From f3eee4cf3fe4b7837148b768c5ee925e612e47b8 Mon Sep 17 00:00:00 2001
From: Andrea Simeoni <andreasimeoni84@gmail.com>
Date: Sun, 20 Nov 2022 21:39:14 +0100
Subject: [PATCH] Get gas price in USD using a Chainlink oracle (#1872)

Co-authored-by: Andrea Simeoni <>
---
 examples/gas_price_usd.rs | 67 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 67 insertions(+)
 create mode 100644 examples/gas_price_usd.rs

diff --git a/examples/gas_price_usd.rs b/examples/gas_price_usd.rs
new file mode 100644
index 00000000..43e9bb2c
--- /dev/null
+++ b/examples/gas_price_usd.rs
@@ -0,0 +1,67 @@
+use ethers::{prelude::*, utils::format_units};
+use std::{
+    error::Error,
+    ops::{Div, Mul},
+    sync::Arc,
+};
+
+abigen!(
+    AggregatorInterface,
+    r#"[
+        latestAnswer() public view virtual override returns (int256 answer)
+    ]"#,
+);
+
+const ETH_DECIMALS: u32 = 18;
+const USD_PRICE_DECIMALS: u32 = 8;
+const ETH_USD_FEED: &str = "0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419";
+const RPC_URI: &str = "https://mainnet.infura.io/v3/c60b0bb42f8a4c6481ecd229eddaca27";
+
+/// Retrieves the USD amount per gas unit, using a Chainlink price oracle.
+/// Function gets the amount of `wei` to be spent per gas unit then multiplies
+/// for the ETH USD value.
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn Error>> {
+    let client = get_client();
+    let oracle = get_oracle(&client);
+
+    let usd_per_eth: I256 = oracle.latest_answer().call().await?;
+    let usd_per_eth: U256 = U256::from(usd_per_eth.as_u128());
+    let wei_per_gas: U256 = client.get_gas_price().await?;
+
+    // Gas stations use to report gas price in gwei units (1 gwei = 10^9 wei)
+    let gwei: f64 = format_units(wei_per_gas, "gwei")?.parse::<f64>()?;
+
+    // Let's convert the gas price to USD
+    let usd_per_gas: f64 = usd_value(wei_per_gas, usd_per_eth)?;
+
+    println!(
+        r#"
+        Gas price
+        ---------------
+        {:>10.2} gwei
+        {:>10.8} usd
+        "#,
+        gwei, usd_per_gas
+    );
+    Ok(())
+}
+
+/// `amount`: Number of wei per gas unit (18 decimals)
+/// `price_usd`: USD price per ETH (8 decimals)
+fn usd_value(amount: U256, price_usd: U256) -> Result<f64, Box<dyn Error>> {
+    let base: U256 = U256::from(10).pow(ETH_DECIMALS.into());
+    let value: U256 = amount.mul(price_usd).div(base);
+    let f: String = format_units(value, USD_PRICE_DECIMALS)?;
+    Ok(f.parse::<f64>()?)
+}
+
+fn get_client() -> Arc<Provider<Http>> {
+    let provider: Provider<Http> = Provider::<Http>::try_from(RPC_URI).expect("Valid URL");
+    Arc::new(provider)
+}
+
+fn get_oracle(client: &Arc<Provider<Http>>) -> AggregatorInterface<Provider<Http>> {
+    let address: Address = ETH_USD_FEED.parse().expect("Valid address");
+    AggregatorInterface::new(address, Arc::clone(client))
+}