Book Image

Tcl 8.5 Network Programming

Book Image

Tcl 8.5 Network Programming

Overview of this book

Tcl (Tool Command Language) is a very powerful and easy to learn dynamic programming language, suitable for a very wide range of uses. Tcl is regarded as one of the best-kept secrets in the software industry. This book gives you a hands-on experience on Tcl, helping you develop network-aware applications using this mature yet evolving language. This book shows you how to create network-aware applications with Tcl language. Packed with practical examples, the book not only takes you through the implementation of network protocols in Tcl, but also key aspects of Tcl programming. The book starts with the basic element of Tcl programming as we take a look at the syntax and fundamental commands of the language. To get us ready for network programming, we look at important Tcl features such as object-oriented programming, accessing files, packaging in TCL, event driven programming, and multithreaded applications. To create standalone single-file executable applications with Tcl we take a look at the Starpack technology, and ensure that we’ll be able to create robust applications with a thorough coverage of troubleshooting and debugging Tcl applications. The book is really about network programming, and it will not let you down with its deep coverage of these topics. Of course we look at protocols, but there are plenty of practical examples to keep things moving along. We start with the TCP and UDP protocols, and look at some other protocols to see examples of synchronizing time with other servers, querying user information and authenticating users over LDAP and performing DNS queries. The book explains Simple Network Management Protocol (SNMP), which is often used for monitoring and gathering information from various devices, such as routers, gateways, printers and many other types of equipment. We’ll also look at web programming in Tcl; processing the requests coming from the clients via the HTTP protocol and responding to these requests. You’ll be able to create a complete solution for creating a client-server application in Tcl. To round things off, you’ll see how to secure your networked applications, build public key infrastructure into your application and use Tcl’s safe interpreter feature to reduce risk of running code from unknown source.
Table of Contents (18 chapters)
Tcl 8.5 Network Programming
Credits
About the Authors
About the Reviewers
Preface
4
Troubleshooting Tcl applications

Handling e-mail


Before working with e-mail, we need to understand a bit about how e-mail works, as well as what it provides and what our application needs to perform on its own. In general, e-mails are easy to understand—someone sends a message, the e-mailing system takes care of delivering it to the correct target machine(s), and the recipients are then able to retrieve that message. From the e-mail system's perspective, it does not care about what the e-mail contains, as long as it knows who it is from and who it should be delivered to.

From the user's perspective, he/she does not need to know how it is delivered—their mail application delivers the message to the server handling their e-mail, and all messages can be retrieved from that same server. When we interact with e-mails, it works the same way for us. In the majority of cases, our application only needs to interact with our e-mail server.

All e-mail messages are built using a common structure—each message consists of headers that...