eos-contracts-best-practices

EOSIO contracts references, examples and best-practices

Examples

Deleting table rows without declaring tables

  void clear_secondary_idx256(name TableName, uint8_t index_num, uint64_t scope){
    uint64_t primary = 0;

    auto key = eosio::key256();
    auto it2 = eosio::_multi_index_detail::secondary_index_db_functions<key256>::db_idx_lowerbound(
      _self.value, 
      scope, 
      (static_cast<uint64_t>(TableName.value) & 0xFFFFFFFFFFFFFFF0ULL)
                                    | (index_num & 0x000000000000000FULL), 
      key, 
      primary);
    while (it2 >= 0) {
        auto del = it2;
        uint64_t dummy;
        it2 = db_idx256_next(it2, &dummy);
        db_idx256_remove(del);
    }
  }
  void clear_primary(name TableName, uint64_t scope){
    auto it = db_lowerbound_i64(_self.value, scope, TableName.value, 0);
    while (it >= 0) {
        auto del = it;
        uint64_t dummy;
        it = db_next_i64(it, &dummy);
        db_remove_i64(del);
    }
  }

  ACTION clearpkgs(){
    require_auth(_self);
    clear_primary("package"_n, _self.value);
    clear_secondary_idx256("package"_n, 0, _self.value);
    clear_secondary_idx256("package"_n, 1, _self.value);
  }

References

Security best-practices

https://github.com/slowmist/eos-smart-contract-security-best-practices/blob/master/README_EN.md

https://github.com/NoneAge/EOS_dApp_Security_Incident_Analysis

Performance best-practices:

https://medium.com/@bytemaster/developing-efficient-contracts-8a8e62011c6d

More References:

• Transfer/Action intercepting contract - https://github.com/GetScatter/RIDL-Contracts/blob/master/scatterfunds/scatterfunds.cpp#L167
• Protecting against intecepting unstaked/refunded tokens by mistake - https://github.com/GetScatter/RIDL-Contracts/commit/1b9480983579de5b5d55837364bb374ef87e5c83
• Random numbers - https://github.com/bada-studio/knights_contract/blob/master/knights/contract/player_control.hpp#L187 - ?
• Events - https://github.com/bancorprotocol/contracts_eos/blob/master/contracts/eos/BancorConverter/BancorConverter.cpp#L98
• Deferred transaction - https://github.com/eosdac/dacservice/blob/master/dacservice.cpp#L53
• Transfer memo as parameter - https://github.com/eosdac/dacservice/blob/master/dacservice.cpp#L25
• Migrate tables - https://github.com/nsjames/EOSIO-Migration-Tutorial/blob/master/migrate.cpp
• Customized token contract example and best practices. - TODO
• Permissions/Authorizations examples - TODO
• Protecting from RAM theft - TODO
• Contract examples using the security best practices from above - TODO
• Submarine Operations (commit/reveal) - TODO
• Atomically erasing an entire table (by replacing pointers) - TODO
• Using asserts efficiently - TODO
• Always-false asserts - TODO
• Context-free actions - TODO
• Ricardian contracts - TODO
• Construct bounds and query secondary index from eosjs - TODO - https://github.com/greymass/eos-voter/blob/c003a04a6bd8937c416e61ad005824fe83c9f517/app/shared/actions/governance/proposals.js#L94

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