ERC20 Token Transfer

So far, we've set up bridge to exchange assets/data between Polygon PoS and Polygon Edge chain. This section will guide you to set up an ERC20 bridge and send tokens between different blockchains.

Step 1: Register resource ID

Firstly, you will register a resource ID that associates resources in a cross-chain environment. A Resource ID is a 32-bytes value that must be unique to the resource that we are transferring between these blockchains. The Resource IDs are arbitrary, but they may have the chain ID of the home chain in the last byte, as a convention (home chain referring to the network on which these resources originated from).

To register resource ID, you can use the cb-sol-cli bridge register-resource command. You will need to give the private key of the admin account.

# For Polygon PoS chain
$ cb-sol-cli bridge register-resource \
  --url https://rpc-mumbai.matic.today \
  --privateKey [ADMIN_ACCOUNT_PRIVATE_KEY] \
  --gasPrice [GAS_PRICE] \
  # Set Resource ID for ERC20
  --resourceId "0x000000000000000000000000000000c76ebe4a02bbc34786d860b355f5a5ce00" \
  --bridge "[BRIDGE_CONTRACT_ADDRESS]" \
  --handler "[ERC20_HANDLER_CONTRACT_ADDRESS]" \
  --targetContract "[ERC20_CONTRACT_ADDRESS]" 

# For Polygon Edge chain
$ cb-sol-cli bridge register-resource \
  --url http://localhost:10002 \
  --privateKey [ADMIN_ACCOUNT_PRIVATE_KEY] \
  # Set Resource ID for ERC20
  --resourceId "0x000000000000000000000000000000c76ebe4a02bbc34786d860b355f5a5ce00" \
  --bridge "[BRIDGE_CONTRACT_ADDRESS]" \
  --handler "[ERC20_HANDLER_CONTRACT_ADDRESS]" \
  --targetContract "[ERC20_CONTRACT_ADDRESS]"

(Optional) Make contracts mintable/burnable

# Let ERC20 contract burn on source chain and mint on destination chain
$ cb-sol-cli bridge set-burn \
  --url http://localhost:10002 \
  --privateKey [ADMIN_ACCOUNT_PRIVATE_KEY] \
  --bridge "[BRIDGE_CONTRACT_ADDRESS]" \
  --handler "[ERC20_HANDLER_CONTRACT_ADDRESS]" \
  --tokenContract "[ERC20_CONTRACT_ADDRESS]"

# Grant minter role to ERC20 Handler contract
$ cb-sol-cli erc20 add-minter \
  --url http://localhost:10002 \
  --privateKey [ADMIN_ACCOUNT_PRIVATE_KEY] \
  --erc20Address "[ERC20_CONTRACT_ADDRESS]" \
  --minter "[ERC20_HANDLER_CONTRACT_ADDRESS]"

Step 2: Transfer ERC20 Token

We will send ERC20 Tokens from the Polygon PoS chain to the Polygon Edge chain.

First, you will get tokens by minting. An account with the minter role can mint new tokens. The account that has deployed the ERC20 contract has the minter role by default. To specify other accounts as members of the minter role, you need to run the cb-sol-cli erc20 add-minter command.

# Mint ERC20 tokens
$ cb-sol-cli erc20 mint \
  --url https://rpc-mumbai.matic.today \
  --privateKey [MINTER_ACCOUNT_PRIVATE_KEY] \
  --gasPrice [GAS_PRICE] \
  --erc20Address "[ERC20_CONTRACT_ADDRESS]" \
  --amount 1000

To check the current balance, you can use cb-sol-cli erc20 balance command.

# Check ERC20 token balance
$ cb-sol-cli erc20 balance \
  --url https://rpc-mumbai.matic.today \
  --erc20Address "[ERC20_CONTRACT_ADDRESS]" \
  --address "[ACCOUNT_ADDRESS]"

[erc20/balance] Account <ACCOUNT_ADDRESS> has a balance of 1000.0

Next, you need to approve ERC20 token transfer from the account by ERC20 Handler

# Approve transfer from the account by ERC20 Handler
$ cb-sol-cli erc20 approve \
  --url https://rpc-mumbai.matic.today \
  --privateKey [USER_ACCOUNT_ADDRESS] \
  --gasPrice [GAS_PRICE] \
  --erc20Address "[ERC20_CONTRACT_ADDRESS]" \
  --recipient "[ERC20_HANDLER_CONTRACT_ADDRESS]" \
  --amount 500

To transfer tokens to Polygon Edge chains, you will call deposit.

# Start transfer from Polygon PoS to Polygon Edge chain
$ cb-sol-cli erc20 deposit \
  --url https://rpc-mumbai.matic.today \
  --privateKey [PRIVATE_KEY] \
  --gasPrice [GAS_PRICE] \
  --amount 10 \
  # ChainID of Polygon Edge chain
  --dest 100 \
  --bridge "[BRIDGE_CONTRACT_ADDRESS]" \
  --recipient "[RECIPIENT_ADDRESS_IN_POLYGON_EDGE_CHAIN]" \
  --resourceId "0x000000000000000000000000000000c76ebe4a02bbc34786d860b355f5a5ce00"

After the deposit transaction was successful, the relayer will get the event and vote for the proposal. It executes a transaction to send tokens to the recipient account in the Polygon Edge chain after the required number of votes are submitted.

INFO[11-19|08:15:58] Handling fungible deposit event          chain=mumbai dest=100 nonce=1
INFO[11-19|08:15:59] Attempting to resolve message            chain=polygon-edge type=FungibleTransfer src=99 dst=100 nonce=1 rId=000000000000000000000000000000c76ebe4a02bbc34786d860b355f5a5ce00
INFO[11-19|08:15:59] Creating erc20 proposal                  chain=polygon-edge src=99 nonce=1
INFO[11-19|08:15:59] Watching for finalization event          chain=polygon-edge src=99 nonce=1
INFO[11-19|08:15:59] Submitted proposal vote                  chain=polygon-edge tx=0x67a97849951cdf0480e24a95f59adc65ae75da23d00b4ab22e917a2ad2fa940d src=99 depositNonce=1 gasPrice=1
INFO[11-19|08:16:24] Submitted proposal execution             chain=polygon-edge tx=0x63615a775a55fcb00676a40e3c9025eeefec94d0c32ee14548891b71f8d1aad1 src=99 dst=100 nonce=1 gasPrice=5

Once the execution transaction has been successful, you will get tokens in the Polygon Edge chain.

# Check the ERC20 balance in Polygon Edge chain
$ cb-sol-cli erc20 balance \
  --url https://localhost:10002 \
  --privateKey [PRIVATE_KEY] \
  --erc20Address "[ERC20_CONTRACT_ADDRESS]" \
  --address "[ACCOUNT_ADDRESS]"

[erc20/balance] Account <RECIPIENT_ACCOUNT_ADDRESS> has a balance of 10.0