JSON-like data structure

[conr2d]

Background

We can write EOSIO application with any languages, but JavaScript is widely used and eosjs is considered as de facto. On the contract side, multi_index or action arguments written in C++ require static types unlike its interface written in JavaScript.

In nodeos, we already use fc::variant which can accept the value that fits the predefined set of types.
https://github.com/EOSIO/fc/blob/0b45f08f/include/fc/variant.hpp#L193-L204

eosio::any (Intentionally, I avoid using the name json, because the detailed specification can be different to support extended features.) supports various type of values by one type.

struct [[eosio::table("records")]] record {
  uint64_t id;
  eosio::any data;

  uint64_t primary_key() const { return id; }
};
typedef eosio::multi_index<"records"_n, record> records;

[[eosio::action]]
void storenum(uint64_t num) {
  records rs(_self, _self.value);
  rs.emplace_back(_self, [&](auto& r) {
    r.id = rs.available_primary_key();
    r.data = num;
  });
}

[[eosio::action]]
void storestring(const std::string& str) {
  records rs(_self, _self.value);
  rs.emplace_back(_self, [&](auto& r) {
    r.id = rs.available_primary_key();
    r.data = str;
  });
}

// `any` can replace the memo of eosio.token::transfer or `receipt` inline actions for recording action result.
[[eosio::action]]
void transfer(eosio::name from, eosio::name to, eosio::asset quantity, eosio::any data);

// An action that needs to handle various type of data (like admin) can use `any`.
[[eosio::action]]
void almighty(eosio::name sender, eosio::any data);

Implementation

• eosio.cdt:
  https://github.com/turnpike/blanc/blob/feature/built_in_type-any/libraries/eosiolib/core/eosio/any.hpp

• eosjs:
  conr2d/eosjs@056b4b0

Above implementation utilizes std::variant infra, so doesn't need consensus change.

// [[eosio::action]]
// void almighty(eosio::name sender, eosio::any data);

(async () => {
  const result = await api.transact({
    actions: [{
      account: 'anytest',
      name: 'almighty',
      authorization: [{
        actor: 'alice',
        permission: 'active',
      }],
      data: {
        sender: 'alice',
        data: {}, // any JSON-compatible type can be here, `null`, boolean, number, string, array, object ...
      },
    }]
  }, {
    blocksBehind: 3,
    expireSeconds: 30,
  });
  console.dir(result);
})();

• eos (abi_serializer):
  haderech/eos@a932ffb

For utilizing the benefit of eosio::any completely, it's necessary to add new built-in type any. Nodeos adopting this can accept JSON directly or return pretty stringified result when querying eosio::any data. Whether adopting built-in type or not doesn't affect data exchange between nodes. (Not consensus change, but interface-level difference)

Without built-in type support:

// get_table_rows RPC
{
  "rows": [{
    "id": 0,
    "data": ["number", 999]
  }, {
    "id": 1,
    "data": ["string", "alice"]
  }]
}

// CLI
cleos push action anytest almighty '["alice", ["number", 999]]' -p alice@active
cleos push action anytest almighty '["alice", ["string", "alice"]]' -p alice@active

With built-in type support:

// get_table_rows RPC
{
  "rows": [{
    "id": 0,
    "data": 999
  }, {
    "id": 1,
    "data": "alice"
  }]
}

// CLI
cleos push action anytest almighty '["alice", "999"]' -p alice@active
cleos push action anytest almighty '["alice", "\"alice\""]' -p alice@active

[conr2d]

A minimal working example:
https://github.com/turnpike/eos/releases/tag/built_in_type-any