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The Internet Server control provides an interface which is similar
to the SocketWrench control, but is specifically designed to simplify
the development of a server application. The control provides a
collection of methods which can be used to easily create an
event-driven server application. The server runs on a separate thread
in the background, automatically managing the individual client
sessions as servers connect and disconnect from the server. Events
are used to notify the application when the client establishes a
connection with the server, sends data to the server or disconnects.
Methods such as Read and Write are used to exchange data with the
clients.
It is important to note that although the server is multithreaded,
the ActiveX control specification requires that event notifications be
marshaled across threads. This means that the event handler code that
is written executes in the context of the thread that created the
control, typically the main UI thread. For languages such as Visual
Basic 6.0, the Internet Server control can be used to easily create a
server which is designed for a limited number of active client
connections. However, for higher volume servers it is recommended that
you use a language that fully supports multithreading.
The following properties, methods and events 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 function 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.
Start
This method starts the server, creating the background thread and
listening for incoming client connections on the specified port
number. You can specify the local address, port number, backlog queue
size and the maximum number of clients that can establish a
connection with the server.
Restart
This method will terminate all active client connections, close the
listening socket and re-create a new listening socket bound to the
same address and port number.
Suspend
This method instructs the server to temporarily suspend accepting new
client connections. Existing connections are unaffected, and any
incoming client connections are queued until the server is resumed.
It is not recommended that you leave a server in a suspended state
for an extended period of time. Once the connection backlog queue has
filled, any subsequent client connections will be automatically
rejected.
Resume
This function instructs the server to resume accepting client
connections after it was suspended. Any pending client connections
are accepted after the server has resumed normal operation.
Throttle
This method is used to control the maximum number of clients that may
connect to the server, the maximum number of clients that can connect
from a single IP address and the rate at which the server will accept
client connections. By default, there are no limits on the number of
active client sessions and connections are accepted immediately. This
method can be useful in preventing denial-of-service attacks where
the the attacker attempts to flood the server with connection
attempts.
Stop
This method will terminate all active client connections, close the
listening socket and terminate the background thread that manages the
server. Any incoming client connections will be refused, and all
resources allocated for the server will be released.
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
When the client establishes a connection with the server, data
is sent and received as a stream of bytes. The following methods can be
used to send and receive data over the socket:
Read
This method reads data from the client and copy it to the string
buffer or byte array provided by the caller. If the client closes its
connection, this method will return zero after all the data has been
read. If the method is successful, it will return the actual number
of bytes read. This method should always be used when reading binary
data from the client into a byte array.
ReadLine
Read a line of text from the client, up to an end-of-line character
sequence or when the client closes the connection. This method is
useful when the client and server are exchanging textual data, as is
common with most command/response application protocols.
Write
This method sends data to the client. If the method succeeds, the
return value is the number of bytes actually written. This method
should always be used when sending binary data to the client.
WriteLine
Write a line of text to the socket, terminating it with an
end-of-line character sequence. This method is useful when the client
and server are exchanging textual data, as is common with most
command/response application protocols.
Broadcast
Broadcasts data to each of the clients that are connected to the
server. This can be useful when the application needs to send the
same data to each active client session, such as broadcasting a
shutdown message when the server is about to be terminated.
IsReadable
This property is used to determine if there is data available to be
read from the client. If the property returns a value of True, the
Read method will return without causing the application to block. If
the property returns False, there is no data available to read from
the current client session.
IsWritable
This property is used to determine if data can be sent to the client.
In most cases this will return True, unless the internal socket
buffers are full.
Local Host Information
Several properties are provided to return information about
the local host, including its fully qualified domain name and the IP
addresses that are configured on the system.
ServerName
Return the fully qualified domain name of the local host, if it has
been configured. If the system has not been configured with a domain
name, then the machine name is returned instead.
ExternalAddress
Return the IP address assigned to the router that connects the local
host to the Internet. This is typically used by an application
executing on a system in a local network that uses a router which
performs Network Address Translation (NAT).
AdapterAddress
This property array returns the IP addresses that are associated with
the local network or remote dial-up network adapters configured on
the system. The AdapterCount property can be used to determine the
number of adapters that are available.
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