Ever wanted to call an action on one EOS contract from another like we can with Solidity? Well we can and it’s super simple! You can find the full code for this example on GitHub.
Before we start…
Executing inline actions requires custom account permissions
Due to security reasons, the release version of EOS now requires the eosio.code permission on the contract invoking an inline action.
Modifying Account Permissions We first need to modify the permissions of our timeline account before we can invoke actions on our user contract. We’re going to overwrite our active key on our caller account with the eosio.code permission and use this later to invoke our inline action. Let’s use the cleos set account permission command to achieve this.
cleos set account permission timeline active
'{
"threshold":1,
"keys":[{
"key":"YOUR_PUBLIC_KEY",
"weight":1
}],
"accounts":[{
"permission":{
"actor":"timeline",
"permission":"eosio.code"
},"weight":1
}]
}'
owner -p timeline@owner
EOS Inter-contract Communication
Let’s take a look at eosio::action to invoke actions between one contract and another. We will write a user contract to handle user registration, activation and validation, and a timeline contract to handle publishing and removing tweets.
Our communication will happen when we attempt to publish a tweet though the timeline contract. Before we store the tweet, we’re first going to call action(PERMISSIONS,TO_ACCOUNT,TO_ACTION,DATA_TUPLE).send() to validate our user’s profile.
require_auth(username);
// Validate user
eosio::action(
permission_level{_self, N(active)},
N(user),
N(validate),
std::make_tuple(username)
).send();
...
// Store tweet
It’s as simple as that! You should be able to call another contract as long as your eosio.code permissions are setup for the contract account making the calls.