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Smart Contract Service

When writing a smart contract in aelf, the first step is to define it so our tools can generate it. aelf contracts are defined and generated using gRPC and protobuf.

Example: Multi-Token Contract​

Here is a simplified part of our multi-token contract definition:

syntax = "proto3";

package token;
option csharp_namespace = "AElf.Contracts.MultiToken.Messages";

service TokenContract {
    option (aelf.csharp_state) = "AElf.Contracts.MultiToken.TokenContractState";

    // Actions
    rpc Create (CreateInput) returns (google.protobuf.Empty) { }
    rpc Transfer (TransferInput) returns (google.protobuf.Empty) { }

    // Views
    rpc GetBalance (GetBalanceInput) returns (GetBalanceOutput) {
        option (aelf.is_view) = true;
    }
}

Service Methods​

There are two types of methods in a service:

Actions​

  • These methods take input and output protobuf messages.
  • They usually modify the state of the chain.

Example:

rpc Create (CreateInput) returns (google.protobuf.Empty) { }
  • Takes a protobuf message as input and returns a protobuf message.
  • google.protobuf.Empty signifies returning nothing.
  • Convention: append Input to protobuf types used as parameters.

Views​

  • These methods do not modify the state of the chain.
  • They are used to query the state.

Example:

rpc GetBalance (GetBalanceInput) returns (GetBalanceOutput) {
    option (aelf.is_view) = true;
}
  • Annotated with a view option to indicate it's read-only.