feat: blocknative gas oracle (#1175)

* gas oracle: add more error variants

* gas oracle: adds BlockNative oracle

* pdate changelog

CHANGELOG.md

@@ -237,6 +237,8 @@
 
 - Ensure a consistent chain ID between a Signer and Provider in SignerMiddleware
   [#1095](https://gakonst/ethers-rs/pull/1095)
+- Add BlockNative gas oracle [#1175](https://github.com/gakonst/ethers-rs/pull/1175)
+
 
 ### 0.6.0
 

ethers-middleware/src/gas_oracle/blocknative.rs

@@ -0,0 +1,130 @@
+use crate::gas_oracle::{GasCategory, GasOracle, GasOracleError, GWEI_TO_WEI};
+use async_trait::async_trait;
+use ethers_core::types::U256;
+use reqwest::{
+    header::{HeaderMap, HeaderValue, AUTHORIZATION},
+    Client, ClientBuilder,
+};
+use serde::Deserialize;
+use std::{collections::HashMap, convert::TryInto, iter::FromIterator};
+use url::Url;
+
+const BLOCKNATIVE_GAS_PRICE_ENDPOINT: &str = "https://api.blocknative.com/gasprices/blockprices";
+
+fn gas_category_to_confidence(gas_category: &GasCategory) -> u64 {
+    match gas_category {
+        GasCategory::SafeLow => 80,
+        GasCategory::Standard => 90,
+        GasCategory::Fast => 95,
+        GasCategory::Fastest => 99,
+    }
+}
+
+/// A client over HTTP for the [BlockNative](https://www.blocknative.com/gas-estimator) gas tracker API
+/// that implements the `GasOracle` trait
+#[derive(Clone, Debug)]
+pub struct BlockNative {
+    client: Client,
+    url: Url,
+    gas_category: GasCategory,
+}
+
+#[derive(Debug, Deserialize, PartialEq)]
+#[serde(rename_all = "camelCase")]
+pub struct BlockNativeGasResponse {
+    system: Option<String>,
+    network: Option<String>,
+    unit: Option<String>,
+    max_price: Option<u64>,
+    block_prices: Vec<BlockPrice>,
+    estimated_base_fees: Vec<HashMap<String, Vec<BaseFeeEstimate>>>,
+}
+
+impl BlockNativeGasResponse {
+    pub fn get_estimation_for(
+        &self,
+        gas_category: &GasCategory,
+    ) -> Result<EstimatedPrice, GasOracleError> {
+        let confidence = gas_category_to_confidence(gas_category);
+        Ok(self
+            .block_prices
+            .first()
+            .ok_or(GasOracleError::InvalidResponse)?
+            .estimated_prices
+            .iter()
+            .find(|p| p.confidence == confidence)
+            .ok_or(GasOracleError::GasCategoryNotSupported)?
+            .clone())
+    }
+}
+
+#[derive(Debug, Deserialize, PartialEq)]
+#[serde(rename_all = "camelCase")]
+pub struct BlockPrice {
+    block_number: u64,
+    estimated_transaction_count: u64,
+    base_fee_per_gas: f64,
+    estimated_prices: Vec<EstimatedPrice>,
+}
+
+#[derive(Clone, Debug, Deserialize, PartialEq)]
+#[serde(rename_all = "camelCase")]
+pub struct EstimatedPrice {
+    confidence: u64,
+    price: u64,
+    max_priority_fee_per_gas: f64,
+    max_fee_per_gas: f64,
+}
+
+#[derive(Debug, Deserialize, PartialEq)]
+#[serde(rename_all = "camelCase")]
+pub struct BaseFeeEstimate {
+    confidence: u64,
+    base_fee: f64,
+}
+
+impl BlockNative {
+    /// Creates a new [BlockNative](https://www.blocknative.com/gas-estimator) gas oracle
+    pub fn new(api_key: &str) -> Self {
+        let header_value = HeaderValue::from_str(api_key).unwrap();
+        let headers = HeaderMap::from_iter([(AUTHORIZATION, header_value)]);
+        let client = ClientBuilder::new().default_headers(headers).build().unwrap();
+        Self {
+            client,
+            url: BLOCKNATIVE_GAS_PRICE_ENDPOINT.try_into().unwrap(),
+            gas_category: GasCategory::Standard,
+        }
+    }
+
+    /// Sets the gas price category to be used when fetching the gas price.
+    #[must_use]
+    pub fn category(mut self, gas_category: GasCategory) -> Self {
+        self.gas_category = gas_category;
+        self
+    }
+
+    /// Perform request to Blocknative, decode response
+    pub async fn request(&self) -> Result<BlockNativeGasResponse, GasOracleError> {
+        Ok(self.client.get(self.url.as_ref()).send().await?.error_for_status()?.json().await?)
+    }
+}
+
+#[cfg_attr(target_arch = "wasm32", async_trait(?Send))]
+#[cfg_attr(not(target_arch = "wasm32"), async_trait)]
+impl GasOracle for BlockNative {
+    async fn fetch(&self) -> Result<U256, GasOracleError> {
+        let prices = self.request().await?.get_estimation_for(&self.gas_category)?;
+        Ok(U256::from(prices.price * 100_u64) * U256::from(GWEI_TO_WEI) / U256::from(100))
+    }
+
+    async fn estimate_eip1559_fees(&self) -> Result<(U256, U256), GasOracleError> {
+        let prices = self.request().await?.get_estimation_for(&self.gas_category)?;
+        let base_fee = U256::from((prices.max_fee_per_gas * 100.0) as u64) *
+            U256::from(GWEI_TO_WEI) /
+            U256::from(100);
+        let prio_fee = U256::from((prices.max_priority_fee_per_gas * 100.0) as u64) *
+            U256::from(GWEI_TO_WEI) /
+            U256::from(100);
+        Ok((base_fee, prio_fee))
+    }
+}

ethers-middleware/src/gas_oracle/mod.rs

@@ -1,3 +1,6 @@
+mod blocknative;
+pub use blocknative::BlockNative;
+
 mod eth_gas_station;
 pub use eth_gas_station::EthGasStation;
 
@@ -35,6 +38,14 @@ pub enum GasOracleError {
     #[error(transparent)]
     HttpClientError(#[from] ReqwestError),
 
+    /// An error decoding JSON response from gas oracle
+    #[error(transparent)]
+    SerdeJsonError(#[from] serde_json::Error),
+
+    /// An error with oracle response type
+    #[error("invalid oracle response")]
+    InvalidResponse,
+
     /// An internal error in the Etherscan client request made from the underlying
     /// gas oracle
     #[error(transparent)]