Solidity Rate Limiting Libraries, composed of DynamicRateLimitLibrary RateLimitedMidpoint and RateLimitedLibrary, provide essential functionality for Ethereum smart contracts to enforce rate limits on operations. These libraries are particularly beneficial in controlling the flow of funds, such as token minting or request rates. This management of a contract's operation speed is achieved through a rate limit per second and a buffer cap which allows the contracts to enforce trailing limits on system throughput.
DynamicRateLimitLibrary introduces a unique feature that allows dynamic adjustment of the buffer cap and rate limit per second proportional to the total value locked (TVL) in the contract. This is especially useful for protocols that need a graceful wind down or a slow increase in TVL without sacrificing safety.
It provides several functions to enforce and manage the rate limits, such as buffer(), depleteBuffer(), replenishBuffer(), sync(), setRateLimitPerSecond(), and setBufferCap(). These functions work around a struct called DynamicRateLimit, which holds key parameters for rate limiting.
Every time the buffer is depleted or replenished, the bufferCap and rateLimitPerSecond are adjusted proportionally to the new TVL. As a result, the buffer cap and rate limit are dynamic and adapt to the contract's TVL.
RateLimitedLibrary provides a basic yet powerful means to apply rate limits on specific actions. This library helps to manage and enforce rate limits, ensuring your contract doesn't perform certain actions too quickly. It contains a RateLimit struct to manage the rate limits and several functions to enforce and manage these limits, similar to DynamicRateLimitLibrary.
This library offers a simple way to enforce rate limits and manage related data in Solidity. By using it, you can create a safety buffer for your operations and prevent transaction failures due to rate limit exceedances.
To implement these libraries in your contract, import them and create instances of the respective struct (either DynamicRateLimit or RateLimit). Adjust the rateLimitPerSecond and bufferCap values to suit your protocol's needs. For DynamicRateLimitLibrary, you'll need to manage and pass the previous total value locked (TVL) amounts to depleteBuffer() and replenishBuffer() for dynamic adjustments.
Using this design, it is possible to create multiple rate limits in a single contract to enforce different rate limits on different actions.
Remember to handle rate-limited operations carefully as exceeding the rate limit or buffer cap will cause transactions to fail.
See RateLimited.sol for an example of how to use the RateLimited library.
RateLimitMidpointCommonLibrary is a rate limit library that provides a midpoint rate limit. This midpoint is useful when designing a system that must allow both mints and burns in a manner that prevents Denial of Service (DoS) attacks. The midpoint rate means the buffer start at the midpoint. When depleted from the midpoint, the buffer moves below the midpoint, and when refilled, it moves above the midpoint if starting at the midpoint. This allows for elasticity in the rate limit, and the ability to merge two buffers that would have normally be separate together.
See MintLimits.sol for an example of how to use the Rate Limited Midpoint library.