Can UDP packets be partially sent like TCP ones?

Question

I've created some type of client/server application that has its own data ACK system. It was originally written in TCP because of some limitations, but the base was written thinking about UDP.

The packets that I sent to the server had their own encapsulation (packet id and packet size headers. I know that UDP has also a checksum so I didn't add a header for that), but how TCP works, I know that the server may not receive the entire packet, so I gathered and buffered the data received until a full valid packet was received.

Now I have the chance to change my client/server program to UDP, and I know that one difference with TCP is that data is not received in the same order as sent (which is why I added a packet id header).

The thing that I want to know is: If I send multiple packets, will they be received with no guaranteed order but with guaranteed encapsulation? I mean, if I send a packet sized 1000 bytes of data and another packet sized 400 bytes of data later, will the server receive 2 packets, one of 1000 bytes and another one of 400 bytes, or is there a chance to receive 200 of that 1000 bytes, then 400 bytes of that 1000 bytes and later the rest of the bytes like TCP does?

Answer 1

UDP is a datagram service. Datagrams may be split for transport, but they will be reassembled before being passed up to the application layer.