[WIP] Make webdriver client handle headers case insensitively (web-pl…

…atform-tests#25680)

Closes web-platform-tests#25039

Co-authored-by: Robert Ma <robertma@chromium.org>

Co-authored-by: Robert Ma <robertma@chromium.org>

tools/webdriver/webdriver/transport.py

@@ -2,6 +2,7 @@
 import select
 
 from six import text_type, PY3
+from six.moves.collections_abc import Mapping
 from six.moves.http_client import HTTPConnection
 from six.moves.urllib import parse as urlparse
 
@@ -10,6 +11,56 @@
 """Implements HTTP transport for the WebDriver wire protocol."""
 
 
+missing = object()
+
+
+class ResponseHeaders(Mapping):
+    """Read-only dictionary-like API for accessing response headers.
+
+    This class:
+      * Normalizes the header keys it is built with to lowercase (such that
+        iterating the items will return lowercase header keys).
+      * Has case-insensitive header lookup.
+      * Always returns all header values that have the same name, separated by
+        commas.
+
+    It does not ensure header types (e.g. binary vs string).
+    """
+    def __init__(self, items):
+        self.headers_dict = {}
+        for key, value in items:
+            key = key.lower()
+            if key not in self.headers_dict:
+                self.headers_dict[key] = []
+            self.headers_dict[key].append(value)
+
+    def __getitem__(self, key):
+        """Get all headers of a certain (case-insensitive) name. If there is
+        more than one, the values are returned comma separated"""
+        values = self.headers_dict[key.lower()]
+        if len(values) == 1:
+            return values[0]
+        else:
+            return ", ".join(values)
+
+    def get_list(self, key, default=missing):
+        """Get all the header values for a particular field name as a list"""
+        try:
+            return self.headers_dict[key.lower()]
+        except KeyError:
+            if default is not missing:
+                return default
+            else:
+                raise
+
+    def __iter__(self):
+        for item in self.headers_dict:
+            yield item
+
+    def __len__(self):
+        return len(self.headers_dict)
+
+
 class Response(object):
     """
     Describes an HTTP response received from a remote end whose
@@ -40,7 +91,7 @@ def error(self):
     def from_http(cls, http_response, decoder=json.JSONDecoder, **kwargs):
         try:
             body = json.load(http_response, cls=decoder, **kwargs)
-            headers = dict(http_response.getheaders())
+            headers = ResponseHeaders(http_response.getheaders())
         except ValueError:
             raise ValueError("Failed to decode response body as JSON:\n" +
                 http_response.read())

webdriver/tests/support/asserts.py

@@ -2,7 +2,7 @@
 import imghdr
 import struct
 
-from six import ensure_binary, text_type, PY3
+from six import ensure_binary, text_type
 
 from webdriver import Element, NoSuchAlertException, WebDriverException
 
@@ -83,15 +83,8 @@ def assert_response_headers(headers):
     """
     assert 'cache-control' in headers
     assert 'no-cache' == headers['cache-control']
-    # In Python 2, HTTPResponse normalizes header keys to lowercase, whereas
-    # Python 3 preserves the case. See
-    # https://github.com/web-platform-tests/wpt/pull/22858#issuecomment-612656097
-    if PY3:
-        assert 'Content-Type' in headers
-        assert 'application/json; charset=utf-8' == headers['Content-Type']
-    else:
-        assert 'content-type' in headers
-        assert 'application/json; charset=utf-8' == headers['content-type']
+    assert 'content-type' in headers
+    assert 'application/json; charset=utf-8' == headers['content-type']
 
 
 def assert_dialog_handled(session, expected_text, expected_retval):