Add retry strategy when downloading model files.

tools/converter.py

@@ -656,6 +656,28 @@ def print_configuration(configs):
     MaceLogger.summary(StringFormatter.table(header, data, title))
 
 
+def download_file(url, dst, num_retries=3):
+    from six.moves import urllib
+
+    def _progress(block_num, block_size, total_size):
+        sys.stdout.write(
+            '\r>> Downloading %s %.1f%%' % (url,
+                                            float(block_num * block_size) /
+                                            float(total_size) * 100.0))
+        sys.stdout.flush()
+
+    try:
+        urllib.request.urlretrieve(url, dst, _progress)
+        MaceLogger.info('\nDownloaded successfully.')
+    except (urllib.URLError, urllib.ContentTooShortError) as e:
+        MaceLogger.warning('Download error:', e.reason)
+        if num_retries > 0:
+            return download_file(url, dst, num_retries - 1)
+        else:
+            return False
+    return True
+
+
 def get_model_files(model_file_path,
                     model_sha256_checksum,
                     model_output_dir,
@@ -670,8 +692,9 @@ def get_model_files(model_file_path,
         if not os.path.exists(model_file) or \
                 sha256_checksum(model_file) != model_sha256_checksum:
             MaceLogger.info("Downloading model, please wait ...")
-            six.moves.urllib.request.urlretrieve(model_file_path, model_file)
-            MaceLogger.info("Model downloaded successfully.")
+            if not download_file(model_file_path, model_file):
+                MaceLogger.error(ModuleName.MODEL_CONVERTER,
+                                 "Model download failed.")
 
     if sha256_checksum(model_file) != model_sha256_checksum:
         MaceLogger.error(ModuleName.MODEL_CONVERTER,
@@ -684,8 +707,9 @@ def get_model_files(model_file_path,
         if not os.path.exists(weight_file) or \
                 sha256_checksum(weight_file) != weight_sha256_checksum:
             MaceLogger.info("Downloading model weight, please wait ...")
-            six.moves.urllib.request.urlretrieve(weight_file_path, weight_file)
-            MaceLogger.info("Model weight downloaded successfully.")
+            if not download_file(weight_file_path, weight_file):
+                MaceLogger.error(ModuleName.MODEL_CONVERTER,
+                                 "Model download failed.")
 
     if weight_file:
         if sha256_checksum(weight_file) != weight_sha256_checksum: