SNIP12: Incorrect use of u64 in docs example

[trishtzy]

📝 Details

The example in SNIP12 incorrectly uses u64 for the expiry field, which is not a supported data type from the official SNIP12 specification.

struct Message {
    recipient: ContractAddress,
    amount: u256,
    nonce: felt252,
    expiry: u64 // not supported, should be u128
}

https://github.com/OpenZeppelin/cairo-contracts/blob/v0.20.0/docs/modules/ROOT/pages/guides/snip12.adoc?plain=1#L76

When trying to re-create the Message struct for off-chain signing using Golang or Python, it results in compilation errors when hashing the Typed Message.

🔢 Code to reproduce bug

package main

import (
  "encoding/json"
  "fmt"

  "github.com/NethermindEth/starknet.go/typedData"
)

func main() {
  jsonData := `{
    "types": {
      "StarknetDomain": [
        { "name": "name", "type": "shortstring" },
        { "name": "version", "type": "shortstring" },
        { "name": "chainId", "type": "shortstring" },
        { "name": "revision", "type": "shortstring" }
      ],
      "Message": [
        { "name": "recipient", "type": "ContractAddress" },
        { "name": "amount", "type": "u256" },
        { "name": "nonce", "type": "felt" },
        { "name": "expiry", "type": "u64" }
      ]
    },
    "primaryType": "Message",
    "domain": {
      "name": "StarkNet Mail",
      "version": "1",
      "chainId": "1",
      "revision": "1"
    },
    "message": {
      "recipient": "0xd392b0c0500700d02d27ab30805ec80ddd3320ff",
      "amount": "100.00",
      "nonce": 0,
      "expiry": 1734859800
    }
  }`

  var ttd typedData.TypedData
  err := json.Unmarshal([]byte(jsonData), &ttd)
  if err != nil {
    panic(fmt.Errorf("fail to unmarshal TypedData: %w", err)) // `panic: fail to unmarshal TypedData: can't parse type u64`
  }
  messageTypeHash, err := ttd.GetTypeHash("Message")
  if err != nil {
    panic(fmt.Errorf("fail to get message type hash: %w", err))
  }
  fmt.Println("message type hash:", messageTypeHash)
}

Running the Go script results in panic: fail to unmarshal TypedData: can't parse type u64

Could I open a pull request to update the example?

const MESSAGE_TYPE_HASH: felt252 = 0xa2a7036c1f406af7c47722b209f23bd2f2d6ac21423c8c73bd92cf28409ee2; // updated hash

#[derive(Copy, Drop, Hash)]
struct Message {
    recipient: ContractAddress,
    amount: u256,
    nonce: felt252,
    expiry: u128 // updated 
}

[andrew-fleming]

Thanks, @trishtzy! Yeah, feel free to open a PR fixing this. Note though that we keep the actual struct member as type u64. We only use u128 for encoding to be compliant with snip12, so really just the type hash and its computation need to be updated.

It's probably helpful to leave a comment regarding u64 <> u128 in the guide:

// Since there's no u64 type in SNIP-12, we use u128 for `expiry` in the type hash generation.
let message_type_hash = ...