From f50c5bb1b2c0ab92d1fb13a334f846acac981dd6 Mon Sep 17 00:00:00 2001
From: Apeksha_2022 <70309060+Apeksha9389@users.noreply.github.com>
Date: Sun, 18 Oct 2026 02:48:16 +0530
Subject: [PATCH] Require complete bytes in Base16 encodings

---
 src/validators/encoding.py | 4 +++-
 tests/test_encoding.py     | 6 ++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/validators/encoding.py b/src/validators/encoding.py
index c4ec2cea..7af12fcd 100644
--- a/src/validators/encoding.py
+++ b/src/validators/encoding.py
@@ -11,6 +11,8 @@
 def base16(value: str, /):
     """Return whether or not given value is a valid base16 encoding.
 
+    Each encoded byte requires two hexadecimal characters.
+
     Examples:
         >>> base16('a3f4b2')
         True
@@ -25,7 +27,7 @@ def base16(value: str, /):
         (Literal[True]): If `value` is a valid base16 encoding.
         (ValidationError): If `value` is an invalid base16 encoding.
     """
-    return re.fullmatch(r"^[0-9A-Fa-f]+$", value) if value else False
+    return re.fullmatch(r"(?:[0-9A-Fa-f]{2})+", value) if value else False
 
 
 @validator
diff --git a/tests/test_encoding.py b/tests/test_encoding.py
index 9728a8fe..c92d04e5 100644
--- a/tests/test_encoding.py
+++ b/tests/test_encoding.py
@@ -38,6 +38,12 @@ def test_returns_failed_validation_on_invalid_base16(value: str):
     assert isinstance(base16(value), ValidationError)
 
 
+@pytest.mark.parametrize("value", ["0", "a", "ABC", "012345678", "abcdef01234567890"])
+def test_base16_rejects_incomplete_bytes(value: str):
+    """Reject a dangling half-byte even when every character is hexadecimal."""
+    assert isinstance(base16(value), ValidationError)
+
+
 # ==> base32 <== #