Build the data bytes to query a contract with the api state_call

Question

I would like to use the rpc call to query a contract.

I try to use the method "call" from the endpoint "state" with the first parameter "ContractsApi_call" but I am not able to fully build the second parameter (data).

Here an example:

In this example the data bytes are:

0xd43593c715fdd31c61141abd04a99fd6822c8558854ccde39a5684e7a56da27d1200ccd8b1a8f39b6d1d69463f5c4281bf9ec5ddfd80eedbba0ee221a30a02a600000000000000000000000000000000000020ba48eafe0c313233

From my understanding the data bytes are decomposed like this:

  - the origin address :  d43593c715fdd31c61141abd04a99fd6822c8558854ccde39a5684e7a56da27d
  - the contract address: 1200ccd8b1a8f39b6d1d69463f5c4281bf9ec5ddfd80eedbba0ee221a30a02a6
  - the missing piece: 00000000000000000000000000000000000020 
  - the selector of the method to call : ba48eafe
  - the args of the method: 0c313233

I would like to understand how is build the missing piece (00000000000000000000000000000000000020), in particular last part(20).

Anyone could help me to understand?

Answer 1

I found myself the answer and I put it there if it can help anyone else.

I need to create the following struct:

ContractCall { origin : AccountId, dest : AccountId, value : Balance, gas_limit : Option, storage_deposit_limit : Option, data: Vec, } In my case the data is the concatenation of:

• the selector of the method: [u8;4]
• the args of the method: Vec

and encode the whole struct.