[stdlib] Add a new validate parameter to the b64decode() function

docs/changelog.md

@@ -36,6 +36,8 @@ what we publish.
 
 ### Standard library changes
 
+- Add a new `validate` parameter to the `b64decode()` function.
+
 - The `int` function to construct an `Int` has been removed, this was a
   temporary workaround when Mojo didn't have a way to distinguish between
   implicit and explicit constructors. You can do a search and replace for `int(`

stdlib/src/base64/base64.mojo

@@ -112,17 +112,24 @@ fn b64encode(input_bytes: Span[Byte, _]) -> String:
 
 
 @always_inline
-fn b64decode(str: StringSlice) -> String:
+fn b64decode[validate: Bool = False](str: StringSlice) raises -> String:
     """Performs base64 decoding on the input string.
 
+    Parameters:
+      validate: If true, the function will validate the input string.
+
     Args:
       str: A base64 encoded string.
 
     Returns:
       The decoded string.
     """
     var n = str.byte_length()
-    debug_assert(n % 4 == 0, "Input length must be divisible by 4")
+
+    @parameter
+    if validate:
+        if n % 4 != 0:
+            raise Error("ValueError: Input length must be divisible by 4")
 
     var p = String._buffer_type(capacity=n + 1)
 
@@ -133,10 +140,10 @@ fn b64decode(str: StringSlice) -> String:
         var c = _ascii_to_value(str[i + 2])
         var d = _ascii_to_value(str[i + 3])
 
-        debug_assert(
-            a >= 0 and b >= 0 and c >= 0 and d >= 0,
-            "Unexpected character encountered",
-        )
+        @parameter
+        if validate:
+            if a < 0 or b < 0 or c < 0 or d < 0:
+                raise Error("ValueError: Unexpected character encountered")
 
         p.append((a << 2) | (b >> 4))
         if str[i + 2] == "=":

stdlib/test/base64/test_base64.mojo

@@ -14,7 +14,7 @@
 
 from base64 import b16decode, b16encode, b64decode, b64encode
 
-from testing import assert_equal
+from testing import assert_equal, assert_raises
 
 
 def test_b64encode():
@@ -60,6 +60,14 @@ def test_b64decode():
 
     assert_equal(b64decode("QUJDREVGYWJjZGVm"), "ABCDEFabcdef")
 
+    with assert_raises(
+        contains="ValueError: Input length must be divisible by 4"
+    ):
+        _ = b64decode[validate=True]("invalid base64 string")
+
+    with assert_raises(contains="ValueError: Unexpected character encountered"):
+        _ = b64decode[validate=True]("invalid base64 string!!!")
+
 
 def test_b16encode():
     assert_equal(b16encode("a"), "61")