From a13792aef3da3f56016e6a78a65a73f0b60aef49 Mon Sep 17 00:00:00 2001
From: payonel <payonel@hotmail.com>
Date: Fri, 15 May 2020 02:28:08 -0700
Subject: [PATCH] fixing and old unicode bug the openos io buffer in utf8 mode
 can splice inside a utf8 sequence this code prevents that by reading the next
 chunk to complete the sequence in the case the stream actually has bad utf8
 sequence, the io buffer decides to return more data than it was asked, rather
 than corrupt the stream closes #1207

---
 .../loot/openos/lib/core/full_buffer.lua      | 28 +++++++++++++++----
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/src/main/resources/assets/opencomputers/loot/openos/lib/core/full_buffer.lua b/src/main/resources/assets/opencomputers/loot/openos/lib/core/full_buffer.lua
index 98d5fae55..d32feadfd 100644
--- a/src/main/resources/assets/opencomputers/loot/openos/lib/core/full_buffer.lua
+++ b/src/main/resources/assets/opencomputers/loot/openos/lib/core/full_buffer.lua
@@ -142,20 +142,36 @@ function buffer:readBytesOrChars(readChunk, n)
     sub = unicode.sub
   end
   local data = ""
-  while len(data) ~= n do
-    if len(self.bufferRead) == 0 then
+  while true do
+    local current_data_len = len(data)
+    local needed = n - current_data_len
+    if needed < 1 then
+      break
+    end
+    -- if the buffer is empty OR there is only 1 char left, read next chunk
+    -- this is to protect that last byte from bad unicode
+    if #self.bufferRead == 0 then
       local result, reason = readChunk(self)
       if not result then
         if reason then
           return result, reason
         else -- eof
-          return #data > 0 and data or nil
+          return current_data_len > 0 and data or nil
         end
       end
     end
-    local left = n - len(data)
-    data = data .. sub(self.bufferRead, 1, left)
-    self.bufferRead = sub(self.bufferRead, left + 1)
+    local splice = self.bufferRead
+    if len(self.bufferRead) > needed then
+      splice = sub(self.bufferRead, 1, needed)
+      if len(splice) ~= needed then
+        -- this can happen if the stream does not represent valid utf8 sequences
+        -- we could search the string for the bad sequence but regardless, we're going to just return the raw data
+        splice = self.bufferRead -- yes this is more than the user is asking for, but this is better than corrupting the stream
+      end
+    -- else -- we will read more chunks
+    end
+    data = data .. splice
+    self.bufferRead = string.sub(self.bufferRead, #splice + 1)
   end
   return data
 end