I have no real way to determine when the data is finished being read, other than there is nothing else coming in.

In that case, if you think about it logically, there is no reliable way for your server to know when the client has finished sending. All proper network protocols give some way for the server to know, eg, client closes connection, client sends an agreed, fixed size of data, client sends a terminator code (\r\n in HTTP), client sends a header that contains the length of the rest of the message etc.

I think you need to rethink your protocol.

Dave.