Decoding events emitted through DSProxy

[antoinedc]

Hello,

I'm trying to implement something similar to https://ethtx.info (ex: https://ethtx.info/mainnet/0x1d8d154006fd2a49cb121695d5cc6ecd3cf98ba393af5edb0cbc37d0395b64a6/)

I've reproduced this transaction locally on a mainnet fork and I'm trying to decode all the events that are emitted during the transaction.
Here is my process:

• Get the address field in the log object
• Get the ABI from the contract at this address (either locally or through Etherscan's API)
• Instantiate an ethers.js Interface with the ABI and try to parse the logs:

const jsonInterface = new ethers.utils.Interface(abi);
const parsedLog = jsonInterface.parseLog(log);

But in the interface that is generated by ethers.js, none of the events signatures match the one from the log, so it's failing with the error Error: no matching event (argument="sighash") ...
This transaction is emitting 10 logs, but the only one that I'm able to decode is the Dai.Transfer one (#12 on the link above).
I'm only having this issue when using this DSProxy contract.

Any idea what I'm missing here? DSProxy is a fairly common pattern but I couldn't find any information on how to decode events.
What would be the way of decoding them?

The signature in topics[0] below matches the execute(address,bytes) function from the proxy contract, but I couldn't figure out why it's matching a function and not an event either...

Thanks!

Here is the log object:

{
   "blockHash":"0x3d61e1f12a3f6c60e0a3a6aeb6265d71feebb275497fe0b7a67504530a7e1cf3",
   "address":"0x9e905F5b2b07b5e1dc71A86901de0E717eEBB12d",
   "logIndex":0,
   "data":"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",
   "topics":[
      "0x1cff79cd00000000000000000000000000000000000000000000000000000000",
      "0x000000000000000000000000f75fcd9849d3365d436d0cd889ed500150c9482a",
      "0x00000000000000000000000082ecd135dce65fbc6dbdd0e4237e0af93ffd5038",
      "0x0000000000000000000000000000000000000000000000000000000000000040"
   ],
   "transactionIndex":0,
   "transactionHash":"0x2b440c0c840b6cb09e35eeca4750af876b7d62b08fd1ba5487bd265eb840e33a",
   "blockNumber":9948023
}

And the ABI:

[
   {
      "outputs":[
         
      ],
      "constant":false,
      "inputs":[
         {
            "type":"address",
            "name":"owner_"
         }
      ],
      "stateMutability":"nonpayable",
      "type":"function",
      "payable":false,
      "name":"setOwner"
   },
   {
      "outputs":[
         {
            "type":"bytes32",
            "name":"response"
         }
      ],
      "constant":false,
      "inputs":[
         {
            "type":"address",
            "name":"_target"
         },
         {
            "type":"bytes",
            "name":"_data"
         }
      ],
      "stateMutability":"payable",
      "type":"function",
      "payable":true,
      "name":"execute"
   },
   {
      "outputs":[
         {
            "type":"address",
            "name":"target"
         },
         {
            "type":"bytes32",
            "name":"response"
         }
      ],
      "constant":false,
      "inputs":[
         {
            "type":"bytes",
            "name":"_code"
         },
         {
            "type":"bytes",
            "name":"_data"
         }
      ],
      "stateMutability":"payable",
      "type":"function",
      "payable":true,
      "name":"execute"
   },
   {
      "outputs":[
         {
            "type":"address",
            "name":""
         }
      ],
      "constant":true,
      "inputs":[
         
      ],
      "stateMutability":"view",
      "type":"function",
      "payable":false,
      "name":"cache"
   },
   {
      "outputs":[
         
      ],
      "constant":false,
      "inputs":[
         {
            "type":"address",
            "name":"authority_"
         }
      ],
      "stateMutability":"nonpayable",
      "type":"function",
      "payable":false,
      "name":"setAuthority"
   },
   {
      "outputs":[
         {
            "type":"address",
            "name":""
         }
      ],
      "constant":true,
      "inputs":[
         
      ],
      "stateMutability":"view",
      "type":"function",
      "payable":false,
      "name":"owner"
   },
   {
      "outputs":[
         {
            "type":"bool",
            "name":""
         }
      ],
      "constant":false,
      "inputs":[
         {
            "type":"address",
            "name":"_cacheAddr"
         }
      ],
      "stateMutability":"nonpayable",
      "type":"function",
      "payable":false,
      "name":"setCache"
   },
   {
      "outputs":[
         {
            "type":"address",
            "name":""
         }
      ],
      "constant":true,
      "inputs":[
         
      ],
      "stateMutability":"view",
      "type":"function",
      "payable":false,
      "name":"authority"
   },
   {
      "inputs":[
         {
            "type":"address",
            "name":"_cacheAddr"
         }
      ],
      "stateMutability":"nonpayable",
      "type":"constructor",
      "payable":false
   },
   {
      "stateMutability":"payable",
      "type":"fallback",
      "payable":true
   },
   {
      "inputs":[
         {
            "indexed":true,
            "type":"bytes4",
            "name":"sig"
         },
         {
            "indexed":true,
            "type":"address",
            "name":"guy"
         },
         {
            "indexed":true,
            "type":"bytes32",
            "name":"foo"
         },
         {
            "indexed":true,
            "type":"bytes32",
            "name":"bar"
         },
         {
            "indexed":false,
            "type":"uint256",
            "name":"wad"
         },
         {
            "indexed":false,
            "type":"bytes",
            "name":"fax"
         }
      ],
      "type":"event",
      "name":"LogNote",
      "anonymous":true
   },
   {
      "inputs":[
         {
            "indexed":true,
            "type":"address",
            "name":"authority"
         }
      ],
      "type":"event",
      "name":"LogSetAuthority",
      "anonymous":false
   },
   {
      "inputs":[
         {
            "indexed":true,
            "type":"address",
            "name":"owner"
         }
      ],
      "type":"event",
      "name":"LogSetOwner",
      "anonymous":false
   }
]

[zemse]

This topic doesn't seem to me like a standard topic. 0x1cff79cd00000000000000000000000000000000000000000000000000000000

Topic is the hash of the event signature, and it is very very unlikely that it can have so many zeros in it. There is a way in solidity to emit logs with custom topics, and when that is done, the standard that is implemented in ethers.js (as well as other libraries) cannot decode it by default, requires a bit more effort.

[antoinedc]

Any particular reason for this use case to not be handled by the parseLog function? Otherwise I can try to do a PR for that

[zemse]

The event is not uniquely decodable

event E1(bytes32 hash) anonymous;
event E2(uint256 amount) anonymous;

E1 's args would have a hex string, while E2's args would have a BigNumber value. If E2 was emitted, the for loop would stop at that decode which does not error, it can be decoded by E1's fragment or E2's whichever is early in the ABI. Does this make sense?

[antoinedc]

Yes that makes sense, thanks! In my case, parsedLog would be filled by the last valid signature then. I guess the only thing I could do would be to leave it to the user to choose which signature they want to use to decode the log, right?

Any idea how https://ethtx.info/mainnet/0x1d8d154006fd2a49cb121695d5cc6ecd3cf98ba393af5edb0cbc37d0395b64a6/ is able to figure out correctly which signature is the right one? Or they don't and this one is just a lucky guess? I looked into the code, but couldn't find the reason...

[zemse]

Any idea how https://ethtx.info/mainnet/0x1d8d154006fd2a49cb121695d5cc6ecd3cf98ba393af5edb0cbc37d0395b64a6/ is able to figure out correctly which signature is the right one? Or they don't and this one is just a lucky guess? I looked into the code, but couldn't find the reason...

Not sure but I was looking at DSProxy's code, their LogNote contains sig, guy, foo, bar, wad, fax. But I don't see sig, foo, bar on ethtx.

[antoinedc]

I noticed the same thing, yes. Maybe they just detect the proxy and make some assumptions from that...I'll try to get in touch with them.
Anyway, thanks for the explanations, I'll mark this as solved.