エラー型に anyhow クレートを利用 + 非同期実行の構造を大幅に整理

.env.example

@@ -0,0 +1 @@
+DATABASE_URL=

Cargo.toml

@@ -15,3 +15,6 @@ rand = "0.8.0"
 # TODO(magurotuna): Upgrade tokio to v1 after sqlx gets compatible with that
 tokio = { version = "0.2.4", features = [ "full" ] }
 hyper = "0.14"
+anyhow = "1.0.37"
+async-trait = "0.1.42"
+futures = "0.3.12"

src/config.rs

@@ -0,0 +1,10 @@
+use anyhow::Result;
+
+pub struct Config {
+    pub database_url: String,
+}
+
+pub fn load_config() -> Result<Config> {
+    let database_url = dotenv::var("DATABASE_URL")?;
+    Ok(Config { database_url })
+}

src/db.rs

@@ -1,12 +1,10 @@
-use dotenv::dotenv;
+use crate::config::Config;
+use anyhow::Result;
 use sqlx::{mysql::MySqlPool, MySql};
-use std::env;
 
-pub async fn new_pool() -> Result<sqlx::Pool<MySql>, sqlx::Error> {
-    dotenv().ok();
-    let url = env::var("DATABASE_URL").expect("DATABASE_URL must be set");
-
-    let pool = MySqlPool::connect(&url).await?;
+pub type DbPool = sqlx::Pool<MySql>;
 
+pub async fn new_pool(config: &Config) -> Result<DbPool> {
+    let pool = MySqlPool::connect(&config.database_url).await?;
     Ok(pool)
 }