FeeCollectorV1

Collects ERC-20 token fees from project contracts when they send cross-chain messages. Deployed and configured by VIA Labs — developers interact with it indirectly through ViaIntegrationV1.setMaxFee().

Currently fees are set to zero on all chains. This contract exists as infrastructure for future fee models.

For the fee mechanics overview, see Fees & Gas.

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How Fees Are Resolved

When pay(sender) is called by the gateway, the fee amount is resolved:

whitelist[sender]	Fee charged	Meaning
0 (default)	feeAmount (global default)	Standard rate
1 to 9998	That exact value	Custom rate for this sender
9999	0	Free pass (FREE constant)
10000+	That exact value	Custom rate

If maxFee[sender] is set and the resolved fee exceeds it, the entire send() reverts with FeeMaxCap.

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Dual-Fee System

FeeCollectorV1 can collect two independent fees in a single pay() call:

1. ERC-20 Token Fee

• Collected via safeTransferFrom(sender, beneficiary, amount)
• Amount resolved by whitelist logic above
• Project auto-approves the token when calling setMessageGateway()

2. Native Gas Fee (Optional)

• Collected in native currency (ETH, MATIC, etc.) via msg.value
• Enabled per-sender via sourceGasAmountWhitelist[sender] = true
• Must be exact — msg.value must equal sourceGasAmount
• Sent to beneficiary via low-level call

Native gas fee is collected before the token fee. Both go to the same beneficiary.

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Functions (Owner)

Function	Parameters	Description
setAmount	uint256 amount	Set the global default fee (in token smallest units)
setToken	address addr	Set the ERC-20 fee token (e.g., USDC)
setBeneficiary	address addr	Set where collected fees go
setWhitelist	address addr, uint256 amount	Per-sender custom fee. 0 = use default, 9999 = free
setSourceGasAmount	uint256 amount	Set native gas fee amount (in wei)
setSourceGasWhitelist	address addr, bool enabled	Enable/disable native gas fee for a sender

Functions (Project)

Function	Parameters	Description
setMaxFee	uint256 amount	Cap the fee per message. Called by the project contract (msg.sender). 0 = no cap.

Functions (Gateway)

Function	Parameters	Description
pay	address sender	Collect fees. Only callable by the gateway.

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Errors

Error	When
CallerMismatch	pay() called by non-gateway address
FeeMaxCap	Resolved fee exceeds maxFee[sender]
InvalidSourceGasFee	msg.value doesn't match sourceGasAmount
SourceGasFeeNotPaid	Native gas fee transfer to beneficiary failed

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Token Approval

Developers don't manually approve the fee token. When ViaIntegrationV1.setMessageGateway() is called, it automatically:

1. Queries gateway.feeCollector() to get this contract's address
2. Queries feeCollector.feeToken() to get the token address
3. Calls feeToken.approve(feeCollector, type(uint256).max)