How to add "time lock" to the EOS tokens

Question

I have issued some tokens base on eosio.token in jungle testnet, and I am able to transfer the tokens between accounts. Now if I want to enforce some control to the tokens sent ( for example, time lock, I do not want the receiver to transfer the tokens to someone else in 2 years). How should I program this function? Thank you for the help!

Answer 1

How about this ?

 /// @abi action
 void transfer( account_name from,
                account_name to,
                asset        quantity,
                string       memo );

 ///@abi action
 void transferf(account_name from,
                account_name to,
                asset        quantity,
                string       memo,
                uint32_t       frozen_days);

...

void token::claim( account_name owner ) {
   require_auth(owner);
   frozens frozen_balance( _self, owner );
   uint32_t n = now();
   for (auto itr = frozen_balance.begin(); itr != frozen_balance.end();) {
       if ( n >= itr->time_limit ){
           add_balance( owner, itr->balance, _self);
           itr = frozen_balance.erase(itr);
       }else {
           itr++; 
       }
   }  
}

void token::add_frozen_balance( account_name owner, asset value, uint32_t frozen_days, account_name ram_payer )
{
   frozens frozen_balance( _self, owner );

   frozen_balance.emplace(ram_payer, [&]( auto& row ){
       row.pkey = frozen_balance.available_primary_key();
       row.balance = value;
       row.time_limit = now() + (frozen_days * 86400);
   });
}

...

void token::transferf( account_name from,
                      account_name to,
                      asset        quantity,
                      string       memo,
                      uint32_t       frozen_days)
{
    eosio_assert( from != to, "cannot transfer to self" );
    require_auth( from );
    eosio_assert( is_account( to ), "to account does not exist");
    auto sym = quantity.symbol.name();
    stats statstable( _self, sym );
    const auto& st = statstable.get( sym );

    require_recipient( from );
    require_recipient( to );

    eosio_assert( quantity.is_valid(), "invalid quantity" );
    eosio_assert( quantity.amount > 0, "must transfer positive quantity" );
    eosio_assert( quantity.symbol == st.supply.symbol, "symbol precision mismatch" );
    eosio_assert( memo.size() <= 256, "memo has more than 256 bytes" );


    sub_balance( from, quantity );
    add_frozen_balance( to, quantity, frozen_days, from );
}

Answer 2

You cannot enforce time lock on eosio.token contract because you do not have ownership over the contract and you can't modify the logic in the contract.

However, you can create your own token contract based on eosio.token and add the time lock logic in your transfer function.

You will need to save the timestamp when the recipient receives the token into a vector or multi-index table depending on your requirements.

Answer 3

You can do that by slightly modifying your token contract.

Things what you need to do is add one more variable for timestamp in your account table or anything else that tracks users.

After that add timestamp by increasing it to two year when user purchase token.

Modify transfer function accordingly that every time checks that timestamp and allow users to transfer tokens after varification.

Answer 4

Hope this will be helpful for you!!! https://github.com/yashbhavsar007/tokentime