Interface Abi

Application Binary Interface (ABI)

ABIs are composed of 3 elements: methods, events, and types.

• The methods define the names of the entries of the smart contract, the corresponding endpoints and the name of the types used.
• The events define possible events triggered by the smart contract and the name of the types used.
• The types contain the description to serialize and deserialize data using proto buffers. It is used to encode/decode the methods and events. These types can be provided in binary format or json format (koilib_types)

To generate the types is necessary to use the dependency protobufjs. The following example shows how to generate the protobuf descriptor from a .proto file.

const fs = require("fs");
const pbjs = require("protobufjs/cli/pbjs");

pbjs.main(
  ["--target", "json", "./token.proto"],
  (err, output) => {
    if (err) throw err;
    fs.writeFileSync("./token-proto.json", output);
  }
);

Then this descriptor can be loaded to define the ABI:

const tokenJson = require("./token-proto.json");
const abiToken = {
  methods: {
    balanceOf: {
      entry_point: 0x15619248,
      argument: "balance_of_arguments",
      return: "balance_of_result",
      read_only: true,
      default_output: { value: "0" },
    },
    transfer: {
      entry_point: 0x62efa292,
      argument: "transfer_arguments",
      return: "transfer_result",
    },
    mint: {
      entry_point: 0xc2f82bdc,
      argument: "mint_argumnets",
      return: "mint_result",
    },
  },
  events: {
    'koinos.contracts.token.mint_event': {
      argument: "mint"
    },
  },
  koilib_types: tokenJson,
};

Note that this example uses "default_output" for the method "balanceOf". This is used when the smart contract returns an empty response (for instance when there are no balance records for a specific address) and you require a default output in such cases.

Definition of events

There are 2 ways to define events in koinos:

• Event names as protobuffer names
• Custom event names

1. Event names as protobuffer names: The name of the event links with the protobuffer definition. In this case there is no need to define the event in the ABI.

Example:

Proto definition

package koinos.contracts.token;

message transfer_arguments {
   bytes from = 1 [(btype) = ADDRESS];
   bytes to = 2 [(btype) = ADDRESS];
   uint64 value = 3 [jstype = JS_STRING];
}

message transfer_event {
   bytes from = 1 [(btype) = ADDRESS];
   bytes to = 2 [(btype) = ADDRESS];
   uint64 value = 3 [jstype = JS_STRING];
}

Contract

// token-contract.ts
transfer(args: token.transfer_arguments): token.transfer_result {
  ...
  System.event("koinos.contracts.token.transfer_event", Protobuf.encode(event, token.transfer_event.encode), impacted);
}

2. Custom event names: The previous definition has a limitation. It's necessary to define a proto message for each event and argument, and they can not be reused. In this second solution, the event names are defined in the ABI and they are linked with the corresponding protobuffer definitions. In this sense, they can be reused.

Example

Proto definition

package koinos.contracts.token;

// only 1 message
message transfer {
   bytes from = 1 [(btype) = ADDRESS];
   bytes to = 2 [(btype) = ADDRESS];
   uint64 value = 3 [jstype = JS_STRING];
}

Contract

// token-contract.ts

// Transfer of tokens
// @event transfer_event token.transfer
transfer(args: token.transfer): void {
  ...
  System.event("transfer_event", Protobuf.encode(event, token.transfer.encode), impacted);
}

ABI

const abiToken = {
  methods: {
    transfer: {
      entry_point: 0x62efa292,
      argument: "transfer",
      return: "",
    },
  },
  events: {
    'transfer_event': {
      argument: "transfer"
    },
  },
  koilib_types: tokenJson,
};