From e00ac3b227d586296e4e043ae9b6500fde0e539f Mon Sep 17 00:00:00 2001
From: Matan Perelman <matan1008@gmail.com>
Date: Tue, 28 Mar 2023 08:32:17 +0300
Subject: [PATCH] fmt_rtp_amr,fmt_rtp_efr: replace damaged packets with silence

Change-Id: I7245aa0bc0955cc8b94d5401a15e694f50498093
---
 src/fmt_rtp_amr.c |  9 +++++++++
 src/fmt_rtp_efr.c | 14 ++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/src/fmt_rtp_amr.c b/src/fmt_rtp_amr.c
index a6a3c9f..4982c83 100644
--- a/src/fmt_rtp_amr.c
+++ b/src/fmt_rtp_amr.c
@@ -27,6 +27,9 @@
 #include <osmocom/gapk/formats.h>
 #include <osmocom/gapk/utils.h>
 
+/* AMR SID frame is according to TS 126 101 4.2.3 */
+static const uint8_t SILENCE[] = {0x80, 0x44, 0x00, 0x00, 0x00, 0x00, 0x00};
+
 /* conversion function: RTP payload -> canonical format */
 static int
 rtp_amr_from_canon(uint8_t *dst, const uint8_t *src, unsigned int src_len)
@@ -42,6 +45,12 @@ rtp_amr_from_canon(uint8_t *dst, const uint8_t *src, unsigned int src_len)
 static int
 rtp_amr_to_canon(uint8_t *dst, const uint8_t *src, unsigned int src_len)
 {
+	/* Detect severely damaged frames according to RFC4867 4.3.2 */
+	if ((src[1] & 0x04) == 0) {
+		src = SILENCE;
+		src_len = sizeof(SILENCE);
+	}
+
 	/* skip Payload Header according to RFC4867 4.4.1 */
 	memcpy(dst, src+1, src_len-1);
 
diff --git a/src/fmt_rtp_efr.c b/src/fmt_rtp_efr.c
index 7afb1a3..214010e 100644
--- a/src/fmt_rtp_efr.c
+++ b/src/fmt_rtp_efr.c
@@ -30,6 +30,17 @@
 #define EFR_LEN	  31
 #define EFR_MAGIC 0xc
 
+/* EFR encoding starts with 0xc, if all other bits are 0 the packet is probably damaged */
+static const uint8_t DAMAGED_PACKET[EFR_LEN] = {
+	0xc0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
+};
+/* EFR SID frame is according to TS 101 318 5.3.2 */
+static const uint8_t SILENCE[EFR_LEN] = {
+	0xcf, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xe0, 0x00, 0x00,
+	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
+};
+
 /* conversion function: RTP payload -> canonical format */
 static int
 rtp_efr_from_canon(uint8_t *dst, const uint8_t *src, unsigned int src_len)
@@ -58,6 +69,9 @@ rtp_efr_to_canon(uint8_t *dst, const uint8_t *src, unsigned int src_len)
 		return EFR_CANON_LEN;
 	}
 
+	if (!memcmp(DAMAGED_PACKET, src, EFR_LEN))
+		src = SILENCE;
+
 	for (i=0; i<(EFR_LEN-1); i++)
 		dst[i] = (src[i] << 4) | (src[i+1] >> 4);
 	dst[EFR_LEN-1] = src[EFR_LEN-1] << 4;