Added frombytes() to allow for unlimited parsing

Tests/test_file_gimppalette.py

@@ -16,11 +16,11 @@ def test_sanity() -> None:
             GimpPaletteFile(fp)
 
     with open("Tests/images/bad_palette_file.gpl", "rb") as fp:
-        with pytest.raises(SyntaxError):
+        with pytest.raises(SyntaxError, match="bad palette file"):
             GimpPaletteFile(fp)
 
     with open("Tests/images/bad_palette_entry.gpl", "rb") as fp:
-        with pytest.raises(ValueError):
+        with pytest.raises(ValueError, match="bad palette entry"):
             GimpPaletteFile(fp)
 
 
@@ -40,12 +40,26 @@ def test_get_palette(filename: str, size: int) -> None:
     assert len(palette) / 3 == size
 
 
-def test_palette_limit() -> None:
+def test_frombytes() -> None:
     with open("Tests/images/full_gimp_palette.gpl", "rb") as fp:
-        data = fp.read()
+        full_data = fp.read()
 
     # Test that __init__ only reads 256 entries
-    data = data.replace(b"#\n", b"") + b"  0   0   0     Index 256"
+    data = full_data.replace(b"#\n", b"") + b"  0   0   0     Index 256"
     b = BytesIO(data)
     palette = GimpPaletteFile(b)
     assert len(palette.palette) / 3 == 256
+
+    # Test that frombytes() can read beyond that
+    palette = GimpPaletteFile.frombytes(data)
+    assert len(palette.palette) / 3 == 257
+
+    # Test that __init__ raises an error if a comment is too long
+    data = full_data[:-1] + b"a" * 100
+    b = BytesIO(data)
+    with pytest.raises(SyntaxError, match="bad palette file"):
+        palette = GimpPaletteFile(b)
+
+    # Test that frombytes() can read the data regardless
+    palette = GimpPaletteFile.frombytes(data)
+    assert len(palette.palette) / 3 == 256

src/PIL/GimpPaletteFile.py

@@ -16,6 +16,7 @@
 from __future__ import annotations
 
 import re
+from io import BytesIO
 from typing import IO
 
 
@@ -24,13 +25,18 @@ class GimpPaletteFile:
 
     rawmode = "RGB"
 
-    def __init__(self, fp: IO[bytes]) -> None:
+    def _read(self, fp: IO[bytes], limit: bool = True) -> None:
         if not fp.readline().startswith(b"GIMP Palette"):
             msg = "not a GIMP palette file"
             raise SyntaxError(msg)
 
         palette: list[int] = []
-        for _ in range(256 + 3):
+        i = 0
+        while True:
+            if limit and i == 256 + 3:
+                break
+
+            i += 1
             s = fp.readline()
             if not s:
                 break
@@ -38,7 +44,7 @@ class GimpPaletteFile:
             # skip fields and comment lines
             if re.match(rb"\w+:|#", s):
                 continue
-            if len(s) > 100:
+            if limit and len(s) > 100:
                 msg = "bad palette file"
                 raise SyntaxError(msg)
 
@@ -48,10 +54,19 @@ class GimpPaletteFile:
                 raise ValueError(msg)
 
             palette += (int(v[i]) for i in range(3))
-            if len(palette) == 768:
+            if limit and len(palette) == 768:
                 break
 
         self.palette = bytes(palette)
 
+    def __init__(self, fp: IO[bytes]) -> None:
+        self._read(fp)
+
+    @classmethod
+    def frombytes(cls, data: bytes) -> GimpPaletteFile:
+        self = cls.__new__(cls)
+        self._read(BytesIO(data), False)
+        return self
+
     def getpalette(self) -> tuple[bytes, str]:
         return self.palette, self.rawmode