Smart Contract Basics¶

A smart contract in Remprotocol consists of actions and persistent storage (tables). The contract can perform all the basic actions as a regular account that are determined by its logic.

Action¶

Push Action Interface¶

Actions determine the basic functionality of your smart contract that affects the state of the network.

$ remcli push action [OPTIONS] account action data

Positionals:
  account TEXT                The account providing the contract to execute (required)
  action TEXT                 A JSON string or filename defining the action to execute on the contract (required)
  data TEXT                   The arguments to the contract (required)

Permission System¶

With the flexibility of the permissions levels on the Remprotocol, you can restrict access to your actions in a smart contract by including require_auth() method in your actions.

Restricted Access Action Example:

[[eosio::action]]
void adduser( name user, string metadata ) {
    require_auth( get_self() );
    auto it = users.find(user.value);
    check(it == rewards_tbl.end(), "account already exists");

    users.modify(*it, get_self(), [&](auto &u) {
        u.user     = user;
        u.metadata = metadata;
        u.balance  = 0;
    });
}

You can find more information about the Permission System here.

Persist Data¶

Each time a smart contract action is called, a wasm code is executed that in turn creates an instance that is destroyed after the wasm code is executed. A smart contract does not store the state of instance after their destruction.

Multi-index or Singleton tables are used to persist data between actions.

struct [[eosio::table, eosio::contract("CONTRACT_NAME")]] users {
     name      user;
     string    metadata;
     uint64_t  balance;

     uint64_t primary_key() const { return account.value; }
  };

You can find more information about the Persist Data.

Dispatchers¶

Every smart contract must provide an apply action handler. The apply action handler is a function that listens to all incoming actions and performs the desired behavior. In order to respond to a particular action, code is required to identify and respond to specific action requests. apply uses the receiver, code, and action input parameters as filters to map to the desired functions that implement particular actions. To simplify the work for contract developers, EOSIO provides the EOSIO_DISPATCH macro, which encapsulates the lower level action mapping details of the apply function, enabling developers to focus on their application implementation.

#include <eosio/eosio.hpp>

using namespace eosio;

class [[eosio::contract]] accounting_system : public contract {
  public:
      using contract::contract;

      [[eosio::action]]
      void adduser( name user, string metadata ) {
         require_auth( get_self() );
         auto it = users.find(user.value);
         check(it == rewards_tbl.end(), "account already exists");

         users.modify(*it, get_self(), [&](auto &u) {
            u.user     = user;
            u.metadata = metadata;
            u.balance  = 0;
        });
      }
  private:
    struct [[eosio::table]] users {
       name      user;
       string    metadata;
       uint64_t  balance;

       uint64_t primary_key() const { return account.value; }
    };
    typedef eosio::multi_index<"users"_n, users> users_index;
};
EOSIO_DISPATCH(accounting_system, (adduser))

Refer to EOSIO’s glossary.