Add type annotations

Add missing type annotations in download.py, fetcher.py
and requests_fetcher.py
Update docstrings to match the new style.

Signed-off-by: Teodora Sechkova <tsechkova@vmware.com>

Author: sechkova

tuf/ngclient/_internal/download.py

@@ -1,30 +1,13 @@
-#!/usr/bin/env python
-
 # Copyright 2012 - 2017, New York University and the TUF contributors
 # SPDX-License-Identifier: MIT OR Apache-2.0
 
+"""Provides a class handling the download of URL contents to a file"
 """
-<Program Name>
-  download.py
-
-<Started>
-  February 21, 2012.  Based on previous version by Geremy Condra.
-
-<Author>
-  Konstantin Andrianov
-  Vladimir Diaz <vladimir.v.diaz@gmail.com>
 
-<Copyright>
-  See LICENSE-MIT OR LICENSE for licensing information.
-
-<Purpose>
-  Download metadata and target files and check their validity.  The hash and
-  length of a downloaded file has to match the hash and length supplied by the
-  metadata of that file.
-"""
 import logging
 import tempfile
 from contextlib import contextmanager
+from typing import IO, Iterator
 from urllib import parse
 
 from tuf import exceptions
@@ -41,14 +24,14 @@ class FileDownloader:
             the network IO library.
     """
 
-    def __init__(self, fetcher):
+    def __init__(self, fetcher: "FetcherInterface"):
         if fetcher is None:
             fetcher = RequestsFetcher()
 
         self._fetcher = fetcher
 
     @contextmanager
-    def download_file(self, url, required_length):
+    def download_file(self, url: str, required_length: int) -> Iterator[IO]:
         """Opens a connection to 'url' and downloads the content
         up to 'required_length'.
 
@@ -74,8 +57,7 @@ def download_file(self, url, required_length):
         logger.debug("Downloading: %s", url)
 
         number_of_bytes_received = 0
-        # This is the temporary file that we will return to contain the
-        # contents of the downloaded file.
+
         with tempfile.TemporaryFile() as temp_file:
             chunks = self._fetcher.fetch(url, required_length)
             for chunk in chunks:
@@ -88,7 +70,7 @@ def download_file(self, url, required_length):
             temp_file.seek(0)
             yield temp_file
 
-    def download_bytes(self, url, required_length):
+    def download_bytes(self, url: str, required_length: int) -> bytes:
         """Download bytes from given url
 
         Returns the downloaded bytes, otherwise like download_file()

tuf/ngclient/_internal/requests_fetcher.py

@@ -7,6 +7,7 @@
 
 import logging
 import time
+from typing import Iterator
 from urllib import parse
 
 # Imports
@@ -47,7 +48,7 @@ def __init__(self):
         # Some cookies may not be HTTP-safe.
         self._sessions = {}
 
-    def fetch(self, url, required_length):
+    def fetch(self, url: str, required_length: int) -> Iterator[bytes]:
         """Fetches the contents of HTTP/HTTPS url from a remote server.
 
         Ensures the length of the downloaded data is up to 'required_length'.
@@ -89,7 +90,9 @@ def fetch(self, url, required_length):
         return self._chunks(response, required_length)
 
     @staticmethod
-    def _chunks(response, required_length):
+    def _chunks(
+        response: "requests.Response", required_length: int
+    ) -> Iterator[bytes]:
         """A generator function to be returned by fetch. This way the
         caller of fetch can differentiate between connection and actual data
         download."""

tuf/ngclient/fetcher.py

@@ -6,6 +6,7 @@
 
 # Imports
 import abc
+from typing import Iterator
 
 
 # Classes
@@ -20,7 +21,7 @@ class FetcherInterface:
     __metaclass__ = abc.ABCMeta
 
     @abc.abstractmethod
-    def fetch(self, url, required_length):
+    def fetch(self, url: str, required_length: int) -> Iterator[bytes]:
         """Fetches the contents of HTTP/HTTPS url from a remote server.
 
         Ensures the length of the downloaded data is up to 'required_length'.