From ba7a8664a12cb9ce98b0fa0dbbd51f59ce231381 Mon Sep 17 00:00:00 2001
From: Wim Taymans <wtaymans@redhat.com>
Date: Mon, 11 Nov 2024 11:49:20 +0100
Subject: [PATCH] module-rtp: calculate payload_size based on MTU

The actual payload size depends on the MTU but should not include the
IP/UDP and RTP headers.

Fixes #4396
---
 src/modules/module-rtp/midi.c   | 5 +++--
 src/modules/module-rtp/stream.c | 8 +++++++-
 src/modules/module-rtp/stream.h | 3 +++
 3 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/src/modules/module-rtp/midi.c b/src/modules/module-rtp/midi.c
index 314f64f57..663be0dc0 100644
--- a/src/modules/module-rtp/midi.c
+++ b/src/modules/module-rtp/midi.c
@@ -354,7 +354,7 @@ static void rtp_midi_flush_packets(struct impl *impl,
 	struct rtp_header header;
 	struct rtp_midi_header midi_header;
 	struct iovec iov[3];
-	uint32_t len, prev_offset, base;
+	uint32_t len, prev_offset, base, max_size;
 
 	spa_zero(header);
 	header.v = 2;
@@ -371,6 +371,7 @@ static void rtp_midi_flush_packets(struct impl *impl,
 	iov[2].iov_len = 0;
 
 	prev_offset = len = base = 0;
+	max_size = impl->payload_size - sizeof(midi_header);
 
 	SPA_POD_SEQUENCE_FOREACH(sequence, c) {
 		void *ev;
@@ -384,7 +385,7 @@ static void rtp_midi_flush_packets(struct impl *impl,
 
 		offset = c->offset * impl->rate / rate;
 
-		if (len > 0 && (len + size > impl->mtu ||
+		if (len > 0 && (len + size > max_size ||
 		    offset - base > impl->psamples)) {
 			/* flush packet when we have one and when it's either
 			 * too large or has too much data. */
diff --git a/src/modules/module-rtp/stream.c b/src/modules/module-rtp/stream.c
index 93755e388..de0019a89 100644
--- a/src/modules/module-rtp/stream.c
+++ b/src/modules/module-rtp/stream.c
@@ -69,6 +69,7 @@ struct impl {
 	uint32_t ts_offset;
 	uint32_t psamples;
 	uint32_t mtu;
+	uint32_t payload_size;
 
 	struct spa_ringbuffer ring;
 	uint8_t buffer[BUFFER_SIZE];
@@ -439,6 +440,11 @@ struct rtp_stream *rtp_stream_new(struct pw_core *core,
 
 	impl->payload = pw_properties_get_uint32(props, "rtp.payload", impl->payload);
 	impl->mtu = pw_properties_get_uint32(props, "net.mtu", DEFAULT_MTU);
+	if (impl->mtu <= PACKET_HEADER_SIZE) {
+		pw_log_error("invalid MTU %d, using %d", impl->mtu, DEFAULT_MTU);
+		impl->mtu = DEFAULT_MTU;
+	}
+	impl->payload_size = impl->mtu - PACKET_HEADER_SIZE;
 
 	impl->seq = pw_rand32();
 
@@ -476,7 +482,7 @@ struct rtp_stream *rtp_stream_new(struct pw_core *core,
 			pw_log_warn("rtp.ptime doesn't match rtp.framecount. Choosing rtp.ptime");
 		}
 	} else {
-		impl->psamples = impl->mtu / impl->stride;
+		impl->psamples = impl->payload_size / impl->stride;
 		impl->psamples = SPA_CLAMP(impl->psamples, min_samples, max_samples);
 		if (direction == PW_DIRECTION_INPUT) {
 			pw_properties_set(props, "rtp.ptime",
diff --git a/src/modules/module-rtp/stream.h b/src/modules/module-rtp/stream.h
index 0221b5f1e..e4c09edbc 100644
--- a/src/modules/module-rtp/stream.h
+++ b/src/modules/module-rtp/stream.h
@@ -19,6 +19,9 @@ struct rtp_stream;
 #define ERROR_MSEC		2.0f
 #define DEFAULT_SESS_LATENCY	100.0f
 
+/* 28 bytes IP/UDP, 12 bytes RTP header */
+#define PACKET_HEADER_SIZE	(12+28)
+
 #define DEFAULT_MTU		1280
 #define DEFAULT_MIN_PTIME	2.0f
 #define DEFAULT_MAX_PTIME	20.0f