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How to bridge non-fungible tokens

The Non-Fungible Token (NFT) Connector enables the bridging of NFTs between NEAR and Calimero. This guide provides step-by-step instructions on how to bridge NFTs from NEAR Testnet to Calimero and back.

Bridging NFTs from NEAR to Calimero​

To bridge an NFT from NEAR Testnet to Calimero, follow these steps:

  1. Lock the desired NFT by calling a single transaction to transfer it to the NFT Connector contract on NEAR. Ensure that you use the nft_transfer_call function instead of nft_transfer to prevent token loss.

    Here's an example of locking a non-fungible token on NEAR Testnet:

    near call nft-test.igi.testnet nft_transfer_call --args '{"receiver_id":"nft_connector.cali99.dev.calimero.testnet", "token_id":"0", "msg":""}' --accountId igi.testnet --depositYocto 1 --gas 300000000000000

  2. Once the token is transferred, the bridge service will be notified and attempt to verify the locking of tokens on NEAR. If the verification is successful, a wrapped token representing the NFT will be minted on the Calimero shard.

danger

When locking NFTs on the source side NFT Connector, you MUST use the nft_transfer_call function. If you try to use nft_transfer, the tokens will be LOST.

Withdrawing NFTs back to NEAR​

To withdraw a bridged NFT from Calimero back to NEAR, follow these steps:

  1. Call the withdraw function on the bridged token contract deployed on Calimero.

    • This action will effectively burn the token on Calimero.
    • The bridge service will be notified of the burn event and attempt to verify it on the NFT Connector contract on NEAR.
    • If the verification is successful, the tokens will be unlocked and made available on NEAR Testnet.

    Here's an example of withdrawing/burning the NFT token on Calimero:

    calimero cali99-calimero-testnet call nft-test_igi.nft_deployer.cali99.calimero.testnet withdraw --args '{"token_id":"0"}' --accountId igi.testnet --depositYocto 1 --gas 300000000000000

Wrapped Tokens Naming​

Wrapped or bridged NFTs are named using the same method as Fungible Tokens (FTs). For a detailed description of the naming process, refer to the Fungible Token documentation.

Helper CLI​

To simplify commands on the Calimero side, you can create a Calimero alias. Run the following command, replacing dev with staging for staging environments or removing it for production:

alias calimero='calimero_wrapper() {
    local command="$2";
    local max_gas="300000000000000";
    local node_url="https://api.dev.calimero.network/api/v1/shards/$1/neard-rpc/";
    local args=();
    if [[ "$command" == "call" ]]; then
        args=("${@:2}");
        near "${args[@]}" --gas $max_gas --nodeUrl "$node_url" --networkId "$1";
    else
        args=("${@:2}");
        near "${args[@]}" --nodeUrl "$node_url" --networkId "$1";
    fi
}; calimero_wrapper'

Bridging NFTs from Calimero to NEAR​

If the NFT was originally minted on Calimero and needs to be bridged to NEAR, the process is similar to the one described above. The only difference is that a lock transaction needs to be called on the Calimero side, and a withdraw transaction needs to be called on the NEAR side to bring the token back to Calimero.