pythongh-61206: Support zstandard compression in the zipimport module (pythonGH-138254)

* pythongh-61206: support zstd in zipimport

* NEWS entry

* versionchanged doc

Author: gpshead

Doc/library/zipimport.rst

@@ -30,6 +30,9 @@ Any files may be present in the ZIP archive, but importers are only invoked for
 corresponding :file:`.pyc` file, meaning that if a ZIP archive
 doesn't contain :file:`.pyc` files, importing may be rather slow.
 
+.. versionchanged:: next
+   Zstandard (*zstd*) compressed zip file entries are supported.
+
 .. versionchanged:: 3.13
    ZIP64 is supported
 

Lib/test/test_zipimport.py

@@ -14,7 +14,7 @@
 from test.support import import_helper
 from test.support import os_helper
 
-from zipfile import ZipFile, ZipInfo, ZIP_STORED, ZIP_DEFLATED
+from zipfile import ZipFile, ZipInfo, ZIP_STORED, ZIP_DEFLATED, ZIP_ZSTANDARD
 
 import zipimport
 import linecache
@@ -193,19 +193,38 @@ def testAFakeZlib(self):
         # occur in that case (builtin modules are always found first),
         # so we'll simply skip it then. Bug #765456.
         #
-        if "zlib" in sys.builtin_module_names:
-            self.skipTest('zlib is a builtin module')
-        if "zlib" in sys.modules:
-            del sys.modules["zlib"]
-        files = {"zlib.py": test_src}
+        if self.compression == ZIP_DEFLATED:
+            mod_name = "zlib"
+            if zipimport._zlib_decompress:  # validate attr name
+                # reset the cached import to avoid test order dependencies
+                zipimport._zlib_decompress = None  # reset cache
+        elif self.compression == ZIP_ZSTANDARD:
+            mod_name = "_zstd"
+            if zipimport._zstd_decompressor_class:  # validate attr name
+                # reset the cached import to avoid test order dependencies
+                zipimport._zstd_decompressor_class = None
+        else:
+            mod_name = "zlib"  # the ZIP_STORED case below
+
+        if mod_name in sys.builtin_module_names:
+            self.skipTest(f"{mod_name} is a builtin module")
+        if mod_name in sys.modules:
+            del sys.modules[mod_name]
+        files = {f"{mod_name}.py": test_src}
         try:
-            self.doTest(".py", files, "zlib")
+            self.doTest(".py", files, mod_name)
         except ImportError:
-            if self.compression != ZIP_DEFLATED:
-                self.fail("expected test to not raise ImportError")
-        else:
             if self.compression != ZIP_STORED:
-                self.fail("expected test to raise ImportError")
+                # Expected - fake compression module can't decompress
+                pass
+            else:
+                self.fail("expected test to not raise ImportError for uncompressed")
+        else:
+            if self.compression == ZIP_STORED:
+                # Expected - no compression needed, so fake module works
+                pass
+            else:
+                self.fail("expected test to raise ImportError for compressed zip with fake compression module")
 
     def testPy(self):
         files = {TESTMOD + ".py": test_src}
@@ -1000,10 +1019,15 @@ def assertDataEntry(name):
 
 
 @support.requires_zlib()
-class CompressedZipImportTestCase(UncompressedZipImportTestCase):
+class DeflateCompressedZipImportTestCase(UncompressedZipImportTestCase):
     compression = ZIP_DEFLATED
 
 
+@support.requires_zstd()
+class ZStdCompressedZipImportTestCase(UncompressedZipImportTestCase):
+    compression = ZIP_ZSTANDARD
+
+
 class BadFileZipImportTestCase(unittest.TestCase):
     def assertZipFailure(self, filename):
         self.assertRaises(zipimport.ZipImportError,

Lib/zipimport.py

@@ -557,11 +557,16 @@ def _read_directory(archive):
 )
 
 _importing_zlib = False
+_zlib_decompress = None
 
 # Return the zlib.decompress function object, or NULL if zlib couldn't
 # be imported. The function is cached when found, so subsequent calls
 # don't import zlib again.
-def _get_decompress_func():
+def _get_zlib_decompress_func():
+    global _zlib_decompress
+    if _zlib_decompress:
+        return _zlib_decompress
+
     global _importing_zlib
     if _importing_zlib:
         # Someone has a zlib.py[co] in their Zip file
@@ -571,15 +576,62 @@ def _get_decompress_func():
 
     _importing_zlib = True
     try:
-        from zlib import decompress
+        from zlib import decompress as _zlib_decompress
     except Exception:
         _bootstrap._verbose_message('zipimport: zlib UNAVAILABLE')
         raise ZipImportError("can't decompress data; zlib not available")
     finally:
         _importing_zlib = False
 
     _bootstrap._verbose_message('zipimport: zlib available')
-    return decompress
+    return _zlib_decompress
+
+
+_importing_zstd = False
+_zstd_decompressor_class = None
+
+# Return the _zstd.ZstdDecompressor function object, or NULL if _zstd couldn't
+# be imported. The result is cached when found.
+def _get_zstd_decompressor_class():
+    global _zstd_decompressor_class
+    if _zstd_decompressor_class:
+        return _zstd_decompressor_class
+
+    global _importing_zstd
+    if _importing_zstd:
+        # Someone has a _zstd.py[co] in their Zip file
+        # let's avoid a stack overflow.
+        _bootstrap._verbose_message("zipimport: zstd UNAVAILABLE")
+        raise ZipImportError("can't decompress data; zstd not available")
+
+    _importing_zstd = True
+    try:
+        from _zstd import ZstdDecompressor as _zstd_decompressor_class
+    except Exception:
+        _bootstrap._verbose_message("zipimport: zstd UNAVAILABLE")
+        raise ZipImportError("can't decompress data; zstd not available")
+    finally:
+        _importing_zstd = False
+
+    _bootstrap._verbose_message("zipimport: zstd available")
+    return _zstd_decompressor_class
+
+
+def _zstd_decompress(data):
+    # A simple version of compression.zstd.decompress() as we cannot import
+    # that here as the stdlib itself could be being zipimported.
+    results = []
+    while True:
+        decomp = _get_zstd_decompressor_class()()
+        results.append(decomp.decompress(data))
+        if not decomp.eof:
+            raise ZipImportError("zipimport: zstd compressed data ended before "
+                                 "the end-of-stream marker")
+        data = decomp.unused_data
+        if not data:
+            break
+    return b"".join(results)
+
 
 # Given a path to a Zip file and a toc_entry, return the (uncompressed) data.
 def _get_data(archive, toc_entry):
@@ -613,16 +665,23 @@ def _get_data(archive, toc_entry):
         if len(raw_data) != data_size:
             raise OSError("zipimport: can't read data")
 
-    if compress == 0:
-        # data is not compressed
-        return raw_data
-
-    # Decompress with zlib
-    try:
-        decompress = _get_decompress_func()
-    except Exception:
-        raise ZipImportError("can't decompress data; zlib not available")
-    return decompress(raw_data, -15)
+    match compress:
+        case 0:  # stored
+            return raw_data
+        case 8:  # deflate aka zlib
+            try:
+                decompress = _get_zlib_decompress_func()
+            except Exception:
+                raise ZipImportError("can't decompress data; zlib not available")
+            return decompress(raw_data, -15)
+        case 93:  # zstd
+            try:
+                return _zstd_decompress(raw_data)
+            except Exception:
+                raise ZipImportError("could not decompress zstd data")
+        # bz2 and lzma could be added, but are largely obsolete.
+        case _:
+            raise ZipImportError(f"zipimport: unsupported compression {compress}")
 
 
 # Lenient date/time comparison function. The precision of the mtime

Misc/NEWS.d/next/Core_and_Builtins/2025-08-30-00-55-35.gh-issue-61206.HeFLvl.rst

@@ -0,0 +1 @@
+:mod:`zipimport` now supports zstandard compressed zip file entries.