# ethers-middleware

Your ethers application interacts with the blockchain through a [`Provider`](ethers_providers::Provider) abstraction. [`Provider`](ethers_providers::Provider) is a special type of [`Middleware`](ethers_providers::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`](ethers_providers::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](https://gakonst.com/ethers-rs).

## 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. Allows to sign multiple consecutive transactions without waiting for them to hit the mempool.
-   [`Gas Escalator`](./gas_escalator/struct.GasEscalatorMiddleware.html): Bumps transactions gas price in the background to avoid getting them stuck in the memory pool. A [`GasEscalatorMiddleware`](crate::gas_escalator::GasEscalatorMiddleware) supports different escalation strategies (see [GasEscalator](crate::gas_escalator::GasEscalator)) and bump frequencies (see [Frequency](crate::gas_escalator::Frequency)).
-   [`Gas Oracle`](./gas_oracle/struct.GasOracleMiddleware.html): 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`](./transformer/trait.Transformer.html): Allows intercepting and
    transforming a transaction to be broadcasted via a proxy wallet, e.g.
    [`DSProxy`](./transformer/struct.DsProxy.html).

## Examples

Each [`Middleware`](ethers_providers::Middleware) implements the trait [MiddlewareBuilder](crate::MiddlewareBuilder). This trait helps a developer to compose a custom [`Middleware`](ethers_providers::Middleware) stack.

The following example shows how to build a composed [`Middleware`](ethers_providers::Middleware) starting from a [`Provider`](ethers_providers::Provider):

```rust
# use ethers_providers::{Middleware, Provider, Http};
# use ethers_signers::{LocalWallet, Signer};
# use ethers_middleware::{gas_oracle::GasNow, MiddlewareBuilder};
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
# Ok::<_, Box<dyn std::error::Error>>(())
```

The [wrap_into](crate::MiddlewareBuilder::wrap_into) function can be used to wrap [`Middleware`](ethers_providers::Middleware) layers explicitly. This is useful when pushing [`Middleware`](ethers_providers::Middleware)s not directly handled by the builder interface.

```rust,no_run
# use ethers_providers::{Middleware, Provider, Http};
# use std::convert::TryFrom;
# use ethers_signers::{LocalWallet, Signer};
# use ethers_middleware::{*,gas_escalator::*,gas_oracle::*};
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
# Ok::<_, Box<dyn std::error::Error>>(())
```

A [`Middleware`](ethers_providers::Middleware) stack can be also constructed manually. This is achieved by explicitly wrapping layers.

```rust,no_run
# use ethers_providers::{Provider, Http};
# use ethers_signers::{LocalWallet, Signer};
# use ethers_middleware::{
#     gas_escalator::{GasEscalatorMiddleware, GeometricGasPrice, Frequency},
#     gas_oracle::{GasOracleMiddleware, GasCategory, GasNow},
#     signer::SignerMiddleware,
#     nonce_manager::NonceManagerMiddleware,
# };
// 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);
# Ok::<_, Box<dyn std::error::Error>>(())
```