From e56ecaa999c065a4bca8b9eb2fd97f8160bff3c0 Mon Sep 17 00:00:00 2001
From: Deon George <deon@dege.au>
Date: Thu, 7 Dec 2023 20:19:48 +1100
Subject: [PATCH] Fix for processing packets, where our EOM or EOP is split
 across buffer reads

---
 app/Classes/FTN/Packet.php | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/app/Classes/FTN/Packet.php b/app/Classes/FTN/Packet.php
index 9457bf7..68fc85e 100644
--- a/app/Classes/FTN/Packet.php
+++ b/app/Classes/FTN/Packet.php
@@ -250,29 +250,35 @@ class Packet extends FTNBase implements \Iterator, \Countable
 				->singleOrFail();
 		}
 
-		$buf_ptr = 0;
-		$message = '';
-		$readbuf = '';
-		$last = '';
+		$buf_ptr = 0;		// Pointer to the end of the current message
+		$message = '';		// Current message we are building
+		$readbuf = '';		// What we are reading to determine the message contents
+		$last = '';			// If during buffer reads, the end of the last buffer had our NULL end of message marker
 
+		// We loop through reading from the buffer, to find our end of message tag
 		while ($buf_ptr || (! feof($f) && ($readbuf=fread($f,self::BLOCKSIZE)))) {
 			if (! $buf_ptr)
 				$read_ptr = ftell($f);
 
 			// Packed messages are Message::HEADER_LEN, prefixed with self::PACKED_MSG_LEAD
+			// If we havent got our header yet
 			if (strlen($message) < (Message::HEADER_LEN+strlen(self::PACKED_MSG_LEAD))) {
 				$addchars = (Message::HEADER_LEN+strlen(self::PACKED_MSG_LEAD))-strlen($message);
 				$message .= substr($readbuf,$buf_ptr,$addchars);
 				$buf_ptr += $addchars;
 
 				// If our buffer wasnt big enough...
+				// @todo can this be true?
 				if ($buf_ptr >= strlen($readbuf)) {
+					throw new \Exception('We found a situation that this is true');
 					$buf_ptr = 0;
 					continue;
 				}
 			}
 
 			// Take 2 chars from the buffer and check if we have our end packet signature
+			// $last is set, because we detected a NULL, so we'll add two more chars and see if we have our EOM
+			// signature. Some of those chars may belong to the next message, if $last has more than 1 NULL.
 			if ($last && ($buf_ptr === 0)) {
 				$last .= substr($readbuf,0,2);
 
@@ -286,21 +292,27 @@ class Packet extends FTNBase implements \Iterator, \Countable
 					continue;
 				}
 
+				// We didnt have an EOM marker
 				$last = '';
 			}
 
+			// See if our EOM marker is in the read buffer
 			if (($end=strpos($readbuf,"\x00".self::PACKED_MSG_LEAD,$buf_ptr)) === FALSE) {
 				// Just in case our packet break is at the end of the buffer
 				$last = substr($readbuf,-2);
 
-				if ((str_contains($last,"\x00")) && ($size-$read_ptr > 2)) {
+				// We have an EOM or EOP marker here, so loop around to get the next read
+				if (str_contains($last,"\x00")) {
 					$message .= substr($readbuf,$buf_ptr);
 					$buf_ptr = 0;
 
 					continue;
 				}
 
+				// No EOM marker
 				$last = '';
+
+				// See if we have an EOP marker
 				$end = strpos($readbuf,"\x00\x00\x00",$buf_ptr);
 			}
 
@@ -312,6 +324,7 @@ class Packet extends FTNBase implements \Iterator, \Countable
 
 					continue;
 
+				// No more to read, so the packet is bad
 				} else
 					throw new InvalidPacketException(sprintf('Cannot determine END of message/packet: %s|%s',get_class($o),hex_dump($message)));