Crate ethers_middleware

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§ethers-middleware

Your ethers application interacts with the blockchain through a Provider abstraction. Provider is a special type of Middleware that can be composed with others to obtain a layered architecture. This approach promotes “Open Closed Principle”, “Single Responsibility” and composable patterns. The building process happens in a wrapping fashion, and starts from a Provider being the first element in the stack. This process continues having new middlewares being pushed on top of a layered data structure.

For more information, please refer to the book.

Warning

This library is in the process of being deprecated. See #2667 for more information.

§Available Middleware

  • Signer: Signs transactions locally, with a private key or a hardware wallet.
  • Nonce Manager: Manages nonces locally. Allows to sign multiple consecutive transactions without waiting for them to hit the mempool.
  • Gas Escalator: Bumps transactions gas price in the background to avoid getting them stuck in the memory pool. A GasEscalatorMiddleware supports different escalation strategies (see GasEscalator) and bump frequencies (see Frequency).
  • Gas Oracle: Allows getting your gas price estimates from places other than eth_gasPrice, including REST based gas stations (i.e. Etherscan, ETH Gas Station etc.).
  • Transformer: Allows intercepting and transforming a transaction to be broadcasted via a proxy wallet, e.g. DSProxy.

§Examples

Each Middleware implements the trait MiddlewareBuilder. This trait helps a developer to compose a custom Middleware stack.

The following example shows how to build a composed Middleware starting from a Provider:

let key = "fdb33e2105f08abe41a8ee3b758726a31abdd57b7a443f470f23efce853af169";
let signer = key.parse::<LocalWallet>()?;
let address = signer.address();
let gas_oracle = GasNow::new();

let provider = Provider::<Http>::try_from("http://localhost:8545")?
    .gas_oracle(gas_oracle)
    .with_signer(signer)
    .nonce_manager(address); // Outermost layer

The wrap_into function can be used to wrap Middleware layers explicitly. This is useful when pushing Middlewares not directly handled by the builder interface.

let key = "fdb33e2105f08abe41a8ee3b758726a31abdd57b7a443f470f23efce853af169";
let signer = key.parse::<LocalWallet>()?;
let address = signer.address();
let escalator = GeometricGasPrice::new(1.125, 60_u64, None::<u64>);

let provider = Provider::<Http>::try_from("http://localhost:8545")?
    .wrap_into(|p| GasEscalatorMiddleware::new(p, escalator, Frequency::PerBlock))
    .wrap_into(|p| SignerMiddleware::new(p, signer))
    .wrap_into(|p| GasOracleMiddleware::new(p, GasNow::new()))
    .wrap_into(|p| NonceManagerMiddleware::new(p, address)); // Outermost layer

A Middleware stack can be also constructed manually. This is achieved by explicitly wrapping layers.

// Start the stack
let provider = Provider::<Http>::try_from("http://localhost:8545")?;

// Escalate gas prices
let escalator = GeometricGasPrice::new(1.125, 60u64, None::<u64>);
let provider = GasEscalatorMiddleware::new(provider, escalator, Frequency::PerBlock);

// Sign transactions with a private key
let key = "fdb33e2105f08abe41a8ee3b758726a31abdd57b7a443f470f23efce853af169";
let signer = key.parse::<LocalWallet>()?;
let address = signer.address();
let provider = SignerMiddleware::new(provider, signer);

// Use GasNow as the gas oracle
let gas_oracle = GasNow::new();
let provider = GasOracleMiddleware::new(provider, gas_oracle);

// Manage nonces locally
let provider = NonceManagerMiddleware::new(provider, address);

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