Palm OS Network Programming

Summary

In this chapter, we explored the functions that allow Palm OS networking applications to accept incoming connection requests. NetLibSocketOpen opens a socket, for either connecting or listening. NetLibSocketBind names the socket. This is mostly used for listening sockets, especially listening sockets that are bound to a specific port. NetLibSocketListen sets the socket to the passive listening mode. In this mode, the protocol stack accepts connection requests addressed to this socket.

We also discussed the mechanics of retrieving a directory listing from an FTP server. To achieve this, we needed to implement a data connection on its own socket. The semantics of FTP require that the FTP client act as the server on the data connection, accepting the FTP server’s connection request. We extended FtpView to support retrieving the server’s directory listing.

Along the way, we encountered two limitations that make Palm OS devices relatively unsuited for the job of serving connections:

• Only four sockets are allowed. This means that in addition to the listening socket, we can only have three additional sockets.

• Listening supports queue length of one. Once a connection request is completed, the protocol stack denies all further requests until our application accepts the connection.

Palm OS devices do make excellent clients, however. And now that we’ve added data handling, we have everything we need to build a fully functional FTP client. We will leave it as an exercise for the reader ...