Ethers uses a middleware-based architecture. You start the middleware stack with
a [`Provider`](ethers_providers::Provider), and wrap it with additional
middleware functionalities that you need.

## Available Middleware

- [`Signer`](./signer/struct.SignerMiddleware.html): Signs transactions locally,
  with a private key or a hardware wallet
- [`Nonce Manager`](./nonce_manager/struct.NonceManagerMiddleware.html): Manages
  nonces locally, allowing the rapid broadcast of transactions without having to
  wait for them to be submitted
- [`Gas Escalator`](./gas_escalator/struct.GasEscalatorMiddleware.html): Bumps
  transaction gas prices in the background
- [`Gas Oracle`](./gas_oracle/struct.GasOracleMiddleware.html): Allows getting
  your gas price estimates from places other than `eth_gasPrice`.
- [`Transformer`](./transformer/trait.Transformer.html): Allows intercepting and
  transforming a transaction to be broadcasted via a proxy wallet, e.g.
  [`DSProxy`](./transformer/struct.DsProxy.html).

## Example of a middleware stack

```rust no_run
use ethers_providers::{Provider, Http};
use ethers_signers::{LocalWallet, Signer};
use ethers_middleware::{
    gas_escalator::{GasEscalatorMiddleware, GeometricGasPrice, Frequency},
    gas_oracle::{GasOracleMiddleware, EthGasStation, GasCategory},
    signer::SignerMiddleware,
    nonce_manager::NonceManagerMiddleware,
};
use ethers_core::rand;
use std::convert::TryFrom;

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

// 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 signer = LocalWallet::new(&mut rand::thread_rng());
let address = signer.address();
let provider = SignerMiddleware::new(provider, signer);

// Use EthGasStation as the gas oracle
let gas_oracle = EthGasStation::new(None);
let provider = GasOracleMiddleware::new(provider, gas_oracle);

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

// ... do something with the provider
```
## Example of a middleware stack using a builder

Each [`Middleware`](ethers_providers::Middleware) implements the trait [MiddlewareBuilder](crate::MiddlewareBuilder) to help composition of a [`Middleware`](ethers_providers::Middleware) stack. As usual the composition acts in a wrapping fashion. Adding a new layer results in wrapping its predecessor.
Builder can be used as follows:
```rust
use ethers_providers::{Middleware, Provider, Http};
use std::sync::Arc;
use std::convert::TryFrom;
use ethers_signers::{LocalWallet, Signer};
use ethers_middleware::{*,gas_escalator::*,gas_oracle::*};

fn builder_example() {
    let key = "fdb33e2105f08abe41a8ee3b758726a31abdd57b7a443f470f23efce853af169";
    let signer = key.parse::<LocalWallet>().unwrap();
    let address = signer.address();
    let escalator = GeometricGasPrice::new(1.125, 60_u64, None::<u64>);
    let gas_oracle = EthGasStation::new(None);

    let provider = Provider::<Http>::try_from("http://localhost:8545")
        .unwrap()
        .wrap_into(|p| GasEscalatorMiddleware::new(p, escalator, Frequency::PerBlock)) 
        .gas_oracle(gas_oracle)
        .with_signer(signer)
        .nonce_manager(address); // Outermost layer
}

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

    let provider = Provider::<Http>::try_from("http://localhost:8545")
        .unwrap()
        .wrap_into(|p| GasEscalatorMiddleware::new(p, escalator, Frequency::PerBlock))
        .wrap_into(|p| SignerMiddleware::new(p, signer))
        .wrap_into(|p| GasOracleMiddleware::new(p, EthGasStation::new(None)))
        .wrap_into(|p| NonceManagerMiddleware::new(p, address)); // Outermost layer
}
```