Test for faulty files, and document how MAT2 is behaving wrt. them

doc/implementation_notes.md

@@ -9,6 +9,14 @@ that only cleans the superficial metadata of your file, but not
 the ones that might be in **embeded** resources. Like for example,
 images in a PDF or an office document.
 
+Race conditions
+---------------
+
+MAT2 does its very best to avoid crashing at runtime. This is why it's checking
+if the file is valid __at parser creation__. MAT2 doesn't take any measure to
+ensure that the file is not changed between the time the parser is
+instantiated, and the call to clean or show the metadata.
+
 Symlink attacks
 ---------------
 

src/images.py

@@ -20,6 +20,13 @@ class PNGParser(abstract.AbstractParser):
             'Compression', 'Filter', 'Interlace', 'BackgroundColor', 'ImageSize',
             'Megapixels', 'ImageHeight'}
 
+    def __init__(self, filename):
+        super().__init__(filename)
+        try:  # better fail here than later
+            cairo.ImageSurface.create_from_png(self.filename)
+        except MemoryError:
+            raise ValueError
+
     def get_meta(self):
         out = subprocess.check_output(['/usr/bin/exiftool', '-json', self.filename])
         meta = json.loads(out.decode('utf-8'))[0]

src/parser_factory.py

@@ -30,5 +30,8 @@ def get_parser(filename: str) -> (T, str):
 
     for c in _get_parsers():
         if mtype in c.mimetypes:
+            try:
                 return c(filename), mtype
+            except ValueError:
+                return None, mtype
     return None, mtype

src/pdf.py

@@ -11,7 +11,7 @@ import io
 import cairo
 import gi
 gi.require_version('Poppler', '0.18')
-from gi.repository import Poppler
+from gi.repository import Poppler, GLib
 
 from . import abstract
 
@@ -28,6 +28,10 @@ class PDFParser(abstract.AbstractParser):
         super().__init__(filename)
         self.uri = 'file://' + os.path.abspath(self.filename)
         self.__scale = 2  # how much precision do we want for the render
+        try:  # Check now that the file is valid, to avoid surprises later
+            Poppler.Document.new_from_file(self.uri, None)
+        except GLib.GError:  # Invalid PDF
+            raise ValueError
 
     def remove_all_lightweight(self):
         """
@@ -116,8 +120,9 @@ class PDFParser(abstract.AbstractParser):
     def get_meta(self):
         """ Return a dict with all the meta of the file
         """
-        document = Poppler.Document.new_from_file(self.uri, None)
         metadata = {}
+        document = Poppler.Document.new_from_file(self.uri, None)
+
         for key in self.meta_list:
             if document.get_property(key):
                 metadata[key] = document.get_property(key)

tests/test_libmat2.py

@@ -16,6 +16,18 @@ class TestParserFactory(unittest.TestCase):
         self.assertEqual(mimetype, 'audio/mpeg')
         self.assertEqual(parser.__class__, audio.MP3Parser)
 
+class TestCorruptedFiles(unittest.TestCase):
+    def test_pdf(self):
+        shutil.copy('./tests/data/dirty.png', './tests/data/clean.png')
+        with self.assertRaises(ValueError):
+            pdf.PDFParser('./tests/data/clean.png')
+        os.remove('./tests/data/clean.png')
+
+    def test_png(self):
+        shutil.copy('./tests/data/dirty.pdf', './tests/data/clean.pdf')
+        with self.assertRaises(ValueError):
+            images.PNGParser('./tests/data/clean.pdf')
+        os.remove('./tests/data/clean.pdf')
 
 class TestGetMeta(unittest.TestCase):
     def test_pdf(self):