From ebbf920a502d6d460ff3ea8a57db0c624e3a0747 Mon Sep 17 00:00:00 2001
From: "Alfred E. Heggestad" <alfred.heggestad@gmail.com>
Date: Tue, 23 May 2017 19:43:29 +0200
Subject: rtpext: add RTP Header Extensions (RFC 5285) (#257)

* rtpext: add RTP Header Extensions (RFC 5285)

* whitespace fix
---
 src/core.h   |  30 ++++++++++++++++
 src/rtpext.c | 112 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/srcs.mk  |   1 +
 3 files changed, 143 insertions(+)
 create mode 100644 src/rtpext.c

diff --git a/src/core.h b/src/core.h
index 51bfa6d..5dc5e9d 100644
--- a/src/core.h
+++ b/src/core.h
@@ -271,6 +271,36 @@ int  reg_debug(struct re_printf *pf, const struct reg *reg);
 int  reg_status(struct re_printf *pf, const struct reg *reg);
 
 
+/*
+ * RTP Header Extensions
+ */
+
+#define RTPEXT_HDR_SIZE        4
+#define RTPEXT_TYPE_MAGIC 0xbede
+
+enum {
+	RTPEXT_ID_MIN  =  1,
+	RTPEXT_ID_MAX  = 14,
+};
+
+enum {
+	RTPEXT_LEN_MIN =  1,
+	RTPEXT_LEN_MAX = 16,
+};
+
+struct rtpext {
+	unsigned id:4;
+	unsigned len:4;
+	uint8_t data[RTPEXT_LEN_MAX];
+};
+
+
+int rtpext_hdr_encode(struct mbuf *mb, size_t num_bytes);
+int rtpext_encode(struct mbuf *mb, unsigned id, unsigned len,
+		  const uint8_t *data);
+int rtpext_decode(struct rtpext *ext, struct mbuf *mb);
+
+
 /*
  * RTP keepalive
  */
diff --git a/src/rtpext.c b/src/rtpext.c
new file mode 100644
index 0000000..82a6f6e
--- /dev/null
+++ b/src/rtpext.c
@@ -0,0 +1,112 @@
+/**
+ * @file rtpext.c  RTP Header Extensions
+ *
+ * Copyright (C) 2017 Creytiv.com
+ */
+
+#include <string.h>
+#include <re.h>
+#include <baresip.h>
+#include "core.h"
+
+
+/*
+ * RFC 5285 A General Mechanism for RTP Header Extensions
+ *
+ * - One-Byte Header:  Supported
+ * - Two-Byte Header:  Not supported
+ */
+
+
+int rtpext_hdr_encode(struct mbuf *mb, size_t num_bytes)
+{
+	int err = 0;
+
+	if (!mb || !num_bytes)
+		return EINVAL;
+
+	if (num_bytes & 0x3) {
+		warning("rtpext: hdr_encode: num_bytes (%zu) must be multiple"
+			" of 4\n", num_bytes);
+		return EINVAL;
+	}
+
+	err |= mbuf_write_u16(mb, htons(RTPEXT_TYPE_MAGIC));
+	err |= mbuf_write_u16(mb, htons(num_bytes / 4));
+
+	return err;
+}
+
+
+int rtpext_encode(struct mbuf *mb, unsigned id, unsigned len,
+		  const uint8_t *data)
+{
+	size_t start;
+	int err;
+
+	if (!mb || !data)
+		return EINVAL;
+
+	if (id < RTPEXT_ID_MIN || id > RTPEXT_ID_MAX)
+		return EINVAL;
+	if (len < RTPEXT_LEN_MIN || len > RTPEXT_LEN_MAX)
+		return EINVAL;
+
+	start = mb->pos;
+
+	err  = mbuf_write_u8(mb, id << 4 | (len-1));
+	err |= mbuf_write_mem(mb, data, len);
+	if (err)
+		return err;
+
+	/* padding */
+	while ((mb->pos - start) & 0x03)
+		err |= mbuf_write_u8(mb, 0x00);
+
+	return err;
+}
+
+
+int rtpext_decode(struct rtpext *ext, struct mbuf *mb)
+{
+	uint8_t v;
+	int err;
+
+	if (!ext || !mb)
+		return EINVAL;
+
+	if (mbuf_get_left(mb) < 1)
+		return EBADMSG;
+
+	memset(ext, 0, sizeof(*ext));
+
+	v = mbuf_read_u8(mb);
+
+	ext->id  = v >> 4;
+	ext->len = (v & 0x0f) + 1;
+
+	if (ext->id < RTPEXT_ID_MIN || ext->id > RTPEXT_ID_MAX) {
+		warning("rtpext: invalid ID %u\n", ext->id);
+		return EBADMSG;
+	}
+	if (ext->len > mbuf_get_left(mb)) {
+		warning("rtpext: short read\n");
+		return ENODATA;
+	}
+
+	err = mbuf_read_mem(mb, ext->data, ext->len);
+	if (err)
+		return err;
+
+	/* skip padding */
+	while (mbuf_get_left(mb)) {
+		uint8_t pad = mbuf_buf(mb)[0];
+
+		if (pad != 0x00)
+			break;
+
+		mbuf_advance(mb, 1);
+	}
+
+	return 0;
+}
diff --git a/src/srcs.mk b/src/srcs.mk
index cdb2a26..686ca7c 100644
--- a/src/srcs.mk
+++ b/src/srcs.mk
@@ -28,6 +28,7 @@ SRCS	+= net.c
 SRCS	+= play.c
 SRCS	+= realtime.c
 SRCS	+= reg.c
+SRCS	+= rtpext.c
 SRCS	+= rtpkeep.c
 SRCS	+= sdp.c
 SRCS	+= sipreq.c
-- 
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