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The Telnet Protocol control enables an application to connect to a
Telnet server, which provides an interactive terminal session similar
to how character based consoles and terminals work. The user can login,
enter commands and interact with applications programmatically or in
conjunction with the terminal emulation control.
The following methods are available for use by your application:
Initialize
Initialize the control and validate the runtime license key for the
current process. This method is normally not used if the control is
placed on a form in languages such as Visual Basic. However, if the
control is being created dynamically using a method similar to
CreateObject, then the application must call this method to
initialize the component before setting any properties or calling any
other methods in the control.
Connect
Establish a connection to the server. Once the connection has been
established, the other methods in the control may be used to interact
with the server.
Disconnect
Disconnect from the server and release any resources that have been
allocated for the client session. After this method is called, the
client session is no longer valid.
Uninitialize
Unload the Windows Sockets library and release any resources that
have been allocated for the current process. This is the last method
call that the application should make prior to terminating. This is
only necessary if the application has previously called the
Initialize method.
Input and Output
Once connected to the Telnet server, any output generated by a
program on the server will be sent as data for the client to read. Any
input to the program is sent by the client and received and processed
by the server. The following methods are used:
Read
Reads any output that has been generated by the program executing on
the server. When the client first connects, the server typically
executes a login program that requests the users authenticate
themselves by entering a user name and password. Once the user has
logged in, they are usually given a command line prompt where they
can enter commands to be executed on the server. If the server closes
the connection, the Read method will indicate that with an error
result and the client can disconnect from the server at that
point.
Write
Send data to the Telnet server which will be received as input to the
program. If the local echo option is enabled, then the client is also
responsible for writing the input data to the display device, if
there is one. If local echo is not enabled, the server will
automatically echo back any characters written as data to be read by
the client.
Telnet Modes
Telnet supports several modes of operation and the option
negotiation phase, which occurs when a connection is established, is
handled automatically by the control. There are two key modes which
affect how the client session works:
Binary
If this property is set to True, the data between the client and
server is not buffered and the high bit is not removed from any
characters. If the application is executing a program which uses text
mode windowing features (i.e.: it draws boxes on the display) then
this mode must be enabled to ensure that the client processes the
data correctly and it isn't buffered a line at a time. If this mode
is disabled, then the data exchanged between the client and server
will be buffered a line at a time and any 8bit characters will be
stripped. This mode is enabled by default.
LocalEcho
If this property is set to True, it is the responsibility of the
client to echo any data that it is sending to the server. For
example, if the character "A" is sent to the server, the
application must also send the character "A" to whatever
interface the user is interacting with, such as a terminal emulation
window. The default mode is for this option to be disabled, which
means that the server will echo back any data that is sent to it.
Command Processing
The Telnet protocol can be used to connect to a server, log in and
execute one or more commands, process the output from those commands
and display it to an end-user using a graphical interface. The user
never sees or interacts with the actual terminal session. The Telnet
interface provides methods which can simplify this kind of application,
reducing the amount of code needed to process the data stream returned
by the server.
Login
This method is used to automatically log a user in, using the
specific user name and password. This method is specifically designed
for UNIX based servers or Windows servers which emulate the same
basic login sequence.
Search
This method is used to search for a specific character or sequence of
characters in the data stream returned by the server. The control
will accumulate all of the data received up to the point where the
character sequence is encountered. This can be used to capture all of
the output from a command, or search for specific results returned by
the command as it executes on the server.
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