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POHow to retrieve a file from Internet via HTTP?
 

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  1. POHow to retrieve a file from Internet via HTTP?
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    <p>I want to download a file from Internet and InternetReadFile seem a good and easy solution at the first glance. Actually, too good to be true. Indeed, digging a bit I have started to see that actually there are a lot of issues with it. People are complaining about all kinds of problems when using this code. </p> <p>Problems could appear because:</p> <ul> <li>the application freezes temporarily until the HTTP server responds</li> <li>the application freezes temporarily because the Internet connections breaks</li> <li>the application locks up because the HTTP server never responds</li> <li>the InternetOpen (I just discovered this recently) MUST be called only once during application life time</li> </ul> <p>I could not find a complete example about how to use it properly and robustly. Does anybody have an idea about how to implement it in a separate thread and with a time out? There is another SIMPLE way to robustly download a file from Internet. Though I don't want to complicate my life with very large libraries like Jedi or even Indy.</p> <pre><code>function GetFileHTTP (const fileURL, FileName: String): boolean; CONST BufferSize = 1024; VAR hSession, hURL: HInternet; Buffer: array[1..BufferSize] of Byte; BufferLen: DWORD; f: File; sAppName: string; begin // result := false; sAppName := ExtractFileName(Application.ExeName) ; hSession := InternetOpen(PChar(sAppName), INTERNET_OPEN_TYPE_PRECONFIG, nil, nil, 0) ; { be aware that InternetOpen need only be called once in your application!!!!!!!!!!!!!! } TRY hURL := InternetOpenURL(hSession, PChar(fileURL), nil, 0, 0, 0) ; TRY AssignFile(f, FileName) ; Rewrite(f, 1) ; REPEAT InternetReadFile(hURL, @Buffer, SizeOf(Buffer), BufferLen); BlockWrite(f, Buffer, BufferLen) UNTIL BufferLen = 0; CloseFile(f) ; Result:= True; FINALLY InternetCloseHandle(hURL) end FINALLY InternetCloseHandle(hSession) END; END; </code></pre> <p>Edit: This functions checks if Internet connection is available. It seems to work on Win98 also.</p> <pre><code>{ Are we connected to the Internet? } function IsConnectedToInternet: Boolean; { Call SHELL32.DLL for Win &lt; Win98 otherwise call URL.dll } var InetIsOffline: function(dwFlags: DWORD): BOOL; stdcall; begin Result:= FALSE; if IsApiFunctionAvailable('URL.DLL', 'InetIsOffline', @InetIsOffline) then Result:= NOT InetIsOffLine(0) else if IsApiFunctionAvailable('SHELL32.DLL', 'InetIsOffline', @InetIsOffline) then Result:= NOT InetIsOffLine(0) end; </code></pre> <p>I am using Delphi 7. Many thanks.</p> <hr> <p>Edit:</p> <p>Losing customers because the application hangs at the first start up is the perfect recipe for losing money.</p> <p>Writing your code to be Microsoft platform dependent is bad. You never know if the customer has the IE version x.x installed.</p> <p>Installing stuff into a user's computer is like playing with guns. It will backfire.</p> <p>(see more about this here: <a href="http://thesunstroke.blogspot.com/2010/06/programmig-like-there-is-no-ms-windows.html" rel="nofollow noreferrer">http://thesunstroke.blogspot.com/2010/06/programmig-like-there-is-no-ms-windows.html</a>)</p>
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    1. COthis is a usefull question,please add download and/or file-download to tags(along with delphi tag) also wininet and indy(if they are applicable)
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    2. COThis question relates to: http://stackoverflow.com/questions/3135003/the-connection-does-not-timeout-while-downloading-file-from-internet/3136503#3136503
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