This is an Ink! smartcontract implementing a coupon payments logic.
With this contract you can emit coupons worth an amount of tokens for blockchain users to make exchange operations or payments.

• Contract set-up with owner, set by constructor's argument, or set caller by default.
• After initialization the contract can be replenished with tokens that will be used for coupon redemption.
• Adding new coupons:
  • Coupon is a sr25519 public key, with defined balance
  • If contract balance is enough it puts the coupon into storage and reserves the appropriate funds for redemption.
  • If contract balance is not enough the coupon is rejected for registration.
  • Multiple coupons can be registered at a time.
• Coupon redemption:
  • User's coupon has a sr25519 secret key.
  • Before activation a coupon can be checked in the contract using it's public key - coupon status ('active' or 'burned') and coupon value will be delivered.
  • For payout - set receiver, coupon public key and private signature.
    • Signature is a receiver's wallet address encrypted with the private key of the coupon.
    • After send request if params & signature are valid, the contract unlocks reserved tokens and transfers them to connected receiver's wallet.
• Owner methods:
  • An owner can get info about 'free' funds on the smartcontract (that are not reserved for registered coupons)
  • Free tokens (unused by coupons) can be transferred to owner's private address.
  • Ownership of the contract with all funds and liabilities can be transferred to another user.

Please follow installation instructions provided here.

git clone https://github.com/bsn-si/ocex-smartcontract

cd ocex-smartcontract
cargo +nightly test --features=test

cargo +nightly contract build

Video guide link:

You may encounter compilation or optimization errors in wasm builds. Build tested on nightly-2022-08-08 toolchain, with rustc 1.64.0 (a55dd71d5 2022-09-19) version, if you have compilation errors try changing the toolkit and compiler version to the specified one. Also you need wasm target and dylint. For install specified toolchain & targets run:

rustup toolchain install nightly-2022-08-08
rustup target add wasm32-unknown-unknown
cargo install cargo-dylint

In case you get a compilation error during the wasm optimization step, make sure you have binaryen installed.

As an alternative to the standard build, you can build the smartcontract in a docker. For contract build and copy run the following commands in the source code dir:

docker build -t ocex-contract .
docker create -ti --name ocex ocex-contract bash
docker cp ocex:/contract/target/ink/ocex.contract ~/ocex.contract

Simple cli tool for making coupon redemption signature. Set a contract address, coupon secret key and funds receiver's address.

cargo +nightly build --examples --features=test

...and then use it like

./target/debug/examples/make-coupon-signature \
  --contract 5Ev9VH31P4asHN11VkWRSsBZNFBy82PxU9TTLEehfKt27sQG \
  --coupon 0x398f0c28f98885e046333d4a41c19cee4c37368a9832c6502f6cfd182e2aef89 \
  --receiver 5FLSigC9HGRKVhB9FiEo4Y3koPsNmBmLJbpXg2mp1hXcS59Y

First setup and start substrate-contracts-node, go to Polkadot Portal UI for setting up a test contract.

After creating an instance of the contract on the blockchain you can use a core owner from test accounts list like Alice. After that you need to send funds to the contract. Now you can call contract's methods from Polkadot Portal UI.

• Instantiate new contract with Alice owner.
• Send funds to the contract. Coupons can not be created without providing liquidity.
• From Polkadot Portal UI call addCoupon method, for field coupon set user Bob - this is our first coupon public key.
• For amount set the allowed coupon amount, if amount greater than contract balance - the sending will be rejected.
• Call method with Execute action on Polkadot Portal UI.
• After adding a coupon you can check coupon Bob with checkCoupon method that returns a tuple of the coupon's statuses, (is_active, amount)
• Try to activate the coupon with make-coupon-signature helper, described in the past article. You can check Bob secret key with subkey tool.

➜  ~ subkey inspect //Bob
Secret Key URI `//Bob` is account:
  Network ID:        substrate 
  Secret seed:       0x398f0c28f98885e046333d4a41c19cee4c37368a9832c6502f6cfd182e2aef89
  Public key (hex):  0x8eaf04151687736326c9fea17e25fc5287613693c912909cb226aa4794f26a48
  Account ID:        0x8eaf04151687736326c9fea17e25fc5287613693c912909cb226aa4794f26a48
  Public key (SS58): 5FHneW46xGXgs5mUiveU4sbTyGBzmstUspZC92UhjJM694ty
  SS58 Address:      5FHneW46xGXgs5mUiveU4sbTyGBzmstUspZC92UhjJM694ty

• We know the secret key for Bob coupon is 0x398f0c28f98885e046333d4a41c19cee4c37368a9832c6502f6cfd182e2aef89 and after that we can call command like that.

./target/debug/examples/make-coupon-signature \
  --contract <YOU_CONTRACT_ADDRESS> \
  --coupon 0x398f0c28f98885e046333d4a41c19cee4c37368a9832c6502f6cfd182e2aef89 \
  --receiver <RECEIVER_ADDRESS>

• Now call activateCoupon method, set the selected receiver, select coupon Bob and set the signature from the previous command.
• Execute in Polkadot Portal UI and congrats! Funds were transferred to the receiver's account.

• OCEX coupon activation dapp
• OCEX smart contract API client
• OCEX CLI management tool
• JS/Wasm library for coupon activation signatures
• CosmWasm! smart contract for ZK delivery evidence based on the principles of the OCEX

Apache License 2.0 © Bela Supernova (bsn.si)