From d58d2c3d0f8755dcd982071e3dc12e9f14db55f6 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Thu, 5 Dec 2024 16:11:44 -0600
Subject: [PATCH] Disable zero copy writes in the ``StreamWriter`` (#10125)

---
 CHANGES/10125.bugfix.rst  |  1 +
 aiohttp/http_writer.py    |  2 +-
 tests/test_http_writer.py | 27 +++++++++++++--------------
 3 files changed, 15 insertions(+), 15 deletions(-)
 create mode 100644 CHANGES/10125.bugfix.rst

diff --git a/CHANGES/10125.bugfix.rst b/CHANGES/10125.bugfix.rst
new file mode 100644
index 00000000000..4ece1e68d96
--- /dev/null
+++ b/CHANGES/10125.bugfix.rst
@@ -0,0 +1 @@
+Disabled zero copy writes in the ``StreamWriter`` -- by :user:`bdraco`.
diff --git a/aiohttp/http_writer.py b/aiohttp/http_writer.py
index c66fda3d8d0..edd19ed65da 100644
--- a/aiohttp/http_writer.py
+++ b/aiohttp/http_writer.py
@@ -90,7 +90,7 @@ def _writelines(self, chunks: Iterable[bytes]) -> None:
         transport = self._protocol.transport
         if transport is None or transport.is_closing():
             raise ClientConnectionResetError("Cannot write to closing transport")
-        transport.writelines(chunks)
+        transport.write(b"".join(chunks))
 
     async def write(
         self, chunk: bytes, *, drain: bool = True, LIMIT: int = 0x10000
diff --git a/tests/test_http_writer.py b/tests/test_http_writer.py
index 69e89bb34c2..65afc05ae10 100644
--- a/tests/test_http_writer.py
+++ b/tests/test_http_writer.py
@@ -123,16 +123,15 @@ async def test_write_large_payload_deflate_compression_data_in_eof(
     assert transport.write.called  # type: ignore[attr-defined]
     chunks = [c[1][0] for c in list(transport.write.mock_calls)]  # type: ignore[attr-defined]
     transport.write.reset_mock()  # type: ignore[attr-defined]
-    assert not transport.writelines.called  # type: ignore[attr-defined]
 
     # This payload compresses to 20447 bytes
     payload = b"".join(
         [bytes((*range(0, i), *range(i, 0, -1))) for i in range(255) for _ in range(64)]
     )
     await msg.write_eof(payload)
-    assert not transport.write.called  # type: ignore[attr-defined]
-    assert transport.writelines.called  # type: ignore[attr-defined]
-    chunks.extend(transport.writelines.mock_calls[0][1][0])  # type: ignore[attr-defined]
+    chunks.extend([c[1][0] for c in list(transport.write.mock_calls)])  # type: ignore[attr-defined]
+
+    assert all(chunks)
     content = b"".join(chunks)
     assert zlib.decompress(content) == (b"data" * 4096) + payload
 
@@ -202,7 +201,7 @@ async def test_write_payload_deflate_compression_chunked(
     await msg.write(b"data")
     await msg.write_eof()
 
-    chunks = [b"".join(c[1][0]) for c in list(transport.writelines.mock_calls)]  # type: ignore[attr-defined]
+    chunks = [c[1][0] for c in list(transport.write.mock_calls)]  # type: ignore[attr-defined]
     assert all(chunks)
     content = b"".join(chunks)
     assert content == expected
@@ -238,7 +237,7 @@ async def test_write_payload_deflate_compression_chunked_data_in_eof(
     await msg.write(b"data")
     await msg.write_eof(b"end")
 
-    chunks = [b"".join(c[1][0]) for c in list(transport.writelines.mock_calls)]  # type: ignore[attr-defined]
+    chunks = [c[1][0] for c in list(transport.write.mock_calls)]  # type: ignore[attr-defined]
     assert all(chunks)
     content = b"".join(chunks)
     assert content == expected
@@ -257,16 +256,16 @@ async def test_write_large_payload_deflate_compression_chunked_data_in_eof(
     # This payload compresses to 1111 bytes
     payload = b"".join([bytes((*range(0, i), *range(i, 0, -1))) for i in range(255)])
     await msg.write_eof(payload)
-    assert not transport.write.called  # type: ignore[attr-defined]
 
-    chunks = []
-    for write_lines_call in transport.writelines.mock_calls:  # type: ignore[attr-defined]
-        chunked_payload = list(write_lines_call[1][0])[1:]
-        chunked_payload.pop()
-        chunks.extend(chunked_payload)
+    compressed = []
+    chunks = [c[1][0] for c in list(transport.write.mock_calls)]  # type: ignore[attr-defined]
+    chunked_body = b"".join(chunks)
+    split_body = chunked_body.split(b"\r\n")
+    while split_body:
+        if split_body.pop(0):
+            compressed.append(split_body.pop(0))
 
-    assert all(chunks)
-    content = b"".join(chunks)
+    content = b"".join(compressed)
     assert zlib.decompress(content) == (b"data" * 4096) + payload