Chainlink Terra

Developing

Requirements

This demo requires the following components:

• Rust:
  • rustup with cargo 1.44.1+.
  • rustc and cargo 1.44.1+.
  • Install the wasm32-unknown-unknown target for Rust: rustup target add wasm32-unknown-unknown
• NodeJS 14 LTS or later.
• Docker
• A C compiler such as the one included in GCC.

Confirm that the necessary requirements are installed:

rustc --version
cargo --version
rustup target list --installed
docker --version
node --version

Compile a contract

Example contracts are available in the ./contracts directory of this repository. Make sure you can compile and run the contracts before making any changes. From the base of your cloned repository, run cargo wasm to produce a wasm build for each contract:

cargo wasm

This produces a .wasm build file in the ./target/wasm32-unknown-unknown/release/ directory for each contract.

Generating JSON Schema

While the Wasm calls (init, handle, query) accept JSON, this is not enough information to use it. We need to expose the schema for the expected messages to the clients. You can generate this schema by calling cargo schema, which will output four files in ./YOUR_CONTRACT/schema, corresponding to the three message types the contract accepts, as well as the internal State.

cd ./contracts/YOUR_CONTRACT && cargo schema

These files are in standard json-schema format, which should be usable by various client side tools, either to auto-generate codecs, or just to validate incoming json with regard to the defined schema.

Preparing the Wasm bytecode for production

Before we upload it to a chain, we need to ensure the smallest output size possible, as this will be included in the body of a transaction. We also want to have a reproducible build process, so third parties can verify that the uploaded Wasm code did indeed come from the claimed rust code.

To do this, use the following rust-optimizer (or to be specific in our case - workspace-optimizer), a docker image to produce an extremely small build output in a consistent manner. From the base of your cloned repository, run the workspace-optimizer container:

docker run --rm -v "$(pwd)":/code \
  --mount type=volume,source="$(basename "$(pwd)")_cache",target=/code/target \
  --mount type=volume,source=registry_cache,target=/usr/local/cargo/registry \
  cosmwasm/workspace-optimizer:0.11.4

This produces an ./artifacts directory in the root of the workspace. It contains the compiled and optimized WebAssembly output of the contracts along with a Sha256 checksum in ./artifacts/checksums.txt.

Deploying and Instantiating Price Consumer Contract, and Reading the Latest Price

This example uses the readLatestPrice.mjs script to deploy, instantiate, and read the Price Consumer Contract.

Install the Terra.js package, which supports several wallet functions in the script:

npm install @terra-money/terra.js

Export your wallet seed phrase to the TERRA_SEED environment variable. The script uses the seed phrase to determine the wallet key that you want to use to deploy and call the smart contract.

export TERRA_SEED="YOUR SEED PHRASE"

Run the script:

node ./scripts/readLatestPrice.mjs

After the script runs, the price consumer contract should be deployed and instantiated on the Terra testnet. The console prints the latest LUNA/USD price.

{
  round_data_response: {
    round_id: 39516,
    answer: '3706000000',
    started_at: 1634497952,
    updated_at: 1634497952,
    answered_in_round: 39516
  }
}