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Pseudo-Introspection, or standard interface detection #165
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This would be particularly useful for ENS resolvers, and would allow removing the
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A couple of other suggestions:
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Discussing this with Chris in the Solidity channel, he pointed out that an interface is more than its ABI; it's possible for two interfaces with the same set of function signatures to have different expectations of how they operate (especially since function signatures don't include parameter names!). So, the interface ID should be a pseudorandom value with low probability of colliding with any other interface ID; it doesn't need to bear a strict relationship to the source (and arguably, shouldn't, so people don't make assumptions about it being usable as some kind of test). I agree - so ignore my earlier suggestions about constructing the interface ID from the constituent functions. Edit: On the other hand, Go does 'duck typed interfaces' and generally doesn't have a problem; although you can have two interfaces with the same ABI but different intents, the chances of both of them being relevant in a given scenario seem vanishingly small. For instance, it's easy to avoid a collision in interface definitions for ENS resolvers, and nobody's going to ask an ENS resolver if it implements, say , a token-related interface. |
After some more discussion, I think we did settle on just using the xor of the function identifiers that are part of the interface as a canonical identifier. |
@chriseth @Arachnid I am of the belief that we should be either copying how Go does this or how Rust does this in regards to our interfaces. They should be their own type. Something looking like this: contract C {
interface I {
foo(uint256) returns (uint256);
bar(bool, string) returns (bool);
}
}
contract A {
struct MyStruct {
function foo(uint256) returns (uint256);
function bar(bool, string) returns (bool);
}
MyStruct _myStruct;
D someContract;
function a_call() {
d.f(_myStruct); //passes in _myStruct as interface to D
}
}
contract B {
E _e;
D _d;
function call_D() {
_d.f(_e); //passes in E to D and thus will clear because functions align.
}
}
contract E {
function foo (uint256) returns (uint256) {
//some function
}
function bar (bool, string) returns (bool) {
//some function
}
}
contract D is C {
function f(_interface I) {
switch type(_interface) { //switch on the types of objects passed into the interface (i think this should be mandatory to some extent)
case A:
uint a = _interface.foo(1);
case B:
bool truth = _interface.bar(true, "something");
default: throw;
}
}
} I'm not sure about xor-ing it...that may work, I'm just not sure I understand it yet, need to look. What I think we can do for the type assertion is to hash for these types based on their actual function opcodes that they are utilizing/generating on the stack portion. This will make it so that we can verify that only these contracts are calling externally and can make the interface quite a useful safety mechanism. |
@VoR0220 I think what you're talking about is language design, and thus orthogonal to this EIP, which is mostly about how to implement the feature at the EVM level. |
I believe you might be correct. Will reread this in the morning. |
Okay. 2 Months later, I have reread it and with some help I think I understand the proposal better. Here's my question. How might we distinguish between different versions of a contract interface? Would that need to be included? Or would it be "Version independent"? |
Here are the modifications that I would do in the standard: 1.- I would keep GenericInterface very simple with just one single method: With this definition, You can test if a contract implements EIP165 or not by trying to call For saving gas, a single generic EIP165Cache contract can exist in the blockchain. You can see an how this implementation would be here: https://github.com/jbaylina/EIP165Cache/blob/master/contracts/EIP165Cache.sol |
I broadly agree, although I'm not sure it's necessary to be able to test |
@Arachnid I believe that there are some contracts (like wallets or normal addresses) that don't throw. They just do nothing. If you agree on this, I will make some tests with the most used contracts so that they return false. We will see if this "double check" is necessary or not. |
@Arachnid Another question, I see that in the ENS implementation, the fingerprint is: function supportsInterface(bytes4 _interfaceID) constant returns (bool); instead of function supportsInterface(bytes32 _interfaceID) constant returns (bool); I think it's better to use bytes32 instead of bytes4 even if we use only 4 bytes. This will give space for future ampliations. And may be it's too late now, but I think it would be good to also return true for the 0xf1753550 -> supportsInterface(bytes32) |
There's certainly no harm in having contracts return true for the Since you're working on this, any interest in submitting a PR that formalises it? |
@Arachnid: You mean a PR for the standard or for the ENS? |
I mean a pr for the current understanding of this standard.
…On Wed, 3 May 2017, 18:42 Jordi Baylina, ***@***.***> wrote:
@Arachnid <https://github.com/Arachnid>: You mean a PR for the standard
or for the ENS?
—
You are receiving this because you were mentioned.
Reply to this email directly, view it on GitHub
<#165 (comment)>, or mute
the thread
<https://github.com/notifications/unsubscribe-auth/AABFyUtSWd1ksEn-ZlhPOtymbZZtsX7xks5r2LyFgaJpZM4KjYmN>
.
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@Arachnid Ok, I'm going to prepare it! |
I have the first draft of the Specification Here: I have also created and tested the EIP165Cache contract Here: Please, comment/correct in the doc before creating the formal PR. |
Looks like a good start, but it would be much easier to leave comments against the PR than in a Google Doc (and they'll be preserved for posterity). |
Ok. Then I'll Create the PR. |
Just deployed the contract in testnet: https://ropsten.etherscan.io/address/0xb60739c904b6d202c7cb2ba4be0fd4b733374c4e#readContract |
Right now we have a few solutions for what we are trying to solve:
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VERSION 3: Added assembly parts Also, we could just be a boss and do actual introspection on the blockchain from a contract.
pragma solidity ^0.4.19;
contract ContractIntrospector {
enum Result {No, Yes, PleaseCallAgainToContinueSearching}
mapping (address => mapping(bytes4 => bool)) private contractFunctionSelectorSupported;
mapping (address => bytes4[]) public contractFunctionSelectors;
mapping (address => uint) private searchProgress;
mapping (address => bool) public doneSearching;
function getFunctionSignature(string _function) external pure returns (bytes4) {
return bytes4(keccak256(_function));
}
// Save lookup table in memory
function getBytesForOpcodes() private pure returns (uint256[256] retval) {
// Initialize bytesForInstruction
// Read the Yellow Paper, find α for each opcode
for (uint i = 0; i < 256; i++) {
retval[i] = uint256(-1); // Default return value
}
retval[0x00] = uint256(-1); // HALT
retval[0x01] = 1 + 32*1; // ADD
retval[0x02] = 1 + 32*1; // MUL
//...
}
function getSize(address _addr) public view returns (uint256 _size) {
assembly {
_size := extcodesize(_addr)
}
}
function getCode(address _addr, uint256 _start, uint256 _length)
public
view
returns (bytes _code)
{
_code = new bytes(_length);
assembly {
extcodecopy(_addr, add(_code, 0x20), _start, _length)
}
}
function howManyBytesCanWeProcessWorstCaseWithRemainingGas()
private
returns (uint256 _size)
{
//TODO: implement this better
return 20;
}
function doesContractSupportFunctionSelector (
address _addr,
bytes4 _functionSelector
)
public
returns (Result)
{
if (contractFunctionSelectorSupported[_addr][_functionSelector]) {
return Result.Yes;
}
uint contractSize = getSize(_addr);
uint start = searchProgress[_addr]; // starts at zero
if (start >= contractSize) {
return Result.No;
}
uint256[256] memory bytesForOpcode = getBytesForOpcodes();
uint length = howManyBytesCanWeProcessWorstCaseWithRemainingGas();
bytes memory code = getCode(_addr, start, length);
uint ptr = 0;
while (ptr < length) {
if (code[ptr] == 0x63) { // PUSH4
bytes4 selector = code[ptr+1] | // TODO: is endian here correct?
code[ptr+2] << 8 |
code[ptr+3] << 16 |
code[ptr+4] << 24;
contractFunctionSelectorSupported[_addr][selector] = true;
contractFunctionSelectors[_addr].push(selector);
if (selector == _functionSelector) {
searchProgress[_addr] = start + ptr;
if (start + ptr > contractSize) {
doneSearching[_addr] = true;
}
return Result.Yes;
}
}
if (code[ptr] == 0x5b) { // JUMPDEST
searchProgress[_addr] = uint256(-1);
doneSearching[_addr] = true;
return Result.No;
}
ptr += bytesForOpcode[uint256(code[ptr])];
}
if (ptr >= length) {
searchProgress[_addr] = uint256(-1); // the maximum uint value
return Result.No;
}
return Result.PleaseCallAgainToContinueSearching;
}
} Yeah, this is mostly a joke/though experiment. But maybe you were thinking it too, so just wanted to say it. |
Haha, yes, I non-seriously considered decompiling too. (Btw, the current selector prequel has a gas cost linear in number of functions, but low constant cost is quite doable using a map, but would break decompiling approaches.) Just to be clear. With 'heuristics' in my earlier comment I meant something similar to @jbaylina's I'm not a big fan of EIP-820. 1) It complicates deployment, which will complicate development and testing and hurt adoption. This standard is pretty much code-copy paste to implement, easy for adoption. 2) EIP820 in its current form relies on user-provided strings for ids. I foresee contracts incorrectly claiming to support the ERC20 interface. 3) It allows for other contracts to implement an interface on behalf of the contract, this adds an extra layer of complication to using interfaces on contracts as you now need to support a layer of indirection. This indirection can change at any moment, so you can not cache it. This seems like a very big gas cost overhead to me. In fact, this indirection can change mid-transaction. Finally, what happens if a malicious token contract 'claims' that its 'transfer' interface is implemented by an unrelated valuable token? My favorite is 165-view. The only problematic caching case is when a contract drops support for a interface. (Adding can be solved by manually invalidating cache, which is trustless) But this is already a problematic case without EIP165. Contracts that plan to do this should say so in advance (lest developers will depend on an interface) and when they plan in advance they can also say not to rely on interface caches. |
Quick updates:
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OK. I am going to go forward with writing this up for EIP165-VIEW variant. PR coming. |
@recmo Sorry, that link broke, can you please send again? |
Hello channel. #881 is very far along. I have described it faithfully as was discussed here ("165-VIEW" as above). As yet, I have seen no controversy in the 165-VIEW approach. Previously there was an inconsistency with the 165-VIEW approach and the EIP165Cache from @jbaylina. I have resolved this by rewriting the cache. Previously there was an open item from 165-PURE discussion about the gas cost of using an interface mapping versus using the PURE approach. Both implementations are shown and the gas costs are discussed. Please support me by going to #881 and reacting with a party emoji 🎉 if you believe this EIP should be accepted. Acceptance is NOT final. The significance of acceptance is detailed in EIP-1:
|
The supporting documentation for RJ @VoR0220, Hudson @Souptacular and Griff @GriffGreen I do not have access to that history. FILE-> VERSION HISTORY -> PRIOR VERSIONS. Would you please review this history and attest that these three individuals should be listed as authors? If you recommendation a deletion, please suggest it here and at #881. If you can make the attestation, this will be helpful to document for posterity. |
The PR for this in #881 has been merged |
FYI: On the NEO blockchain, this requirement was solved in the following way: https://github.com/neo-project/proposals/blob/master/nep-10.mediawiki |
//Ownable ¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? contract Ownable{ address public owner; //¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? function Ownable(){ owner = msg.sender; } //¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? modifier onlyOwner(){ require(msg.sender == owner); _; } //¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?newOwner¿? function transferOwnership(address newOwner)onlyOwner{ if(newOwner != address(0)){ owner =newOwner; } } } contract pigAccessControl is Ownable{ /** *government¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? *¿?¿?¿?¿?¿?¿?¿?pigcore¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? */ ///¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? //¿?¿?¿?¿?¿? address public governmentAdddress; User public user; //¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? bool public paused = false; enum Role{Farm, Slaugthethouse, Logistics, Market}//¿?¿? struct User{ address roleAddress; uint256 roleId; string location; Role role; } mapping (address => User) public FarmMap; mapping (address => User) public SlaughterhouseMap; mapping (address => User) public LogisticsMap; mapping (address => User) public MarkeMap; //¿?¿?government¿?¿?¿?¿?¿?¿?¿?¿? modifier onlyGovernment(){ require(msg.sender == governmentAdddress); _; } //¿?¿?farm¿?¿?¿?¿?¿?¿?¿?¿? modifier onlyFarm(){ require(msg.sender == user.roleAddress); _; } //¿?¿?slaughterhouse¿?¿?¿?¿?¿?¿?¿?¿? modifier onlySlaughterhouse(){ require(msg.sender == user.roleAddress); _; } //¿?¿?logistics¿?¿?¿?¿?¿?¿?¿?¿? modifier onlyLogistics(){ require(msg.sender == user.roleAddress); _; } //¿?¿?market¿?¿?¿?¿?¿?¿?¿?¿? modifier onlyMarket(){ require(msg.sender == user.roleAddress); _; } //¿?¿?¿?¿?¿?¿?¿?¿?¿?government,¿?¿?¿?¿?¿?¿?government¿?¿?¿? //_newGovernment¿?¿?government¿?¿?¿? function setGovernment(address _newGovernment)external onlyOwner { require(_newGovernment != address(0)); governmentAdddress = _newGovernment; } function newUser(uint256 ID, string location,Role role) returns(bool, address,Role,string){ if(role == Role.Farm){ //user = FarmMap[msg.sender]; user.roleAddress = msg.sender; user.roleId = ID; user.location = location; user.role = role; FarmMap[msg.sender] = user; }else if(role == Role.Slaugthethouse){ //user = SlaughterhouseMap[msg.sender]; user.roleAddress = msg.sender; user.roleId = ID; user.location = location; user.role = role; SlaughterhouseMap[msg.sender] = user; }else if(role == Role.Logistics){ // user = LogisticsMap[msg.sender]; user.roleAddress = msg.sender; user.roleId = ID; user.location = location; user.role = role; LogisticsMap[msg.sender] = user; }else if(role == Role.Market){ //user = MarkeMap[msg.sender]; user.roleAddress = msg.sender; user.roleId = ID; user.location = location; user.role = role; MarkeMap[msg.sender] = user; }else{ return (false,user.roleAddress, user.role,"the actor is not belong"); } if(user.roleId != 0x0){ return (false, user.roleAddress, user.role,"this ID has been occupied!"); } user.roleAddress = msg.sender; user.roleId = ID; user.location = location; user.role = role; return (true, user.roleAddress, user.role,"Success"); } //¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? modifier whennotPaused{ require(!paused); _; } //¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? modifier whenPaused{ require(paused); _; } //¿?¿?government¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?,¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? function pause() external onlyGovernment whennotPaused{ paused == true; } //¿?¿?government¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?,¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? function unpause() public onlyGovernment whenPaused { paused == false; } } ///¿?¿?ERC721¿?¿?¿?¿?¿? contract ERC721 { // Required methods //¿?¿?¿?¿?token¿?¿?¿? function totalSupply() public view returns (uint256 total); //¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? function balanceOf(address _owner) public view returns (uint256 balance); //¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? function ownerOf(uint256 _tokenId) external view returns (address owner); //¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? function transfer(address _to, uint256 _tokenId) external; // Events event Transfer(address from, address to, uint256 tokenId); function tokensOfOwner(address _owner) external view returns (uint256[] tokenIds); // ERC-165 Compatibility (ethereum/EIPs#165) function supportsInterface(bytes4 _interfaceID) external view returns (bool); } /// ¿?¿?pig¿?¿?¿?¿?¿?¿?¿?pig¿?¿?¿?¿?¿? contract pigBase is pigAccessControl{ //¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?Birth¿?¿?¿? event Birth(uint256 pigID, address owner, uint64 birthTime, uint256 breed, uint256 weight, int8 gender); //¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? event Transfer(address from, address to, uint256 tokenId); /** * pig¿?¿?¿? */ struct pig{ //¿?¿?¿?¿?¿? address currentAddress; //¿?¿?¿?¿? uint64 birthTime; //¿?¿? uint256 breed; //¿?¿? uint256 weight; //¿?¿? int8 gender; } //¿?¿?¿?¿?¿?¿?pig¿?¿?¿?¿?¿?,¿?¿?pig¿?ID¿?¿?¿?¿?¿?¿?¿?¿? pig[] pigs; //¿?pigID¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? mapping(uint256 => address) public pigIndexToOwner; //¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? mapping(address => uint256) public ownershipTokenCount; //¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? function _transfer(address _from, address _to, uint256 _tokenId)internal{ ownershipTokenCount[_to]++; // ¿?¿?¿?¿? pigIndexToOwner[_tokenId] = _to; // ¿?¿?¿?¿?¿?¿?¿?¿?¿?0x0¿?¿?¿? if(_from != address(0)){ ownershipTokenCount[_from]--; } //¿?¿?¿?¿?¿?¿?¿?¿? Transfer(_from, _to, _tokenId); } /** * ¿?¿?¿?¿?newpig¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? * ¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?,¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? * ¿?¿?¿?Birth¿?¿?¿?Transfer¿?¿?¿? */ function createPig ( uint256 _breed, uint256 _weight, int8 _gender ) external returns (uint256) { pig memory _pig = pig({ currentAddress : msg.sender, birthTime : uint64(now), breed : _breed, weight : _weight, gender : _gender }); uint256 newPigID = pigs.push(_pig) - 1; // ¿?¿?Birth¿?¿? emit Birth(newPigID, msg.sender,uint64(now), _breed, _weight, _gender); // ¿?¿?¿?¿?¿?¿?¿?¿?¿?Transfer¿?¿? // ¿?¿?ERC721¿?¿? _transfer(0, msg.sender, newPigID); return newPigID; } } /// ¿?¿?¿?¿?¿?KittyBase¿?ERC721¿?¿?¿?ERC721¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? contract pigOwnership is pigBase,ERC721{ //¿?¿?ERC721¿?Name¿?symbol¿?¿?¿?¿?¿?¿?¿?Token string public constant name = "Pig¿?s Life"; string public constant symbol = "PIE"; bytes4 constant InterfaceSignature_ERC165 = bytes4(keccak256('supportsInterface(bytes4)')); bytes4 constant InterfaceSignature_ERC721 = bytes4(keccak256('name()')) ^ bytes4(keccak256('symbol()')) ^ bytes4(keccak256('totalSupply()')) ^ bytes4(keccak256('balanceOf(address)')) ^ bytes4(keccak256('ownerOf(uint256)')) ^ bytes4(keccak256('approve(address,uint256)')) ^ bytes4(keccak256('transfer(address,uint256)')) ^ bytes4(keccak256('transferFrom(address,address,uint256)')) ^ bytes4(keccak256('tokensOfOwner(address)')) ^ bytes4(keccak256('tokenMetadata(uint256,string)')); //¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?ERC721¿?ERC165¿?¿? function supportsInterface(bytes4 _interfaceID)external view returns(bool){ return((_interfaceID == InterfaceSignature_ERC721) || (_interfaceID == InterfaceSignature_ERC165)); } // ¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? // _currentAddress ¿?¿?¿?¿?¿?¿?¿?¿? function _owns(address _currentAddress, uint256 _tokenId) internal view returns (bool){ return pigIndexToOwner[_tokenId] == _currentAddress; } //¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? function balanceOf(address _owner)public view returns(uint256 count){ return ownershipTokenCount[_owner]; } //¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?ERC-721¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? function transfer(address _to, uint256 _tokenId) external { // ¿?¿?¿?¿?¿?0x0 require(_to != address(0)); require(_to !=address(this)); // ¿?¿?¿?¿?¿?¿?¿?¿? require(_owns(msg.sender,_tokenId)); // ¿?¿?¿?¿?¿?¿?¿?Transfer¿?¿? _transfer(msg.sender, _to, _tokenId); pig storage Pig = pigs[_tokenId]; Pig.currentAddress = pigIndexToOwner[_tokenId]; // pigs.push(Pig); emit Transfer(msg.sender, _to, _tokenId); } //¿?¿?¿?¿?¿?¿?¿?¿? function totalSupply()public view returns(uint){ return pigs.length; } //¿?¿?¿?¿?¿?¿?¿?¿? function ownerOf(uint256 _tokenId)external view returns(address owner){ owner = pigIndexToOwner[_tokenId]; require(owner != address(0)); } // ¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿? function tokensOfOwner(address _owner)external view returns(uint256[] ownerTokens){ // ¿?¿?_owner¿?¿?¿?¿?¿?¿?¿? uint256 tokenCount = balanceOf(_owner); if(tokenCount == 0){ // ¿?¿?¿?¿?¿?¿?¿?¿?¿? return new uint256[](0); }else{ //¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?¿?result¿?¿?¿?¿?tokenCount uint256[] memory result = new uint256[](tokenCount); // ¿?¿?¿?¿?¿?¿?¿?¿? uint256 tolalPigs = totalSupply(); // ¿?¿?¿?¿?¿?¿? uint256 resultIndex = 0; } // ¿?¿?ID¿?1¿?¿?¿?¿? uint256 pigID; // ¿?1¿?¿?¿?¿?¿?¿?¿?¿?¿?tolalPigs for(pigID =0; pigID < tolalPigs; pigID++){ // ¿?¿?¿?¿?pigID¿?¿?¿?¿?¿?¿?¿?_owner if(pigIndexToOwner[pigID] == _owner){ // ¿?¿?¿?¿?¿?pigID¿?¿?result¿?¿?resultIndex¿?¿? result[resultIndex] = pigID; resultIndex++; } } return result; } } contract pigSeparation is pigOwnership{ //¿?¿?¿?¿?¿?¿? //¿?¿?¿?¿?¿?¿? } ///¿?¿?¿? contract pigCore is pigOwnership{ function getPig(uint256 _id) external view returns( address currentAddress, uint64 birthTime, uint256 breed, uint256 weight, int8 gender ){ pig storage Pig = pigs[_id]; currentAddress = address(Pig.currentAddress); birthTime = uint64(Pig.birthTime); breed = uint256(Pig.breed); weight = uint256(Pig.weight); gender = int8(Pig.gender); } }
There is a bug in the code in this EIP caused by reading from reused memory that is not zeroed out. success := staticcall(
30000, // 30k gas
_contract, // To addr
x, // Inputs are stored at location x
0x24, // Inputs are 36 bytes long
x, // Store output over input (saves space) <-----
0x20) // Outputs are 32 bytes long
result := mload(x) // <----- If the call reverts, or if it succeeds but does not return anything (e.g an EOA), OpenZeppelin's implementation does not have this bug. Has anyone deployed the code in the EIP? |
Thanks for sharing. So if the call returns less that 32 bytes wont that just only lay down the bytes that returned? ERC-165 is pretty extensive with the three-part test. I can't think of a case that would break that implementation when an unexpected short response is produced. Also interested to hear if anybody is use the reference code as-is. In general, I will ask please that if allegations of a EIP are raised after final status, that they include runnable test cases. Preferably in a minified repository that also runs with Travis CI or similar. |
It's true that the three-part test mitigates the bug in a way that it doesn't seem to have any practical consequences. |
Is interface detection implemented automatically, or does registration have to manually occur? |
This EIP is being further developed as #881
For some "standard interfaces" like the token interface ( #20 ), it is sometimes useful to query whether a contract supports the interface and if yes, which version of the interface, in order to adapt the way in which the contract is interfaced with. Specifically for #20, a version identifier has already been proposed. This proposal wants to generalize the concept of interfaces and interface versions to interface identifiers:
Every "standard interface" should be assigned a unique identifier (the sha3 hash of its source representation would be suitable) as a bytes32 value. Interfaces that support pseudo-introspection should provide the following methods. Note that this is especially targeted at contracts that can also provide multiple non-conflicting interfaces. This is useful if e.g. a standard token contract also allows a "cheque" functionality, which would have its own interface ID, or if the token does not support allowances.
Example implementation and usage:
Note:
Since the EVM does not provide any guarantees for the semantics of contracts, any such information returned by other contracts can only be used as a guideline.
Note2:
The convenient access to the interface ID via
Token.interfaceID
is not yet supported by solidity ( ethereum/solidity#1290 ).Credits: This is the result of a discussion with @konradkonrad and @frozeman
The text was updated successfully, but these errors were encountered: