On EOS, incoming transfers can have rules applied to them. Exchanges and accounts can enforce their memo fields to stop transfers that don't enter the correct details on memo for example.
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Transfer filter contract

EOS has a method to check incoming transfers and This contract makes token transfers to it fail, if memo in those transfers does not satisfy certain conditions. Currently set conditions are:

  • Memo has to be exactly 8 symbols long;
  • Contain only digits;

You add different asserts in ontransfer action to modify these conditions.

Only transfers wher contract is receiver are currently filtered.


eosiocpp -o transferfilter.wast transferfilter.cpp


cleos set code <your-account-name> transferfilter.wast


Without memo

$ cleos transfer eosio <your-account-name> "10.0000 SYS"
Error 3050003: eosio_assert_message assertion failure

With non digit

$ cleos transfer eosio <your-account-name> "10.0000 SYS" "1234567a"
Error 3050003: eosio_assert_message assertion failure


$ cleos transfer eosio <your-account-name> "10.0000 SYS" "00345670"
executed transaction: 747ceb78a0359ffd426df96d3ce4c844bfe7402e1634638a14ebc2d91c676a91  136 bytes  607 us
#   eosio.token <= eosio.token::transfer        {"from":"eosio","to":"<your-account-name>","quantity":"10.0000 SYS","memo":"00345670"}
#         eosio <= eosio.token::transfer        {"from":"eosio","to":"<your-account-name>","quantity":"10.0000 SYS","memo":"00345670"}
#      <your-account-name> <= eosio.token::transfer        {"from":"eosio","to":"<your-account-name>","quantity":"10.0000 SYS","memo":"00345670"}
warning: transaction executed locally, but may not be confirmed by the network yet    ]