fix re-download not trigger when weights update (#2617)

ppdet/utils/download.py

@@ -23,6 +23,8 @@ import shutil
 import requests
 import tqdm
 import hashlib
+import base64
+import binascii
 import tarfile
 import zipfile
 
@@ -257,20 +259,21 @@ 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
-        logger.debug("Found {}".format(fullpath))
-    else:
-        exist_flag = False
-        fullname = _download(url, root_dir, md5sum)
+        if _check_exist_file_md5(fullpath, md5sum, url):
+            logger.debug("Found {}".format(fullpath))
+            return fullpath, True
+        else:
+            os.remove(fullpath)
 
-        # new weights format which postfix is 'pdparams' not
-        # need to decompress
-        if osp.splitext(fullname)[-1] not in ['.pdparams', '.yml']:
-            _decompress(fullname)
+    fullname = _download(url, root_dir, md5sum)
 
-    return fullpath, exist_flag
+    # new weights format which postfix is 'pdparams' not
+    # need to decompress
+    if osp.splitext(fullname)[-1] not in ['.pdparams', '.yml']:
+        _decompress(fullname)
+
+    return fullpath, False
 
 
 def download_dataset(path, dataset=None):
@@ -324,7 +327,8 @@ def _download(url, path, md5sum=None):
     fullname = osp.join(path, fname)
     retry_cnt = 0
 
-    while not (osp.exists(fullname) and _md5check(fullname, md5sum)):
+    while not (osp.exists(fullname) and _check_exist_file_md5(fullname, md5sum,
+                                                              url)):
         if retry_cnt < DOWNLOAD_RETRY_LIMIT:
             retry_cnt += 1
         else:
@@ -355,8 +359,30 @@ def _download(url, path, md5sum=None):
                     if chunk:
                         f.write(chunk)
         shutil.move(tmp_fullname, fullname)
-
-    return fullname
+        return fullname
+
+
+def _check_exist_file_md5(filename, md5sum, url):
+    # if md5sum is None, and file to check is weights file, 
+    # read md5um from url and check, else check md5sum directly
+    return _md5check_from_url(filename, url) if md5sum is None \
+            and filename.endswith('pdparams') \
+            else _md5check(filename, md5sum)
+
+
+def _md5check_from_url(filename, url):
+    # For weights in bcebos URLs, MD5 value is contained
+    # in request header as 'content_md5'
+    req = requests.get(url, stream=True)
+    content_md5 = req.headers.get('content-md5')
+    req.close()
+    if not content_md5 or _md5check(
+            filename,
+            binascii.hexlify(base64.b64decode(content_md5.strip('"'))).decode(
+            )):
+        return True
+    else:
+        return False
 
 
 def _md5check(fullname, md5sum=None):