blockchain-playground

blockchain-playground

This is an example application for me to experiment with blockchain and smart contracts. A smart contract is a piece of code that runs in the blockchain that can automatically execute when certain conditions are met (for example, automatically release funds when token holders vote in favor of a proposal). This is a useful tool in situations where the parties involved do not trust each other.

In this demo, I define an Ethereum smart contract that simulates a shipment scenario. A customer orders a product from the vendor. The vendor creates a non-fungible token (NFT) using the delivery contract (which is viewable by all parties). To accept delivery, the designated recipient (and only the designated recipient) must purchase the token from the vendor. This serves as definitive proof that the goods have traded hands, and that the designated recipient was the one who received them.

Applicability in the Real World

This is a toy scenario, but solutions like this have real-world value. The following scenarios should be relatable:

• "I paid for expedited shipping, and it arrived too late to be useful"
• Customer: "I didn't get my stuff!". Vendor: "Too bad, my records show it was delivered."
• "I asked for signature verification, but the driver just dropped it on my porch and left"

Running it

Install dependencies

Install OpenZeppelin, which provides the implementation of the NFT standard (ERC721) that I am extending. From the root of the project:

npm install

Install Quorum, a development ethereum blockchain that runs locally in docker:

1. Check out two git repositories. The directories must be side-by-side for some of the scripts to work.

   ~$ mkdir kaleido-io
   ~$ cd kaleido-io
   ~/kaleido-io$ git clone git@github.com:kaleido-io/quorum-tools.git
   ~/kaleido-io$ git clone git@github.com:kaleido-io/quorum.git
   

2. Overwrite the default genesis file in the quorum mount directories. This sets up the initial block of the chain, including things like starting off with Ether in the sample account. This genesis file is what I needed to get it working, but YMMV.

   # Substitute with your own
   QUORUM_PATH=~/kaleido-io/quorum-tools/examples
   ~/blockchain-playground$ cp genesis.json $QUORUM_PATH/qdata_1/ethereum
   ~/blockchain-playground$ cp genesis.json $QUORUM_PATH/qdata_2/ethereum
   ~/blockchain-playground$ cp genesis.json $QUORUM_PATH/qdata_3/ethereum
   ~/blockchain-playground$ cp genesis.json $QUORUM_PATH/qdata_4/ethereum
   

3. Run quorum

   ~/kaleido-io$ cd quorum-tools/examples
   # on your machine you might need "docker-compose" instead of "docker compose"
   ~/kaleido-io/quorum-tools/examples$ docker compose up
   

Spin up a fresh database locally.

1. From the blockchain-playground base directory:

   ~/blockchain-playground$ cd database
   ~/blockchain-playground/database$ docker compose up -d
   

2. This will take a minute to come up. Run docker ps and Make sure you see mariadb in the list of running containers

   You can Connect to the database with your favorite tool. I use mysql-client from the linux package manager. Connect with the following credentials:

   • username: db_user
   • password: mysqlPassword
   • host: 127.0.0.1

Run the microservice

Option 1: Run it as a standalone app

Run the service with a private key that matches up with the test queries below. This is the key the server will use for signing requests to the blockchain.

go run . -privatekey "ae65abc8077ef5dd90eb22615f6ae708196bd4e580eae02a09d671cd83305c7b"

If you have an existing smart contract deployed and you don't want to recreate it, simply provide the existing address:

go run . -privatekey "<...>" -contractAddress "0xa8BBE18821035E7CBf64dA9d784e2846994b174E"

Option 2: Build and run using docker

~/blockchain-playground$ docker build -t blockchain-playground .
~/blockchain-playground$ docker run --rm -p 8080:8080 blockchain-playground

Using the API

If you have the microservice running, you can view the interactive swagger page at http://localhost:8080/swagger/index.html.

If you prefer static docs over interactive ones, they can be found at ./docs.

Here is some test data to get you going:

Server's data:

• private key: ae65abc8077ef5dd90eb22615f6ae708196bd4e580eae02a09d671cd83305c7b
• address: 0x6066A53027eD103D934cD122Cd0C7AF2b9279c69

Customer's data:

• private key: e958f5d3e336803b8b23c389e77d6b29a74ff0d369f0a1d8aeeec1e27254624b
• address: 0x7E0C39B48D52ADBc8660c1B03288Ef189787A133

Demonstration flow

These can all be done through the swagger UI or your tool of choice.

1. Place an order:

   This tells the microservice to create an order. You should see it in the database as well as the server's logs. This will mint a token and assign it to the server's account address.

   curl -X 'POST' \
       'http://localhost:8080/api/v1/order?itemId=7&buyerAddress=0x7E0C39B48D52ADBc8660c1B03288Ef189787A133' \
       -H 'accept: application/json'
   

2. Grab the order ID from the response and use it to see who owns the token. This executes a method in the contract.

   curl -X 'GET' \
       'http://localhost:8080/api/v1/order/{orderId}/owner' \
       -H 'accept: application/json'
   

3. Pay for the order:

   curl -X 'POST' \
       'http://localhost:8080/api/v1/payment/order/{orderId}?customerKey=e958f5d3e336803b8b23c389e77d6b29a74ff0d369f0a1d8aeeec1e27254624b' \
       -H 'accept: application/json'
   

4. Accept delivery of the order:

   This will cause the customer to purchase the token from the vendor for the total cost plus shipping. Transmitting your private key to a server is not a realistic scenario, but it serves the purpose for the demo.

   curl -X 'POST' \
       'http://localhost:8080/api/v1/order/{orderId}?customerKey=e958f5d3e336803b8b23c389e77d6b29a74ff0d369f0a1d8aeeec1e27254624b' \
       -H 'accept: application/json' \
       -H 'Content-Type: application/json' \
       -d '{"status": "delivered"}'
   

5. See that the customer now owns the token:

    curl -X 'GET' \
        'http://localhost:8080/api/v1/order/{orderId}/owner' \
        -H 'accept: application/json'
   

6. Burn the token

   The customer does not need to retain the delivery receipt forever, so destroy it!

   curl -X 'POST' \
       'http://localhost:8080/api/v1/order/{orderId}?customerKey=e958f5d3e336803b8b23c389e77d6b29a74ff0d369f0a1d8aeeec1e27254624b' \
       -H 'accept: application/json' \
       -H 'Content-Type: application/json' \
       -d '{"status": "burned"}'
   

7. See that the token no longer exists

    curl -X 'GET' \
        'http://localhost:8080/api/v1/order/{orderId}/owner' \
        -H 'accept: application/json'
   

Developing

This requires a few dev tools:

• solc - compiles the solidity code to bytecode that runs on the Ethereum Virtual Machine (EVM)
  • Installation instructions
• abigen - generates the ABI definition and the Go bindings that provide wrappers around the raw JSON-RPC calls
  • Part of the go-ethereum package

Generating the doc site

The API docs are generated with swaggo: https://github.com/swaggo/swag

Regenerate the API docs:

swag init -g controllers/router.go

Building the Go bindings for the smart contract

./rebuild_contracts.sh