Transfer WETH from xDai to ETH on Mainnet

A guide on using block explorers to transfer Wrapped ETH from the xDai chain to the Ethereum Mainnet in the form of ETH native tokens.

Background

In some cases it is convenient to use ETH, the native token for the Ethereum Mainnet, in form of ERC20 token - this allows to unify interfaces for the operations with assets. The recent Wrapped ETH token contract is WETH9.

When the ETH-xDai OmniBridge first started, wrapped ETH was bridged to the xDai chain in form of ERC677 token: Wrapped ETH on xDai.

Although the bridged token can be transferred back to ETH, it is still be in form of the ERC20 token, and it cannot be used in transactions to pay for gas fees. In this case, if a user has no ETH, it is impossible for them to unwrap these ETH tokens.

This set of instructions demonstrates how the Wrapped ETH can be bridged from the xDai chain directly to ETH tokens using a new relay-and-call feature implemented recently in the OmniBridge contracts. In the last section of the manual there is also an instruction on how to transfer ETH to WETH on the xDai chain using a single operation. This may not be used often but some users may find it handy.

This instruction assumes that you have access to BlockScout and Etherscan. You also must have a bit of xDai to pay for gas fees for a bridge transaction on the xDai chain.

Bridge WETH on xDai to ETH

1. Change the chain to xDai in MetaMask/NiftyWallet.

2. Find the Wrapped ETH token in BlockScout:

WETH token in the xDai chain: 0x6A023CCd1ff6F2045C3309768eAd9E68F978f6e1.

3. Go to the Write Proxy tab.

4. Scroll to the transferAndCall method.

Enter the following information in the fields:

• _to (address) the address of the OmniBridge contract on the xDai chain: 0xf6A78083ca3e2a662D6dd1703c939c8aCE2e268d

• _value (uint256) with amount of WETH to be bridged (bridge fees will be subtracted from this value)

• _data (bytes) with two pieces concatenated:

  • the address of the WETH OmniBridge helper contract on the Ethereum Mainnet (0xa6439Ca0FCbA1d0F80df0bE6A17220feD9c9038a)

  • the address of the ETH recipient without 0x.

  E.g. for the recipient 0xbf3d6f830ce263cae987193982192cd990442b53 the value in _data field is 0xa6439ca0fcba1d0f80df0be6a17220fed9c9038abf3d6f830ce263cae987193982192cd990442b53

Press Write to send the transaction.

5. As soon as the transaction is included in the block, click on the transaction link to get the transaction details:

6. Use "View in ALM App" link on the page with transaction details to track status of the transfer and finalize bridge operations if required.

7. Eventually, when an executing transaction on the Mainnet is processed, the WETH will be unlocked and unwrapped to ETH native tokens:

Bridge ETH to the xDai chain

1. Visit the WETH OmniBridge helper contract on Etherscan: 0xa6439Ca0FCbA1d0F80df0bE6A17220feD9c9038a

2. Go to the Write Contract tab:

and connect your wallet.

3. Scroll to the wrapAndRelayTokens method and enter the amount of ETH to bridge to the xDai chain:

Press Write to send the transaction.

4. As soon as the transaction is included in the block, press the "View you transaction" button to get the transaction hash which can be used in the AMB Live Monitoring app to track the status of the transaction.