From ed09d4ae54b35930ca947f01b997cc8c79e3fa51 Mon Sep 17 00:00:00 2001
From: hg <4683435+hgtw@users.noreply.github.com>
Date: Wed, 12 Feb 2020 20:05:28 -0500
Subject: [PATCH] Send packet uncompressed if zlib deflates to a larger size
 than input

It's not guaranteed that deflate output will be smaller than the input.

In some cases zlib-ng (Z_BEST_SPEED) compression is causing packets to
increase in size and exceed m_max_packet_size. This results in the
packets never being fully received by the client.

Currently this is most reproducible in the spell_book section of the
OP_PlayerProfile message. After using #scribespells this portion of the
player profile has a lot of incrementing spellids which may be affecting
the compression algorithm. The client never processes the player profile
(MSG_SEND_PC) message and times out on zone entry.

This isn't necessarily a bug with zlib-ng since it inflates back to the
original input and normal zlib could do this too, but the current netcode
doesn't handle this.
---
 common/net/daybreak_connection.cpp | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/common/net/daybreak_connection.cpp b/common/net/daybreak_connection.cpp
index 8448049f5..bd0c39489 100644
--- a/common/net/daybreak_connection.cpp
+++ b/common/net/daybreak_connection.cpp
@@ -1047,12 +1047,14 @@ void EQ::Net::DaybreakConnection::Compress(Packet &p, size_t offset, size_t leng
 	uint8_t new_buffer[2048] = { 0 };
 	uint8_t *buffer = (uint8_t*)p.Data() + offset;
 	uint32_t new_length = 0;
+	bool send_uncompressed = true;
 
 	if (length > 30) {
 		new_length = Deflate(buffer, (uint32_t)length, new_buffer + 1, 2048) + 1;
 		new_buffer[0] = 0x5a;
+		send_uncompressed = (new_length > length);
 	}
-	else {
+	if (send_uncompressed) {
 		memcpy(new_buffer + 1, buffer, length);
 		new_buffer[0] = 0xa5;
 		new_length = length + 1;
@@ -1380,7 +1382,7 @@ void EQ::Net::DaybreakConnection::InternalQueuePacket(Packet &p, int stream_id,
 	}
 
 	auto stream = &m_streams[stream_id];
-	auto max_raw_size = m_max_packet_size - m_crc_bytes - DaybreakReliableHeader::size();
+	auto max_raw_size = m_max_packet_size - m_crc_bytes - DaybreakReliableHeader::size() - 1; // -1 for compress flag
 	size_t length = p.Length();
 	if (length > max_raw_size) {
 		DaybreakReliableFragmentHeader first_header;