fix(ipc): Fallback folder not being user-specific (#2684)

If two users start a bar with IPC and don't have XDG_RUNTIME_DIR set,
polybar will create the fallback directory `/tmp/polybar`.
However, that directory is only accessible by the user that created it
and so polybar running under the second user will fail to open its
socket there.

We add the UID to the fallback directory to prevent this.

Fixes #2683

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 - `custom/script`: Output clearing when `exec-if` fails ([`#2674`](https://github.com/polybar/polybar/issues/2674))
 - `internal/battery`: `poll-interval` not working ([`#2649`](https://github.com/polybar/polybar/issues/2649), [`#2677`](https://github.com/polybar/polybar/pull/2677))
+- ipc: Polybar failing to open IPC channel after another user already ran polybar, if `XDG_RUNTIME_DIR` is not set ([`#2683`](https://github.com/polybar/polybar/issues/2683), [`#2684`](https://github.com/polybar/polybar/pull/2684))
 
 ## [3.6.2] - 2022-04-03
 ### Fixed

include/ipc/ipc.hpp

@@ -1,7 +1,5 @@
 #pragma once
 
-#include <uv.h>
-
 #include <set>
 
 #include "common.hpp"

src/components/controller.cpp

@@ -1,7 +1,5 @@
 #include "components/controller.hpp"
 
-#include <uv.h>
-
 #include <csignal>
 #include <utility>
 

src/ipc/util.cpp

@@ -1,6 +1,7 @@
 #include "ipc/util.hpp"
 
 #include <sys/stat.h>
+#include <unistd.h>
 
 #include "errors.hpp"
 #include "utils/env.hpp"
@@ -12,8 +13,14 @@ POLYBAR_NS
 namespace ipc {
 
   static constexpr auto SUFFIX = ".sock";
+  static constexpr auto XDG_RUNTIME_DIR = "XDG_RUNTIME_DIR";
 
   string get_runtime_path() {
+    if (env_util::has(XDG_RUNTIME_DIR)) {
+      return env_util::get("XDG_RUNTIME_DIR") + "/polybar";
+    } else {
+      return "/tmp/polybar-" + to_string(getuid());
+    }
     return env_util::get("XDG_RUNTIME_DIR", "/tmp") + "/polybar";
   }