Define return values for Read API 'no result' cases

[cgewecke]

@njgheorghita @pipermerriam

After looking over the registry implementations again I wonder if we should consider giving clear definitions to the ERC1319 Read API return values for "error" or "no-result" .

I'm worried about this because at the moment we gate-keep some view methods with require checks that return an error reason string. But web3.js doesn't support that for calls - instead it returns un-decoded bytecode strings without throwing.

Do these require statements work as expected for Python's web3?

What are your views about amending the EIP to define a set of null return values which signal that the view request failed? And documenting a canonical way of generating these in Solidity (since their format in Python, JS etc will vary)?

Examples

getAllPackageIds ... returns (bytes32[], uint)

bytes32[] memory ids;
uint256 ptr;
return (ids, ptr); 

getPackageName...returns (string)

return '';

getReleaseId...returns (bytes32)

return bytes32(0); 

getAllReleaseIds...returns (bytes32[], uint)

bytes32[] memory ids;
uint256 ptr;
return (ids, ptr); 

generateReleaseId...returns(bytes32)

return bytes32(0);

getReleaseData...returns(string, string, string)

return ('','','');

numPackageIds...returns(uint)

return 0; 

numReleaseIds...returns(uint)

return 0;