fisherBridgeSend

Function Type: external
Function Signature: fisherBridgeSend(address,address,address,uint256,uint256,bytes)
Access Control: onlyFisherExecutor
Returns: void

Facilitates cross-chain withdrawals through the fisher bridge system by validating user signatures and emitting events for external chain processing. This function enables gasless withdrawals where authorized fisher executors can initiate transfers on behalf of users.

Parameters

Parameter	Type	Description
from	address	User initiating the withdrawal from EVVM
addressToReceive	address	Recipient address on the external chain
tokenAddress	address	Token contract address or address(0) for native coin
priorityFee	uint256	Fee amount paid to the fisher executor
amount	uint256	Amount to withdraw from user's EVVM balance
signature	bytes	Cryptographic signature (EIP-191) from the from address authorizing this withdrawal.

Access Control

modifier onlyFisherExecutor() {
    if (msg.sender != fisherExecutor.current) {
        revert();
    }
    _;
}

Only addresses with the current fisherExecutor role can call this function.

Workflow

1. Principal Token Validation

if (tokenAddress == Evvm(evvmAddress).getEvvmMetadata().principalTokenAddress)
    revert ErrorsLib.PrincipalTokenIsNotWithdrawable();

Prevents withdrawal of the ecosystem's principal token to maintain system integrity.

2. Balance Verification

if (Evvm(evvmAddress).getBalance(from, tokenAddress) < amount)
    revert ErrorsLib.InsufficientBalance();

Ensures the user has sufficient EVVM balance before processing the withdrawal.

3. Signature Verification

if (!SignatureUtils.verifyMessageSignedForFisherBridge(
    from,
    addressToReceive,
    nextFisherExecutionNonce[from],
    tokenAddress,
    priorityFee,
    amount,
    signature
)) revert ErrorsLib.InvalidSignature();

info

For more information about the signature structure, refer to the Fisher Bridge Signature Structure.

4. Nonce Management

nextFisherExecutionNonce[from]++;

Increments the user's execution nonce to prevent replay attacks.

5. Balance Updates

User Balance Debit

executerEVVM(false, from, tokenAddress, amount + priorityFee);

Removes the total amount (withdrawal + priority fee) from the user's EVVM balance.

Fisher Fee Credit

if (priorityFee > 0)
    executerEVVM(true, msg.sender, tokenAddress, priorityFee);

Credits the priority fee to the fisher executor's EVVM balance if specified.

6. Event Emission

emit FisherBridgeSend(
    from,
    addressToReceive,
    tokenAddress,
    priorityFee,
    amount,
    nextFisherExecutionNonce[from] - 1
);

Emits an event containing all transfer details for external chain monitoring and processing.

Event Definition

event FisherBridgeSend(
    address indexed from,
    address indexed addressToReceive,
    address indexed tokenAddress,
    uint256 priorityFee,
    uint256 amount,
    uint256 nonce
);

Event Parameters

• from: User who initiated the withdrawal (indexed)
• addressToReceive: Recipient on external chain (indexed)
• tokenAddress: Token being withdrawn (indexed)
• priorityFee: Fee paid to fisher executor
• amount: Withdrawal amount
• nonce: Execution nonce used for this transaction

External Chain Processing

The emitted event serves as a signal for external chain operations. The corresponding external chain station or fisher services should:

1. Monitor for FisherBridgeSend events
2. Extract transfer details from event parameters
3. Execute the actual token transfer on the external chain
4. Transfer amount of tokenAddress to addressToReceive

Security Features

Signature Security

• EIP-191 Compliance: Standard Ethereum signed message format
• Nonce Protection: Prevents signature replay attacks
• User Authorization: Cryptographic proof of user consent

Balance Protection

• Principal Token Guard: Prevents withdrawal of ecosystem's core token
• Sufficient Balance Check: Validates user has adequate funds
• Atomic Operations: Balance updates are processed atomically

Access Control

• Fisher Authorization: Only current fisher executor can initiate withdrawals
• Signature Validation: Requires valid user signature for each transaction (see signature format)

Fee Structure

The priority fee mechanism incentivizes fisher executors:

• User Pays: Total debit of amount + priorityFee from user balance
• Fisher Receives: Priority fee credited to executor's EVVM balance
• Net Transfer: User receives amount on external chain

Error Conditions

Error	Condition
PrincipalTokenIsNotWithdrawable	Attempting to withdraw principal token
InsufficientBalance	User lacks sufficient EVVM balance
InvalidSignature	Signature verification fails
Access Control Revert	Called by unauthorized address

Usage Flow

1. User Intent: User wants to withdraw tokens from EVVM to external chain
2. Signature Creation: User signs withdrawal authorization message
3. Fisher Execution: Authorized fisher calls fisherBridgeSend with signature
4. Validation: Function validates signature and user balance
5. Balance Update: EVVM balances updated (user debited, fisher credited fee)
6. Event Emission: Event emitted for external chain processing
7. External Transfer: External services process the actual token transfer

Off-chain Coordination Required

This function only updates EVVM balances and emits events. The actual token transfer on the external chain must be handled by off-chain services monitoring these events.