Fix zstd decompression for chunked zstd response (#11623)

Author: ZhaoMJ

CHANGES/11623.bugfix

@@ -0,0 +1 @@
+Switched to `backports.zstd` for Python <3.14 and fixed zstd decompression for chunked zstd streams -- by :user:`ZhaoMJ`.

CONTRIBUTORS.txt

@@ -270,6 +270,7 @@ Mikhail Burshteyn
 Mikhail Kashkin
 Mikhail Lukyanchenko
 Mikhail Nacharov
+Mingjie Zhao
 Misha Behersky
 Mitchell Ferree
 Morgan Delahaye-Prat

aiohttp/compression_utils.py

@@ -22,18 +22,14 @@
     HAS_BROTLI = False
 
 try:
-    from compression.zstd import (  # type: ignore[import-not-found]  # noqa: I900
-        ZstdDecompressor,
-    )
+    if sys.version_info >= (3, 14):
+        from compression.zstd import ZstdDecompressor  # noqa: I900
+    else:  # TODO(PY314): Remove mentions of backports.zstd across codebase
+        from backports.zstd import ZstdDecompressor
 
     HAS_ZSTD = True
 except ImportError:
-    try:
-        from zstandard import ZstdDecompressor
-
-        HAS_ZSTD = True
-    except ImportError:
-        HAS_ZSTD = False
+    HAS_ZSTD = False
 
 
 MAX_SYNC_CHUNK_SIZE = 1024
@@ -298,12 +294,12 @@ def __init__(self) -> None:
         if not HAS_ZSTD:
             raise RuntimeError(
                 "The zstd decompression is not available. "
-                "Please install `zstandard` module"
+                "Please install `backports.zstd` module"
             )
         self._obj = ZstdDecompressor()
 
     def decompress_sync(self, data: bytes) -> bytes:
-        return self._obj.decompress(data)  # type: ignore[no-any-return]
+        return self._obj.decompress(data)
 
     def flush(self) -> bytes:
         return b""

aiohttp/http_parser.py

@@ -938,7 +938,7 @@ def __init__(self, out: StreamReader, encoding: str | None) -> None:
             if not HAS_ZSTD:
                 raise ContentEncodingError(
                     "Can not decode content-encoding: zstandard (zstd). "
-                    "Please install `zstandard`"
+                    "Please install `backports.zstd`"
                 )
             self.decompressor = ZSTDDecompressor()
         else:

docs/client_quickstart.rst

@@ -191,7 +191,7 @@ just install `Brotli <https://pypi.org/project/Brotli/>`_
 or `brotlicffi <https://pypi.org/project/brotlicffi/>`_.
 
 You can enable ``zstd`` transfer-encodings support,
-install `zstandard <https://pypi.org/project/zstandard/>`_.
+install `backports.zstd <https://pypi.org/project/backports.zstd/>`_.
 If you are using Python >= 3.14, no dependency should be required.
 
 JSON Request

requirements/base-ft.txt

@@ -44,5 +44,5 @@ typing-extensions==4.15.0
     #   multidict
 yarl==1.21.0
     # via -r requirements/runtime-deps.in
-zstandard==0.25.0 ; platform_python_implementation == "CPython" and python_version < "3.14"
+backports.zstd==0.5.0 ; platform_python_implementation == "CPython" and python_version < "3.14"
     # via -r requirements/runtime-deps.in

requirements/base.txt

@@ -46,5 +46,5 @@ uvloop==0.21.0 ; platform_system != "Windows" and implementation_name == "cpytho
     # via -r requirements/base.in
 yarl==1.21.0
     # via -r requirements/runtime-deps.in
-zstandard==0.25.0 ; platform_python_implementation == "CPython" and python_version < "3.14"
+backports.zstd==0.5.0 ; platform_python_implementation == "CPython" and python_version < "3.14"
     # via -r requirements/runtime-deps.in

requirements/constraints.txt

@@ -299,7 +299,7 @@ zlib-ng==1.0.0
     # via
     #   -r requirements/lint.in
     #   -r requirements/test-common.in
-zstandard==0.25.0 ; implementation_name == "cpython"
+backports.zstd==0.5.0 ; implementation_name == "cpython"
     # via
     #   -r requirements/lint.in
     #   -r requirements/runtime-deps.in

requirements/dev.txt

@@ -290,7 +290,7 @@ zlib-ng==1.0.0
     # via
     #   -r requirements/lint.in
     #   -r requirements/test-common.in
-zstandard==0.25.0 ; platform_python_implementation == "CPython" and python_version < "3.14"
+backports.zstd==0.5.0 ; platform_python_implementation == "CPython" and python_version < "3.14"
     # via
     #   -r requirements/lint.in
     #   -r requirements/runtime-deps.in

requirements/lint.in

@@ -1,4 +1,5 @@
 aiodns
+backports.zstd; implementation_name == "cpython"
 blockbuster
 freezegun
 isal
@@ -14,4 +15,3 @@ trustme
 uvloop; platform_system != "Windows"
 valkey
 zlib_ng
-zstandard; implementation_name == "cpython"