c# stream received all data?

Question

I'm using C#.Net and the Socket class from the System.Net.Sockets namespace. I'm using the asynchronous receive methods. I understand this can be more easily done with something like a web service; this question is borne out of my curiosity rather than a practical need.

My question is: assume the client is sending some binary-serialized object of an unknown length. On my server with the socket, how do I know the entire object has been received and that it is ready for deserialization? I've considered prepending the object with the length of the object in bytes, but this seems unnecessary in the .Net world. What happens if the object is larger than the buffer? How would I know, 'hey, gotta resize the buffer because the object is too big'?

Answer 1

If you use pure sockets, you need to know the length. Otherwise, the size of the buffer is not relevant, because even if you have a buffer of the size of the whole data, it still may not read all into it - check Stream.Read method, it returns the nr of bites actually read, so you need to loop until all data is received.

Answer 2

Yeah, you won't deserialize until you've rxed all the bytes.

Answer 3

You either need the protocol to be self-terminating (like XML is, effectively - you know when you've finished receiving an XML document when it closes the root element) or you need to length-prefix the data, or you need the other end to close the stream when it's done.

In the case of a self-terminated protocol, you need to have enough hooks in so that the reading code can tell when it's finished. With binary serialization you may well not have enough hooks. Length-prefix is by far the easiest solution here.