From 2688ba0a1753ef7b7e8869e349018d5b120bef35 Mon Sep 17 00:00:00 2001
From: Sagar <sagarchaudhary.1march@gmail.com>
Date: Sat, 10 Oct 2026 22:56:01 +0530
Subject: [PATCH] Fix LineBuffer payload byte accounting

---
 spectator/writer/line_buffer.py  |  7 +++++--
 tests/writer/test_line_buffer.py | 28 +++++++++++++++++++++++++++-
 2 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/spectator/writer/line_buffer.py b/spectator/writer/line_buffer.py
index 35d1599..24cf339 100644
--- a/spectator/writer/line_buffer.py
+++ b/spectator/writer/line_buffer.py
@@ -2,7 +2,7 @@
 
 
 class LineBuffer:
-    """Line buffer for Writers."""
+    """Line buffer for Writers, sized in UTF-8 bytes including newline separators."""
 
     def __init__(self, max_size: int) -> None:
         self._size: int = 0
@@ -14,8 +14,11 @@ def __len__(self) -> int:
 
     def append(self, line: str) -> bool:
         """Return value indicates whether the buffer should be flushed."""
+        line_size = len(line.encode("utf-8"))
+        if self._lines:
+            self._size += 1  # Newline inserted between lines by flush().
         self._lines.append(line)
-        self._size += len(line)
+        self._size += line_size
         return self._size >= self._max_size
 
     def flush(self) -> str:
diff --git a/tests/writer/test_line_buffer.py b/tests/writer/test_line_buffer.py
index 98373c1..32be25d 100644
--- a/tests/writer/test_line_buffer.py
+++ b/tests/writer/test_line_buffer.py
@@ -14,7 +14,7 @@ def test_all_methods(self):
         self.assertFalse(should_flush)
 
         should_flush = buffer.append("e")
-        self.assertEqual(5, len(buffer))
+        self.assertEqual(6, len(buffer))
         self.assertTrue(should_flush)
 
         self.assertEqual("abcd\ne", buffer.flush())
@@ -26,3 +26,29 @@ def test_all_methods(self):
 
         self.assertEqual("abcdefghij", buffer.flush())
         self.assertEqual(0, len(buffer))
+
+    def test_flush_threshold_includes_newline_separators(self):
+        buffer = LineBuffer(7)
+        self.assertFalse(buffer.append("abc"))
+        self.assertTrue(buffer.append("def"))
+        self.assertEqual(7, len(buffer))
+        self.assertEqual("abc\ndef", buffer.flush())
+
+    def test_size_matches_utf8_payload(self):
+        buffer = LineBuffer(6)
+        self.assertFalse(buffer.append("é"))
+        self.assertEqual(2, len(buffer))
+        self.assertTrue(buffer.append("€"))
+        self.assertEqual(6, len(buffer))
+        payload = buffer.flush()
+        self.assertEqual(6, len(payload.encode("utf-8")))
+        self.assertEqual(0, len(buffer))
+        self.assertFalse(buffer.append("abc"))
+        self.assertEqual(3, len(buffer))
+
+    def test_empty_lines_include_separators(self):
+        buffer = LineBuffer(1)
+        self.assertFalse(buffer.append(""))
+        self.assertTrue(buffer.append(""))
+        self.assertEqual(1, len(buffer))
+        self.assertEqual("\n", buffer.flush())