Which stream is suitable for serialization over UDP?

Question

I am trying to serialize and recover objects over UDP using the Boost.Serialization and Boost.Asio libraries. The following points sum up what I know so far:

The main concept of Boost.Serialization is the archive. An archive is a sequence of bytes that represent serialized C++ objects.
The class boost::archive::text_oarchive serializes data as a text stream, and the class boost::archive::text_iarchive restores data from such a text stream.
Constructors of archives expect an input or output stream as a parameter. The stream is used to serialize or restore data.

^{source: https://theboostcpplibraries.com/boost.serialization-archive}

I understand that I must pass a stream as a parameter to the archive. However, there are a few different types of streams which are suitable candidates. See the following digram:

^{source: https://stackoverflow.com/a/8116698/3599179}

I have seen online serialization examples that used ostream and istream, other examples used ostringstream and istringstream and some others used streambuf, which acts as both an input and output buffer if I am not mistaken.

(File streams are out of the equation because I need to write/read from a socket not from a file.)

What advantages/disadvantages offer each of the aforementioned streams?
Considering that I must send the serialized objects over UDP, which stream is the best candidate?

Considering that you want a stream, and probably reliable delivery, UDP is perhaps not the ideal choice. — molbdnilo, Jun 20 '18 at 12:34
@molbdnilo UDP is a formal requirement, so I *must* use it with all its consequences. Streams are required by the Boost.Serialization archive, not because I want to. — codeaviator, Jun 20 '18 at 12:40

score 4 · Accepted Answer · answered Jun 20 '18 at 12:04

Take time to read descriptions of the streams you mentioned on cppreference.com Input/output library, it is quite instructive.

If you want to serialize into memory only one stream works for you: ostringstream. Then you extract the string from it and send it however you please. For deserialization use istringstream. Alternatively, stringstream for both cases.

score 2 · Answer 2 · answered Jun 20 '18 at 13:35

To add to Maxim's answer, if you really want to use UDP, you need to take care of splitting your stream into datagrams and ensure consistency of the data stream yourself. UDP is datagram-oriented and comes with no guarantees of data consistency.

What needs to be taken into account when using UDP:

Datagrams may get lost in transit.
Datagrams may arrive more than once.
Datagrams may become corrupted in transit (there is a checksum but it's optional and weak).
Datagrams may arrive out-of-order.
The bandwidth of the network or the recipient may be insufficient for the rate at which the sender is sending.

If any of these are an issue, you need to implement appropriate countermeasures as part of your protocol, e.g. a packet sequence number and a way to request packet retransmission.

Large datagrams may get fragmented and severely reduce performance. Some people recommend a max datagram size of 512 bytes.

So, given these restrictions, I would suggest to use a compact, binary serialization format. For example, protobuf or msgpack. Boost isn't very compact, though can be good enough (source: cpp-serializers).

The benchmark of the serializers was really helpful. Thank you. — codeaviator, Jun 21 '18 at 13:07

Which stream is suitable for serialization over UDP?

2 Answers2