Trying to pass a sha256 hash to my contract and store it

Question

I'm new to the EOS platform.

For my use case I'm trying to pass a sha256 hash to a function in my contract and store it in a table which is indexed by that hash.

I've realized you can't have the primary key of a table be anything other than a uint64_t, but apparently you can create a secondary index with a 256 bit type.

Looks like I'm supposed to use a key256 type as my secondary index, can get my contract wasm to compile and deploy a contract using that. But when I go to use it I get "The type defined i n the ABI is invalid".

Looks like in the ABI it created this section:

"types": [
    {
        "new_type_name": "key256",
        "type": "fixed_key<32>"
    }
],

Something wrong with the abigen or am I using the wrong type for a hash?

Answer 1

Figured it out, trick was to use a combination of checksum256 and key256.

Used the dice contract as an example:

  struct offer {
     uint64_t          id;
     account_name      owner;
     asset             bet;
     checksum256       commitment;
     uint64_t          gameid = 0;

     uint64_t primary_key()const { return id; }

     uint64_t by_bet()const { return (uint64_t)bet.amount; }

     key256 by_commitment()const { return get_commitment(commitment); }

     static key256 get_commitment(const checksum256& commitment) {
        const uint64_t *p64 = reinterpret_cast<const uint64_t *>(&commitment);
        return key256::make_from_word_sequence<uint64_t>(p64[0], p64[1], p64[2], p64[3]);
     }

     EOSLIB_SERIALIZE( offer, (id)(owner)(bet)(commitment)(gameid) )
  };

  typedef eosio::multi_index< N(offer), offer,
     indexed_by< N(bet), const_mem_fun<offer, uint64_t, &offer::by_bet > >,
     indexed_by< N(commitment), const_mem_fun<offer, key256,  &offer::by_commitment> >
   > offer_index;