Support setting environment variables in JSON config

leaf/src/config/common.rs

@@ -514,6 +514,7 @@ pub struct Router {
 #[derive(Serialize, Deserialize, Debug, Clone, Default)]
 pub struct Config {
     pub log: Option<Log>,
+    pub env: Option<HashMap<String, String>>,
     pub inbounds: Option<Vec<Inbound>>,
     pub outbounds: Option<Vec<Outbound>>,
     pub router: Option<Router>,

leaf/src/config/json/config.rs

@@ -20,8 +20,21 @@ pub fn to_internal(config: Config) -> Result<internal::Config> {
     common::to_internal(config)
 }
 
+fn apply_env(config: &common::Config) {
+    if let Some(env) = &config.env {
+        for (k, v) in env {
+            if !k.trim().is_empty() {
+                std::env::set_var(k, v);
+            }
+        }
+    }
+}
+
 pub fn json_from_string(config: &str) -> Result<common::Config> {
-    serde_json::from_str(config).map_err(|e| anyhow!("deserialize json config failed: {}", e))
+    let config: common::Config = serde_json::from_str(config)
+        .map_err(|e| anyhow!("deserialize json config failed: {}", e))?;
+    apply_env(&config);
+    Ok(config)
 }
 
 pub fn from_string(s: &str) -> Result<internal::Config> {

leaf/src/config/json/tests/test_config.rs

@@ -143,6 +143,22 @@ fn test_dns_config() {
     assert_eq!(dns.servers.as_ref().unwrap()[0], "1.1.1.1");
 }
 
+#[test]
+fn test_env_config_sets_process_env() {
+    let key = "LEAF_JSON_ENV_TEST_KEY";
+    std::env::remove_var(key);
+    let json_str = r#"
+    {
+        "env": {
+            "LEAF_JSON_ENV_TEST_KEY": "json-env-value"
+        }
+    }
+    "#;
+    let _ = crate::config::json::json_from_string(json_str).unwrap();
+    assert_eq!(std::env::var(key).unwrap(), "json-env-value");
+    std::env::remove_var(key);
+}
+
 #[test]
 fn test_tls_outbound_ech_config_mapping() {
     let json_str = r#"

leaf/tests/common.rs

@@ -127,6 +127,7 @@ fn new_socks_outbound(
     }];
     let config = leaf::config::json::Config {
         log: None,
+        env: None,
         inbounds: None,
         outbounds: Some(outbounds),
         router: None,