THINGS TO WATCH OUT FOR

Circular references. It is often logical for you to have a socket associated with some other data type, such as an EditField subclass, or something along those lines. In this case, the EditField subclass has a reference to the socket. When the socket is done with whatever you wanted it to do, it’s often necessary to let the EditField subclass know that the socket is done. This might mean that your socket has a reference to your EditField subclass (if your socket is subclasses as well). This will cause a circular reference! You will leak memory if you have a circular reference! You can break the circular reference by setting one of the two objects to nil (most likely the socket, since it is done with what the EditField had it doing).

Orphaned sockets that never close. If you orphan a socket, you need to be certain that at some point, that socket will get a disconnect message from its connection. For example, some web servers will not release a socket once the data has been transferred to it (for efficiency reasons). So once you are done with the socket, unless you explicitly call SocketCore.Close, it will remain active and connected. If you think your socket could be in a state where it is left open, keep a reference to the socket around somewhere, and use SocketCore.Close to terminate the connection. (Note that calling TCPCore.Disconnect also applies instead of calls to SocketCore.Close).

Once your socket has received an Error event, it has been closed. The connection has been torn down and the internal send buffers have been released. This means that once an error has occurred, and you have left the SocketCore.Error event, the socket will no longer be connected, has nothing in its send buffer, and is ready to be used again (without calling SocketCore.Close or TCPSocket.Disconnect). The information that is retained is: the socket’s port, address (in the case of TCPSockets) and LastErrorCode properties, as well as any data left in the socket’s receive buffer. If you attempt to call Connect or Listen on the socket, the internal receive buffer will then be destroyed, so your socket can start over afresh.

Calling SocketCore.Close tears down the socket, and will close any connections the socket might have. The information that is retained is: the socket’s port, address (in the case of TCPSockets) and LastErrorCode properties, as well as any data left in the socket’s receive buffer. If you attempt to call Connect or Listen on the socket, the internal receive buffer will then be destroyed so your socket can start over afresh. This also applies to calls to TCPCore.Disconnect.

System.PPPConnect behaves slightly differently, depending on how you use it. If you pass in the value ‘true’, on the Mac, there will be no intervention. There are no standard dialogs provided for the user to choose which connection to use on Macintosh. If you pass in ‘true’ on Windows, and the user is running on NT 4 or later, then the standard RAS Manager dialogs will appear, and ask the user for connection information. If the user is running Windows 95/98/ME, or you pass in ‘false’ (or leave the parameter blank), then the system will attempt the connection using the first phonebook entry it can find.

Beware of endian-ness! There are two different endian standards. On Macintosh systems you have “big endian-ness”, and on Windows and x86 Linux you have “little endian-ness”. Sockets work with streams of data and do not muck with the endian-ness of the data you are transferring. This is fine in many cases if you are transferring strings from one platform to another (like from Mac OS X to Windows XP). But if you are transferring binary data (such as from a BinaryStream or a MemoryBlock), you will want to ensure that the endian-ness matches from server to client regardless of what platform you are on. You can do this by setting the “LittleEndian” flag on MemoryBlocks or BinaryStreams to the same value for your client and your server. Failure to ensure that the endian-ness is consistent will result in a possible byte-order conflict in your application.