FIX: validate BinaryConverter bit width per converted word

pyrit/converter/binary_converter.py

@@ -64,18 +64,18 @@ def _build_identifier(self) -> ComponentIdentifier:
             }
         )
 
-    def validate_input(self, prompt: str) -> None:
+    def _validate_word(self, word: str) -> None:
         """
-        Check if ``bits_per_char`` is sufficient for the characters in the prompt.
+        Check if ``bits_per_char`` is sufficient for the characters in a word being converted.
 
         Args:
-            prompt (str): The input text prompt to validate.
+            word (str): The word that is about to be converted.
 
         Raises:
-            ValueError: If ``bits_per_char`` is too small to represent any character in the prompt.
+            ValueError: If ``bits_per_char`` is too small to represent any character in the word.
         """
         bits = self.bits_per_char.value
-        max_code_point = max((ord(char) for char in prompt), default=0)
+        max_code_point = max((ord(char) for char in word), default=0)
         min_bits_required = max_code_point.bit_length()
         if bits < min_bits_required:
             raise ValueError(
@@ -92,7 +92,14 @@ async def convert_word_async(self, word: str) -> str:
 
         Returns:
             str: The converted word.
+
+        Raises:
+            ValueError: If ``bits_per_char`` is too small to represent any character in the word.
         """
+        # Validated per word rather than over the whole prompt: a word selection strategy may
+        # leave words untouched, and a character that is never encoded cannot overflow
+        # bits_per_char.
+        self._validate_word(word)
         bits = self.bits_per_char.value
         return " ".join(format(ord(char), f"0{bits}b") for char in word)
 

tests/unit/converter/test_binary_converter.py

@@ -4,6 +4,7 @@
 import pytest
 
 from pyrit.converter import BinaryConverter, ConverterResult
+from pyrit.converter.text_selection_strategy import WordIndexSelectionStrategy
 
 
 async def test_binary_converter_8_bit_ascii():
@@ -38,3 +39,23 @@ async def test_binary_converter_32_bit_emoji():
 async def test_binary_converter_invalid_bits_per_char():
     with pytest.raises(TypeError, match="bits_per_char must be an instance of BinaryConverter.BitsPerChar Enum."):
         BinaryConverter(bits_per_char=10)  # Invalid bits_per_char
+
+
+async def test_binary_converter_raises_when_selected_word_exceeds_bits():
+    converter = BinaryConverter(bits_per_char=BinaryConverter.BitsPerChar.BITS_16)
+    with pytest.raises(ValueError, match="bits_per_char=16 is too small"):
+        await converter.convert_async(prompt="hello 👋", input_type="text")
+
+
+async def test_binary_converter_ignores_unselected_word_exceeding_bits():
+    # Only "hello" is converted, so the emoji in the unselected word is passed
+    # through untouched and must not fail validation.
+    converter = BinaryConverter(
+        bits_per_char=BinaryConverter.BitsPerChar.BITS_16,
+        word_selection_strategy=WordIndexSelectionStrategy(indices=[0]),
+    )
+    result = await converter.convert_async(prompt="hello 👋", input_type="text")
+    expected_hello = " ".join(format(ord(char), "016b") for char in "hello")
+    space_binary = format(ord(" "), "016b")
+    assert result.output_text == f"{expected_hello} {space_binary} 👋"
+    assert result.output_type == "text"