fee

import "github.com/luxfi/node/vms/types/fee"

Package fee defines the unified FeePolicy interface that every Lux VM accepting user-submitted transactions MUST satisfy.

Background. A 2026-05 audit of vms/* found five chains accepting user txs while charging nothing (dexvm, bridgevm, keyvm, zkvm, aivm) and one charging 1,000x too little (quantumvm). The root cause was that fee policy lived as ad-hoc fields on each VM's Config — there was no shared surface to enforce a non-zero floor, and no sentinel for chains that legitimately accept no user txs (mpcvm, oraclevm, relayvm — committee-driven, no user mempool).

This package provides exactly one way to declare a fee policy:

• vms.Policy is the interface every VM Manager calls into.
• FlatPolicy is the canonical implementation for "burn a fixed amount of LUX per tx".
• NoUserTxPolicy is the explicit sentinel for committee-only chains. Manager wiring uses this to distinguish "explicitly no user fees" from "forgot to set policy".
• Validate(p) is the boot-time check Manager runs against each VM's declared policy to refuse zero-fee user-facing chains before they ever accept a block.

Migration plan (per audit follow-up): each offending VM declares a FlatPolicy in its Config, the VM's mempool calls Policy.ValidateFee at the same point it currently does (or fails to do) the fee check, and Manager runs Validate at chain bootstrap. No new abstraction layers, no per-VM bespoke fee structs — one interface, one validator.

Functions

Validate

func Validate(p Policy) error

Validate is the boot-time check Manager runs against each VM's declared Policy. Returns ErrZeroMinFee if a non-sentinel policy declares MinTxFee() == 0. Returns nil for NoUserTxPolicy regardless of fee (it's the explicit opt-out). Returns nil if MinTxFee > 0.

Types

FlatPolicy

FlatPolicy charges a fixed fee per user tx. The canonical implementation for VMs without dynamic gas pricing — dexvm, bridgevm, keyvm, zkvm, aivm use this (quantumvm is NoUserTxPolicy per LP-0130 §6).

func (p FlatPolicy) FeeAssetID() ids.ID

func (p FlatPolicy) MinTxFee() uint64

func (p FlatPolicy) ValidateFee(paid uint64, asset ids.ID) error

NoUserTxPolicy

NoUserTxPolicy is the sentinel policy for chains that accept no user-submitted txs — committee-driven only (mpcvm, oraclevm, relayvm). Distinguishing this from "policy not set" is what makes Manager's boot-time Validate able to refuse zero-fee user-facing chains without false-positive-ing the committee chains.

func (NoUserTxPolicy) FeeAssetID() ids.ID

func (NoUserTxPolicy) MinTxFee() uint64

func (NoUserTxPolicy) ValidateFee(uint64, ids.ID) error

Policy

Policy defines how a VM charges for user-submitted txs. Every chain that accepts user txs MUST declare a non-nil Policy whose MinTxFee() returns a value > 0. Chains that accept no user txs declare a NoUserTxPolicy sentinel instead — this is the only legal way to opt out of charging.