feature: support a simple config loader

Author: tyrchen

Cargo.lock

@@ -9,3 +9,5 @@ edition = "2021"
 anyhow = "1.0.83"
 arc-swap = "1.7.1"
 crossbeam-channel = "0.5.12"
+serde = { version = "1.0.203", features = ["derive"] }
+serde_yaml = "0.9.34"

Cargo.toml

@@ -1,3 +1,3 @@
 # Geektime Rust 语言训练营
 
-0512 答疑
+答疑代码

README.md

@@ -0,0 +1,99 @@
+use anyhow::Result;
+use serde::Deserialize;
+
+trait ConfigMerge {
+    fn merge(&mut self, to_merge: Self) -> Result<()>;
+}
+
+#[derive(Debug, Default, Deserialize)]
+pub struct Config {
+    #[serde(default)]
+    pub server: ServerConfig,
+    #[serde(default)]
+    pub database: DatabaseConfig,
+}
+
+#[derive(Debug, Default, Deserialize)]
+pub struct ServerConfig {
+    #[serde(default)]
+    pub port: u16,
+}
+
+#[derive(Debug, Default, Deserialize)]
+pub struct DatabaseConfig {
+    #[serde(default)]
+    pub host: String,
+    #[serde(default)]
+    pub dbname: String,
+    #[serde(default)]
+    pub user: String,
+    #[serde(default)]
+    pub password: String,
+}
+
+impl Config {
+    pub fn load(env: &str) -> Result<Config> {
+        let mut base = Config::load_default()?;
+        match env {
+            "prod" => {
+                let config = std::fs::read_to_string("fixtures/prod.yml")?;
+                let to_merge = serde_yaml::from_str(&config)?;
+                base.merge(to_merge)?
+            }
+            "dev" => {
+                let config = std::fs::read_to_string("fixtures/dev.yml")?;
+                let to_merge = serde_yaml::from_str(&config)?;
+                base.merge(to_merge)?
+            }
+            _ => panic!("Unknown environment"),
+        };
+        Ok(base)
+    }
+
+    fn load_default() -> Result<Config> {
+        let config = include_str!("../fixtures/default.yml");
+        let config: Config = serde_yaml::from_str(config)?;
+        Ok(config)
+    }
+}
+
+impl ConfigMerge for ServerConfig {
+    fn merge(&mut self, to_merge: Self) -> Result<()> {
+        if to_merge.port != 0 {
+            self.port = to_merge.port;
+        }
+        Ok(())
+    }
+}
+
+impl ConfigMerge for DatabaseConfig {
+    fn merge(&mut self, to_merge: Self) -> Result<()> {
+        if !to_merge.host.is_empty() {
+            self.host = to_merge.host;
+        }
+        if !to_merge.dbname.is_empty() {
+            self.dbname = to_merge.dbname;
+        }
+        if !to_merge.user.is_empty() {
+            self.user = to_merge.user;
+        }
+        if !to_merge.password.is_empty() {
+            self.password = to_merge.password;
+        }
+        Ok(())
+    }
+}
+
+impl ConfigMerge for Config {
+    fn merge(&mut self, to_merge: Self) -> Result<()> {
+        self.server.merge(to_merge.server)?;
+        self.database.merge(to_merge.database)?;
+        Ok(())
+    }
+}
+
+fn main() -> Result<()> {
+    let config = Config::load("prod")?;
+    println!("{:?}", config);
+    Ok(())
+}

examples/config.rs

@@ -0,0 +1,8 @@
+server:
+  port: 8080
+
+database:
+  host: localhost:5432
+  user: myuser
+  password: vault:secret:mydb:myuser
+  dbname: mydb

fixtures/default.yml

@@ -0,0 +1,2 @@
+server:
+  port: 8081

fixtures/dev.yml

@@ -0,0 +1,5 @@
+server:
+  port: 80
+
+database:
+  host: db.acme.com:5432