How can I retrieve my account's Augur (REP) token balance via JSON-RPC?

Question

How can I check the contract balance, like Augur (REP), on an address with JSON-RPC? There doesn't seem to be alot of documentation about this.

Answer 1

To get the REP token balance via JSON-RPC, you will have to use the eth_call method. See How to call a contract method using the eth_call JSON-RPC API for more details on using eth_call.

And from augur-core/src/repContract.se , the balanceOf(...) function is defined as:

def balanceOf(address: address):
    return(self.reporting[address]: uint256)

And this matches the ERC: Token standard #20, where the balanceOf(...) function should have the signature:

function balanceOf(address _owner) constant returns (uint256 balance)

To find the function signature in geth, I run the following command:

> web3.sha3('balanceOf(address)').substring(0,10)
"0x70a08231"

For an example, we will use the REP token balance for the address 0xab11204cfeaccffa63c2d23aef2ea9accdb0a0d5 with the following balance:

I now have to use the function signature from above with a left zero padded representation of the address to be passed to the balanceOf(...) function:

0x70a08231000000000000000000000000ab11204cfeaccffa63c2d23aef2ea9accdb0a0d5

From etherscan.io/token/REP, the REP contract address is 0x48c80F1f4D53D5951e5D5438B54Cba84f29F32a5.

I ran the following JSON-RPC command against my Parity node (for geth, you can leave off the --header parameter):

curl localhost:8545 -X POST --header 'Content-type: application/json' --data '{"jsonrpc":"2.0", "method":"eth_call", "params":[{"to": "0x48c80F1f4D53D5951e5D5438B54Cba84f29F32a5", "data": "0x70a08231000000000000000000000000ab11204cfeaccffa63c2d23aef2ea9accdb0a0d5"}], "id":1}'

The result from the command above is:

{"jsonrpc":"2.0","result":"0x000000000000000000000000000000000000000000010843f6b148a2ec22c604","id":1}

And to confirm the results are correct, I ran the following command in geth:

> new BigNumber("000000000000000000000000000000000000000000010843f6b148a2ec22c604", 16)/1e18
1247958.4593995938

You will have to convert the hex result into a number in your application.

Update Oct 18 2016

As documented in RPC error "invalid or missing value for params" when calling contract constant void functions, you may have to add a block parameter to the params list. Your command with the block parameter will be:

curl localhost:8545 -X POST --header 'Content-type: application/json' --data '{"jsonrpc":"2.0", "method":"eth_call", "params":[{"to": "0x48c80F1f4D53D5951e5D5438B54Cba84f29F32a5", "data": "0x70a08231000000000000000000000000ab11204cfeaccffa63c2d23aef2ea9accdb0a0d5"}, "latest"], "id":1}'

Reference The default block parameter and eth_call.

eth_call without the block parameter worked previously, but now seems to be mandatory.