From ee74a932c6f25fc5e28aada4334ace0b9b5e6197 Mon Sep 17 00:00:00 2001
From: Robin Gareus <robin@gareus.org>
Date: Thu, 12 Nov 2020 16:51:48 +0100
Subject: [PATCH] Zero length Events are illegal

This would later trigger an assert() in MidiRingBuffer<T>::read
when reading the status-byte, and cause undefined behavior down
in optimized builds.

It is unsure if this can happen, but it may explain
https://marcan.st/paste/LHDXNQ9x.txt
---
 libs/ardour/ardour/event_ring_buffer.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/libs/ardour/ardour/event_ring_buffer.h b/libs/ardour/ardour/event_ring_buffer.h
index 2ccb11dc2d..1d47cbbcbf 100644
--- a/libs/ardour/ardour/event_ring_buffer.h
+++ b/libs/ardour/ardour/event_ring_buffer.h
@@ -118,7 +118,8 @@ template<typename Time>
 inline uint32_t
 EventRingBuffer<Time>::write(Time time, Evoral::EventType type, uint32_t size, const uint8_t* buf)
 {
-	if (!buf || write_space() < (sizeof(Time) + sizeof(Evoral::EventType) + sizeof(uint32_t) + size)) {
+	assert (size > 0);
+	if (!buf || size == 0 || write_space() < (sizeof(Time) + sizeof(Evoral::EventType) + sizeof(uint32_t) + size)) {
 		return 0;
 	} else {
 		PBD::RingBufferNPT<uint8_t>::write ((uint8_t*)&time, sizeof(Time));