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Fungible Token Connector

The fungible token connector consists of four contracts:

  • ft connector
  • bridge token deployer
  • bridge token
  • permissions manager

Once you install the FT connector on the console, the contracts are automatically installed as well.

Setting up the Fungible Token Connectors​

The setup of ft connectors is done automatically when the bridge is installed on the console, requiring no additional actions from users.

Bridging FT from NEAR to Calimero (when the original token is on NEAR)​

In this process, we lock FTs on NEAR and mint wFTs (wrapped FTs) on Calimero. The following steps are involved:

  1. Call ft transfer call on the FT contract on NEAR (lock on NEAR):

    • Users/DApps send FTs to the ft connector contract on NEAR, effectively locking the fungible tokens on the NEAR side.

  2. Call NEAR RPC for transaction status:

    • Retrieve the transaction status, including the receipt with the event denoting a lock, which will be used to prove the transaction on Calimero.

  3. Call the Calimero light client for the current height:

    • Ensure that the current height on the Calimero light client contract is higher than the block height where the FTs were locked on the source chain.

  4. Call NEAR RPC for light client proof:

    • Gather all the proof data from the archival node on NEAR, necessary to validate the successful execution of the transaction.

  5. Call mint() on Calimero ft connector:

    • Perform the following steps:
      • If this is the first time transferring the FT, deploy the bridge token on Calimero since wFT does not exist yet on Calimero.
      • Validate the outcome using the proof (fails if the proof is invalid), and mint wFTs on Calimero.
      • Retrieve the metadata for wFT on Calimero. If it's empty, fetch the metadata from NEAR and set it on Calimero.
      • Map the Calimero FT contract with the NEAR FT contract using map contract on NEAR ft connector.
      • Congratulations, wFT now exists on Calimero.

Bridging back FT from Calimero to NEAR (burn the wrapped FT)​

This process involves burning/withdrawing wFTs on Calimero and unlocking FTs on NEAR:

  1. Call view mapping on ft connector on Calimero:

    • Retrieve the name of the wFT to be burned since the transfer initiator may only know the FT name on NEAR.

  2. Call withdraw on the wFT (bridge token) on Calimero:

    • Burn the desired amount of wFTs on Calimero.
    • This transaction needs to be proven to demonstrate that the burn actually occurred.

  3. Call Calimero RPC for transaction status:

    • Verify the receipt denoting the burn of a specific wFT with the given amount and the account to unlock it on the NEAR side.

  4. Call NEAR light client for the current height:

    • Ensure that the current height is higher than the block height where the wFT withdrawal occurred on the destination chain.

  5. Call Calimero RPC for light client proof:

    • Obtain the light client proof from Calimero.

  6. Call unlock() on NEAR ft connector with the obtained proof and a valid block height:

    • Unlock FTs on NEAR by providing the proof and a valid block height.

  7. Prove the outcome, and if successful, the FTs are now unlocked on the source network.

Bridging between Calimero and NEAR when the original asset is on Calimero​

If the original asset exists only on Calimero and not on NEAR, bridging to NEAR will create a wrapped FT on NEAR. All steps from the previous sections apply, but inversely, as the bridge operates in a bidirectional manner.

Automatic Bridging​

All of these steps are automated with the Calimero Bridge service. Users of Calimero private shards do not need to make all the calls manually. Users/DApps only need to make an ft transfer call to lock FTs on a chain, and the bridge service will handle the rest, automatically transferring the wrapped assets to the other chain. Similarly, when someone wants to unlock the funds, they simply need to make a withdraw call on the FT contract, and the bridge service will automatically update all the components. If the tokens were burnt on the starting chain, they will be unlocked on the other side.