[compression] Add Protocol _Decompressor (#14885)

stdlib/@tests/test_cases/check_compression.py

@@ -0,0 +1,58 @@
+from __future__ import annotations
+
+import io
+import sys
+from _typeshed import ReadableBuffer
+from bz2 import BZ2Decompressor
+from lzma import LZMADecompressor
+from typing import cast
+from typing_extensions import assert_type
+from zlib import decompressobj
+
+if sys.version_info >= (3, 14):
+    from compression._common._streams import DecompressReader, _Decompressor, _Reader
+    from compression.zstd import ZstdDecompressor
+else:
+    from _compression import DecompressReader, _Decompressor, _Reader
+
+###
+# Tests for DecompressReader/_Decompressor
+###
+
+
+class CustomDecompressor:
+    def decompress(self, data: ReadableBuffer, max_length: int = -1) -> bytes:
+        return b""
+
+    @property
+    def unused_data(self) -> bytes:
+        return b""
+
+    @property
+    def eof(self) -> bool:
+        return False
+
+    @property
+    def needs_input(self) -> bool:
+        return False
+
+
+def accept_decompressor(d: _Decompressor) -> None:
+    d.decompress(b"random bytes", 0)
+    assert_type(d.eof, bool)
+    assert_type(d.unused_data, bytes)
+
+
+fp = cast(_Reader, io.BytesIO(b"hello world"))
+DecompressReader(fp, decompressobj)
+DecompressReader(fp, BZ2Decompressor)
+DecompressReader(fp, LZMADecompressor)
+DecompressReader(fp, CustomDecompressor)
+accept_decompressor(decompressobj())
+accept_decompressor(BZ2Decompressor())
+accept_decompressor(LZMADecompressor())
+accept_decompressor(CustomDecompressor())
+
+if sys.version_info >= (3, 14):
+    DecompressReader(fp, ZstdDecompressor)
+    accept_decompressor(ZstdDecompressor())