Feat middleware stack builder (#1890)

* ProviderBuilder struct + docs

* README

* Docs typos

* Removed useless Arc
Rename module

* Unit tests

* cargo +nightly fmt

* CHANGELOG

* CHANGELOG typo

* ci: fix docs job

* review: Removed Option<M>. Builder functions directly consume self.

* feat: `with_signer` builder function

* feat: `nonce_manager` builder function

* feat: `gas_oracle` builder function

* Unit tests

* Docs

* fix: cargo +nightly fmt

* Update ethers-middleware/src/builder.rs

Typo

Co-authored-by: Matthias Seitz <matthias.seitz@outlook.de>

* Builder functions provided as a trait
Update docs
Update tests

* cargo +nightly fmt

* CHANGELOG

Co-authored-by: Andrea Simeoni <>
Co-authored-by: Matthias Seitz <matthias.seitz@outlook.de>

CHANGELOG.md

@@ -3,7 +3,7 @@
 ## ethers-core
 
 ### Unreleased
-
+-   `MiddlewareBuilder` trait to instantiate a `Provider` as `Middleware` layers.
 -   An `Event` builder can be instantiated specifying the event filter type, without the need to instantiate a contract.
 -   Add 'ethers_core::types::OpCode' and use in 'ethers_core::types::VMOperation' [1857](https://github.com/gakonst/ethers-rs/issues/1857)
 -   Remove rust_decimals dependency for ethers-core

ethers-middleware/README.md

@@ -4,22 +4,22 @@ 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).
+- [`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
 
-```no_run
+```rust no_run
 use ethers_providers::{Provider, Http};
 use ethers_signers::{LocalWallet, Signer};
 use ethers_middleware::{
@@ -53,3 +53,43 @@ 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
+}
+```

ethers-middleware/src/builder.rs

@@ -0,0 +1,91 @@
+use crate::{
+    gas_oracle::{GasOracle, GasOracleMiddleware},
+    NonceManagerMiddleware, SignerMiddleware,
+};
+use ethers_core::types::Address;
+use ethers_providers::Middleware;
+use ethers_signers::Signer;
+
+/// A builder trait to compose different [`Middleware`](ethers_providers::Middleware) layers
+/// and then build a composed [`Provider`](ethers_providers::Provider) architecture.
+/// [`Middleware`](ethers_providers::Middleware) composition acts in a wrapping fashion. Adding a
+/// new layer results in wrapping its predecessor.
+///
+/// ```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
+/// }
+/// ```
+pub trait MiddlewareBuilder: Middleware + Sized + 'static {
+    /// Wraps `self` inside a new [`Middleware`](ethers_providers::Middleware).
+    ///
+    /// `f` Consumes `self`, must be used to return a new
+    /// [`Middleware`](ethers_providers::Middleware) around `self`.
+    fn wrap_into<F, T>(self, f: F) -> T
+    where
+        F: FnOnce(Self) -> T,
+        T: Middleware,
+    {
+        f(self)
+    }
+
+    /// Wraps `self` inside a [`SignerMiddleware`](crate::SignerMiddleware).
+    ///
+    /// [`Signer`] ethers_signers::Signer
+    fn with_signer<S>(self, s: S) -> SignerMiddleware<Self, S>
+    where
+        S: Signer,
+    {
+        SignerMiddleware::new(self, s)
+    }
+
+    /// Wraps `self` inside a [`NonceManagerMiddleware`](crate::NonceManagerMiddleware).
+    ///
+    /// [`Address`] ethers_core::types::Address
+    fn nonce_manager(self, address: Address) -> NonceManagerMiddleware<Self> {
+        NonceManagerMiddleware::new(self, address)
+    }
+
+    /// Wraps `self` inside a [`GasOracleMiddleware`](crate::gas_oracle::GasOracleMiddleware).
+    ///
+    /// [`Address`] ethers_core::types::Address
+    fn gas_oracle<G>(self, gas_oracle: G) -> GasOracleMiddleware<Self, G>
+    where
+        G: GasOracle,
+    {
+        GasOracleMiddleware::new(self, gas_oracle)
+    }
+}
+
+impl<M> MiddlewareBuilder for M where M: Middleware + Sized + 'static {}

ethers-middleware/src/lib.rs

@@ -36,3 +36,8 @@ pub use policy::PolicyMiddleware;
 /// before the chain tip
 pub mod timelag;
 pub use timelag::TimeLag;
+
+/// The [MiddlewareBuilder](crate::MiddlewareBuilder) provides a way to compose many
+/// [`Middleware`](ethers_providers::Middleware) in a concise way
+pub mod builder;
+pub use builder::MiddlewareBuilder;

ethers-middleware/tests/builder.rs

@@ -0,0 +1,69 @@
+#![cfg(not(target_arch = "wasm32"))]
+#[cfg(not(feature = "celo"))]
+mod tests {
+    use ethers_core::{rand::thread_rng, types::U64};
+    use ethers_middleware::{
+        builder::MiddlewareBuilder,
+        gas_escalator::{Frequency, GasEscalatorMiddleware, GeometricGasPrice},
+        gas_oracle::{EthGasStation, GasOracleMiddleware},
+        nonce_manager::NonceManagerMiddleware,
+        signer::SignerMiddleware,
+    };
+    use ethers_providers::{Middleware, Provider};
+    use ethers_signers::{LocalWallet, Signer};
+
+    #[tokio::test]
+    async fn build_raw_middleware_stack() {
+        let (provider, mock) = Provider::mocked();
+
+        let signer = LocalWallet::new(&mut thread_rng());
+        let address = signer.address();
+        let escalator = GeometricGasPrice::new(1.125, 60u64, None::<u64>);
+
+        let provider = provider
+            .wrap_into(|p| GasEscalatorMiddleware::new(p, escalator, Frequency::PerBlock))
+            .wrap_into(|p| GasOracleMiddleware::new(p, EthGasStation::new(None)))
+            .wrap_into(|p| SignerMiddleware::new(p, signer))
+            .wrap_into(|p| NonceManagerMiddleware::new(p, address));
+
+        // push a response
+        mock.push(U64::from(12u64)).unwrap();
+        let block: U64 = provider.get_block_number().await.unwrap();
+        assert_eq!(block.as_u64(), 12);
+
+        provider.get_block_number().await.unwrap_err();
+
+        // 2 calls were made
+        mock.assert_request("eth_blockNumber", ()).unwrap();
+        mock.assert_request("eth_blockNumber", ()).unwrap();
+        mock.assert_request("eth_blockNumber", ()).unwrap_err();
+    }
+
+    #[tokio::test]
+    async fn build_declarative_middleware_stack() {
+        let (provider, mock) = Provider::mocked();
+
+        let signer = LocalWallet::new(&mut thread_rng());
+        let address = signer.address();
+        let escalator = GeometricGasPrice::new(1.125, 60u64, None::<u64>);
+        let gas_oracle = EthGasStation::new(None);
+
+        let provider = provider
+            .wrap_into(|p| GasEscalatorMiddleware::new(p, escalator, Frequency::PerBlock))
+            .gas_oracle(gas_oracle)
+            .with_signer(signer)
+            .nonce_manager(address);
+
+        // push a response
+        mock.push(U64::from(12u64)).unwrap();
+        let block: U64 = provider.get_block_number().await.unwrap();
+        assert_eq!(block.as_u64(), 12);
+
+        provider.get_block_number().await.unwrap_err();
+
+        // 2 calls were made
+        mock.assert_request("eth_blockNumber", ()).unwrap();
+        mock.assert_request("eth_blockNumber", ()).unwrap();
+        mock.assert_request("eth_blockNumber", ()).unwrap_err();
+    }
+}