Neo: RPC: "invoke" returns incorrect results

[joeqian10]

An exchange reported this issue to me, and I tried to repeat this issue. I created a testnet using the latest code of neo-cli 2.x on solo mode. Then I deployed a modified NEP-5 contract, and for testing purpose I modified "balanceOf" as following:
```C#
if (operation == "balanceOf")
{
if (args.Length != 1) return 0;
byte[] account = (byte[])args[0];
return account;
//return BalanceOf(account);
}

And here are the requests sent using RPC:
using "invoke":
```json
{
  "jsonrpc": "2.0",
  "method": "invoke",
  "params": [
    "08a91ebb95656fca3e9eb3fdfe4286dabdcd0da5",
    [
        {
            "type":"String",
            "value":"balanceOf"
        },
        {
            "type":"String",
            "value":"651897dcd926ab80a2026eaf7f1aa451361d60d2"
        }
    ]
  ],
  "id": 3
}

using "invokefunction":

{
  "jsonrpc": "2.0",
  "method": "invokefunction",
  "params": [
    "08a91ebb95656fca3e9eb3fdfe4286dabdcd0da5",
    "balanceOf",
    [
        {
            "type":"String",
            "value":"651897dcd926ab80a2026eaf7f1aa451361d60d2"
        }
    ]
  ],
  "id": 3
}

"invoke" returned an empty byte[]:

{
    "jsonrpc": "2.0",
    "id": 3,
    "result": {
        "script": "28363531383937646364393236616238306132303236656166376631616134353133363164363064320962616c616e63654f6667a50dcdbdda8642fefdb39e3eca6f6595bb1ea908",
        "state": "HALT",
        "gas_consumed": "0.121",
        "stack": [
            {
                "type": "ByteArray",
                "value": ""
            }
        ],
        "tx": "d1014828363531383937646364393236616238306132303236656166376631616134353133363164363064320962616c616e63654f6667a50dcdbdda8642fefdb39e3eca6f6595bb1ea908000000000000000000000000"
    }
}

"invokefunction" returned correct result:

{
    "jsonrpc": "2.0",
    "id": 3,
    "result": {
        "script": "283635313839376463643932366162383061323032366561663766316161343531333631643630643251c10962616c616e63654f6667a50dcdbdda8642fefdb39e3eca6f6595bb1ea908",
        "state": "HALT",
        "gas_consumed": "0.13",
        "stack": [
            {
                "type": "ByteArray",
                "value": "36353138393764636439323661623830613230323665616637663161613435313336316436306432"
            }
        ],
        "tx": "d1014a283635313839376463643932366162383061323032366561663766316161343531333631643630643251c10962616c616e63654f6667a50dcdbdda8642fefdb39e3eca6f6595bb1ea908000000000000000000000000"
    }
}

PS: in neo3, "invoke" is removed.

[joeqian10]

I think I have figured out the reason caused this issue:
"invoke" calls the following code:
```C#
public static ScriptBuilder EmitAppCall(this ScriptBuilder sb, UInt160 scriptHash, params ContractParameter[] parameters)
{
for (int i = parameters.Length - 1; i >= 0; i--)
sb.EmitPush(parameters[i]);
return sb.EmitAppCall(scriptHash);
}

and "invokefunction" calls the following code:
```C#
        public static ScriptBuilder EmitAppCall(this ScriptBuilder sb, UInt160 scriptHash, string operation, params ContractParameter[] args)
        {
            for (int i = args.Length - 1; i >= 0; i--)
                sb.EmitPush(args[i]);
            sb.EmitPush(args.Length);
            sb.Emit(OpCode.PACK);
            sb.EmitPush(operation);
            sb.EmitAppCall(scriptHash);
            return sb;
        }

After I changed the "invoke" code as following:
```C#
public static ScriptBuilder EmitAppCall(this ScriptBuilder sb, UInt160 scriptHash, params ContractParameter[] parameters)
{
for (int i = parameters.Length - 1; i >= 1; i--)
sb.EmitPush(parameters[i]);
sb.EmitPush(parameters.Length - 1);
sb.Emit(OpCode.PACK);
sb.EmitPush(parameters[0].Value.ToString());
return sb.EmitAppCall(scriptHash);
}

and resent the request using "invoke", I got the correct response:
```json
{
    "jsonrpc": "2.0",
    "id": 3,
    "result": {
        "script": "283635313839376463643932366162383061323032366561663766316161343531333631643630643251c10962616c616e63654f6667a50dcdbdda8642fefdb39e3eca6f6595bb1ea908",
        "state": "HALT",
        "gas_consumed": "0.13",
        "stack": [
            {
                "type": "ByteArray",
                "value": "36353138393764636439323661623830613230323665616637663161613435313336316436306432"
            }
        ],
        "tx": "d1014a283635313839376463643932366162383061323032366561663766316161343531333631643630643251c10962616c616e63654f6667a50dcdbdda8642fefdb39e3eca6f6595bb1ea908000000000000000000000000"
    }
}

[lock9]

Hi @joeqian10, is this a new problem?
I think that these endpoints have different purposes.
The first expects 2 parameters: operation and args, while the second is more generic. You can have a smart contract that does not obey the "operation + args" signature, maybe that is the reason they are different.

[vncoelho]

Nice investigation anyway, @joeiqan10.
But I think Rick is right, maybe this invoke template needs an extra param as default. Lets double check.

[joeqian10]

@lock9 Yes, this is a new problem reported by an exchange. I agree that these two endpoints have different purposes. But the more generic one ("invoke") doesn't return correct response under this specific request, which makes it not so "generic". @vncoelho More investigation is needed.

[lock9]

@joeqian10 I checked git history, and it has been a really long time since this was last changed.
I think that they need to use invokefunction instead of invoke
This is from May 2018:

[joeqian10]

@lock9 I have informed the exchange to use only invokefunction for now. And in NEO3, invoke is totally removed.

[lock9]

If the problem is solved, could you please close this issue?
Thanks.

Sent from my iPhone

On 9 Jul 2019, at 01:52, joeqian [e-mail] wrote:

@lock9 I have informed the exchange to use only invokefunction for now. And in NEO3, invoke is totally removed.

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