Use '%20' for encoding spaces in query parameters.

httpx/_urls.py

@@ -616,7 +616,14 @@ def __eq__(self, other: typing.Any) -> bool:
         return sorted(self.multi_items()) == sorted(other.multi_items())
 
     def __str__(self) -> str:
-        return urlencode(self.multi_items())
+        """
+        Note that we use '%20' encoding for spaces, and treat '/' as a safe
+        character.
+
+        See https://github.com/encode/httpx/issues/2536 and
+        https://docs.python.org/3/library/urllib.parse.html#urllib.parse.urlencode
+        """
+        return urlencode(self.multi_items(), safe="/", quote_via=quote)
 
     def __repr__(self) -> str:
         class_name = self.__class__.__name__

tests/models/test_url.py

@@ -350,6 +350,22 @@ def test_url_with_empty_query():
     assert url.raw_path == b"/path?"
 
 
+def test_url_query_encoding():
+    """
+    URL query parameters should use '%20' to encoding spaces,
+    and should treat '/' as a safe character. This behaviour differs
+    across clients, but we're matching browser behaviour here.
+
+    See https://github.com/encode/httpx/issues/2536
+    and https://github.com/encode/httpx/discussions/2460
+    """
+    url = httpx.URL("https://www.example.com/?a=b c&d=e/f")
+    assert url.raw_path == b"/?a=b%20c&d=e/f"
+
+    url = httpx.URL("https://www.example.com/", params={"a": "b c", "d": "e/f"})
+    assert url.raw_path == b"/?a=b%20c&d=e/f"
+
+
 def test_url_with_url_encoded_path():
     url = httpx.URL("https://www.example.com/path%20to%20somewhere")
     assert url.path == "/path to somewhere"