The SocketTools ActiveX Edition provides a comprehensive collection
of ActiveX controls for performing a variety of Internet related
programming tasks. Although the number of properties, methods and
events may appear daunting, once you begin using SocketTools in your
own applications you'll find that the various controls are designed to
work together in a cohesive fashion. After you've familiarized yourself
with one control, the others will become much simpler to use.
Throughout the Developer's Guide there are some general concepts and
terminology used that are essential to understanding how SocketTools
works. Each of these concepts is explored in detail, however a general,
broad overview can also be useful when you are just getting
started.
Protocols
A protocol, in terms of how the word is used in SocketTools,
refers to the rules for how programs communicate with one another
over a network. There are low level networking protocols such as TCP
and UDP, as well as high level application protocols like FTP and
HTTP. It can be helpful to think of a protocol as a sort of language;
for two programs to communicate with each other, they must agree upon
a protocol and understand how it is implemented.
Connections
The process of establishing a connection enables one program to
communicate with another. Connection requests are made by client
applications, and accepted by server applications. When the server
accepts the connection request, the connection is completed. When you
use the Connect method to successfully establish a connection to a
server, a client session is created. SocketTools uses a one-to-one
relationship between an instance of a control and a client session.
By creating multiple instances of a control, an application can
create multiple client/server sessions if necessary.
Sessions
A session refers to an active connection between a client and
server program. This term is typically used interchangeably with
connection; however in some cases a single session may involve
multiple network connections. For example, the File Transfer Protocol
control establishes one connection, called the command channel, when
the client initially connects to the server. However, when a file is
being uploaded or downloaded, a second connection called the data
channel is created just for that transfer. When the transfer
completes, the second connection is terminated while the original
command channel connection remains active. Even though there are
multiple connections being made, SocketTools considers it to be a
single client session. An active session is referenced by the
instance of the control that was used to create the session. When the
session is no longer needed, the control's Disconnect method will
terminate the connection to the server and release the resources
allocated for that session. After that point, the session is no
longer valid and subsequent function calls using the control cannot
be made until another connection is established.
Authentication
Many servers require that clients authenticate themselves by
providing user names and passwords. Different application protocols
implement several different types of authentication, and some
protocols may support more than one authentication method.
SocketTools provides one of two general types of authentication
methods, depending on the protocol. For protocols which require the
client to authenticate itself, the controls will provide a Login
method. For protocols where authentication is optional, the controls
will provide an Authenticate method. Refer to the technical reference
for the specific protocol to determine if authentication is
required.
Events
Developers who use programming languages such as Visual Basic will
find the concept of events and event handling to be very familiar. In
general terms, the SocketTools documentation uses "event"
to refer to a mechanism where the control notifies the application
that an operation has completed, some action has taken place or a
change in status has occurred. One example of an event is a
connection event, which is generated whenever an asynchronous network
connection is completed by the client. Another example is a progress
event, which is generated periodically by the control to inform the
client of its progress as it sends or receives data. To determine
what events are available in a specific control, refer to the
documentation. More specific information about event handling is
provided later in this guide.