Broken TCP messages

You need message framing. The protocol must specify how large the messages are - usually either a constant well-known size, a length prefix, or using message delimiters.

The is no such thing as packets in TCP. It is a stream oriented protocol. That means when you read the socket you can get less data than you're expecting. You need to check the read size and if you got a short read then read again for the rest of the data.

For an example in C:

int read_data(int sock, int size, unsigned char *buf) {
   int bytes_read = 0, len = 0;
   while (bytes_read < size && 
         ((len = recv(sock, buf + bytes_read,size-bytes_read, 0)) > 0)) {
       bytes_read += len;
   }
   if (len == 0 || len < 0) doerror();
   return bytes_read;
}