Modernize feresectl and add bounded IPC event streaming

crates/ferese-ipc/src/socket.rs

@@ -0,0 +1,49 @@
+use std::ffi::OsStr;
+use std::io;
+use std::path::{Path, PathBuf};
+
+/// Resolve an IPC target: explicit path, FERESE_SOCKET, then the runtime default.
+pub fn resolve(explicit: Option<&Path>) -> io::Result<PathBuf> {
+    resolve_with(
+        explicit,
+        std::env::var_os("FERESE_SOCKET").as_deref(),
+        std::env::var_os("XDG_RUNTIME_DIR").as_deref(),
+    )
+}
+
+fn resolve_with(explicit: Option<&Path>, socket: Option<&OsStr>, runtime: Option<&OsStr>) -> io::Result<PathBuf> {
+    if let Some(path) = explicit {
+        if path.as_os_str().is_empty() {
+            return Err(io::Error::new(io::ErrorKind::InvalidInput, "IPC socket path is empty"));
+        }
+        return Ok(path.to_owned());
+    }
+    if let Some(socket) = socket.filter(|value| !value.is_empty()) {
+        return Ok(PathBuf::from(socket));
+    }
+    runtime
+        .filter(|value| !value.is_empty())
+        .map(|directory| PathBuf::from(directory).join("ferese/control.sock"))
+        .ok_or_else(|| io::Error::new(io::ErrorKind::NotFound, "XDG_RUNTIME_DIR is not set"))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn explicit_nested_target_wins_over_the_host_environment() {
+        let runtime = Some(OsStr::new("/run/user/1000"));
+        let host = OsStr::new("/run/user/1000/ferese/control.sock");
+        let nested = Path::new("/tmp/nested/ferese/control.sock");
+        assert_eq!(resolve_with(Some(nested), Some(host), runtime).unwrap(), nested);
+        assert_eq!(resolve_with(None, Some(nested.as_os_str()), runtime).unwrap(), nested);
+        assert_eq!(resolve_with(None, None, runtime).unwrap(), Path::new(host));
+        assert_eq!(
+            resolve_with(None, Some(OsStr::new("")), runtime).unwrap(),
+            Path::new(host)
+        );
+        assert!(resolve_with(None, None, None).is_err());
+        assert!(resolve_with(Some(Path::new("")), Some(host), runtime).is_err());
+    }
+}