Add standard compliant default identifier

pydyf/__init__.py

@@ -411,11 +411,14 @@ def data(self):
 
 class PDF:
     """PDF document."""
-    def __init__(self, version=b'1.7', identifier=None):
+    def __init__(self, version=b'1.7', identifier=False):
         """Create a PDF document.
 
         :param bytes version: PDF version.
-        :param bytes identifier: PDF file identifier.
+        :param identifier: PDF file identifier. Default is :obj:`False`
+          to include no identifier, can be set to :obj:`True` to generate an
+          automatic identifier.
+        :type identifier: :obj:`bytes` or :obj:`bool`
 
         """
         #: PDF version, as :obj:`bytes`.
@@ -489,18 +492,21 @@ def write_line(self, content, output):
         self.current_position += len(content) + 1
         output.write(content + b'\n')
 
-    def write(self, output, version=None, identifier=None, compress=False):
+    def write(self, output, version=None, identifier=False, compress=False):
         """Write PDF to output.
 
         :param output: Output stream.
         :type output: binary :term:`file object`
         :param bytes version: PDF version.
-        :param bytes identifier: PDF file identifier.
+        :param identifier: PDF file identifier. Default is :obj:`False`
+          to include no identifier, can be set to :obj:`True` to generate an
+          automatic identifier.
+        :type identifier: :obj:`bytes` or :obj:`bool`
         :param bool compress: whether the PDF uses a compressed object stream.
 
         """
         version = self.version if version is None else _to_bytes(version)
-        identifier = self.identifier if identifier is None else identifier
+        identifier = self.identifier or identifier
 
         # Write header
         self.write_line(b'%PDF-' + version, output)
@@ -568,10 +574,12 @@ def write(self, output, version=None, identifier=None, compress=False):
                 'Root': self.catalog.reference,
                 'Info': self.info.reference,
             }
-            if identifier is not None:
+            if identifier:
                 data = b''.join(
                     obj.data for obj in self.objects if obj.free != 'f')
                 data_hash = md5(data).hexdigest().encode()
+                if identifier is True:
+                    identifier = data_hash
                 extra['ID'] = Array((
                     String(identifier).data, String(data_hash).data))
             dict_stream = Stream([xref_stream], extra, compress)
@@ -601,10 +609,12 @@ def write(self, output, version=None, identifier=None, compress=False):
             self.write_line(f'/Size {len(self.objects)}'.encode(), output)
             self.write_line(b'/Root ' + self.catalog.reference, output)
             self.write_line(b'/Info ' + self.info.reference, output)
-            if identifier is not None:
+            if identifier:
                 data = b''.join(
                     obj.data for obj in self.objects if obj.free != 'f')
                 data_hash = md5(data).hexdigest().encode()
+                if identifier is True:
+                    identifier = data_hash
                 self.write_line(
                     b'/ID [' + String(identifier).data + b' ' +
                     String(data_hash).data + b']', output)

tests/test_pydyf.py

@@ -1,4 +1,5 @@
 import io
+import re
 
 import pydyf
 
@@ -704,11 +705,34 @@ def test_text():
     ''')
 
 
-def test_identifier():
+def test_no_identifier():
+    document = pydyf.PDF()
+    pdf = io.BytesIO()
+    document.write(pdf, identifier=False)
+    assert re.search(
+        b'/ID \\[\\((?P<hash>[0-9a-f]{32})\\) \\((?P=hash)\\)\\]',
+        pdf.getvalue()
+    ) is None
+
+
+def test_default_identifier():
+    document = pydyf.PDF()
+    pdf = io.BytesIO()
+    document.write(pdf, identifier=True)
+    assert re.search(
+        b'/ID \\[\\((?P<hash>[0-9a-f]{32})\\) \\((?P=hash)\\)\\]',
+        pdf.getvalue()
+    ) is not None
+
+
+def test_custom_identifier():
     document = pydyf.PDF()
     pdf = io.BytesIO()
     document.write(pdf, identifier=b'abc')
-    assert b'abc' in pdf.getvalue()
+    assert re.search(
+        b'/ID \\[\\(abc\\) \\(([0-9a-f]{32})\\)\\]',
+        pdf.getvalue()
+    ) is not None
 
 
 def test_version():