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." y* C0 d+ d; W. f! F. v+ f
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:! G$ m+ O) l F3 F, M5 H/ [
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。# [" M. h+ @" x
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 $7.1)。. \3 T* d h% Y& W8 u& M0 w
这些 token 都都都都销毁了 (⊙?⊙) }: Z( O3 Y9 _0 D+ O
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Dexaran 认识到了这个问题,
Contracts that are not designed to work with tokens must reject incoming token transactions. Otherwise, each token becomes a potential token trap. g T" d4 f0 J9 r D$ g d
ERC20 token standard issues.(google docs)+ a- T1 a" p( \, g# o" |# T
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 {) w4 f( a; \" R/ W$ K
function transfer(address to, uint value, bytes data) {
uint codeLength;9 r" V6 Y. V: p3 {$ Q9 \, }& c
assembly {
codeLength := extcodesize(_to)7 i; O$ I- S) X, B4 y. R0 a: E; e1 U
}
balances[msg.sender] = balances[msg.sender].sub(_value);
balances[_to] = balances[_to].add(_value);- X& \! ]5 D. b: `" k: a
if(codeLength>0) {
// Require proper transaction handling.
ERC223Receiver receiver = ERC223Receiver(_to);+ I. E8 E$ I1 m; f7 R$ s3 b+ t7 @
receiver.tokenFallback(msg.sender, _value, _data);
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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The biggest change is that ERC223 no longer allow token to be transferred to a contract that does not allow token to be withdrawn.* W* @1 {1 [ L, X; w3 D. I
https://medium.com/cryptomover/what-are-erc20-and-erc223-tokens-307badcca5a& X! A$ I, U8 E5 i" K