Cross-Chain Transfer

Cross-chain transfers only support bound BEP2 or BEP8 tokens on BC and BEP20 tokens on BSC.

Verify Token Info

First, you should make sure that it's already bound. For example, you could see the binding info of BNB:

## mainnet
bnbcli token info --symbol BNB --trust-node --node http://dataseed4.binance.org:80

## testnet
tbnbcli token info --symbol BNB --trust-node --node http://data-seed-pre-0-s3.binance.org:80 

{
  "type": "bnbchain/Token",
  "value": {
    "name": "Binance Chain Native Token",
    "symbol": "BNB",
    "original_symbol": "BNB",
    "total_supply": "200000000.00000000",
    "owner": "tbnb1l9ffdr8e2pk7h4agvhwcslh2urwpuhqm2u82hy",
    "mintable": false,
    "contract_address": "0x0000000000000000000000000000000000000000",
    "contract_decimals": 18
  }
}

As BNB is the native token on both chains, so we use 0x0000000000000000000000000000000000000000 as the corresponding contract address. Besides, on BSC, the native token decimals is 18, while the decimals on BC is 8. So if you transfer 1e8:BNB to BSC, the recipient balance will gain 1e18.

Transfer BNB from BC to BSC

Example:

## mainnet
bnbcli bridge transfer-out --to 0xEe9546E92e6876EdF6a234eFFbD72d75360d91f0 --expire-time 1597543193 --chain-id Binance-Chain-Tigris --from owner --amount 100000000:BNB --node http://dataseed4.binance.org:80

## testnet
tbnbcli bridge transfer-out --to 0xEe9546E92e6876EdF6a234eFFbD72d75360d91f0 --expire-time 1597543193 --chain-id Binance-Chain-Ganges --from owner --amount 100000000:BNB --node http://data-seed-pre-0-s3.binance.org:80

Result:

Committed at block 465899 (tx hash: 68FFF82197E27A3EC14AFF8C99A035FA9CA7120312AA55E98D11DFC0F8D9F3B9, response: {Code:0 Data:[] Log:Msg 0:  Info: GasWanted:0 GasUsed:0 Events:[{Type: Attributes:[{Key:[84 114 97 110 115 102 101 114 79 117 116 83 101 113 117 101 110 99 101] Value:[49 49] XXX_NoUnkeyedLiteral:{} XXX_unrecognized:[] XXX_sizecache:0} {Key:[69 120 112 105 114 101 84 105 109 101] Value:[49 53 57 55 53 52 51 49 57 51] XXX_NoUnkeyedLiteral:{} XXX_unrecognized:[] XXX_sizecache:0} {Key:[97 99 116 105 111 110] Value:[99 114 111 115 115 84 114 97 110 115 102 101 114 79 117 116] XXX_NoUnkeyedLiteral:{} XXX_unrecognized:[] XXX_sizecache:0}] XXX_NoUnkeyedLiteral:{} XXX_unrecognized:[] XXX_sizecache:0}] Codespace: XXX_NoUnkeyedLiteral:{} XXX_unrecognized:[] XXX_sizecache:0})

Transfer BNB from BSC to BC

transferOut

Call transferOut of TokenHub contract in MyEtherWallet:

Parameter Name	Type	Description
contractAddr	address	for BNB, the value must be 0x0000000000000000000000000000000000000000
recipient	address	decode bech32 address, starting with 0x . To transfer to hex string. This is a online too to decode bech32: https://slowli.github.io/bech32-buffer/
amount	uint256	The BNB decimals on BSC is 18. If you want to transfer one BNB, then the value should be 1e18. Besides, the value must be N * 1e10
expireTime	uint256	Timestamp, counted by second

The value here should follow this equation:

txValue = (amount + RelayFee)/1e18

RelayFee should be 0.01BNB and it can be updated by on-chain governance. For example, if you transfer 1BNB from BSC to BC, the value should be at least 1.01BNB.

After all the above parameters have been set to proper values, users can click the transact button to build transactions, and metamask plugin will be ejected. Then users can click the confirm button in metamask to sign and broadcast transactions.

batchTransferOutBNB

Call batchTransferOutBNB of TokenHub contract in MyEtherWallet:

Parameter Name	Type	Description
recipientAddrs	address[]	decode bech32 address to hex string. This is a online too to decode bech32: https://slowli.github.io/bech32-buffer/0
amounts	uint256[]	amount for each recipient, should be N * 1e10
refundAddrs	address[]	sender can specify some address as the refund address if the cross chain transfer is failed.
expireTime	uint256	Timestamp, counted by second

The value here should follow this equation:

txValue = (sumOfAmounts + RelayFee * batchSize)/1e18

Transfer BEP2 to BSC

Execute the following command to transfer ABC-A64 token to BSC:

## mainnet
bnbcli bridge transfer-out --to 0xEe9546E92e6876EdF6a234eFFbD72d75360d91f0 --expire-time 1597543193 --chain-id Binance-Chain-Tigris --from owner --amount 10000000000:ABC-A64 --node http://dataseed4.binance.org:80

## testnet
tbnbcli bridge transfer-out --to 0xEe9546E92e6876EdF6a234eFFbD72d75360d91f0 --expire-time 1597543193 --chain-id Binance-Chain-Ganges --from owner --amount 10000000000:ABC-A64 --node http://data-seed-pre-0-s3.binance.org:80

Transfer BEP20 to BC

Before calling transferOut or batchTransferOut, users need to call approve method to grant enough allowance to TokenHub contract. For transferOut method, the allowance should equal the transfer amount. For batchTransferOut, the allowance should be the sum of the amount array.

transferOut

Parameter Name	Type	Description
contractAddr	address	BEP20 contract address
recipient	address	decode bech32 address to hex string. This is a online too to decode bech32: https://slowli.github.io/bech32-buffer/
amount	uint256	BEP20 token amount. Here the decimals is 18, so the amount must be N * 1e10.
expireTime	uint256	Timestamp, counted by second

The value here should be RelayFee.

Mint

If both the BEP20 token and bep2 token are mintable, then token owners can still mint their tokens even after token binding. Besides, token owners need to ensure the total supply and the locked amount on both chains are still matched, otherwise, users might can’t transfer their tokens to another chain.

Mint token on BC

1. Execute the following command to mint 10000 ABC-A64:

   ## mainnet
   bnbcli token mint --symbol ABC-A64 --amount 1000000000000 --from owner --chain-id Binance-Chain-Tigris --node http://dataseed4.binance.org:80
   
   ## testnet
   tbnbcli token mint --symbol ABC-A64 --amount 1000000000000 --from owner --chain-id Binance-Chain-Ganges --node http://data-seed-pre-0-s3.binance.org:80
   

2. Mint token on BSC and lock the new minted token:

3. Call mint method of BEP20 contract, the mint amount should be 1e22.
4. Transfer all minted ABC token to tokenHub contract: 0x0000000000000000000000000000000000001004

Mint token on BSC

1. Call mint of BEP20 contract to mint 10000 ABC, the mint amount should be 1e22(18 decimals).

2. Mint token on BC and lock the new minted token:

3. Execute the following command to mint 10000 ABC-A64:

   ## mainnet
   bnbcli token mint --symbol ABC-A64 --amount 1000000000000 --from owner --chain-id Binance-Chain-Tigris --node http://dataseed4.binance.org:80
   
   ## testnet
   tbnbcli token mint --symbol ABC-A64 --amount 1000000000000 --from owner --chain-id Binance-Chain-Ganges --node http://data-seed-pre-0-s3.binance.org:80
   

4. Transfer all minted ABC-A64 token to the pure-code-controlled address: tbnb1v8vkkymvhe2sf7gd2092ujc6hweta38xnc4wpr(mainnet address: bnb1v8vkkymvhe2sf7gd2092ujc6hweta38xadu2pj)