bpo-38216, bpo-36274: Allow subclasses to separately override validation and encoding behavior (GH-16448)

* bpo-38216: Allow bypassing input validation

* bpo-36274: Also allow the URL encoding to be overridden.

* bpo-38216, bpo-36274: Add tests demonstrating a hook for overriding validation, test demonstrating override encoding, and a test to capture expectation of the interface for the URL.

* Call with skip_host to avoid tripping on the host checking in the URL.

* Remove obsolete comment.

* Make _prepare_path_encoding its own attr.

This makes overriding just that simpler.

Also, don't use the := operator to make backporting easier.

* Add a news entry.

* _prepare_path_encoding -> _encode_prepared_path()

* Once again separate the path validation and request encoding, drastically simplifying the behavior. Drop the guarantee that all processing happens in _prepare_path.

Lib/test/test_httplib.py

@@ -1155,6 +1155,34 @@ class BasicTest(TestCase):
         thread.join()
         self.assertEqual(result, b"proxied data\n")
 
+    def test_putrequest_override_validation(self):
+        """
+        It should be possible to override the default validation
+        behavior in putrequest (bpo-38216).
+        """
+        class UnsafeHTTPConnection(client.HTTPConnection):
+            def _validate_path(self, url):
+                pass
+
+        conn = UnsafeHTTPConnection('example.com')
+        conn.sock = FakeSocket('')
+        conn.putrequest('GET', '/\x00')
+
+    def test_putrequest_override_encoding(self):
+        """
+        It should be possible to override the default encoding
+        to transmit bytes in another encoding even if invalid
+        (bpo-36274).
+        """
+        class UnsafeHTTPConnection(client.HTTPConnection):
+            def _encode_request(self, str_url):
+                return str_url.encode('utf-8')
+
+        conn = UnsafeHTTPConnection('example.com')
+        conn.sock = FakeSocket('')
+        conn.putrequest('GET', '/☃')
+
+
 class ExtendedReadTest(TestCase):
     """
     Test peek(), read1(), readline()
@@ -1279,6 +1307,7 @@ class ExtendedReadTest(TestCase):
         p = self.resp.peek(0)
         self.assertLessEqual(0, len(p))
 
+
 class ExtendedReadTestChunked(ExtendedReadTest):
     """
     Test peek(), read1(), readline() in chunked mode