Preserve empty query values in mapping matchers

Author: bensynapse

doc/howto.rst

@@ -48,6 +48,11 @@ query string as a dictionary.
 
 Behind the scenes an additional step is done by the library: it parses up the
 query_string into the dict and then compares it with the dict provided.
+Empty values are preserved. For example, ``query_string={"flag": ""}`` matches
+both ``?flag=`` and ``?flag``. Neither matches an empty dictionary.
+If a parameter appears more than once, a dictionary matches its first value,
+including an empty value. A ``werkzeug.datastructures.MultiDict`` matches all
+values, including empty ones.
 
 
 URI matching

pytest_httpserver/httpserver.py

@@ -234,12 +234,13 @@ def __init__(self, query_dict: Mapping[str, str] | MultiDict[str, str]) -> None:
             key-value mapping where both key and value should be string. If there are multiple
             values specified for the same key in the request, the first element will be used.
             If you want to match multiple values, use a MultiDict object from werkzeug, which
-            represents multiple values for one key.
+            represents multiple values for one key. Empty values are kept, including
+            parameters without an equals sign. An empty value is distinct from a missing key.
         """
         self.query_dict = query_dict
 
     def get_comparing_values(self, request_query_string: bytes) -> tuple[Mapping[str, str], Mapping[str, str]]:
-        query = MultiDict(urllib.parse.parse_qsl(request_query_string.decode("utf-8")))
+        query = MultiDict(urllib.parse.parse_qsl(request_query_string.decode("utf-8"), keep_blank_values=True))
         if isinstance(self.query_dict, MultiDict):
             return (query, self.query_dict)
         else:

releasenotes/notes/empty-query-values-4e70831a4cba318c.yaml

@@ -0,0 +1,6 @@
+fixes:
+  - |
+    Preserve empty query values when matching dictionaries and MultiDict objects.
+    Both ``flag=`` and ``flag`` match ``{"flag": ""}`` and no longer match ``{}``.
+    For repeated parameters, dictionary matching uses the first value even when it
+    is empty. MultiDict matching includes every empty value.

tests/test_querymatcher.py

@@ -1,3 +1,4 @@
+import pytest
 from werkzeug.datastructures import MultiDict
 
 from pytest_httpserver.httpserver import BooleanQueryMatcher
@@ -55,3 +56,40 @@ def test_qm_mapping_multiple_values():
     md = MultiDict([("k1", "v1"), ("k1", "v2")])
     qm = MappingQueryMatcher(md)
     assert_match(qm, b"k1=v1&k1=v2")
+
+
+@pytest.mark.parametrize("query_string", [b"flag=", b"flag", b"flag=&", b"&flag="])
+def test_qm_mapping_empty_value(query_string):
+    qm = MappingQueryMatcher({"flag": ""})
+    assert_match(qm, query_string)
+    assert_not_match(qm, b"")
+    assert_not_match(qm, b"flag=value")
+
+
+@pytest.mark.parametrize("query_string", [b"flag=", b"flag", b"flag=&flag="])
+def test_qm_mapping_empty_value_is_not_missing(query_string):
+    qm = MappingQueryMatcher({})
+    assert_not_match(qm, query_string)
+    assert_match(qm, b"")
+
+
+@pytest.mark.parametrize("query_string", [b"flag=&flag=value", b"flag&flag=value"])
+def test_qm_mapping_first_value_is_empty(query_string):
+    assert_match(MappingQueryMatcher({"flag": ""}), query_string)
+    assert_not_match(MappingQueryMatcher({"flag": "value"}), query_string)
+    assert_match(MappingQueryMatcher({"flag": "value"}), b"flag=value&flag=")
+
+
+@pytest.mark.parametrize("query_string", [b"flag=&flag=value", b"flag&flag=value"])
+def test_qm_mapping_multiple_values_include_empty(query_string):
+    qm = MappingQueryMatcher(MultiDict([("flag", ""), ("flag", "value")]))
+    assert_match(qm, query_string)
+    assert_not_match(qm, b"flag=value")
+    assert_not_match(qm, b"flag=")
+
+
+def test_qm_mapping_empty_encoded_name():
+    qm = MappingQueryMatcher({"empty name": "", "": "value"})
+    assert_match(qm, b"empty%20name=&=value")
+    assert_match(qm, b"=value&empty+name=")
+    assert_not_match(qm, b"=value")

tests/test_querystring.py

@@ -1,4 +1,6 @@
+import pytest
 import requests
+from werkzeug.datastructures import MultiDict
 
 from pytest_httpserver import HTTPServer
 
@@ -32,3 +34,23 @@ def test_querystring_dict(httpserver: HTTPServer):
     httpserver.check_assertions()
     assert response.text == "example_response"
     assert response.status_code == 200
+
+
+@pytest.mark.parametrize("query_string", [{"flag": ""}, MultiDict([("flag", ""), ("flag", "value")])])
+def test_querystring_empty_value(httpserver: HTTPServer, query_string):
+    httpserver.expect_request("/foobar", query_string=query_string).respond_with_data("example_response")
+    response = requests.get(
+        httpserver.url_for("/foobar"),
+        params=query_string.items(multi=True) if isinstance(query_string, MultiDict) else query_string,
+    )
+    httpserver.check_assertions()
+    assert response.status_code == 200
+    assert response.text == "example_response"
+
+
+def test_querystring_empty_value_does_not_match_missing(httpserver: HTTPServer):
+    httpserver.expect_request("/foobar", query_string={}).respond_with_data("example_response")
+    response = requests.get(httpserver.url_for("/foobar"), params={"flag": ""})
+    assert response.status_code == 500
+    with pytest.raises(AssertionError, match="No handler found"):
+        httpserver.check_assertions()