res_musiconhold.c: Restart MOH if previous hold just reached end-of-file

On MOH activation, moh_files_readframe() is called while the current
stream attached to the channel is NULL and it calls ast_moh_files_next()
immediately.  However, it won't call ast_moh_files_next() again if sample
reading fails.  The failure may occur because res_musiconhold retains the
last sample reading position in the channel data and MOH during the
previous hold/retrieve just reached EOF.  Obviously, a bit of bad luck is
required here.

* Restructured moh_files_readframe() to try a second time to start MOH if
there was no stream setup and the saved position was at EOF.  Also added
comments describing what is going on for each step.

ASTERISK-28029

Change-Id: I1508cf2c094f8feca22d6f76deaa9fdfa9944860

diff --git a/res/res_musiconhold.c b/res/res_musiconhold.c
index 137f83bac79bfa91c5e26c3379e4d8eb47d51b00..5c739ab8fdc95b6fb873bf523c4e7b3e736197b9 100644 (file)
--- a/res/res_musiconhold.c
+++ b/res/res_musiconhold.c
@@ -402,11 +402,28 @@ static int ast_moh_files_next(struct ast_channel *chan)
 
 static struct ast_frame *moh_files_readframe(struct ast_channel *chan)
 {
-       struct ast_frame *f = NULL;
-
-       if (!(ast_channel_stream(chan) && (f = ast_readframe(ast_channel_stream(chan))))) {
-               if (!ast_moh_files_next(chan))
+       struct ast_frame *f;
+
+       f = ast_readframe(ast_channel_stream(chan));
+       if (!f) {
+               /* Either there was no file stream setup or we reached EOF. */
+               if (!ast_moh_files_next(chan)) {
+                       /*
+                        * Either we resetup the previously saved file stream position
+                        * or we started a new file stream.
+                        */
                        f = ast_readframe(ast_channel_stream(chan));
+                       if (!f) {
+                               /*
+                                * We can get here if we were very unlucky because the
+                                * resetup file stream was saved at EOF when MOH was
+                                * previously stopped.
+                                */
+                               if (!ast_moh_files_next(chan)) {
+                                       f = ast_readframe(ast_channel_stream(chan));
+                               }
+                       }
+               }
        }
 
        return f;