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You get the data that comes in using the GetData method. Here's a short example of getting the data:. Notice that the sender is getting, the data and it's passing s as a ByRef variable. The event passes the control to the DataArrival subroutine through the sender control, allowing you to send information right back to it.
Sending and receiving data is done using the Send and GetData methods respectively. You've just seen how the control raises the DataArrival event when data comes in - let's take a look now at how that data is sent out and received by the user. Using these three overloads, you should be able to send any kind of data you want - provided you convert it to a byte array for sending - just make sure you know what you are retrieving when it is received.
The string and bitmap overloads will both convert their respective data into a byte array and then send it out using the third overload. There is a significant difference between the VB 6 version and this version here, however.
In the VB 6 version, if you chose to hold off using the GetData method in the DataArrival routine and the DataArrival routine ran more than once, when you finally use GetData , it retrieves the entire buffer.
With this control, it will grab the first data in a FIFO first in first out method. This data is stored as a byte array in a collection until you use one of the GetData overloads, which it then pops out of the collection and performs the necessary conversion if any is needed before returning it to you.
Be sure to use the correct overload for the incoming data. One thing you should remember when you are done communicating with the server - or client - is that you should close the connection. Do so using the Close method. OK, now for the meat of it - the nitty gritty. You want to know how it's done. The key - sockets, and of course asynchronous function calls threads too!
I'll just go over a little bit of the code as most of it is pretty self explanatory. The Listen method starts up a new thread, running a continuous async call as in the following code:. Here, I'm declaring a temporary socket used to accept the new connection, and pass it to the ConnectionRequest event - which of course starts right back again. Again, I use async calls to begin the connection see Public Sub Connect.
This takes us over to the OnConnected subroutine. OnConnected actually calls another sub to finalize the connection why?? I can't remember any more , but the Finalize connection sub starts our reader.
Again - this is another async call. Once the data has been pulled into the byte array, it is sent over to the AddToBuffer sub. Let's take a look at this routine:. Here, the bytes that were received from the socket and the number of bytes received are passed as arguments. The number received is necessary as the socket will completely fill the byte array - even though it desn't use it all. This will allow us to separate the junk from the data, which is what happens during the first Array.
Copy call. The EOT character is appended to all data you send using this control. It allows the control to separate overlapping data - the demo project shows an example of this when sending a picture twice, the receiving sockets receive it as one block of data so we need to be able to separate that as well. This is what goes on during the While loop, the saving of the first object data to the buffer collection used for data retrieval during GetData , and truncating that object out of the byte buffer.
Finally, the While loop raises the DataArrival event so you can grab the object just sent to the buffer collection. For backwards compatability, and for other languages that don't send EOTs automatically, we check that the byte count is less than the length of the original byte array - telling us if it's finished receiving or not, but only calling the DataArrival event if there is data that is in the buffer.
Dynamic connections - ah the joys of dynamics. In VB 6, you would have to create a control array and increment the array as you need more. You could only remove a connection once the upper bound connection was closed at least easily , and to an unused connection from one that was closed while another connection was open - you would have to iterate through the array to find one that was closed, and use that one.
Not anymore! NET, we have collections, which are much better than arrays for storing data this way. Let's walk through the process of using Winsock connection collections! The first thing you'll notice here is that I have a collection within the collection. This was necessary to store the key values for my particular application a chat server as the Winsock control didn't have a property for a key value. You'll also notice the message boxes I put in the various Try Catch blocks just to know quickly, while it is running, where the errors occur.
Other than that - this is a pretty standard inherited collection. Now that we have our collection - it should be declared with the proper scope for your project, for me this was form global. Here, you'll notice y. ToString was a unique identifier for my users, this was how I tied my users to their connection - hence the key for the collection provided easy access to the users' connections.
Notice also the order of operations here. I first create the new Winsock object, then add it to the collection, and finally add the handlers and accept the connection. If I had added the handlers and accepted before adding the Winsock object to the collection, I would have had problems using the object later on.
The DataArrival subroutine does not need anything special done to it - as it already receives a copy of the connection via the sender. First, take notice of WskRemoval. Winsock control to handle this client as it did the first. If a Winsock control is in the closed state, it can. The final step you might want to try is using the client on. After you make the connection, a new entry is added.
The only difference is that the IP listed is the. Play with the clients and server a bit to get a feel for how they. Figure 15 -6 is a state diagram for a TCP socket. The transitions are straightforward and don't require explanation except. Because of the TCP half-close, there are two transition paths from this state for. Once one side of the TCP connection issues a Close method, that side can't send.
The other side of the connection receives the Close event and enters the sckClosing state. This is why there are two paths out of sckClosing for the SendData method. The side that receives the Close event can freely send data and receive any remaining data. The Winsock control is clearly useful and easy to use; unfortunately, a few bugs make the control. The bugs discussed in this section apply to the latest version.
The first bug is relatively minor and deals with dynamically loading and unloading the control. This is why we don't load and.
Once the control is loaded. The second bug involves closing a socket connection before all data queued is sent on the wire. You can get around this problem by. This would then trigger the Close event on the. The last and most severe bug is the dropping of data when a large buffer is submitted for transfer.
Unfortunately, there is no completely perfect workaround for this. The best method is to submit data in chunks less than bytes. Once a buffer is submitted,. This is a pain, but it's still the. The latest Winsock control shipping in Visual Basic 6. If you issue a Close command after calling SendData, the socket closes immediately without.
While it would have been wonderful to have all the bugs fixed, the remaining. As you saw in Chapter s 6 through 14, an application can encounter quite a few Winsock errors.
However, in the following two sections we will discuss the errors that are. The "Local address in use" error occurs when you bind to a local port, either through the Bind method or. This is most often encountered in the TCP. If a socket is not properly. If an attempt is made to. A common mistake on the client side also.
If the LocalPort property is set to 0 and a connection is established, LocalPort is. If you plan to reuse the. Otherwise, if. The "Invalid operation at current state" error is probably the most frequently seen error.
It occurs when a. Winsock control method is called but the current state of the control prohibits that action. Take a look at. To write robust code, always. Winsock errors will be generated through the Error event. The se are the same errors as the errors from. For a more detailed description of Winsock errors, refer to Chapter 7,. The major difference is that. Also, some. The Windows. CE Winsock control is no exception. The main difference in programming is that the Connect method is.
The re is no Connect event. Once you attempt a connection by calling Connect, the call will. Additionally, the VBCE 1. As a result, the only way to handle multiple. Realistically, this. The end result is that you must call the Accept method on the control to which the connection. The connection request that triggers the ConnectionRequest event is handled by the. In this section, we'll briefly introduce a sample application using the Windows CE Winsock control.
Figure 15 -7 shows the code behind the Windows CE Winsock control. Figure 15 The Windows CE Winsock example. We won't go into the specifics of the sample code in Figure 15 -7 because it is similar to the SockTCP.
The only differences between the two are the known limitations mentioned in. One thing you will notice is that the Windows CE Winsock control is a bare-bones. That is, it isn't as well polished as the desktop version. The type libraries aren't fully. In addition, there is the problem with the socket state enumerated type mentioned in. Handling infrared connections is not that different from handling TCP connections. The one exception. An infrared server is known by its.
CE Winsock control has an additional property named ServiceName. You set this property to the text. For example, the following code snippet puts the Windows CE. Winsock control named Ce Winsock into listening mode under the name "MyServer. The re are no other requirements for publishing a service under infrared sockets. You need to specify.
For some odd reason, these values are defined in the. The Visual Basic Winsock control is useful for simple, noncritical applications that require network.
A few problems with the Visual Basic 5. The control offers the ability to add simple network communication to a Visual. Basic application with relatively little effort. Of course, the control is limited in its overall abilities, and. As we mentioned earlier, we have. This process was extremely time-consuming and prone to numerous errors, such as mismatching the type declarations. We'll first cover the properties and methods of the control and then present several examples that use the control.
A Service Pack 3 released later did not change the control from the SP2 version. It does not provide the best performance because it buffers data within the control before it passes it to the system, thus adding a bit of overhead and uncertainty.
Properties Now that you have an idea of what functionality the control provides, let's look at the properties exposed by the control. Use the GetData method to retrieve the data. Extended embed settings. You have already flagged this document. Thank you, for helping us keep this platform clean. The editors will have a look at it as soon as possible. Self publishing.
Share Embed Flag. TAGS control winsock socket basic visual server close port client connection chapter microsoft beknowledge www. You also want an ePaper? Before the control was available, the only option for Winsock network programming from Visual Basic was to import all the Winsock functions from the DLL and redefine the necessary structures, which are many.
However, if you need the extra flexibility offered by directly importing Winsock into Visual Basic , take a look at the Visual Basic examples that are available throughout Part II of this book. A revised version of the control became available with the Visual Studio Service Pack 2. The various version differences are discussed toward the end of this chapter. Unlike Winsock , which is a protocol-independent interface, the Winsock control can use only the IP transport.
Additionally, the control is based on the Winsock 1. The control itself is not able to access any socket options, which means that features such as multicasting and broadcasting aren't available. Basic ally, the Winsock control is useful only if you require basic data networking capabilities.
Table 15 -1 contains a list of the properties available for affecting the control's behavior and for obtaining information about the control's state. Table 15 LocalPort Long No Returns or sets the local port to use. Specifying 0 for the port tells the system to randomly choose an available port. Generally, only a client uses 0. RemoteHost String No Returns or sets the remote machine name. You can use either the string host name or the dotted decimal string representation.
For TCP connections, this field is set upon a successful connection. RemotePort Long No Returns or sets the remote port to connect to. SocketHandle Long Yes Returns a value that corresponds to the socket handle. State Integer Yes Returns the state of the control, which is an enumerated type. See Table 15 -2 for the socket state constants. A few properties that don't relate well to the Winsock API do need to be set to use the control properly.
The control performs the actual socket creation under the hood, and this property is the only control you have over it. The SocketHandle property can be read after a connection succeeds or after a server binds to wait for connections.
The State property can be used to obtain information about what the control is currently doing. This is important because the control is asynchronous, and events can be fired at any time. Use this property to make sure that the socket is in a valid state for any subsequent operations. Table 15 -2 contains the possible socket states and their meanings. Methods The Winsock control has only a handful of methods. With a couple of exceptions, most of these method names mirror their Winsock equivalents.
Normally you would call the GetData method once the DataArrival event is triggered, notifying you that data has arrived. As always, message peeking is evil and should be avoided at all costs. The methods themselves will be discussed in more detail in the client and server example sections later in this chapter.
Use this method to accept incoming connections when handling a ConnectionRequest event. Use Bind if you have multiple network adapters.
Bind must be called before Listen. Close None Void Closes the connection or the listening socket. Page 3 of 27 Void Retrieves the current data pending. The Type and MaxLen parameters are optional. The Type parameter defines the type of the data to be read. The MaxLen parameter specifies how many bytes or characters to retrieve. GetData ignores the MaxLen parameter for types other than byte array and string.
Listen is used only for TCP connections. In your Visual Basic application, you must handle the various events that might be generated by the Winsock control in order to successfully use the control. This tells your Winsock application that the other side is no longer sending data.
Your application then reads any remaining data and calls the Close method on your end to completely shut down the connection. Table 15 -4 lists all possible Winsock events that can be triggered, along with a description of each event.
Winsock control events Void Behaves exactly like GetData except that the data is not removed from the system's buffer. SendData Data Void Sends data to the remote computer. Always use a byte array for binary data. When the project is compiled and run, you will see a dialog similar to the one illustrated in Figure 15 This sample application is both a sender and a receiver of UDP messages, and therefore you can use just one instance to send and receive messages.
Additionally, all the code behind the form, buttons, and Winsock controls is given in Figure 15 One control is used to send datagrams, and the other is used to receive datagrams. You can also see three group boxes: one for the sender, one for the receiver, and one for general Winsock information.
For the sender, you need somewhere to put the recipient's host name or IP address. When you set the RemoteHost property, you can use either the machine's textual name or a string representation of the dotted-decimal numeric IP address. The control resolves the name if needed.
For the sender, it doesn't really matter which local port you send the data on, only which port you're sending to. If you leave the local port set to 0, the system assigns an unused port. To send datagrams, you must bind the Winsock control to a remote address, a remote port, and a local port before you can send any data. This means that if you want to change any one of these three parameters, you need to close the socket first and then rebind to the new parameters. That is why the form has a Close Socket button.
Text sockSend. Text cmdCloseSend. SendData txtSendData. Text ' ' Disable this button since it would be an error to bind ' twice a close needs to be done before rebinding occurs ' cmdListen. Close cmdCloseSend. Close ' Enable the right buttons ' cmdListen. LocalIP cmdCloseListen. Close End. EventArgs Handles AxWinsock1. ConnectEvent Button1. Focus TextBox4. GetString byteData TextBox4.
EventArgs Handles TextBox5. GotFocus TextBox5. KeyPress If e. Net AJAX. Net, etc. More on lists, exceptions, loops and validation. Visual Basic Fundamental Concepts. Restore your computer to that backup image. If the Step 1 fails to resolve the winsock. Step 2: If recently installed C-Free or related software , uninstall then try reinstalling C-Free software.
After the software has been fully uninstalled, restart your PC and reinstall C-Free software. If this Step 2 fails as well, please proceed to the Step 3 below. In the Windows Update dialog box, click " Check for Updates " or similar button depending on your Windows version If updates are available for download, click " Install Updates ". After the update is completed, restart your PC.
Please follow the steps below to download and properly replace you file: Locate your Windows operating system version in the list of below "Download winsock. Click the appropriate "Download Now" button and download your Windows file version. Download winsock. Files Related to winsock. Other Files Related to winsock. C-Free 5. Extensible Markup Language.
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