How to retrive parameters from a Michelson function?

Question

I'm developing a Flutter application and used Dartez plugin to transfer token contracts from one wallet to another wallet.

The Dartez package has a function named sendContractInvocationOperation for this purpose.

I used this function in my project like this:

final token = TokenModel(...);
var server = '';

var keyStore = KeyStoreModel(
      publicKey: 'edpk.....rrj',
      secretKey: 'edsk.....yHH',
      publicKeyHash: 'tz1.....hxy',
    );
int amount = 10000; // just as sample
String withdrawalAddress = "tz1.....xyz";

var signer = await Dartez.createSigner(
        Dartez.writeKeyWithHint(keyStore.secretKey, 'edsk'));

var contractAddress = ['KT1.....xMY'];

final parameters = token.isFA1
          ? '''(Pair "${keyStore.publicKeyHash}" (Pair "$withdrawalAddress" $amount))'''
          : '''{Pair "${keyStore.publicKeyHash}" {Pair "$withdrawalAddress" (Pair $tokenId $amount)}}''';

      final dynamic resultInvoke = await Dartez.sendContractInvocationOperation(
        server,
        signer as SoftSigner,
        keyStore,
        contractAddress,
        [0],
        customFee,
        1000,
        customFee,
        ['transfer'],
        [parameters],
        codeFormat: TezosParameterFormat.Michelson,
      );

print("Operation groupID ===> $resultInvoke['operationGroupID']");

But the problem is when my token standard is "fa2" then the transaction failed with this error: please click here to see the error log

The above error was about the Crunch token, which is a token with the "fa2" standard.

I also checked the transfer function entypoints from here: CRUNCH entypoints and the transfer function is:

Json schema:
"schema:list:object": [
    {
        "from_:address": "address",
        "txs:list:object": [
            {
                "to_:address": "address",
                "token_id:nat": "nat",
                "amount:nat": "nat"
            }
        ]
    }
]
Michelson type:
(list %transfer (pair (address %from_)
                     (list %txs (pair (address %to_) (pair (nat %token_id) (nat %amount))))))

As you see, it provides the function in Michelson type, but I'm not sure whether the parameters that I retrieved from this Michelson function and used inside "Dartez.sendContractInvocationOperation" function is the correct format or not.

Note: I don't understand the Michelson language and don't know the correct syntax.

Answer 1

I don't know Dart, Flutter, or this library so my help will be limited. From looking at your code you have 2 sets of Michelson that is decided based on whether its FA1 or 2

final parameters = token.isFA1
          ? '''(Pair "${keyStore.publicKeyHash}" (Pair "$withdrawalAddress" $amount))'''
          : '''{Pair "${keyStore.publicKeyHash}" {Pair "$withdrawalAddress" (Pair $tokenId $amount)}}''';

Crunch is an FA2 token, so it should be the second set, which would send 4 pieces of data:

• Source address
• Destination Address
• TokenID
• Amount to send

Taking a look at the TzKT link you sent and clicking the button to view the raw operation JSON, I can see that only 3 pieces of data was sent:

• Source address
• Destination Address
• Amount to send

It looks like your token.isFA1 code is broken to me

Answer 2

In addition to @simon-mcloughlin's answer, if you don't know how to build Michelson parameters you can use a helper endpoint in TzKT API: https://api.tzkt.io/#operation/Contracts_BuildEntrypointParametersGET

So, looking at the JSON schema on TzKT:

"schema:list:object": [
    {
        "from_:address": "address",
        "txs:list:object": [
            {
                "to_:address": "address",
                "token_id:nat": "nat",
                "amount:nat": "nat"
            }
        ]
    }
]

your parameters (in JSON format) should look like this:

[
    {
        "from_": "tz1LK2aE2zmvqqsVYGAaCTauz7peWQ3gAuqK",
        "txs": [
            {
                "to_": "tz1NJrXkEhwcqNxkARvb44psCCb4VyJ4Qh1b",
                "token_id": "0",
                "amount": "100000000"
            }
        ]
    }
]

Then, just pass it to the API: https://api.tzkt.io/v1/contracts/KT1BHCumksALJQJ8q8to2EPigPW6qpyTr7Ng/entrypoints/transfer/build?value=[{%22from_%22:%22tz1LK2aE2zmvqqsVYGAaCTauz7peWQ3gAuqK%22,%22txs%22:[{%22to_%22:%22tz1NJrXkEhwcqNxkARvb44psCCb4VyJ4Qh1b%22,%22token_id%22:%220%22,%22amount%22:%22100000000%22}]}]

and here is the result:

[
  {
    "prim": "Pair",
    "args": [
      {
        "bytes": "000007601f902f440e65f9e1acb29c8a361a65ba70f2"
      },
      [
        {
          "prim": "Pair",
          "args": [
            {
              "bytes": "00001d47fdd96fb5cc1141cbed92ef36d82515a69053"
            },
            {
              "prim": "Pair",
              "args": [
                {
                  "int": "0"
                },
                {
                  "int": "100000000"
                }
              ]
            }
          ]
        }
      ]
    ]
  }
]

This is what you should specify in the transaction.