Add DerObject.__repr__()

lib/Crypto/Util/asn1.py

@@ -22,7 +22,7 @@
 
 import struct
 
-from Crypto.Util.py3compat import byte_string, bchr, bord
+from Crypto.Util.py3compat import byte_string, bchr, bord, is_bytes
 
 from Crypto.Util.number import long_to_bytes, bytes_to_long
 
@@ -45,6 +45,40 @@ def _is_number(x, only_non_negative=False):
     return not only_non_negative or x >= 0
 
 
+def _try_decode(maybe_der_encoded):
+    """Internal helper function to be called within DerObject.__repr__().
+    Not general-purpose."""
+
+    try:
+        if not is_bytes(maybe_der_encoded):
+            raise TypeError()
+        tag_octet = maybe_der_encoded[0]
+        if (tag_octet & 0x80) and (tag_octet & 0x20):
+            # constructed and context-specific; assuming EXPLICIT
+            tag_octet = maybe_der_encoded[1]
+        asn1id = tag_octet & 0x1f
+        if asn1id == 0x01:
+            return DerBoolean().decode(maybe_der_encoded)
+        if asn1id == 0x02:
+            return DerInteger().decode(maybe_der_encoded)
+        if asn1id == 0x03:
+            return DerBitString().decode(maybe_der_encoded)
+        if asn1id == 0x04:
+            return DerOctetString().decode(maybe_der_encoded)
+        if asn1id == 0x05:
+            return DerNull().decode(maybe_der_encoded)
+        if asn1id == 0x06:
+            return DerObjectId().decode(maybe_der_encoded)
+        if asn1id == 0x10:
+            return DerSequence().decode(maybe_der_encoded)
+        if asn1id == 0x11:
+            return DerSetOf().decode(maybe_der_encoded)
+        # Sometimes, a bytestring is just a bytestring...
+        return maybe_der_encoded
+    except (TypeError, ValueError, IndexError):
+        return maybe_der_encoded
+
+
 class BytesIO_EOF(object):
     """This class differs from BytesIO in that a ValueError exception is
     raised whenever EOF is reached."""
@@ -258,6 +292,28 @@ def _decodeFromStream(self, s, strict):
                     if p.remaining_data() > 0:
                         raise ValueError("Unexpected extra data after the DER structure")
 
+        def __repr__(self):
+                tag_octet = self._tag_octet
+                # is_constructed = bool(tag_octet & 0x20)
+                is_overridden = bool(tag_octet & 0x80)
+                is_explicit = hasattr(self, '_inner_tag_octet')
+                asn1id = tag_octet & 0x1f
+                if hasattr(self, 'value'):
+                        # non-sequence types with a native Python value
+                        args_repr = repr(self.value)
+                elif hasattr(self, '_seq'):
+                        # sequence types
+                        args_repr = repr(list(map(_try_decode, self._seq)))
+                else:
+                        # non-sequence types with no native Python value
+                        args_repr = repr(_try_decode(self.payload))
+                if is_overridden:
+                        if not is_explicit:
+                                args_repr += ', implicit=%i' % (asn1id, )
+                        else:
+                                args_repr += ', explicit=%i' % (asn1id, )
+                return '%s(%s)' % (self.__class__.__name__, args_repr)
+
 
 class DerInteger(DerObject):
         """Class to model a DER INTEGER.
@@ -696,6 +752,9 @@ def __init__(self):
 
         DerObject.__init__(self, 0x05, b'', None, False)
 
+    def __repr__(self):
+        return '%s()' % (self.__class__.__name__, )
+
 
 class DerObjectId(DerObject):
     """Class to model a DER OBJECT ID.