Add TUF version number, and user agent

Author: trishankatdatadog

setup.py

@@ -75,12 +75,26 @@
 from setuptools import find_packages
 
 
+def find_version(*file_paths):
+    """
+    https://github.com/pypa/pip/blob/404838abcca467648180b358598c597b74d568c9/setup.py#L18-L28
+    """
+
+    version_file = read(*file_paths)
+    version_match = re.search(r"^__version__ = ['\"]([^'\"]*)['\"]",
+                              version_file, re.M)
+    if version_match:
+        return version_match.group(1)
+    raise RuntimeError("Unable to find version string.")
+
+
 with open('README.md') as file_object:
   long_description = file_object.read()
 
+
 setup(
   name = 'tuf',
-  version = '0.11.1',
+  version = find_version("tuf", "__init__.py"),
   description = 'A secure updater framework for Python',
   long_description = long_description,
   long_description_content_type='text/markdown',

tuf/__init__.py

@@ -0,0 +1 @@
+__version__ = "0.11.1"

tuf/download.py

@@ -232,13 +232,15 @@ def _download_file(url, required_length, STRICT_REQUIRED_LENGTH=True):
 
   try:
     # Attach some default headers to every Session.
+    requests_user_agent = _session.headers['User-Agent']
+    # Follows the RFC: https://tools.ietf.org/html/rfc7231#section-5.5.3
+    tuf_user_agent = 'tuf/' + tuf.__version__ + ' ' + requests_user_agent
     _session.headers.update({
         # Tell the server not to compress or modify anything.
         # https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept-Encoding#Directives
         'Accept-Encoding': 'identity',
         # The TUF user agent.
-        # TODO: Attach version number, which cannot be easily found right now.
-        'User-Agent': 'tuf'
+        'User-Agent': tuf_user_agent
     })
 
     # Get the requests.Response object for this URL.