From 55c5f1fc16e61f576f05d31c1f9bbd324943729c Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Sat, 15 Mar 2025 12:01:20 -1000
Subject: [PATCH 1/2] Add benchmark for JSON post requests that check the
 content type (#10553)

---
 tests/test_benchmarks_client.py | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/tests/test_benchmarks_client.py b/tests/test_benchmarks_client.py
index ac3131e9750..ae89bc1f667 100644
--- a/tests/test_benchmarks_client.py
+++ b/tests/test_benchmarks_client.py
@@ -319,3 +319,30 @@ async def run_client_benchmark() -> None:
     @benchmark
     def _run() -> None:
         loop.run_until_complete(run_client_benchmark())
+
+
+def test_one_hundred_json_post_requests(
+    loop: asyncio.AbstractEventLoop,
+    aiohttp_client: AiohttpClient,
+    benchmark: BenchmarkFixture,
+) -> None:
+    """Benchmark 100 JSON POST requests that check the content-type."""
+    message_count = 100
+
+    async def handler(request: web.Request) -> web.Response:
+        _ = request.content_type
+        _ = request.charset
+        return web.Response()
+
+    app = web.Application()
+    app.router.add_route("POST", "/", handler)
+
+    async def run_client_benchmark() -> None:
+        client = await aiohttp_client(app)
+        for _ in range(message_count):
+            await client.post("/", json={"key": "value"})
+        await client.close()
+
+    @benchmark
+    def _run() -> None:
+        loop.run_until_complete(run_client_benchmark())

From 44e669be1ab1a60c40183f92f172670d912cb834 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Sat, 15 Mar 2025 12:56:28 -1000
Subject: [PATCH 2/2] Cache parsing of the content-type (#10552)

---
 CHANGES/10552.misc.rst |  1 +
 aiohttp/helpers.py     | 24 +++++++++++++++++++-----
 2 files changed, 20 insertions(+), 5 deletions(-)
 create mode 100644 CHANGES/10552.misc.rst

diff --git a/CHANGES/10552.misc.rst b/CHANGES/10552.misc.rst
new file mode 100644
index 00000000000..6755cbf7396
--- /dev/null
+++ b/CHANGES/10552.misc.rst
@@ -0,0 +1 @@
+Improved performance of parsing content types by adding a cache in the same manner currently done with mime types -- by :user:`bdraco`.
diff --git a/aiohttp/helpers.py b/aiohttp/helpers.py
index e53647e274c..22a459586c7 100644
--- a/aiohttp/helpers.py
+++ b/aiohttp/helpers.py
@@ -24,7 +24,7 @@
 from http.cookies import SimpleCookie
 from math import ceil
 from pathlib import Path
-from types import TracebackType
+from types import MappingProxyType, TracebackType
 from typing import (
     TYPE_CHECKING,
     Any,
@@ -367,6 +367,20 @@ def parse_mimetype(mimetype: str) -> MimeType:
     )
 
 
+@functools.lru_cache(maxsize=56)
+def parse_content_type(raw: str) -> Tuple[str, MappingProxyType[str, str]]:
+    """Parse Content-Type header.
+
+    Returns a tuple of the parsed content type and a
+    MappingProxyType of parameters.
+    """
+    msg = HeaderParser().parsestr(f"Content-Type: {raw}")
+    content_type = msg.get_content_type()
+    params = msg.get_params(())
+    content_dict = dict(params[1:])  # First element is content type again
+    return content_type, MappingProxyType(content_dict)
+
+
 def guess_filename(obj: Any, default: Optional[str] = None) -> Optional[str]:
     name = getattr(obj, "name", None)
     if name and isinstance(name, str) and name[0] != "<" and name[-1] != ">":
@@ -733,10 +747,10 @@ def _parse_content_type(self, raw: Optional[str]) -> None:
             self._content_type = "application/octet-stream"
             self._content_dict = {}
         else:
-            msg = HeaderParser().parsestr("Content-Type: " + raw)
-            self._content_type = msg.get_content_type()
-            params = msg.get_params(())
-            self._content_dict = dict(params[1:])  # First element is content type again
+            content_type, content_mapping_proxy = parse_content_type(raw)
+            self._content_type = content_type
+            # _content_dict needs to be mutable so we can update it
+            self._content_dict = content_mapping_proxy.copy()
 
     @property
     def content_type(self) -> str: