ethers-rs/book/middleware/middleware.md

Middlewares

In ethers-rs, middleware is a way to customize the behavior of certain aspects of the library by injecting custom logic into the process of interacting with the Ethereum JSON-RPC API. Middlewares act in a chain of responsibility and can be combined to achieve the desired behavior.

The library allows developers to create custom middlewares, going beyond standard operations and unlocking powerful use cases.

A JSON-RPC client instance can be constructed as a stack of middlewares, backed by a common instance of Provider of one specific type among JsonRpcClient and PubSubClient.

{{#include ../mermaid-style.txt}}

flowchart TB
    subgraph ide1 [Client]
    middleware2--inner-->middleware1--inner-->middleware0--inner-->provider
    end
    subgraph ide2 [Transport]
    provider--PubSubClient-->ws
    provider--PubSubClient-->ipc
    provider--JsonRpcClient<br>PubSubClient-->http
    provider--JsonRpcClient<br>PubSubClient-->retry
    provider--JsonRpcClient<br>PubSubClient-->quorum
    provider--JsonRpcClient<br>PubSubClient-->rw
    end

The following middlewares are currently supported:

• Gas Escalator: Avoids transactions being stucked in the mempool, by bumping the gas price in background.
• Gas Oracle: Allows retrieving the current gas price from common RESTful APIs, instead of retrieving it from blocks.
• Nonce Manager: Manages nonces of transactions locally, without waiting for them to hit the mempool.
• Policy: Allows to define rules or policies that should be followed when submitting JSON-RPC API calls.
• Signer: Signs transactions locally, with a private key or a hardware wallet.
• Time lag: Poses a block delay on JSON-RPC interactions, allowing to shift the block number back of a predefined offset.
• Transformer: Allows intercepting and transforming a transaction to be broadcasted via a proxy wallet.