res/res_stasis_snoop: generate silence when audiohook returns null

Currently when rtp is paused, no packets are written to the
recorded audio file, causing the silence to be skipped and recording
not properly time aligned.  The read handler as been adapted to
return a silence frame of the correct size.

ASTERISK-27128 #close

Change-Id: I2d7f60650457860b9c70907b14426756b058a844

res/res_stasis_snoop.c

@@ -72,6 +72,8 @@ struct stasis_app_snoop {
 	unsigned int whisper_active:1;
 	/*! \brief Uniqueid of the channel this snoop is snooping on */
 	char uniqueid[AST_MAX_UNIQUEID];
+	/*! \brief A frame of silence to use when the audiohook returns null */
+	struct ast_frame silence;
 };
 
 /*! \brief Destructor for snoop structure */
@@ -91,6 +93,11 @@ static void snoop_destroy(void *obj)
 		ast_audiohook_destroy(&snoop->whisper);
 	}
 
+	if (snoop->silence.data.ptr) {
+		ast_free(snoop->silence.data.ptr);
+		snoop->silence.data.ptr = NULL;
+	}
+
 	ast_free(snoop->app);
 
 	ast_channel_cleanup(snoop->chan);
@@ -197,7 +204,7 @@ static struct ast_frame *snoop_read(struct ast_channel *chan)
 	frame = ast_audiohook_read_frame(&snoop->spy, snoop->spy_samples, snoop->spy_direction, snoop->spy_format);
 	ast_audiohook_unlock(&snoop->spy);
 
-	return frame ? frame : &ast_null_frame;
+	return frame ? frame : &snoop->silence;
 }
 
 /*! \brief Callback function for hanging up a Snoop channel */
@@ -383,6 +390,19 @@ struct ast_channel *stasis_app_control_snoop(struct ast_channel *chan,
 
 		snoop->spy_samples = ast_format_get_sample_rate(snoop->spy_format) / (1000 / SNOOP_INTERVAL);
 		snoop->spy_active = 1;
+
+		snoop->silence.frametype = AST_FRAME_VOICE,
+		snoop->silence.datalen = snoop->spy_samples * sizeof(uint16_t),
+		snoop->silence.samples = snoop->spy_samples,
+		snoop->silence.mallocd = 0,
+		snoop->silence.offset = 0,
+		snoop->silence.src = __PRETTY_FUNCTION__,
+		snoop->silence.subclass.format = snoop->spy_format,
+		snoop->silence.data.ptr = ast_calloc(snoop->spy_samples, sizeof(uint16_t));
+		if (!snoop->silence.data.ptr) {
+			ast_hangup(snoop->chan);
+			return NULL;
+		}
 	}
 
 	/* If whispering is enabled set up the audiohook */