From 0a48bfe79a890ff6ea070b9c5328533fb772c64f Mon Sep 17 00:00:00 2001
From: Philip Withnall <pwithnall@gnome.org>
Date: Wed, 13 Nov 2024 13:21:44 +0000
Subject: [PATCH] tests: Factor out a function to convert FD to path
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This could potentially eventually become a public GLib API, but there
doesn’t seem to be a huge need for it right now (e.g. this file contains
the only use of `/proc/self/fd/%d` in GLib), so let’s keep it private
for now and avoid committing to API stability just yet.

This gives time for other platforms to add their platform-specific
implementations for it too, if they need. I’ve added a couple of
pointers to what I *think* the right APIs might be, from my research,
but I have not prototyped those implementations.

Signed-off-by: Philip Withnall <pwithnall@gnome.org>
---
 gio/tests/fake-desktop-portal.c | 54 ++++++++++++++++++++++++---------
 1 file changed, 40 insertions(+), 14 deletions(-)

diff --git a/gio/tests/fake-desktop-portal.c b/gio/tests/fake-desktop-portal.c
index 4cba067d3..cb38b9ddc 100644
--- a/gio/tests/fake-desktop-portal.c
+++ b/gio/tests/fake-desktop-portal.c
@@ -206,15 +206,52 @@ handle_request (GFakeDesktopPortalThread *self,
   return G_DBUS_METHOD_INVOCATION_HANDLED;
 }
 
+/* This is currently private as there’s only one user of it, but it could become
+ * a public API in future. */
+static char *
+_g_fd_query_path (int      fd,
+                  GError **error)
+{
+#if defined(__FreeBSD__)
+  struct kinfo_file kf;
+  kf.kf_structsize = sizeof (kf);
+  if (fcntl (fd, F_KINFO, &kf) < 0)
+    {
+      int saved_errno = errno;
+      g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                   "Error querying file information for FD %d: %s",
+                   fd, g_strerror (saved_errno));
+      return NULL;
+    }
+
+  return g_strdup (kf.kf_path);
+#elif defined(G_OS_UNIX)
+  char *path = NULL;
+  char *proc_path = g_strdup_printf ("/proc/self/fd/%d", fd);
+  path = g_file_read_link (proc_path, error);
+  g_free (proc_path);
+  return g_steal_pointer (&path);
+#else
+  /*  - A NetBSD implementation would probably use `fcntl()` with `F_GETPATH`:
+   *    https://man.netbsd.org/fcntl.2
+   *  - A Windows implementation would probably use `GetFinalPathNameByHandleW()`:
+   *    https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-getfinalpathnamebyhandlea
+   *  - A Hurd implementation could open("/dev/fd/%u"):
+   *    https://gitlab.gnome.org/GNOME/glib/-/merge_requests/4396#note_2279923
+   */
+  #error "_g_fd_query_path() not supported on this platform"
+#endif
+}
+
 static char *
 handle_to_uri (GVariant    *handle,
                GUnixFDList *fd_list)
 {
   int fd = -1;
   int fd_id;
-  char *proc_path = NULL;
   char *path;
   char *uri;
+  GError *local_error = NULL;
 
   fd_id = g_variant_get_handle (handle);
   fd = g_unix_fd_list_get (fd_list, fd_id, NULL);
@@ -222,21 +259,10 @@ handle_to_uri (GVariant    *handle,
   if (fd == -1)
     return NULL;
 
-#ifdef __FreeBSD__
-  struct kinfo_file kf;
-  kf.kf_structsize = sizeof (kf);
-  if (fcntl (fd, F_KINFO, &kf) == -1)
-    return NULL;
-  path = g_strdup (kf.kf_path);
-
-#else
-  proc_path = g_strdup_printf ("/proc/self/fd/%d", fd);
-  path = g_file_read_link (proc_path, NULL);
-#endif
-  g_assert_nonnull (path);
+  path = _g_fd_query_path (fd, &local_error);
+  g_assert_no_error (local_error);
 
   uri = g_filename_to_uri (path, NULL, NULL);
-  g_free (proc_path);
   g_free (path);
   close (fd);