journal-remote: modernize source_free()

- make it return NULL,
- suppress log message about reference counter of writer unless trace
  logging is enabled,
- introduce cleanup function for RemoteSource.

src/journal-remote/journal-remote-parse.c

@@ -6,20 +6,20 @@
 #include "parse-util.h"
 #include "string-util.h"
 
-void source_free(RemoteSource *source) {
+RemoteSource* source_free(RemoteSource *source) {
         if (!source)
-                return;
+                return NULL;
 
         journal_importer_cleanup(&source->importer);
 
-        log_debug("Writer ref count %u", source->writer->n_ref);
+        log_trace("Writer ref count %u", source->writer->n_ref);
         writer_unref(source->writer);
 
         sd_event_source_unref(source->event);
         sd_event_source_unref(source->buffer_event);
 
         free(source->encoding);
-        free(source);
+        return mfree(source);
 }
 
 /**

src/journal-remote/journal-remote-parse.h

@@ -19,5 +19,6 @@ typedef struct RemoteSource {
 } RemoteSource;
 
 RemoteSource* source_new(int fd, bool passive_fd, char *name, Writer *writer);
-void source_free(RemoteSource *source);
+RemoteSource* source_free(RemoteSource *source);
+DEFINE_TRIVIAL_CLEANUP_FUNC(RemoteSource*, source_free);
 int process_source(RemoteSource *source, JournalFileFlags file_flags);