How to send an action from one contract to another?

Question

From contract A, I want to send an action to contract B. How to do that?

There is SEND_INLINE_ACTION but that seems to need a pointer to the contract (usually *this), correct?

Solution

Using action.send as suggested by Leo works when having set eosio.code permission to the contract's account.

Answer 1

Maybe you can try to use N(yourcontract) instead of *this. If it does not work you can also try this:

    action(permission_level{ from, N(active) },
           N(eosio.token), N(transfer),
           std::make_tuple(from, self, price, std::string(""))
    ).send();

Instead of N(eosio.token) and N(transfer) you would use the external contract that you want.

The external contract should allow transactions coming from your contract.

Answer 2

Here we can see an example from Monstereos sending an inline action for the battlecreate function:

void pet::battlecreate(name host, battle_mode mode, checksum256 secret) {
  require_auth(host);

  _tb_battle tb_battles(_self, _self);
  auto itr_battle = tb_battles.find(host);

  eosio_assert(itr_battle == tb_battles.end(), "you already host a battle!");
  eosio_assert(mode == V1 || mode == V2 || mode == V3, "invalid battle mode");

  // check and increase busy arenas counter
  auto pc = _get_pet_config();
  pc.battle_busy_arenas++;
  eosio_assert(pc.battle_busy_arenas <= pc.battle_max_arenas, "all arenas are busy");

  tb_battles.emplace(_self, [&](auto& r) {
    r.host = host;
    r.mode = mode;
  });
  _update_pet_config(pc);

  SEND_INLINE_ACTION( *this, battlejoin, {host,N(active)}, {host, host, secret} );
}

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SEND_INLINE_ACTION | Docs

Parameters

CONTRACT - The account this action is intended for
NAME - The name of the action
... - The member of the action specified as ("action_member1_name", action_member1_value)("action_member2_name", action_member2_value)

So:

*this is the dereferenced pointer of value contract

battlejoin being the name of the action

battlejoin calls for: name host, name player, checksum256 secret

So we give it host with an active permission level for verification, host for host, host for player, and checksum256 for match's secret ID.