02-init.md

---

sidebar_position: 2
description: Create the blockchain for the interchain exchange app.

---

App Init

Initialize the Blockchain

In this chapter, you create the basic blockchain module for the interchain exchange app. You scaffold the blockchain, the module, the transaction, the IBC packets, and messages. In later chapters, you integrate more code into each of the transaction handlers.

Create the Blockchain

Scaffold a new blockchain called interchange:

ignite scaffold chain interchange --no-module

A new directory named interchange is created.

Change into this directory where you can scaffold modules, types, and maps:

cd interchange

The interchange directory contains a working blockchain app.

A local GitHub repository has been created for you with the initial scaffold.

Next, create a new IBC module.

Create the dex Module

Scaffold a module inside your blockchain named dex with IBC capabilities.

The dex module contains the logic to create and maintain order books and route them through IBC to the second blockchain.

ignite scaffold module dex --ibc --ordering unordered --dep bank

Create CRUD logic for Buy and Sell Order Books

Scaffold two types with create, read, update, and delete (CRUD) actions.

Run the following Ignite CLI type commands to create sellOrderBook and buyOrderBook types:

ignite scaffold map sell-order-book amountDenom priceDenom --no-message --module dex
ignite scaffold map buy-order-book amountDenom priceDenom --no-message --module dex

The values are:

• amountDenom: the token to be sold and in which quantity

• priceDenom: the token selling price

The --no-message flag specifies to skip the message creation. Custom messages will be created in the next steps.

The --module dex flag specifies to scaffold the type in the dex module.

Create the IBC Packets

Create three packets for IBC:

• An order book pair createPair

• A sell order sellOrder

• A buy order buyOrder

ignite scaffold packet create-pair sourceDenom targetDenom --module dex
ignite scaffold packet sell-order amountDenom amount:int priceDenom price:int --ack remainingAmount:int,gain:int --module dex
ignite scaffold packet buy-order amountDenom amount:int priceDenom price:int --ack remainingAmount:int,purchase:int --module dex

The optional --ack flag defines field names and types of the acknowledgment returned after the packet has been received by the target chain. The value of the --ack flag is a comma-separated list of names (no spaces). Append optional types after a colon (:).

Cancel messages

Cancelling orders is done locally in the network, there is no packet to send.

Use the message command to create a message to cancel a sell or buy order:

ignite scaffold message cancel-sell-order port channel amountDenom priceDenom orderID:int --desc "Cancel a sell order" --module dex
ignite scaffold message cancel-buy-order port channel amountDenom priceDenom orderID:int --desc "Cancel a buy order" --module dex

Use the optional --desc flag to define a description of the CLI command that is used to broadcast a transaction with the message.

Trace the Denom

The token demons must have the same behavior as described in the ibc-transfer module:

• An external token received from a chain has a unique denom, referred to as voucher.

• When a token is sent to a blockchain and then sent back and received, the chain can resolve the voucher and convert it back to the original token denomination.

Voucher tokens are represented as hashes, therefore you must store which original denomination is related to a voucher. You can do this with an indexed type.

For a voucher you store, define the source port ID, source channel ID, and the original denom:

ignite scaffold map denom-trace port channel origin --no-message --module dex

Create the Configuration for Two Blockchains

Add two config files mars.yml and venus.yml to test two blockchain networks with specific token for each.

Add the config files in the interchange folder.

The native denoms for Mars are marscoin, and for Venus venuscoin.

Create the mars.yml file with your content:

version: 1
build:
  proto:
    path: proto
    third_party_paths:
    - third_party/proto
    - proto_vendor
accounts:
- name: alice
  coins:
  - 1000token
  - 100000000stake
  - 1000marscoin
- name: bob
  coins:
  - 500token
  - 1000marscoin
  - 100000000stake
faucet:
  name: bob
  coins:
  - 5token
  - 100000stake
  host: 0.0.0.0:4500
genesis:
  chain_id: mars
validators:
- name: alice
  bonded: 100000000stake
  home: $HOME/.mars

Create the venus.yml file with your content:

version: 1
build:
  proto:
    path: proto
    third_party_paths:
    - third_party/proto
    - proto_vendor
accounts:
- name: alice
  coins:
  - 1000token
  - 1000000000stake
  - 1000venuscoin
- name: bob
  coins:
  - 500token
  - 1000venuscoin
  - 100000000stake
faucet:
  name: bob
  coins:
  - 5token
  - 100000stake
  host: :4501
genesis:
  chain_id: venus
validators:
- name: alice
  bonded: 100000000stake
  app:
    api:
      address: :1318
    grpc:
      address: :9092
    grpc-web:
      address: :9093
  config:
    p2p:
      laddr: :26658
    rpc:
      laddr: :26659
      pprof_laddr: :6061
  home: $HOME/.venus

In order to run two blockchains side by side on a single machine, you need to start them on different ports. venus.yml has a validators configuration that stars services HTTP API, gRPC, P2P and RPC services on custom ports.

After scaffolding, now is a good time to make a commit to the local GitHub repository that was created for you.

git add .
git commit -m "Scaffold module, maps, packages and messages for the dex"

Implement the code for the order book in the next chapter.