From 678a3d34bf04992662caa765340ed22a353eebd7 Mon Sep 17 00:00:00 2001
From: Tunglies <tunglies@outlook.com>
Date: Thu, 14 Mar 2024 12:42:22 +0800
Subject: [PATCH] Fix httpx is not encoding with symbol '%s' (#3140)

Add parsing symbol '%s' test
---
 httpx/_urlparse.py       | 22 ++++++++++++++++------
 tests/models/test_url.py |  2 ++
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/httpx/_urlparse.py b/httpx/_urlparse.py
index 232269ee4d..e3e012f8c4 100644
--- a/httpx/_urlparse.py
+++ b/httpx/_urlparse.py
@@ -424,13 +424,23 @@ def is_safe(string: str, safe: str = "/") -> bool:
     """
     Determine if a given string is already quote-safe.
     """
-    NON_ESCAPED_CHARS = UNRESERVED_CHARACTERS + safe + "%"
-
-    # All characters must already be non-escaping or '%'
-    for char in string:
-        if char not in NON_ESCAPED_CHARS:
+    NON_ESCAPED_CHARS = UNRESERVED_CHARACTERS + safe
+    i = 0
+    while i < len(string):
+        char = string[i]
+        if char in NON_ESCAPED_CHARS:
+            i += 1
+            continue
+        # Check if the character is a start of a valid percent-encoded sequence
+        elif (
+            char == "%"
+            and i + 2 < len(string)
+            and string[i + 1 : i + 3].isalnum()
+            and len(string[i + 1 : i + 3]) == 2
+        ):
+            i += 3
+        else:
             return False
-
     return True
 
 
diff --git a/tests/models/test_url.py b/tests/models/test_url.py
index 79e1605a5a..a81dbc6248 100644
--- a/tests/models/test_url.py
+++ b/tests/models/test_url.py
@@ -284,6 +284,8 @@ def test_url_leading_dot_prefix_on_relative_url():
 def test_param_requires_encoding():
     url = httpx.URL("http://webservice", params={"u": "with spaces"})
     assert str(url) == "http://webservice?u=with%20spaces"
+    url = httpx.URL("http://webservice", params={"u": "%"})
+    assert str(url) == "http://webservice?u=%25"
 
 
 def test_param_does_not_require_encoding():