Internet Server  

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 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.

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.

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.

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.

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.

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.

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.

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:

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.

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.

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.

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.

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.

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.

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.

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.

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).

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.