media: Fix crash when determining sample count of a frame during shutdown.

When shutting down Asterisk the codecs are cleaned up. As a result anything
attempting to get a codec based on ID or details will find that no codec
exists. This currently occurs when determining the sample count of a frame.
This code did not take this situation into account.

This change fixes this by getting the codec directly from the format and
eliminates the lookup. This is both faster and also provides a guarantee
that the codec will exist and will be valid.

ASTERISK-24604 #close
Reported by: Matt Jordan

Review: https://reviewboard.asterisk.org/r/4260/
........

Merged revisions 429497 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/certified/branches/13.1@429871 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/format.h

@@ -275,6 +275,17 @@ void ast_format_set_attribute_data(struct ast_format *format, void *attribute_da
  */
 const char *ast_format_get_name(const struct ast_format *format);
 
+/*!
+ * \brief Get the codec associated with a format
+ *
+ * \param format The media format
+ *
+ * \return The codec
+ *
+ * \note The reference count of the returned codec is increased by 1 and must be decremented
+ */
+struct ast_codec *ast_format_get_codec(const struct ast_format *format);
+
 /*!
  * \brief Get the codec identifier associated with a format
  *

main/codec.c

@@ -355,10 +355,7 @@ unsigned int ast_codec_samples_count(struct ast_frame *frame)
 		return 0;
 	}
 
-	/* BUGBUG - why not just get the codec pointer off the format?
-	This is a bit roundabout
-	*/
-	codec = ast_codec_get_by_id(ast_format_get_codec_id(frame->subclass.format));
+	codec = ast_format_get_codec(frame->subclass.format);
 
 	if (codec->samples_count) {
 		samples = codec->samples_count(frame);

main/format.c

@@ -323,6 +323,11 @@ void ast_format_generate_sdp_fmtp(const struct ast_format *format, unsigned int
 	format->interface->format_generate_sdp_fmtp(format, payload, str);
 }
 
+struct ast_codec *ast_format_get_codec(const struct ast_format *format)
+{
+	return ao2_bump(format->codec);
+}
+
 unsigned int ast_format_get_codec_id(const struct ast_format *format)
 {
 	return format->codec->id;