.(google docs)+ _8 F" V. N' Z& K
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并在 github 创建了一个 issue。
tokenFallback 函数,当转账到不能转出的智能合约地址时,将自动取消。
contract ERC223 {$ k. o5 B M' s6 B: W) Q( U
function transfer(address to, uint value, bytes data) {
uint codeLength;
assembly {8 ^) I# _- S: |7 M s/ ~
codeLength := extcodesize(_to)6 C9 k7 x q' K
} f" D( W8 B7 q6 g: j- {
balances[msg.sender] = balances[msg.sender].sub(_value);
balances[_to] = balances[_to].add(_value);
if(codeLength>0) {2 F% f8 Y$ t2 B8 t, o5 k& M
// Require proper transaction handling.
ERC223Receiver receiver = ERC223Receiver(_to);# J6 Y6 C* W0 A9 c
receiver.tokenFallback(msg.sender, _value, _data);" g" ]" ^7 _- C5 S( q c* b
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}
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【todo】:代码解释
The biggest change is that ERC223 no longer allow token to be transferred to a contract that does not allow token to be withdrawn.
https://medium.com/cryptomover/what-are-erc20-and-erc223-tokens-307badcca5a