Database*: fix nullptr dereference when no database is configured

src/DatabaseGlue.cxx

@@ -87,6 +87,18 @@ GetDatabase()
 	return db;
 }
 
+const Database *
+GetDatabase(GError **error_r)
+{
+	assert(db == nullptr || db_is_open);
+
+	if (db == nullptr)
+		g_set_error_literal(error_r, db_quark(), DB_DISABLED,
+				    "No database");
+
+	return db;
+}
+
 bool
 db_is_simple(void)
 {

src/DatabaseGlue.hxx

@@ -21,6 +21,7 @@
 #define MPD_DATABASE_GLUE_HXX
 
 #include "gcc.h"
+#include "gerror.h"
 
 class Database;
 
@@ -32,4 +33,12 @@ gcc_pure
 const Database *
 GetDatabase();
 
+/**
+ * Returns the global #Database instance.  May return NULL if this MPD
+ * configuration has no database (no music_directory was configured).
+ */
+gcc_pure
+const Database *
+GetDatabase(GError **error_r);
+
 #endif

src/DatabasePlaylist.cxx

@@ -43,11 +43,15 @@ search_add_to_playlist(const char *uri, const char *playlist_path_utf8,
 		       const struct locate_item_list *criteria,
 		       GError **error_r)
 {
+	const Database *db = GetDatabase(error_r);
+	if (db == nullptr)
+		return false;
+
 	const DatabaseSelection selection(uri, true, criteria);
 
 	using namespace std::placeholders;
 	const auto f = std::bind(AddSong, playlist_path_utf8, _1, _2);
-	return GetDatabase()->Visit(selection, f, error_r);
+	return db->Visit(selection, f, error_r);
 }
 
 bool

src/DatabasePrint.cxx

@@ -115,6 +115,10 @@ bool
 db_selection_print(struct client *client, const DatabaseSelection &selection,
 		   bool full, GError **error_r)
 {
+	const Database *db = GetDatabase(error_r);
+	if (db == nullptr)
+		return false;
+
 	using namespace std::placeholders;
 	const auto d = selection.match == nullptr
 		? std::bind(PrintDirectory, client, _1)
@@ -126,7 +130,7 @@ db_selection_print(struct client *client, const DatabaseSelection &selection,
 			    client, _1, _2)
 		: VisitPlaylist();
 
-	return GetDatabase()->Visit(selection, d, s, p, error_r);
+	return db->Visit(selection, d, s, p, error_r);
 }
 
 struct SearchStats {
@@ -154,6 +158,10 @@ searchStatsForSongsIn(struct client *client, const char *name,
 		      const struct locate_item_list *criteria,
 		      GError **error_r)
 {
+	const Database *db = GetDatabase(error_r);
+	if (db == nullptr)
+		return false;
+
 	const DatabaseSelection selection(name, true, criteria);
 
 	SearchStats stats;
@@ -163,7 +171,7 @@ searchStatsForSongsIn(struct client *client, const char *name,
 	using namespace std::placeholders;
 	const auto f = std::bind(stats_visitor_song, std::ref(stats),
 				 _1);
-	if (!GetDatabase()->Visit(selection, f, error_r))
+	if (!db->Visit(selection, f, error_r))
 		return false;
 
 	printSearchStats(client, &stats);
@@ -206,18 +214,21 @@ listAllUniqueTags(struct client *client, int type,
 		  const struct locate_item_list *criteria,
 		  GError **error_r)
 {
+	const Database *db = GetDatabase(error_r);
+	if (db == nullptr)
+		return false;
+
 	const DatabaseSelection selection("", true, criteria);
 
 	if (type == LOCATE_TAG_FILE_TYPE) {
 		using namespace std::placeholders;
 		const auto f = std::bind(PrintSongURIVisitor, client, _1);
-		return GetDatabase()->Visit(selection, f, error_r);
+		return db->Visit(selection, f, error_r);
 	} else {
 		using namespace std::placeholders;
 		const auto f = std::bind(PrintUniqueTag, client,
 					 (enum tag_type)type, _1);
-		return GetDatabase()->VisitUniqueTags(selection,
-						      (enum tag_type)type,
-						      f, error_r);
+		return db->VisitUniqueTags(selection, (enum tag_type)type,
+					   f, error_r);
 	}
 }

src/DatabaseQueue.cxx

@@ -49,11 +49,15 @@ bool
 findAddIn(struct player_control *pc, const char *uri,
 	  const struct locate_item_list *criteria, GError **error_r)
 {
+	const Database *db = GetDatabase(error_r);
+	if (db == nullptr)
+		return false;
+
 	const DatabaseSelection selection(uri, true, criteria);
 
 	using namespace std::placeholders;
 	const auto f = std::bind(AddToQueue, pc, _1, _2);
-	return GetDatabase()->Visit(selection, f, error_r);
+	return db->Visit(selection, f, error_r);
 }
 
 bool