auto-discover daemon state dir from /proc when RSS_STATE_DIR is unset

src/state.rs

@@ -4,9 +4,46 @@ pub fn runtime_dir() -> PathBuf {
     if let Ok(dir) = std::env::var("RSS_STATE_DIR") {
         return PathBuf::from(dir);
     }
+    if let Some(dir) = discover_daemon_state_dir() {
+        return dir;
+    }
     PathBuf::from("/tmp/rss")
 }
 
+fn discover_daemon_state_dir() -> Option<PathBuf> {
+    let proc_dir = std::fs::read_dir("/proc").ok()?;
+    for entry in proc_dir {
+        let entry = entry.ok()?;
+        let pid = entry.file_name().to_str()?.to_string();
+        if !pid.bytes().all(|b| b.is_ascii_digit()) {
+            continue;
+        }
+        let comm = std::fs::read_to_string(format!("/proc/{}/comm", pid)).ok()?;
+        if comm.trim() != "rss" {
+            continue;
+        }
+        let cmdline = std::fs::read(format!("/proc/{}/cmdline", pid)).ok()?;
+        let args: Vec<&str> = cmdline
+            .split(|&b| b == 0)
+            .filter_map(|s| std::str::from_utf8(s).ok())
+            .collect();
+        if !args.contains(&"daemon") {
+            continue;
+        }
+        let environ = std::fs::read(format!("/proc/{}/environ", pid)).ok()?;
+        for var in environ.split(|&b| b == 0) {
+            if let Ok(var_str) = std::str::from_utf8(var) {
+                if let Some(val) = var_str.strip_prefix("RSS_STATE_DIR=") {
+                    if !val.is_empty() {
+                        return Some(PathBuf::from(val));
+                    }
+                }
+            }
+        }
+    }
+    None
+}
+
 pub fn socket_path() -> PathBuf {
     if let Ok(p) = std::env::var("RSS_SOCKET") {
         return PathBuf::from(p);