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Add excluded_content_types parameter to GZipMiddleware #3091

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Add excluded_content_types parameter to GZipMiddleware #3091

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45 changes: 37 additions & 8 deletions starlette/middleware/gzip.py
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Original file line number Diff line number Diff line change
Expand Up @@ -5,14 +5,28 @@
from starlette.datastructures import Headers, MutableHeaders
from starlette.types import ASGIApp, Message, Receive, Scope, Send

DEFAULT_EXCLUDED_CONTENT_TYPES = ("text/event-stream",)
DEFAULT_EXCLUDED_CONTENT_TYPES = (
"text/event-stream",
"application/zip",
"application/gzip",
"application/x-gzip",
)
Comment on lines +8 to +13
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Copilot AI Jan 10, 2026

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Adding new content types to DEFAULT_EXCLUDED_CONTENT_TYPES is a breaking change. While it's sensible to exclude already-compressed formats (application/zip, application/gzip, application/x-gzip), this changes the default behavior for existing users. Consider documenting this as a breaking change in the release notes and ensuring it's mentioned in the PR description or migration guide.

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class GZipMiddleware:
def __init__(self, app: ASGIApp, minimum_size: int = 500, compresslevel: int = 9) -> None:
def __init__(
self,
app: ASGIApp,
minimum_size: int = 500,
compresslevel: int = 9,
*,
excluded_content_types: tuple[str, ...] = DEFAULT_EXCLUDED_CONTENT_TYPES,
additional_excluded_content_types: tuple[str, ...] = (),
Comment on lines +23 to +24
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Copilot AI Jan 10, 2026

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The new excluded_content_types and additional_excluded_content_types parameters lack test coverage. Consider adding tests that verify:

  1. Custom content types can be excluded from compression using excluded_content_types
  2. Additional content types can be excluded using additional_excluded_content_types
  3. The default excluded content types (application/zip, application/gzip, application/x-gzip) are properly excluded from compression

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Comment on lines +23 to +24
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The documentation in docs/middleware.md should be updated to describe the new excluded_content_types and additional_excluded_content_types parameters. The current documentation at lines 240-244 mentions the default exclusion behavior but doesn't document that these can now be customized.

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) -> None:
self.app = app
self.minimum_size = minimum_size
self.compresslevel = compresslevel
self.excluded_content_types = excluded_content_types + additional_excluded_content_types

async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
if scope["type"] != "http": # pragma: no cover
Expand All @@ -22,19 +36,27 @@ async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
headers = Headers(scope=scope)
responder: ASGIApp
if "gzip" in headers.get("Accept-Encoding", ""):
responder = GZipResponder(self.app, self.minimum_size, compresslevel=self.compresslevel)
responder = GZipResponder(
self.app,
self.minimum_size,
excluded_content_types=self.excluded_content_types,
compresslevel=self.compresslevel,
)
else:
responder = IdentityResponder(self.app, self.minimum_size)
responder = IdentityResponder(
self.app, self.minimum_size, excluded_content_types=self.excluded_content_types
)

await responder(scope, receive, send)


class IdentityResponder:
content_encoding: str

def __init__(self, app: ASGIApp, minimum_size: int) -> None:
def __init__(self, app: ASGIApp, minimum_size: int, *, excluded_content_types: tuple[str, ...]) -> None:
self.app = app
self.minimum_size = minimum_size
self.excluded_content_types = excluded_content_types
self.send: Send = unattached_send
self.initial_message: Message = {}
self.started = False
Expand All @@ -53,7 +75,7 @@ async def send_with_compression(self, message: Message) -> None:
self.initial_message = message
headers = Headers(raw=self.initial_message["headers"])
self.content_encoding_set = "content-encoding" in headers
self.content_type_is_excluded = headers.get("content-type", "").startswith(DEFAULT_EXCLUDED_CONTENT_TYPES)
self.content_type_is_excluded = headers.get("content-type", "").startswith(self.excluded_content_types)
elif message_type == "http.response.body" and (self.content_encoding_set or self.content_type_is_excluded):
if not self.started:
self.started = True
Expand Down Expand Up @@ -119,8 +141,15 @@ def apply_compression(self, body: bytes, *, more_body: bool) -> bytes:
class GZipResponder(IdentityResponder):
content_encoding = "gzip"

def __init__(self, app: ASGIApp, minimum_size: int, compresslevel: int = 9) -> None:
super().__init__(app, minimum_size)
def __init__(
self,
app: ASGIApp,
minimum_size: int,
compresslevel: int = 9,
*,
excluded_content_types: tuple[str, ...],
) -> None:
super().__init__(app, minimum_size, excluded_content_types=excluded_content_types)

self.gzip_buffer = io.BytesIO()
self.gzip_file = gzip.GzipFile(mode="wb", fileobj=self.gzip_buffer, compresslevel=compresslevel)
Expand Down
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