From 5aab76ba9f24af59f87c141e0dc78b922243fb9c Mon Sep 17 00:00:00 2001
From: Tyler Hamilton <thamilton@kin.bc.ca>
Date: Tue, 25 Apr 2023 14:52:15 -0700
Subject: [PATCH] Process command sequences before other processing

Changes the order of operations in preprocess so the valid sequence
IAC DO OPT_BINARY is correctly interpreted as a command sequence with
Binmode=false.  As suboption negotiation may contain any byte sequence
all other processing is done after the command sequences are handled.
---
 lib/net/telnet.rb | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/lib/net/telnet.rb b/lib/net/telnet.rb
index 43764f2..e797454 100644
--- a/lib/net/telnet.rb
+++ b/lib/net/telnet.rb
@@ -429,15 +429,8 @@ def binmode=(mode)
     # method yourself if you have read input directly using sysread()
     # or similar, and even then only if in telnet mode.
     def preprocess(string)
-      # combine CR+NULL into CR
-      string = string.gsub(/#{CR}#{NULL}/no, CR) if @options["Telnetmode"]
-
-      # combine EOL into "\n"
-      string = string.gsub(/#{EOL}/no, "\n") unless @options["Binmode"]
-
-      # remove NULL
-      string = string.gsub(/#{NULL}/no, '') unless @options["Binmode"]
-
+      # Handle command sequences first as they may contain characters
+      # which would otherwise be processed
       string.gsub(/#{IAC}(
                    [#{IAC}#{AO}#{AYT}#{DM}#{IP}#{NOP}]|
                    [#{DO}#{DONT}#{WILL}#{WONT}]
@@ -486,6 +479,15 @@ def preprocess(string)
           ''
         end
       end
+
+      # combine CR+NULL into CR
+      string = string.gsub(/#{CR}#{NULL}/no, CR) if @options["Telnetmode"]
+
+      # combine EOL into "\n"
+      string = string.gsub(/#{EOL}/no, "\n") unless @options["Binmode"]
+
+      # remove NULL
+      string = string.gsub(/#{NULL}/no, '') unless @options["Binmode"]
     end # preprocess
 
     # Read data from the host until a certain sequence is matched.