This patch allows you to play any file on your local filesystem (that the MPD server can read) using the `file://` URI syntax.

mpd_fileaccess-v0.20.5.patch

diff --git a/src/client/ClientFile.cxx b/src/client/ClientFile.cxx
index 0382789..9c41d2c 100644
--- a/src/client/ClientFile.cxx
+++ b/src/client/ClientFile.cxx
@@ -33,19 +33,17 @@ Client::AllowFile(Path path_fs) const
 
 	throw ProtocolError(ACK_ERROR_PERMISSION, "Access denied");
 #else
-	if (uid >= 0 && (uid_t)uid == geteuid())
-		/* always allow access if user runs his own MPD
-		   instance */
-		return;
-
-	if (uid < 0)
-		/* unauthenticated client */
-		throw ProtocolError(ACK_ERROR_PERMISSION, "Access denied");
-
 	const FileInfo fi(path_fs);
 
-	if (fi.GetUid() != (uid_t)uid && (fi.GetMode() & 0444) != 0444)
-		/* client is not owner */
-		throw ProtocolError(ACK_ERROR_PERMISSION, "Access denied");
+    /* Check to see if the MPD process has read privlidges on the
+     * requested file. */
+    if ((geteuid() == fi.GetUid() && (fi.GetMode() & 0400) == 0400) ||
+        (getegid() == fi.GetGid() && (fi.GetMode() & 0040) == 0040) ||
+        ((fi.GetMode() & 0004) == 0004)) {
+        return;
+    }
+
+    /* otherwise, we can't read these files */
+	throw ProtocolError(ACK_ERROR_PERMISSION, "Access denied");
 #endif
 }
diff --git a/src/fs/FileInfo.hxx b/src/fs/FileInfo.hxx
index f82da87..ece97a0 100644
--- a/src/fs/FileInfo.hxx
+++ b/src/fs/FileInfo.hxx
@@ -113,6 +113,10 @@ public:
 		return st.st_uid;
 	}
 
+    gid_t GetGid() const {
+        return st.st_gid;
+    }
+
 	mode_t GetMode() const {
 		return st.st_mode;
 	}