bpo-43650: Fix MemoryError on zip.read in shutil._unpack_zipfile for large files (GH-25058)

`shutil.unpack_archive()` tries to read the whole file into memory, making no use of any kind of smaller buffer. Process crashes for really large files: I.e. archive: ~1.7G, unpacked: ~10G. Before the crash it can easily take away all available RAM on smaller systems. Had to pull the code form `zipfile.Zipfile.extractall()` to fix this

Automerge-Triggered-By: GH:gpshead

1 files changed, 6 insertions, 10 deletions

diff --git a/Lib/shutil.py b/Lib/shutil.py
index 55cfe35..1982b1c 100644
--- a/Lib/shutil.py
+++ b/Lib/shutil.py
@@ -1163,20 +1163,16 @@ def _unpack_zipfile(filename, extract_dir):
             if name.startswith('/') or '..' in name:
                 continue
 
-            target = os.path.join(extract_dir, *name.split('/'))
-            if not target:
+            targetpath = os.path.join(extract_dir, *name.split('/'))
+            if not targetpath:
                 continue
 
-            _ensure_directory(target)
+            _ensure_directory(targetpath)
             if not name.endswith('/'):
                 # file
-                data = zip.read(info.filename)
-                f = open(target, 'wb')
-                try:
-                    f.write(data)
-                finally:
-                    f.close()
-                    del data
+                with zip.open(name, 'r') as source, \
+                        open(targetpath, 'wb') as target:
+                    copyfileobj(source, target)
     finally:
         zip.close()