From a741c6db62a80b949ba44965dd3a65ff63fe8143 Mon Sep 17 00:00:00 2001
From: Utkarsh Tiwari <utkarsh7854@gmail.com>
Date: Mon, 27 Jul 2026 01:50:38 +0530
Subject: [PATCH 1/2] Remove consumed frames in place

Deleting the consumed prefix preserves the bytearray's amortized left-delete behavior instead of copying the entire remaining buffer after every frame.

Closes #474
---
 src/h2/frame_buffer.py    |  2 +-
 tests/test_basic_logic.py | 14 ++++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/h2/frame_buffer.py b/src/h2/frame_buffer.py
index c2f8a5411..e7eaaa577 100644
--- a/src/h2/frame_buffer.py
+++ b/src/h2/frame_buffer.py
@@ -155,7 +155,7 @@ def __next__(self) -> Frame:
 
         # At this point, as we know we'll use or discard the entire frame, we
         # can update the data.
-        self._data = self._data[9+length:]
+        del self._data[:9+length]
 
         # Pass the frame through the header buffer.
         new_frame = self._update_header_buffer(f)
diff --git a/tests/test_basic_logic.py b/tests/test_basic_logic.py
index 1df989e06..2bef59c45 100644
--- a/tests/test_basic_logic.py
+++ b/tests/test_basic_logic.py
@@ -23,6 +23,20 @@
 from . import helpers
 
 
+class TestFrameBuffer:
+    def test_consumed_frames_are_removed_in_place(self) -> None:
+        frame = hyperframe.frame.SettingsFrame(0).serialize()
+        buffer = h2.frame_buffer.FrameBuffer()
+        buffer.max_frame_size = 65535
+        buffer.add_data(frame * 2)
+        data = buffer._data
+
+        next(buffer)
+
+        assert buffer._data is data
+        assert buffer._data == frame
+
+
 class TestBasicClient:
     """
     Basic client-side tests.

From 3a59b4acaf8345bcf7b38c4fa6fde3d405dc6be1 Mon Sep 17 00:00:00 2001
From: Utkarsh Tiwari <utkarsh7854@gmail.com>
Date: Tue, 28 Jul 2026 15:04:09 +0530
Subject: [PATCH 2/2] Document in-place prefix deletion and the identity
 assertion

---
 src/h2/frame_buffer.py    | 7 +++++++
 tests/test_basic_logic.py | 4 ++++
 2 files changed, 11 insertions(+)

diff --git a/src/h2/frame_buffer.py b/src/h2/frame_buffer.py
index e7eaaa577..cab6f9056 100644
--- a/src/h2/frame_buffer.py
+++ b/src/h2/frame_buffer.py
@@ -155,6 +155,13 @@ def __next__(self) -> Frame:
 
         # At this point, as we know we'll use or discard the entire frame, we
         # can update the data.
+        # Deleting the consumed prefix mutates the bytearray in place instead
+        # of copying the remaining bytes into a new object, as slicing would.
+        # ``del s[i:j]`` is documented for mutable sequences in
+        # https://docs.python.org/3/library/stdtypes.html#mutable-sequence-types
+        # and CPython's bytearray tracks an internal offset (``ob_start`` in
+        # Objects/bytearrayobject.c) that makes repeated deletes from the
+        # front amortized O(1) per byte rather than O(len) per frame.
         del self._data[:9+length]
 
         # Pass the frame through the header buffer.
diff --git a/tests/test_basic_logic.py b/tests/test_basic_logic.py
index 2bef59c45..d1bc0f1eb 100644
--- a/tests/test_basic_logic.py
+++ b/tests/test_basic_logic.py
@@ -33,6 +33,10 @@ def test_consumed_frames_are_removed_in_place(self) -> None:
 
         next(buffer)
 
+        # ``is`` checks object identity (CPython compares ``id(...)`` of both
+        # operands): the buffer must still be the very same bytearray object,
+        # proving the consumed frame was deleted in place rather than the
+        # buffer being replaced by a sliced copy.
         assert buffer._data is data
         assert buffer._data == frame