BUG: Fix images issue 4 bits encoding and LUT starting with UTF16_BOM (…

…#2675)

Closes #2660.

pypdf/_writer.py

@@ -27,7 +27,6 @@
 # ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 # POSSIBILITY OF SUCH DAMAGE.
 
-import codecs
 import collections
 import decimal
 import enum
@@ -180,13 +179,7 @@ def __init__(
 
         # info object
         info = DictionaryObject()
-        info.update(
-            {
-                NameObject("/Producer"): create_string_object(
-                    codecs.BOM_UTF16_BE + "pypdf".encode("utf-16be")
-                )
-            }
-        )
+        info.update({NameObject("/Producer"): create_string_object("pypdf")})
         self._info_obj: PdfObject = self._add_object(info)
 
         # root object

pypdf/generic/_base.py

@@ -508,6 +508,28 @@ class TextStringObject(str, PdfObject):  # noqa: SLOT000
     to occur.
     """
 
+    autodetect_pdfdocencoding: bool
+    autodetect_utf16: bool
+    utf16_bom: bytes
+
+    def __new__(cls, value: Any) -> "TextStringObject":
+        if isinstance(value, bytes):
+            value = value.decode("charmap")
+        o = str.__new__(cls, value)
+        o.autodetect_utf16 = False
+        o.autodetect_pdfdocencoding = False
+        o.utf16_bom = b""
+        if value.startswith(("\xfe\xff", "\xff\xfe")):
+            o.autodetect_utf16 = True
+            o.utf16_bom = value[:2].encode("charmap")
+        else:
+            try:
+                encode_pdfdocencoding(o)
+                o.autodetect_pdfdocencoding = True
+            except UnicodeEncodeError:
+                o.autodetect_utf16 = True
+        return o
+
     def clone(
         self,
         pdf_dest: Any,
@@ -518,13 +540,11 @@ def clone(
         obj = TextStringObject(self)
         obj.autodetect_pdfdocencoding = self.autodetect_pdfdocencoding
         obj.autodetect_utf16 = self.autodetect_utf16
+        obj.utf16_bom = self.utf16_bom
         return cast(
             "TextStringObject", self._reference_clone(obj, pdf_dest, force_duplicate)
         )
 
-    autodetect_pdfdocencoding = False
-    autodetect_utf16 = False
-
     @property
     def original_bytes(self) -> bytes:
         """
@@ -542,20 +562,32 @@ def get_original_bytes(self) -> bytes:
         # would have been used to create this object, based upon the autodetect
         # method.
         if self.autodetect_utf16:
-            return codecs.BOM_UTF16_BE + self.encode("utf-16be")
+            if self.utf16_bom == codecs.BOM_UTF16_LE:
+                return codecs.BOM_UTF16_LE + self.encode("utf-16le")
+            elif self.utf16_bom == codecs.BOM_UTF16_BE:
+                return codecs.BOM_UTF16_BE + self.encode("utf-16be")
+            else:
+                return self.encode("utf-16be")
         elif self.autodetect_pdfdocencoding:
             return encode_pdfdocencoding(self)
         else:
-            raise Exception("no information about original bytes")
+            raise Exception("no information about original bytes")  # pragma: no cover
 
     def get_encoded_bytes(self) -> bytes:
         # Try to write the string out as a PDFDocEncoding encoded string.  It's
         # nicer to look at in the PDF file.  Sadly, we take a performance hit
         # here for trying...
         try:
+            if self.autodetect_utf16:
+                raise UnicodeEncodeError("", "forced", -1, -1, "")
             bytearr = encode_pdfdocencoding(self)
         except UnicodeEncodeError:
-            bytearr = codecs.BOM_UTF16_BE + self.encode("utf-16be")
+            if self.utf16_bom == codecs.BOM_UTF16_LE:
+                bytearr = codecs.BOM_UTF16_LE + self.encode("utf-16le")
+            elif self.utf16_bom == codecs.BOM_UTF16_BE:
+                bytearr = codecs.BOM_UTF16_BE + self.encode("utf-16be")
+            else:
+                bytearr = self.encode("utf-16be")
         return bytearr
 
     def write_to_stream(

pypdf/generic/_utils.py

@@ -147,6 +147,7 @@ def create_string_object(
                 if string.startswith((codecs.BOM_UTF16_BE, codecs.BOM_UTF16_LE)):
                     retval = TextStringObject(string.decode("utf-16"))
                     retval.autodetect_utf16 = True
+                    retval.utf16_bom = string[:2]
                     return retval
                 else:
                     # This is probably a big performance hit here, but we need

tests/test_generic.py

@@ -1,5 +1,6 @@
 """Test the pypdf.generic module."""
 
+import codecs
 from base64 import a85encode
 from copy import deepcopy
 from io import BytesIO
@@ -485,14 +486,13 @@ def test_rectangleobject():
 
 def test_textstringobject_exc():
     tso = TextStringObject("foo")
-    with pytest.raises(Exception) as exc:
-        tso.get_original_bytes()
-    assert exc.value.args[0] == "no information about original bytes"
+    assert tso.get_original_bytes() == b"foo"
 
 
 def test_textstringobject_autodetect_utf16():
     tso = TextStringObject("foo")
     tso.autodetect_utf16 = True
+    tso.utf16_bom = codecs.BOM_UTF16_BE
     assert tso.get_original_bytes() == b"\xfe\xff\x00f\x00o\x00o"
 
 
@@ -1107,20 +1107,37 @@ def test_indirect_object_invalid_read():
     assert exc.value.args[0] == "Error reading indirect object reference at byte 0x5"
 
 
-def test_create_string_object_utf16be_bom():
+def test_create_string_object_utf16_bom():
+    # utf16-be
     result = create_string_object(
         b"\xfe\xff\x00P\x00a\x00p\x00e\x00r\x00P\x00o\x00r\x00t\x00 \x001\x004\x00\x00"
     )
     assert result == "PaperPort 14\x00"
     assert result.autodetect_utf16 is True
+    assert result.utf16_bom == b"\xfe\xff"
+    assert (
+        result.get_encoded_bytes()
+        == b"\xfe\xff\x00P\x00a\x00p\x00e\x00r\x00P\x00o\x00r\x00t\x00 \x001\x004\x00\x00"
+    )
 
-
-def test_create_string_object_utf16le_bom():
+    # utf16-le
     result = create_string_object(
         b"\xff\xfeP\x00a\x00p\x00e\x00r\x00P\x00o\x00r\x00t\x00 \x001\x004\x00\x00\x00"
     )
     assert result == "PaperPort 14\x00"
     assert result.autodetect_utf16 is True
+    assert result.utf16_bom == b"\xff\xfe"
+    assert (
+        result.get_encoded_bytes()
+        == b"\xff\xfeP\x00a\x00p\x00e\x00r\x00P\x00o\x00r\x00t\x00 \x001\x004\x00\x00\x00"
+    )
+
+    # utf16-be without bom
+    result = TextStringObject("ÿ")
+    result.autodetect_utf16 = True
+    result.utf16_bom = b""
+    assert result.get_encoded_bytes() == b"\x00\xFF"
+    assert result.original_bytes == b"\x00\xFF"
 
 
 def test_create_string_object_force():

tests/test_images.py

@@ -358,6 +358,22 @@ def test_large_compressed_image():
     list(reader.pages[0].images)
 
 
+@pytest.mark.enable_socket()
+def test_ff_fe_starting_lut():
+    """Cf issue #2660"""
+    url = "https://github.com/py-pdf/pypdf/files/15385628/original_before_merge.pdf"
+    name = "iss2660.pdf"
+    writer = PdfWriter(BytesIO(get_data_from_url(url, name=name)))
+    b = BytesIO()
+    writer.write(b)
+    reader = PdfReader(b)
+    url = "https://github.com/py-pdf/pypdf/assets/4083478/6150700d-87fd-43a2-8695-c2c05a44838c"
+    name = "iss2660.png"
+    img = Image.open(BytesIO(get_data_from_url(url, name=name)))
+    assert image_similarity(writer.pages[1].images[0].image, img) == 1.0
+    assert image_similarity(reader.pages[1].images[0].image, img) == 1.0
+
+
 @pytest.mark.enable_socket()
 def test_inline_image_extraction():
     """Cf #2598"""