Web3.js: getPastEvents() causes an error if an event has a function as argument

[haltman-at]

Description

The getPastEvents() function in web3.eth.Contract will cause an error if one of the events has a function external as an argument. (I assume the same problem is present in other similar functions as well.) While I realize it might not be practical at the moment to decode such values, especially as currently you're relying on another package to do the decoding for you, having it cause an error in the whole function is inconvenient because it means one can't get at any of the other events, or, for that matter, the other properties of this event. In short, the error should be localized.

Expected behavior

Instead of causing an error, the function should return as normal, but the returnValues entry for that parameter should be undefined or null or some other way of indicating an error, rather than having the entire function error.

Actual behavior

An error occurs. In my case, doing this from within truffle console, I got the following:

{ Error: invalid type (arg="type", value="function")
    at XMLHttpRequest._onHttpResponseEnd (/home/sniffnoy/truffle/truffle/node_modules/xhr2-cookies/xml-http-request.ts:345:8)
    at XMLHttpRequest._setReadyState (/home/sniffnoy/truffle/truffle/node_modules/xhr2-cookies/xml-http-request.ts:219:8)
    at XMLHttpRequestEventTarget.dispatchEvent (/home/sniffnoy/truffle/truffle/node_modules/xhr2-cookies/xml-http-request-event-target.ts:44:13)
    at XMLHttpRequest.request.onreadystatechange (/home/sniffnoy/truffle/truffle/node_modules/web3/node_modules/web3-providers-http/src/index.js:96:13)
    at /home/sniffnoy/truffle/truffle/packages/truffle-provider/wrapper.js:112:9
    at /home/sniffnoy/truffle/truffle/node_modules/web3-eth-contract/node_modules/web3-core-requestmanager/src/index.js:147:9
    at sendTxCallback (/home/sniffnoy/truffle/truffle/node_modules/web3-eth-contract/node_modules/web3-core-method/src/index.js:473:33)
    at Method.formatOutput (/home/sniffnoy/truffle/truffle/node_modules/web3-eth-contract/node_modules/web3-core-method/src/index.js:159:23)
    at Array.map (<anonymous>)
    at /home/sniffnoy/truffle/truffle/node_modules/web3-eth-contract/node_modules/web3-core-method/src/index.js:160:57
    at Object.Contract._decodeEventABI (/home/sniffnoy/truffle/truffle/node_modules/web3-eth-contract/src/index.js:377:31)
    at ABICoder.decodeLog (/home/sniffnoy/truffle/truffle/node_modules/web3-eth-abi/src/index.js:283:52)
    at ABICoder.decodeParameters (/home/sniffnoy/truffle/truffle/node_modules/web3-eth-abi/src/index.js:229:30)
    at AbiCoder.decode (/home/sniffnoy/truffle/truffle/node_modules/web3-eth-abi/node_modules/ethers/utils/abi-coder.js:901:15)
    at Array.forEach (<anonymous>)
    at AbiCoder.<anonymous> (/home/sniffnoy/truffle/truffle/node_modules/web3-eth-abi/node_modules/ethers/utils/abi-coder.js:910:25)
    at getParamCoder (/home/sniffnoy/truffle/truffle/node_modules/web3-eth-abi/node_modules/ethers/utils/abi-coder.js:862:12)
    at Object.throwError (/home/sniffnoy/truffle/truffle/node_modules/web3-eth-abi/node_modules/ethers/utils/errors.js:68:17)
  reason: 'invalid type',
  code: 'INVALID_ARGUMENT',
  arg: 'type',
  value: 'function' }

Steps to reproduce the behavior

1. Write a Solidity contract with an event that takes a function external parameter. E.g.:

pragma solidity ^0.5.8;

contract EventsTest {
  event takesFunction(function() external);

  function run() public {
    emit takesFunction(this.run);
  }
}

1. Deploy the contract, then cause it to emit such an event. (In this case, deploy it and then run run.)
2. Create a new web3.eth.Contract object for it, and then call that object's getPastEvents method. (Although in my case I was using truffle console and relied on the object created by EventsTest.deployed().)

Error Logs

See above.

Versions

• web3.js: 1.0.0-beta37
• nodejs: 10.15.3
• browser: N/A
• ethereum node: Ganache 2.0.1

[nivida]

Thanks for opening this issue! Does this error still occur in the latest version of Web3?

[haltman-at]

I'm having some trouble trying to test this manually without Truffle (I'm getting errors from getPastEvents regardless of whether such an event is present or not, and it's not obvious to me why), so it's a little hard to say. That said, skimming the code, I don't see anything that would handle it, so my guess is that it's still there.

[haltman-at]

By the way, it seems that attempting to decode indexed parameters of reference type (which as we know cannot actually be decoded) can also crash the event decoder. Also worth accounting for, I think.

[sshelton76]

What could possibly be the use case for passing an external function into an event? I'm genuinely curious.

[digulla]

I have a similar problem when trying to call a contract method which expect a function type/pointer as parameter. See https://ethereum.stackexchange.com/questions/78080/how-do-i-pass-a-function-pointer-to-a-contract-method-from-a-unit-test for a code example.

To see the error, this code is sufficent:

web3.eth.abi.encodeParameter('function', ac.onlyOwner);

where ac is a contract and onlyOwner is a method on that contract.

Is there a way to manually encode the whole function call? Or does that mean I can no longer unit test my code?

[radiant-alex]

Having same issue with web3.eth.abi.decodeLog(CONTRACT_ABI, evenntdata, eventtopics)
when CONTRACT_ABI has 'function' among types, check the contract 0x57ab1e02fee23774580c119740129eac7081e9d3

[digulla]

@nivida Does my comment above contain the clarification you asked for?

[nivida]

@digulla Yep, thanks!:)