Create a Leaderboard Chain

In this section, you will learn:

• How to create an IBC-enabled chain that can receive information from other chains.
• How to send player scores from your extended checkers chain to a global leaderboard chain via IBC.

After the extension of the checkers chain with a leaderboard module, the checkers game can keep track of player stats and it can maintain (on request) a sorted leaderboard. In addition, it can send player stats via the Inter-Blockchain Communication Protocol (IBC) to another chain.

You will now create a leaderboard chain that can receive the Candidate packets to store a global leaderboard.

Determine another folder for your leaderboard chain, and scaffold a chain via Ignite CLI:

Copy ignite scaffold chain leaderboard --no-module

Again, you can include an IBC-enabled leaderboard module in it:

Copy ignite scaffold module leaderboard --ibc

You need a structure to keep track of player information too:

Copy $ ignite scaffold map playerInfo wonCount:uint lostCount:uint forfeitedCount:uint dateUpdated:string --module leaderboard --no-message

And of course a board structure:

Copy $ ignite scaffold single board PlayerInfo:PlayerInfo --module leaderboard --no-message

In addition, you want to receive candidate packets:

Copy ignite scaffold packet candidate PlayerInfo:PlayerInfo --module leaderboard --no-message

This time you use the --no-message flag because this chain is not going to send any player information to another chain.

As in the previous section, you need to make adjustments in the Protobuf files proto/leaderboard/board.proto and proto/leaderboard/genesis.proto. Make sure to import gogoproto/gogo.proto and use [(gogoproto.nullable) = false]; for the PlayerInfo and the Board. You will also need to adjust the x/leaderboard/genesis_test.go like you did in the previous section.

Implement the logic for receiving packets in x/leaderboard/keeper/candidate.go:

Copy ... // OnRecvCandidatePacket processes packet reception func (k Keeper) OnRecvCandidatePacket(ctx sdk.Context, packet channeltypes.Packet, data types.CandidatePacketData) (packetAck types.CandidatePacketAck, err error) { // validate packet data upon receiving if err := data.ValidateBasic(); err != nil { return packetAck, err } allPlayerInfo := k.GetAllPlayerInfo(ctx) found_in_player_list:= false for i := range allPlayerInfo { if allPlayerInfo[i].Index == data.PlayerInfo.Index { allPlayerInfo[i] = *data.PlayerInfo; found_in_player_list = true break } } if !found_in_player_list { k.SetPlayerInfo(ctx, *data.PlayerInfo) } return packetAck, nil } ...

In addition, add a basic validation into x/leaderboard/types/packet_candidate.go:

Copy package types import ( "errors" ) // ValidateBasic is used for validating the packet func (p CandidatePacketData) ValidateBasic() error { // return error if player address is empty if p.PlayerInfo.Index == "" { return errors.New("player address cannot be empty") } return nil }

Now your leaderboard chain can receive player information from chains with the leaderboard module! However, you need to do some more work in order to update the board on this information.

There are two places where you can call for an update on the board structure:

• In OnRecvCandidatePacket, so each player sending information will pay the fee for sorting and clipping the leaderboard.
• Or you can again create a separate transaction for anyone to sort and clip the leaderboard on the leaderboard chain as you did for the checkers chain.

Here you will extend the x/leaderboard/keeper/candidate.go file in order to call for an update in OnRecvCandidatePacket. You need to create some helper functions in x/leaderboard/keeper/board.go and adjust the updateBoard function.

Copy ... func ParseDateAddedAsTime(dateAdded string) (dateAddedParsed time.Time, err error) { dateAddedParsed, errDateAdded := time.Parse(types.TimeLayout, dateAdded) return dateAddedParsed, sdkerrors.Wrapf(errDateAdded, types.ErrInvalidDateAdded.Error(), dateAdded) } func SortPlayerInfo(playerInfoList []types.PlayerInfo) { sort.SliceStable(playerInfoList[:], func(i, j int) bool { if playerInfoList[i].WonCount > playerInfoList[j].WonCount { return true } if playerInfoList[i].WonCount < playerInfoList[j].WonCount { return false } firstPlayerTime, _ := ParseDateAddedAsTime(playerInfoList[i].DateUpdated) secondPlayerTime,_ := ParseDateAddedAsTime(playerInfoList[j].DateUpdated) return firstPlayerTime.After(secondPlayerTime) }) } func (k Keeper) UpdateBoard(ctx sdk.Context, playerInfoList []types.PlayerInfo) { SortPlayerInfo(playerInfoList) if types.LeaderboardWinnerLength < uint64(len(playerInfoList)) { playerInfoList = playerInfoList[:types.LeaderboardWinnerLength] } k.SetBoard(ctx, types.Board { PlayerInfo: playerInfoList, }) }

Again, you need to include the error type in x/leaderboard/types/errors.go:

Copy ErrInvalidDateAdded = sdkerrors.Register(ModuleName, 1120, "dateAdded cannot be parsed: %s")

You also need to define TimeLayout in x/leaderboard/types/keys.go:

Copy TimeLayout = "2006-01-02 15:04:05.999999999 +0000 UTC"

Then you can include a updateBoard call in x/leaderboard/keeper/candidate.go:

Copy ... // OnRecvCandidatePacket processes packet reception func (k Keeper) OnRecvCandidatePacket(ctx sdk.Context, packet channeltypes.Packet, data types.CandidatePacketData) (packetAck types.CandidatePacketAck, err error) { // validate packet data upon receiving if err := data.ValidateBasic(); err != nil { return packetAck, err } allPlayerInfo := k.GetAllPlayerInfo(ctx) found_in_player_list:= false for i := range allPlayerInfo { if allPlayerInfo[i].Index == data.PlayerInfo.Index { allPlayerInfo[i] = *data.PlayerInfo; found_in_player_list = true break } } if !found_in_player_list { k.SetPlayerInfo(ctx, *data.PlayerInfo) } // Here we can fetch the PlayerInfo and update the board playerInfoList := k.GetAllPlayerInfo(ctx) k.UpdateBoard(ctx, playerInfoList) return packetAck, nil } ...

Test it

You can find the sample implementation of the checkers chain extension and the leaderboard chain in this repository (opens new window). There you will also find a Docker network and the relayer settings for an easy test. It also includes a script to create and run games.

Follow the steps described in the repository to run a few tests and to see it in action. If you want to do the tests with your chains, replace modular/b9-checkers-academy-draft with your checkers chain and modular/leaderboard with your leaderboard chain, and build the docker images.