Q on Python serialization/deserialization
- by neil
What chances do I have to instantiate, keep and serialize/deserialize to/from binary data Python classes reflecting this pattern (adopted from RFC 2246 [TLS]):
enum { apple, orange } VariantTag;
struct {
uint16 number;
opaque string<0..10>; /* variable length */
} V1;
struct {
uint32 number;
opaque string[10]; /* fixed length */
} V2;
struct {
select (VariantTag) { /* value of selector is implicit */
case apple: V1; /* VariantBody, tag = apple */
case orange: V2; /* VariantBody, tag = orange */
} variant_body; /* optional label on variant */
} VariantRecord;
Basically I would have to define a (variant) class VariantRecord, which varies depending on the value of VariantTag. That's not that difficult. The challenge is to find a most generic way to build a class, which serializes/deserializes to and from a byte stream... Pickle, Google protocol buffer, marshal is all not an option.
I made little success with having an explicit "def serialize" in my class, but I'm not very happy with it, because it's not generic enough.
I hope I could express the problem.
My current solution in case VariantTag = apple would look like this, but I don't like it too much
import binascii
import struct
class VariantRecord(object):
def __init__(self, number, opaque):
self.number = number
self.opaque = opaque
def serialize(self):
out = struct.pack('>HB%ds' % len(self.opaque), self.number, len(self.opaque), self.opaque)
return out
v = VariantRecord(10, 'Hello')
print binascii.hexlify(v.serialize())
>> 000a0548656c6c6f
Regards
