[Ethereum] RPC error “invalid or missing value for params” when calling contract constant void functions

contract-invocationgo-ethereumjson-rpcsolidity

My contract has a function defined like this:

{"constant":true,"inputs":[],"name":"queryNumEscrows","outputs":
[{"name":"","type":"uint256"}],"payable":false,"type":"function"}

Having no inputs. Its Solidity source code is pretty simple:

function queryNumEscrows() constant returns (uint) {
    return numEscrows;
}

how do I call it from JSON RPC? I've tried this:

endpoint = "queryNumEscrows()" 
web3_sha3(endpoint) = 0x0127efc52bcbe2b7f6d6a1ee29a7acd32c5f2e824b791cd7c97b9c57981bc5ac
no arguments...
data = 0x0127efc5

and when performing the query:

eth_call([{"from": "0xf28dafbfeb41bf32869c9d498da0d651d0206ed4", "to":
"0x27c042342c9ba937214117e11a4970a6145034cb", "data": "0x0127efc5"}])

this is the error it throws:

-32602: invalid or missing value for params[1]

So, I guess probably is something wrong when encoding void parameters into data. How should I do that?

By the way, I used this great explanation: How to call a contract method using the eth_call JSON-RPC API as a reference.

Best Answer

Summary

Adding the block number to the eth_call JSON-RPC call parameters as suggested by the closed bug eth_call requires block as last parameter #2472 will work.


Details

I created a contract using Browser Solidity as shown in the screen shot below: enter image description here

And here is my result:

Iota:ESE bok$ curl localhost:8545 -X POST --header 'Content-type: application/json' --data '{"jsonrpc":"2.0", "method":"eth_call", "params":[{"to": "0xb82020341122e7c8c4ba6551fd25950681af3570", "data": "0x0127efc5"}, "latest"], "id":1}'
{"jsonrpc":"2.0","id":1,"result":"0x000000000000000000000000000000000000000000000000000000000000007b"}

Reference The default block parameter and eth_call.

eth_call without the block parameter worked previously. I've updated my old ESE Q&As on eth_call usage to add a note about this new requirement.

Related Topic