Merge pull request #276 from vladimir-v-diaz/supported-uri-schemes

Add Configuration Option for Supported URI Schemes

Author: vladimir-v-diaz

tests/test_download.py

@@ -160,11 +160,12 @@ def test_download_url_to_tempfileobj_and_performance(self):
   def test_download_url_to_tempfileobj_and_urls(self):
 
     download_file = download.safe_download
+    unsafe_download_file = download.unsafe_download
 
     self.assertRaises(tuf.FormatError,
                       download_file, None, self.target_data_length)
 
-    self.assertRaises(ValueError,
+    self.assertRaises(tuf.FormatError,
                       download_file,
                       self.random_string(), self.target_data_length)
 
@@ -177,8 +178,15 @@ def test_download_url_to_tempfileobj_and_urls(self):
                       download_file,
                       'http://localhost:' + str(self.PORT+1) + '/' + self.random_string(), 
                       self.target_data_length)
- 
 
+    # Specify an unsupported URI scheme.
+    url_with_unsupported_uri = self.url.replace('http', 'file')
+    self.assertRaises(tuf.FormatError, download_file, url_with_unsupported_uri,
+                      self.target_data_length)
+    self.assertRaises(tuf.FormatError, unsafe_download_file,
+                      url_with_unsupported_uri, self.target_data_length)
+
+ 
 
   def test__get_opener(self):
     # Test normal case.

tuf/conf.py

@@ -101,3 +101,10 @@
 # to generate the digests listed in metadata and prepended to the filenames of
 # consistent snapshots.
 REPOSITORY_HASH_ALGORITHMS = ['sha256']
+
+# Software updaters that integrate the framework are required to specify
+# the URL prefix for the mirrors that clients can contact to download updates.
+# The following URI schemes are those that download.py support.  By default,
+# the ['http', 'https'] URI schemes are supported, but may be modified by
+# integrators to schemes that they wish to support for their integration.
+SUPPORTED_URI_SCHEMES = ['http', 'https']

tuf/download.py

@@ -70,7 +70,8 @@ def safe_download(url, required_length):
   
   <Arguments>
     url:
-      A URL string that represents the location of the file. 
+      A URL string that represents the location of the file.  The URI scheme
+      component must be one of 'tuf.conf.SUPPORTED_URI_SCHEMES'.
   
     required_length:
       An integer value representing the length of the file.  This is an exact
@@ -92,6 +93,25 @@ def safe_download(url, required_length):
     A 'tuf.util.TempFile' file-like object that points to the contents of 'url'.
   """
 
+  # Do all of the arguments have the appropriate format?
+  # Raise 'tuf.FormatError' if there is a mismatch.
+  tuf.formats.URL_SCHEMA.check_match(url)
+  tuf.formats.LENGTH_SCHEMA.check_match(required_length)
+
+  # Ensure 'url' specifies one of the URI schemes in
+  # 'tuf.conf.SUPPORTED_URI_SCHEMES'.  Be default, ['http', 'https'] is
+  # supported.  If the URI scheme of 'url' is empty or "file", files on the
+  # local system can be accessed.  Unexpected files may be accessed by
+  # compromised metadata (unlikely to happen if targets.json metadata is signed
+  # with offline keys).  
+  parsed_url = six.moves.urllib.parse.urlparse(url)
+
+  if parsed_url.scheme not in tuf.conf.SUPPORTED_URI_SCHEMES:
+    message = \
+      repr(url) + ' specifies an unsupported URI scheme.  Supported ' + \
+      ' URI Schemes: ' + repr(tuf.conf.SUPPORTED_URI_SCHEMES)
+    raise tuf.FormatError(message)
+  
   return _download_file(url, required_length, STRICT_REQUIRED_LENGTH=True)
 
 
@@ -114,7 +134,8 @@ def unsafe_download(url, required_length):
   
   <Arguments>
     url:
-      A URL string that represents the location of the file. 
+      A URL string that represents the location of the file.  The URI scheme
+      component must be one of 'tuf.conf.SUPPORTED_URI_SCHEMES'.
   
     required_length:
       An integer value representing the length of the file.  This is an upper
@@ -136,6 +157,25 @@ def unsafe_download(url, required_length):
     A 'tuf.util.TempFile' file-like object that points to the contents of 'url'.
   """
 
+  # Do all of the arguments have the appropriate format?
+  # Raise 'tuf.FormatError' if there is a mismatch.
+  tuf.formats.URL_SCHEMA.check_match(url)
+  tuf.formats.LENGTH_SCHEMA.check_match(required_length)
+  
+  # Ensure 'url' specifies one of the URI schemes in
+  # 'tuf.conf.SUPPORTED_URI_SCHEMES'.  Be default, ['http', 'https'] is
+  # supported.  If the URI scheme of 'url' is empty or "file", files on the
+  # local system can be accessed.  Unexpected files may be accessed by
+  # compromised metadata (unlikely to happen if targets.json metadata is signed
+  # with offline keys).  
+  parsed_url = six.moves.urllib.parse.urlparse(url)
+
+  if parsed_url.scheme not in tuf.conf.SUPPORTED_URI_SCHEMES:
+    message = \
+      repr(url) + ' specifies an unsupported URI scheme.  Supported ' + \
+      ' URI Schemes: ' + repr(tuf.conf.SUPPORTED_URI_SCHEMES) 
+    raise tuf.FormatError(message)
+  
   return _download_file(url, required_length, STRICT_REQUIRED_LENGTH=False)