Expected to decode Array<Any> but found a dictionary instead.

[baquedano]

Hi, I'm currently trying to send a transaction to a contract and I'm getting the following error:

▿ DecodingError
  ▿ typeMismatch : 2 elements
    - .0 : Swift.Array<Any>
    ▿ .1 : Context
      - codingPath : 0 elements
      - debugDescription : "Expected to decode Array<Any> but found a dictionary instead."
      - underlyingError : nil

The way I'm sending the transaction is:

 public func send (method name: String, // <---- "AddCandidate"
                                    taking arguments: [AnyObject], // <--- ["This is a string"] as [AnyObject]
                                    extra data:Data = Data(),
                                    from sender: EthereumAddress,
                                    unlocksWith passphrase: String,
                                    completion handler: ((EthereumTransaction?, Bool, Error?)->())? ) {
        var txOptions = TransactionOptions()

        txOptions.gasLimit = TransactionOptions.GasLimitPolicy.automatic
        txOptions.gasPrice = TransactionOptions.GasPricePolicy.automatic
        
        txOptions.from = sender
        
        guard let writeTx = self.web3Contract.write(name, parameters: arguments, transactionOptions: txOptions) else {
            handler? (nil, false, nil)
            return
        }
        let promise = writeTx.sendPromise(password: passphrase, transactionOptions: txOptions)
        
        _ = promise.done(on: DispatchQueue.main, { (results) in
            handler? (writeTx.transaction, true, nil)
        }).catch(on: DispatchQueue.main, { (error) in
            handler? (writeTx.transaction, false, error)
        })
 
    }

and this is the ABI of that method:

{"constant":false,"inputs":[{"name":"candidate","type":"string"}],"name":"AddCandidate","outputs":[],"payable":false,"stateMutability":"nonpayable","type":"function"}

After following a bit around the lib I found that the place where it gets the error is on Promise+Batching.swift --> Batch class --> trigger func --> Line 82, when it calls sendAsync the JSONRPCRequest batch, more specifically the error message comes on Promise+HTTPProvider.swift --> post func --> Line 92, this is the request that is being sent:

(lldb) po request
▿ JSONRPCrequestBatch
  ▿ requests : 1 element
    ▿ 0 : JSONRPCrequest
      - jsonrpc : "2.0"
      ▿ method : Optional<JSONRPCmethod>
        - some : Web3swift.JSONRPCmethod.sendTransaction
      ▿ params : Optional<JSONRPCparams>
        ▿ some : JSONRPCparams
          ▿ params : 1 element
            ▿ 0 : TransactionParameters
              ▿ data : Optional<String>
                - some : "0x7e54b8e20000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000001054686973206973206120737472696e6700000000000000000000000000000000"
              ▿ from : Optional<String>
                - some : "0xf92901dbdfec2a0599ee5108808c5ec85244eaf9"
              ▿ gas : Optional<String>
                - some : "0x15b5f"
              ▿ gasPrice : Optional<String>
                - some : "0x3b9aca00"
              ▿ to : Optional<String>
                - some : "0x11e8e870d72b5fbc46f886f865aa98470d01e249"
              ▿ value : Optional<String>
                - some : "0x0"
      - id : 32

Edit: after inspecting a little more I found that the actual data we get back is:

(lldb) po JSONSerialization.jsonObject(with: data, options: []) 
▿ 2 elements
  ▿ 0 : 2 elements
    - key : jsonrpc
    - value : 2.0
  ▿ 1 : 2 elements
    - key : error
    ▿ value : 2 elements
      ▿ 0 : 2 elements
        - key : message
        - value : The method eth_sendTransaction does not exist/is not available
      ▿ 1 : 2 elements
        - key : code
        - value : -32601

and indeed eth_sendTransaction doesn't exist in infura API, we have eth_sendRawTransaction.

Edit2: Found the issue, it was that I forgot to provide the keystoreManager to the client so it could locally sign the transactions, errors were quite misleading.

[TonioMacaronio]

@baquedano It's great that you were able to solve the problem. I'll close this issue.
If you have more questions - open it again

[DiwakarThapa]

I am having same problem while sending token

{
    error =     {
        code = "-32601";
        message = "The method eth_sendTransaction does not exist/is not available";
    };
    id = 7;
    jsonrpc = "2.0";
}