fix!: create IPC socket in user runtime directory (#1313)

Each user has their own runtime directory at `/run/user/<uid>`. Creating
the IPC socket in there makes sure it is cleaned up regardless of
whether `ncspot` exits normally.

BREAKING CHANGE: move IPC socket location

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Improve error messages generated by the command line
 - Build with crossterm terminal backend by default
+- Move UNIX IPC socket from the user's cache path to the user's runtime directory
 
 ### Fixed
 

doc/users.md

@@ -180,10 +180,12 @@ Note: \<FOO\> - mandatory arg; [BAR] - optional arg
 | `save [current]`                                                 | Save selected item, if `current` is passed the currently playing item will be saved                                                                                                                                                                             |
 
 ## Remote control (IPC)
-Apart from MPRIS, ncspot will also create a domain socket on UNIX platforms
-(Linux, macOS, *BSD) at `~/.cache/ncspot/ncspot.sock`.  Applications or scripts
-can connect to this socket to send commands or be notified of the currently
-playing track, i.e. with `netcat`:
+Apart from MPRIS, ncspot will also create a domain socket on UNIX platforms (Linux, macOS, *BSD).
+The socket will be created in the platform's runtime directory. If XDG_RUNTIME_DIR is set, it will
+be created under `$XDG_RUNTIME_DIR/ncspot`. If XDG_RUNTIME_DIR isn't set, it will be created under
+`/run/user/<uid>` for Linux if it exists. In all other cases, it will be created under
+`/tmp/ncspot-<uid>`. Applications or scripts can connect to this socket to send commands or be
+notified of the currently playing track, i.e. with `netcat`:
 
 ```
 % nc -U ~/.cache/ncspot/ncspot.sock

src/application.rs

@@ -17,7 +17,7 @@ use crate::library::Library;
 use crate::queue::Queue;
 use crate::spotify::{PlayerEvent, Spotify};
 use crate::ui::create_cursive;
-use crate::{authentication, ui};
+use crate::{authentication, ui, utils};
 use crate::{command, queue, spotify};
 
 #[cfg(feature = "mpris")]
@@ -140,7 +140,9 @@ impl Application {
         #[cfg(unix)]
         let ipc = ipc::IpcSocket::new(
             ASYNC_RUNTIME.get().unwrap().handle(),
-            crate::config::cache_path("ncspot.sock"),
+            utils::create_runtime_directory()
+                .unwrap()
+                .join("ncspot.sock"),
             event_manager.clone(),
         )
         .map_err(|e| e.to_string())?;

src/utils.rs

@@ -1,6 +1,6 @@
 #![allow(dead_code)]
 
-use std::fmt::Write;
+use std::{fmt::Write, path::PathBuf};
 
 /// Returns a human readable String of a Duration
 ///
@@ -59,3 +59,54 @@ pub fn download(url: String, path: std::path::PathBuf) -> Result<(), std::io::Er
     std::io::copy(&mut resp, &mut file)?;
     Ok(())
 }
+
+/// Create the application specific runtime directory and return the path to it.
+///
+/// If the directory already exists and has the correct permissions, this function just returns the
+/// existing directory. The contents stored in this directory are not necessarily persisted across
+/// reboots. Stored files should be small since they could reside in memory (like on a tmpfs mount).
+#[cfg(unix)]
+pub fn create_runtime_directory() -> Result<PathBuf, Box<dyn std::error::Error>> {
+    use std::{
+        fs::{self, Permissions},
+        os::unix::prelude::PermissionsExt,
+    };
+
+    let linux_runtime_directory =
+        PathBuf::from(format!("/run/user/{}/", unsafe { libc::getuid() }));
+    let unix_runtime_directory = PathBuf::from("/tmp/");
+
+    let user_runtime_directory = if let Some(xdg_runtime_directory) = xdg_runtime_directory() {
+        Some(xdg_runtime_directory.join("ncspot"))
+    } else if cfg!(linux) && linux_runtime_directory.exists() {
+        Some(linux_runtime_directory.join("ncspot"))
+    } else if unix_runtime_directory.exists() {
+        Some(unix_runtime_directory.join(format!("ncspot-{}", unsafe { libc::getuid() })))
+    } else {
+        None
+    }
+    .ok_or("no runtime directory found")?;
+
+    let creation_result = fs::create_dir(&user_runtime_directory);
+
+    if creation_result.is_ok()
+        || matches!(
+            creation_result.as_ref().unwrap_err().kind(),
+            std::io::ErrorKind::AlreadyExists
+        )
+    {
+        // Needed when created inside a world readable directory, to prevent unauthorized access.
+        // Doesn't hurt otherwise.
+        fs::set_permissions(&user_runtime_directory, Permissions::from_mode(0o700))?;
+
+        Ok(user_runtime_directory)
+    } else {
+        #[allow(clippy::unnecessary_unwrap)]
+        Err(Box::new(creation_result.unwrap_err()))
+    }
+}
+
+#[cfg(unix)]
+fn xdg_runtime_directory() -> Option<PathBuf> {
+    std::env::var("XDG_RUNTIME_DIR").ok().map(Into::into)
+}