check md5 before load weights. (#1663)

* check md5 before load weights.

ppdet/utils/download.py

@@ -124,8 +124,8 @@ def get_dataset_path(path, annotation, image_dir):
                     "Please apply and download the dataset from "
                     "https://www.objects365.org/download.html".format(name))
             data_dir = osp.join(DATASET_HOME, name)
-            # For voc, only check dir VOCdevkit/VOC2012, VOCdevkit/VOC2007
-            if name == 'voc' or name == 'fruit' or name == 'roadsign_voc':
+            # For VOC-style datasets, only check subdirs
+            if name in ['voc', 'fruit', 'roadsign_voc']:
                 exists = True
                 for sub_dir in dataset[1]:
                     check_dir = osp.join(data_dir, sub_dir)
@@ -203,20 +203,26 @@ def get_path(url, root_dir, md5sum=None, check_exist=True):
         if fullpath.find(k) >= 0:
             fullpath = osp.join(osp.split(fullpath)[0], v)
 
-    exist_flag = False
     if osp.exists(fullpath) and check_exist:
-        exist_flag = True
+        # If fullpath is a directory, it has been decompressed
+        # checking MD5 is impossible, so we skip checking when
+        # fullpath is a directory here
+        if osp.isdir(fullpath) or \
+                _md5check_from_req(fullpath,
+                        requests.get(url, stream=True)):
             logger.debug("Found {}".format(fullpath))
+            return fullpath, True
         else:
-        exist_flag = False
+            shutil.rmtree(fullpath)
+
     fullname = _download(url, root_dir, md5sum)
 
-        # new weights format which postfix is 'pdparams' not
-        # need to decompress
+    # new weights format whose postfix is 'pdparams',
+    # which is not need to decompress
     if osp.splitext(fullname)[-1] != '.pdparams':
         _decompress(fullname)
 
-    return fullpath, exist_flag
+    return fullpath, False
 
 
 def download_dataset(path, dataset=None):
@@ -308,11 +314,7 @@ def _download(url, path, md5sum=None):
                         f.write(chunk)
 
         # check md5 after download in Content-MD5 in req.headers
-        content_md5 = req.headers.get('content-md5')
-        if not content_md5 or _md5check(
-                tmp_fullname,
-                binascii.hexlify(base64.b64decode(content_md5.strip(
-                    '"'))).decode()):
+        if _md5check_from_req(tmp_fullname, req):
             shutil.move(tmp_fullname, fullname)
             return fullname
         else:
@@ -322,6 +324,19 @@ def _download(url, path, md5sum=None):
             continue
 
 
+def _md5check_from_req(weights_path, req):
+    # For weights in bcebos URLs, MD5 value is contained
+    # in request header as 'content_md5'
+    content_md5 = req.headers.get('content-md5')
+    if not content_md5 or _md5check(
+            weights_path,
+            binascii.hexlify(base64.b64decode(content_md5.strip('"'))).decode(
+            )):
+        return True
+    else:
+        return False
+
+
 def _md5check(fullname, md5sum=None):
     if md5sum is None:
         return True