A Provable & ZeppelinOS collaboration showing you how to use Provable alongside ZeppelinOS in order to create data-rich smart-contracts leveraging external APIs!
This example shows you how to deploy a simple crowdsale contract which uses Provable to discover the price of ETH in USD in order to correctly set the price for the tokens you're selling to $1!
Pre Flight Checks) You will need Node, NPM & a browser with Metamask installed!
1) First install the Open Zeppelin CLI, Truffle & Ganache globally:
❍ npm i -g @openzeppelin/[email protected] [email protected] [email protected]
2) Now unpack this starter kit in an empty directory:
❍ openzeppelin unpack provable-things/provable-starter-kit
3) Next, fire up a new terminal & start up a local blockchain instance with Ganache via:
❍ ganache-cli --secure -u 0 -u 1 -u 2 --deterministic
4) Then in the root of the repo run the setup script:
❍ npm run setup
5) Then use the Open Zeppelin CLI initialize your project:
❍ openzeppelin init provable-starter-kit
6) Now enter the client directory and run the React app:
❍ cd client && npm run start
7) Once the React app is built you can view it on your localhost by pointing your browser at:
❍ http://localhost:3000
9) Now in your browser you should see that your Provable Starter-kit is up & running! Click on Provable Crowdsale in the top right corner to begin creating the example dapp!
In order to run the smart-contract tests you will need to use the ethereum-bridge to provide a way for the Provable service to listen to events from your locally-based smart-contract(s). To get it up and running:
1) Enter this directory & install dependencies:
❍ npm i
2) Launch the Truffle develop console:
❍ npx truffle develop
3) Open a new console in the same directory & spool up the ethereum-bridge:
❍ npx ethereum-bridge -a 9 -H 127.0.0.1 -p 9545 --dev
4) Once the bridge is ready & listening, go back to the first terminal where you have the Truffle development console running & set the tests going:
❍ truffle(develop)> test
Contract: ❍ Provable Zeppelin Example
❍ Crowdsale Tests
✓ Should deploy a token (136ms)
✓ Should deploy the Provable Zeppelin Crowdsale Contract (139ms)
✓ Should give the crowdsale contract all the tokens (71ms)
✓ Should get web3 instantiation of contract to listen for events
✓ Owner can't init crowdsale before getting ETH price
✓ Non-owner can't get eth prices via Provable
✓ Should get ETH price in cents (6789ms)
✓ Should have stored ETH price in cents in contract
✓ Non-owner can't init crowdsale even if ETH price retrieved (38ms)
✓ Crowdsale should not yet be initialized
✓ Should successfully init crowdsale (46ms)
✓ Crowdsale should now be initialized (71ms)
✓ Should have set price per token in crowdsale contract
✓ Should have calculated price per token in wei correctly
✓ Should not be able to buy < 1 token (65ms)
✓ Should be able to buy a token (89ms)
✓ Should refund any change from buying tokens (100ms)
17 passing (9s)
truffle(develop)>