I'm trying to serializing the following C struct

struct packet
{int id;unsigned char *ce;unsigned char *syms;
};

in Python and send it over a socket. The number of elements pointed by ce and syms are known to be N. Currently I'm doing this way. First, I wrap the struct using ctypes to

class Packet(Structure):_fields_ = [("id",  c_int),("ce", POINTER(c_ubyte)),("syms", POINTER(c_ubyte))]

Then, I populate an object of the following class using its fill_data function from a ctypes.POINTER(Packet):

class DataLoad:def __init__(self):self.id = -1self.ce = []self.syms = []def fill_data(self, pkt_p):""" pkt_p is POINTER(Packet)"""self.id = pkt_p.contents.idself.ce = []for i in range(N):self.ce.append(pkt_p.contents.ce[i])self.syms = []for i in range(N):self.syms.append(pkt_p.contents.syms[i])

Finally, I simply use pickle.dumps(DataLoad) to generate a byte stream and send.

This approach works well. However, it seems to be quite slow. One reason I can see is that pickle.dumps bring much overhead. For example, if the C struct is only 1024 bytes, I may have to send almost 4000 bytes for each struct using pickle. Also, packing/populating DataLoad also takes time.

So my question is, do I have other better choices to serialize this C struct in python and send? I would prefer to avoid pickle and populate a separate class instance. Thanks.

Finally I figured out the following way to manually serialize the `Packet' instance without using pickle.

def serialize(pkt_p, size_g, size_p):""" Serialize Packet instancesize_g - number of elements pointed by cesize_p - number of elements pointed by symsReturn a byte stream""" pktstr = b''pktstr += struct.pack('i', pkt_p.contents.id)pktstr += string_at(pkt_p.contents.ce, size_g)pktstr += string_at(pkt_p.contents.syms, size_p)return pktstrdef deserialize(pkt_p, pktstr, size_g, size_p):""" De-serialize pktstr and fill a POINTER(Packet)"""pkt_p.contents.id = struct.unpack('i', pktstr[0:4])[0]ce = (c_ubyte * size_g).from_buffer_copy(pktstr[4:4+size_g])pkt_p.contents.ce = cast(ce, POINTER(c_ubyte))syms = (c_ubyte * size_p).from_buffer_copy(pktstr[-size_p:])pkt_p.contents.syms = cast(syms, POINTER(c_ubyte))

The string_at() and the from_buffer_copy() functions are the key.