Fix query string parsing regression introduced in 2.18.2 #3106

CHANGELOG.md

@@ -6,6 +6,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 ## [UNRELEASED]
 
 ## Fixed
+- [#3341](https://github.com/plotly/dash/pull/3341) Fixed query string parsing regression introduced in 2.18.2 where values containing unencoded `&` characters were being truncated. [#3106](https://github.com/plotly/dash/issues/3106)
 - [#3279](https://github.com/plotly/dash/pull/3279) Fix an issue where persisted values were incorrectly pruned when updated via callback. Now, callback returned values are correctly stored in the persistence storage. Fix [#2678](https://github.com/plotly/dash/issues/2678)
 - [#3298](https://github.com/plotly/dash/pull/3298) Fix dev_only resources filtering.
 - [#3315](https://github.com/plotly/dash/pull/3315) Fix pages module is package check.

dash/_pages.py

@@ -5,18 +5,17 @@
 import re
 import sys
 from fnmatch import fnmatch
-from pathlib import Path
 from os.path import isfile, join
-from urllib.parse import parse_qs, unquote
+from pathlib import Path
+from urllib.parse import parse_qs
 
 import flask
 
 from . import _validate
-from ._utils import AttributeDict
-from ._get_paths import get_relative_path
 from ._callback_context import context_value
 from ._get_app import get_app
-
+from ._get_paths import get_relative_path
+from ._utils import AttributeDict
 
 CONFIG = AttributeDict()
 PAGE_REGISTRY = collections.OrderedDict()
@@ -114,17 +113,14 @@ def _infer_module_name(page_path):
 
 
 def _parse_query_string(search):
-    search = unquote(search)
-    if search and len(search) > 0 and search[0] == "?":
-        search = search[1:]
-    else:
+    if not search or not search.startswith("?"):
         return {}
 
-    parsed_qs = {}
-    for (k, v) in parse_qs(search).items():
-        v = v[0] if len(v) == 1 else v
-        parsed_qs[k] = v
-    return parsed_qs
+    query_string = search[1:]
+
+    parsed_qs = parse_qs(query_string, keep_blank_values=True)
+
+    return {k: v[0] if len(v) == 1 else v for k, v in parsed_qs.items()}
 
 
 def _parse_path_variables(pathname, path_template):