depositERC20

Function Type: external payable
Function Signature: depositERC20(address,address,uint256,bytes1)
Returns: void

Deposits ERC20 tokens and sends them to host chain via selected cross-chain protocol. Supports Hyperlane, LayerZero, and Axelar protocols for reliable token bridging to EVVM ecosystem.

Parameters

Parameter	Type	Description
toAddress	address	Recipient address for EVVM balance credit
token	address	ERC20 token contract address (cannot be address(0))
amount	uint256	Amount of tokens to deposit
protocolToExecute	bytes1	Cross-chain protocol identifier (0x01, 0x02, or 0x03)

Protocol Identifiers

Value	Protocol	Description
0x01	Hyperlane	Uses Hyperlane mailbox for cross-chain messaging
0x02	LayerZero	Uses LayerZero endpoint for omnichain transfers
0x03	Axelar	Uses Axelar gateway for decentralized cross-chain communication

Workflow

1. Payload Encoding

bytes memory payload = PayloadUtils.encodePayload(token, toAddress, amount);

Creates standardized cross-chain message payload using PayloadUtils library.

2. Token Transfer and Validation

verifyAndDepositERC20(token, amount);

Internally verifies token approval and executes transferFrom to custody tokens in this contract.

3. Protocol-Specific Cross-Chain Execution

Hyperlane (0x01)

uint256 quote = IMailbox(hyperlane.mailboxAddress).quoteDispatch(
    hyperlane.hostChainStationDomainId,
    hyperlane.hostChainStationAddress,
    payload
);
IMailbox(hyperlane.mailboxAddress).dispatch{value: quote}(
    hyperlane.hostChainStationDomainId,
    hyperlane.hostChainStationAddress,
    payload
);

• Quote Calculation: Gets exact dispatch cost from Hyperlane mailbox
• Message Dispatch: Sends encoded payload to host chain station
• Gas Payment: Uses quoted amount for precise fee payment

LayerZero (0x02)

MessagingFee memory fee = _quote(
    layerZero.hostChainStationEid,
    payload,
    options,
    false
);
_lzSend(
    layerZero.hostChainStationEid,
    payload,
    options,
    MessagingFee(fee.nativeFee, 0),
    msg.sender
);

• Fee Quotation: Calculates exact LayerZero messaging costs
• Omnichain Send: Utilizes LayerZero V2 OApp framework
• Refund Handling: Excess fees automatically refunded to sender

Axelar (0x03)

IAxelarGasService(axelar.gasServiceAddress).payNativeGasForContractCall{
    value: msg.value
}(
    address(this),
    axelar.hostChainStationChainName,
    axelar.hostChainStationAddress,
    payload,
    msg.sender
);
gateway().callContract(
    axelar.hostChainStationChainName,
    axelar.hostChainStationAddress,
    payload
);

• Gas Service Payment: Prepays execution gas via Axelar gas service
• Gateway Routing: Routes message through Axelar's decentralized gateway
• Refund Management: Gas refunds processed through Axelar's system

Token Requirements

ERC20 Transfer Process

The function uses an internal validation function for secure token transfers:

verifyAndDepositERC20(token, amount);

This internally:

1. Verifies token is not address(0)
2. Checks user has approved this contract for the deposit amount
3. Executes IERC20(token).transferFrom(msg.sender, address(this), amount)

Prerequisites

• Token Approval: Users must approve the External Chain Station contract for the deposit amount
• Sufficient Balance: User must have adequate token balance for the transfer
• Valid Token: Token contract must be a valid ERC20 implementation

Cross-Chain Message Processing

Payload Structure

bytes memory payload = PayloadUtils.encodePayload(token, toAddress, amount);

Host Chain Processing

Upon successful cross-chain message delivery:

1. Payload Decoding: PayloadUtils.decodePayload() extracts transfer parameters
2. EVVM Integration: core.addAmountToUser(toAddress, token, amount)
3. Balance Credit: Recipient's EVVM balance immediately reflects the deposited tokens

Gas Requirements

Users must provide sufficient native tokens (msg.value) to cover cross-chain messaging costs:

• Hyperlane: Mailbox dispatch fees
• LayerZero: Endpoint messaging fees
• Axelar: Gas service payments for execution

Use the respective quote functions to estimate required amounts:

• getQuoteHyperlane(toAddress, token, amount)
• quoteLayerZero(toAddress, token, amount)

Security Features

Input Validation

• Token Address: verifyAndDepositERC20() prevents address(0) deposits
• Allowance Check: Function reverts with Error.InsufficientBalance() if insufficient approval
• Safe Transfer: Standard IERC20.transferFrom() with approval verification
• Protocol Support: Validates supported protocol identifiers (0x01, 0x02, 0x03)

Cross-Chain Security

• Message Authentication: Each protocol validates sender and origin chain
• Payload Integrity: PayloadUtils ensures consistent encoding/decoding
• Recipient Verification: Direct address binding prevents misdirected funds

Error Conditions

Error	Condition
Error.InsufficientBalance()	User hasn't approved sufficient tokens
Generic Revert	Token address is address(0)
Protocol Revert	Invalid protocolToExecute value
Insufficient Gas	msg.value doesn't cover cross-chain messaging costs

Usage Example

// 1. Approve tokens
IERC20(tokenAddress).approve(externalChainStationAddress, depositAmount);

// 2. Get gas quote
uint256 gasRequired = getQuoteHyperlane(recipientAddress, tokenAddress, depositAmount);

// 3. Execute deposit
depositERC20{value: gasRequired}(
    recipientAddress,
    tokenAddress, 
    depositAmount,
    0x01 // Hyperlane
);

Integration with EVVM

The deposit flow connects external chain assets to EVVM balances:

1. External Chain: User transfers ERC20 tokens to external station
2. Cross-Chain: Message sent to host chain station
3. Host Chain: Host station receives message and credits EVVM balance
4. EVVM: Recipient can use tokens within the EVVM ecosystem

Gas Payment Required

Ensure sufficient native tokens are sent with the transaction to cover cross-chain messaging costs. Insufficient gas will cause transaction failure and potential token loss.

ERC20 Approval Required

Users must approve the external chain station contract before calling this function. The approval should cover at least the deposit amount.