stdlib: Update the stdlib resource's md5 utils

The commit does the following:

- Moves the md5 functions to their own Python module (this will allow us
to use this elsewhere).
- Add functionality to enable md5 values for directories.
- Adds Pyunit tests for the md5 functionality.

Change-Id: I224d4584ed6c35fac3a75e221b3cb48d863ffa6f
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/58849
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>

src/python/SConscript

@@ -208,6 +208,7 @@ PySource('gem5.prebuilt.demo', 'gem5/prebuilt/demo/__init__.py')
 PySource('gem5.prebuilt.demo', 'gem5/prebuilt/demo/x86_demo_board.py')
 PySource('gem5.resources', 'gem5/resources/__init__.py')
 PySource('gem5.resources', 'gem5/resources/downloader.py')
+PySource('gem5.resources', 'gem5/resources/md5_utils.py')
 PySource('gem5.resources', 'gem5/resources/resource.py')
 PySource('gem5.utils', 'gem5/utils/__init__.py')
 PySource('gem5.utils', 'gem5/utils/filelock.py')

src/python/gem5/resources/downloader.py

@@ -34,10 +34,13 @@ import hashlib
 import base64
 import time
 import random
+from pathlib import Path
 from tempfile import gettempdir
 from urllib.error import HTTPError
 from typing import List, Dict
 
+from .md5_utils import md5_file, md5_dir
+
 from ..utils.filelock import FileLock
 
 """
@@ -195,31 +198,6 @@ def _get_resources(resources_group: Dict) -> Dict[str, Dict]:
 
     return to_return
 
-
-def _get_md5(file: str) -> str:
-    """
-    Gets the md5 of a file.
-
-    :param file: The file needing an md5 value.
-
-    :returns: The md5 of the input file.
-    """
-
-    # Note: This code is slightly more complex than you might expect as
-    # `hashlib.md5(<file>)` returns malloc errors for large files (such as
-    # disk images).
-    md5_object = hashlib.md5()
-    block_size = 128 * md5_object.block_size
-    a_file = open(file, "rb")
-    chunk = a_file.read(block_size)
-
-    while chunk:
-        md5_object.update(chunk)
-        chunk = a_file.read(block_size)
-
-    return md5_object.hexdigest()
-
-
 def _download(
     url: str,
     download_to: str,
@@ -343,17 +321,20 @@ def get_resource(
 
         if os.path.exists(to_path):
 
-            if not os.path.isfile(to_path):
-                raise Exception(
-                    "There is a directory at '{}'.".format(to_path)
-                )
+            if os.path.isfile(to_path):
+                md5 = md5_file(Path(to_path))
+            else:
+                md5 = md5_dir(Path(to_path))
 
-            if _get_md5(to_path) == resource_json["md5sum"]:
+            if md5 == resource_json["md5sum"]:
                 # In this case, the file has already been download, no need to
                 # do so again.
                 return
             elif download_md5_mismatch:
-                os.remove(to_path)
+                if os.path.isfile(to_path):
+                    os.remove(to_path)
+                else:
+                    shutil.rmtree(to_path)
             else:
                 raise Exception(
                     "There already a file present at '{}' but "

src/python/gem5/resources/md5_utils.py

@@ -0,0 +1,65 @@
+# Copyright (c) 2022 The Regents of the University of California
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met: redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer;
+# redistributions in binary form must reproduce the above copyright
+# notice, this list of conditions and the following disclaimer in the
+# documentation and/or other materials provided with the distribution;
+# neither the name of the copyright holders nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+from pathlib import Path
+import hashlib
+from _hashlib import HASH as Hash
+
+def _md5_update_from_file(filename:  Path, hash: Hash) -> Hash:
+    assert filename.is_file()
+    with open(str(filename), "rb") as f:
+        for chunk in iter(lambda: f.read(4096), b""):
+            hash.update(chunk)
+    return hash
+
+def _md5_update_from_dir(directory:  Path, hash: Hash) -> Hash:
+    assert directory.is_dir()
+    for path in sorted(directory.iterdir(), key=lambda p: str(p).lower()):
+        hash.update(path.name.encode())
+        if path.is_file():
+            hash = _md5_update_from_file(path, hash)
+        elif path.is_dir():
+            hash = _md5_update_from_dir(path, hash)
+    return hash
+
+def md5_file(filename:  Path) -> str:
+    """
+    Gives the md5 hash of a file
+
+    :filename: The file in which the md5 is to be calculated.
+    """
+    return str(_md5_update_from_file(filename, hashlib.md5()).hexdigest())
+
+def md5_dir(directory: Path) -> str:
+    """
+    Gives the md5 value of a directory.
+
+    This is achieved by getting the md5 hash of all files in the directory.
+
+    Note: The path of files are also hashed so the md5 of the directory changes
+    if empty files are included or filenames are changed.
+    """
+    return str(_md5_update_from_dir(directory, hashlib.md5()).hexdigest())