Overview You've already been introduced to the Internet, but this chapter introduces some exciting and highly useful new material. The new WinInet API functions provide easy access to common Internet protocols and provide a high-level API that provides a fast and direct path to making Internet-enabled applications. Microsoft has promised that future versions of MFC will continue to wrap these functions into useful classes in typical MFC fashion and simplify the programming even more.
This DLL currently can be redistributed with Win32 applications, and in future releases of Windows this functionality will be incorporated directly into all Microsoft operating systems.
These advantages stem mainly from the high-level interface provided, which hides many of the gory details and the complexity inherent in programming Internet applications. Let's look at some of these advantages. You don't need to write WinSock code directly. The WinInet functions transparently execute WinSock functions for you. The concepts behind these protocols are fairly simple, but their actual implementations can be quite complex. The WinInet functions encapsulate the problems inherent in Internet programming and provide a common solution with consistent behavior across applications.
Because WinInet functions hide the actual implementations of specific protocols within a well structured, well conceived API, you can be assured that your tested WinInet code will work even when specifications change. The API will remain fairly constant, providing you with a secure code base for your applications that is guaranteed to remain up-to-date. DLL to keep pace with evolving technology. The functions have a familiar look and feel, and most return information in a familiar format.
WinInet return values also are easily used in standard Win32 functions. You can make simultaneous calls to WinInet functions from multiple threads without worrying about synchronization problems or deadlock. This is possible because the WinInet functions amazingly handle all multithread synchronization internally. Now that's user-friendly! What this means for you is that your application development can focus on the data itself, rather than on managing the data-cache.
Listing Let's look at each group of functions to see what services WinInet actually provides. The general-purpose WinInet functions are listed in Table Table General-purpose WinInet functions. InternetCloseHandle Closes any Internet handle that an application has opened.
The resultant URL will be canonical. InternetErrorDlg Displays a dialog box that explains why an error occurred. InternetOpen Initializes an application's use of the Win32 Internet functions. InternetQueryDataAvailable Queries the amount of data available. InternetQueryOption Queries an Internet option on the specified handle. InternetSetOption Sets an Internet option on the specified handle.This is a WTL program that is able to test connections with web servers using just about every possible combination of requirements that are commonly encountered.
The program is able to connect:. The program uses asynchronous WinINet calls to handle all communication and reporting. The program also demonstrates how to allow the user to select a personal certificate from the My store. I put this program together to help test some issues I encountered with an unusual firewall configuration and web server security requirements. The output from the WinINet call back routine is very helpful when debugging connection issues. While example code for most of the operations can be found in a variety of locations, I needed to tie everything together into a single application, implemented with consistent error handling.
Simple HTTP Client using WININET
The program started as an amalgamation of several samples from Microsoft. After a few hours of coding and a quick port to WTL, the application was pretty well gutted and rewritten.
I need to give credit where credit is due for this application: the Microsoft examples saved me a lot of time except when they were wrong or incomplete and cost me a lot of time.
The code is very simple to use. Simply download the demonstration and compile it. I am using WTL 8. You may need to download WTL. This is a WTL modal dialog application. I used some wait functions developed by Andy Smith to get around blocking issues when a modal dialog is utilized.
The WinInetCallback method is utilized to supply information like personal certificates or user name and password for resubmission to the web server and pass communication errors to the WinINet loop in SendRequest via the context variable.
There are times when you may need to allow a user to select a personal certificate. For instance, you are writing an application that uses WinINet. Here is some simple code that allows a user to select from a list of personal certificates loaded in their certificate store:.
When you get the error, you need to use InternetSetOption on your OpenRequest handle to supply the certificate and then repeat the OpenRequest. It's really pretty simple. It's just that the docs and samples leave out a lot of the error checking and recovery work that you need.
It helps to have a server setup with a valid SSL certificate and require personal certificates in order to connect. I will add authentication handling for proxy servers in a future revision.
Currently, only one set of credentials may be supplied, but the program needs to allow for two sets of credentials, one for the proxy server and one for the web server. I also want to add a file attachment dialog for testing the POST method with binary data or pseudo form data attached.And no samples are available anywhere on Internet. After a long research and lots of testing, I finally managed to reconstruct a big part of the voluntary?
Why asynchronous is better? Because it can handle timeouts correctly. This has been tested successfully with: IE4. At this state, you can either begin a new connection process or close the session handle.
But before closing it, you should un-register the callback function. Use the lParam to send a session identifier to your callback. I always use the this pointer of my class for it. I assume you know how to handle callbacks. The callback will receive a lots of messages then. Here are their orders along with the dwInternetStatus value:. This function can fail if the content-length field is not in the HTTP header. I use it to store the total size of the received data. You must loop on InternetReadFileEx while the ib.
Before each iteration you must adjust the lpvBuffer pointer and reset the dwBufferLength members of ib : add the received length to the pointer and set dwBufferLength to your remaining buffer size. In most error cases, the connection is closed unexpectedly. This can happen anywhere during the process. This should help those who tried to go through asynchronous mode in WinInet! Sorry, there are no attached files but you should be able to use the functions and create nice classes now.
If you liked this article please add an entry in my guestbook and buy me a license of my shareware.A combination of an attribute to be retrieved and flags that modify the request. For a list of possible attribute and modifier values, see Query Info Flags. A pointer to a buffer to receive the requested information.
This parameter must not be NULL. A pointer to a variable that contains, on entry, the size in bytes of the buffer pointed to by lpvBuffer.
When the function returns successfully, this variable contains the number of bytes of information written to the buffer. In the case of a string, the byte count does not include the string's terminating null character. The calling application can then allocate a buffer of this size or larger, and call the function again. A pointer to a zero-based header index used to enumerate multiple headers with the same name. When calling the function, this parameter is the index of the specified header to return.
When the function returns, this parameter is the index of the next header. To get extended error information, call GetLastError. Like all other aspects of the WinINet API, this function cannot be safely called from within DllMain or the constructors and destructors of global objects. HTTP Sessions.
WinINet Functions. Skip to main content. Exit focus mode. In addition, it should not be used from a service. Is this page helpful? Yes No. Any additional feedback? Skip Submit.This article presents a fully functional implementation of a FTP client. FTP Wanderer is a multithreaded FTP client with the look-and-feel of Windows Explorer, and makes moving files between the Internet and your computer as simple as local file manipulation. This is just a CListView derived class that takes care of displaying the files and enabling you to sort them.
When the application is busy downloading or sorting a directory listing it can display an animation, just like explorer does. The settings of each site are save to disk using serializing. It shows all file transfers currently in progress plus the ones that are in the queue.
You can configure how many transfers are processed simultaneously, so you don't run out of resources. Each download is handled in the background using a separate thread. CDownloadThread creates a new connection with the FTP server and displays a progress dialog that tells you the status of the file transfer.
When the download is completed or aborted it notifies the transfer manager so the UI can be updated. Each upload is handled in the background using a separate thread. CUploadThread creates a new connection with the FTP server and displays a progress dialog that tells you the status of the file transfer. When the upload is completed or aborted it notifies the transfer manager so the UI can be updated. While this application has most of the features you might expect in a FTP client, there are a few things left to do:.Hence this note.
Other ways? If you understand http and Winsock not as tricky as it sounds and are familiar with converting Windows API calls for use in VB, then you can drive the server directly. But WinInet overcomes that need. So lets dive into some detail in that area. The declaration looks something like this.
FuncName is the name you use to refer to the function, libname is the windows dll which will be WinInet in our example and AliasName is the name of the function in the Windows API.
Using WinInet HTTP functions in Full Asynchronous Mode
InternetOpen is declared as. My standard use of InternetOpen is:. Key things to know about this. A standard call:. Much of this needs a quick explanation. For now, assume GET.
FTP Wanderer - FTP Client using WININET
As below, I set it to a null string. There are also "gotchas" around the way that WinInet caches returned values. So in the declares we have:. All we now need to do is send the request and read what the server sends back. Sending is done with HttpSendRequest. This puts the returned data into lpBuffer, a string buffer. Another VB gotcha is the need to delete the file before opening it for writing, otherwise it just overwrites the data at the start of the file, leaving the rest as was.
Does anyone know how I can do this in wininet? The InternetConnect function uses this flag for HTTP connections; all the request handles created under this connection will inherit this flag. Learn more.
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