Fix corner case on empty file and add testcase

Author: lyc8503

Lib/http/server.py

@@ -783,7 +783,13 @@ def send_head(self):
                     # `end` here means suffix length
                     start = max(0, fs.st_size - end)
                     end = fs.st_size - 1
-                if start >= fs.st_size:
+                elif end is None or end >= fs.st_size:
+                    end = fs.st_size - 1
+
+                if start == 0 and end >= fs.st_size - 1:
+                    # Send entire file
+                    self._range = None
+                elif start >= fs.st_size:
                     # 416 REQUESTED_RANGE_NOT_SATISFIABLE means that
                     # none of the range values overlap the extent of
                     # the resource
@@ -792,10 +798,11 @@ def send_head(self):
                     self.send_error(HTTPStatus.REQUESTED_RANGE_NOT_SATISFIABLE,
                                     extra_headers=headers)
                     return None
-                if end is None or end >= fs.st_size:
-                    end = fs.st_size - 1
+
+            if self._range:
                 self.send_response(HTTPStatus.PARTIAL_CONTENT)
-                self.send_header("Content-Range", f"bytes {start}-{end}/{fs.st_size}")
+                self.send_header("Content-Range",
+                    f"bytes {start}-{end}/{fs.st_size}")
                 self.send_header("Content-Length", str(end - start + 1))
 
                 # Update range to be sent to be used later in copyfile

Lib/test/test_httpservers.py

@@ -588,14 +588,29 @@ def test_range_get(self):
 
         response = self.request(route, headers={'Range': 'bytes=--'})
         self.check_status_and_reason(response, HTTPStatus.OK, data=self.data)
-        
+
         response = self.request(route, headers={'Range': 'bytes='})
         self.check_status_and_reason(response, HTTPStatus.OK, data=self.data)
 
         # multipart ranges (not supported currently)
         response = self.request(route, headers={'Range': 'bytes=1-2, 4-7'})
         self.check_status_and_reason(response, HTTPStatus.OK, data=self.data)
 
+        # empty file
+        with open(os.path.join(self.tempdir_name, 'empty'), 'wb'):
+            pass
+        empty_path = self.base_url + '/empty'
+
+        response = self.request(empty_path, headers={'Range': 'bytes=0-512'})
+        self.check_status_and_reason(response, HTTPStatus.OK, data=b'')
+
+        response = self.request(empty_path, headers={'Range': 'bytes=-512'})
+        self.check_status_and_reason(response, HTTPStatus.OK, data=b'')
+
+        response = self.request(empty_path, headers={'Range': 'bytes=1-2'})
+        self.assertEqual(response.getheader('content-range'), 'bytes */0')
+        self.check_status_and_reason(response, HTTPStatus.REQUESTED_RANGE_NOT_SATISFIABLE)
+
     def test_head(self):
         response = self.request(
             self.base_url + '/test', method='HEAD')