[Solved] URLtoStr when web site unavailable

[bobonwhidbey]

I really like this code (below) that I picked up a few years ago. It works very well. When the web site is unavailable  (perhaps the host of the web site is down for maintenance) this routine tries for several minutes before returning a blank string. My question is - what determines the period of time before the routine gives up and assumes the web site is unavailable? Is this under control of the user's computer? Is there a way for my app to limit this time?

p.s. the user with the long wait was Linux. I'm not sure if this is a Win problem.

Code: Pascal  [Select][+][-]

1. function URLtoStr(URL: string): string;
2. var
3.   NetHandle: HINTERNET;
4.   UrlHandle: HINTERNET;
5.   Buffer: array[0..1023] of byte;
6.   BytesRead: dWord;
7.   StrBuffer: utf8string;
8. begin
9.   strbuffer := URL;
10.   Result := '';
11.   NetHandle := InternetOpen('Mozilla/5.0(compatible; WinInet)',
12.     INTERNET_OPEN_TYPE_PRECONFIG, nil, nil, 0);
13.  
14.   // NetHandle valid?
15.   if Assigned(NetHandle) then
16.     try
17.       UrlHandle := InternetOpenUrl(NetHandle, PChar(Url), nil, 0,
18.         INTERNET_FLAG_RELOAD, 0);
19.  
20.       // UrlHandle valid?
21.       if Assigned(UrlHandle) then
22.         try
23.           repeat
24.             BytesRead := 0;
25.             InternetReadFile(UrlHandle, @Buffer, SizeOf(Buffer), BytesRead);
26.             SetString(StrBuffer, pansichar(@Buffer[0]), BytesRead);
27.             Result := Result + StrBuffer;
28.           until BytesRead = 0;
29.         finally
30.           InternetCloseHandle(UrlHandle);
31.         end
32.       // o/w UrlHandle invalid
33.       else
34.         ShowMessage('Cannot open URL: ' + Url);
35.     finally
36.       InternetCloseHandle(NetHandle);
37.     end
38.   // NetHandle invalid
39.   else
40.     raise Exception.Create('Unable to initialize WinInet');
41. end;
42.  
43.  

[dsiders]

I really like this code (below) that I picked up a few years ago. It works very well. When the web site is unavailable  (perhaps the host of the web site is down for maintenance) this routine tries for several minutes before returning a blank string. My question is - what determines the period of time before the routine gives up and assumes the web site is unavailable? Is this under control of the user's computer? Is there a way for my app to limit this time?

p.s. the user with the long wait was Linux. I'm not sure if this is a Win problem.

Code: Pascal  [Select][+][-]

1. function URLtoStr(URL: string): string;
2. var
3.   NetHandle: HINTERNET;
4.   UrlHandle: HINTERNET;
5.   Buffer: array[0..1023] of byte;
6.   BytesRead: dWord;
7.   StrBuffer: utf8string;
8. begin
9.   strbuffer := URL;
10.   Result := '';
11.   NetHandle := InternetOpen('Mozilla/5.0(compatible; WinInet)',
12.     INTERNET_OPEN_TYPE_PRECONFIG, nil, nil, 0);
13.  
14.   // NetHandle valid?
15.   if Assigned(NetHandle) then
16.     try
17.       UrlHandle := InternetOpenUrl(NetHandle, PChar(Url), nil, 0,
18.         INTERNET_FLAG_RELOAD, 0);
19.  
20.       // UrlHandle valid?
21.       if Assigned(UrlHandle) then
22.         try
23.           repeat
24.             BytesRead := 0;
25.             InternetReadFile(UrlHandle, @Buffer, SizeOf(Buffer), BytesRead);
26.             SetString(StrBuffer, pansichar(@Buffer[0]), BytesRead);
27.             Result := Result + StrBuffer;
28.           until BytesRead = 0;
29.         finally
30.           InternetCloseHandle(UrlHandle);
31.         end
32.       // o/w UrlHandle invalid
33.       else
34.         ShowMessage('Cannot open URL: ' + Url);
35.     finally
36.       InternetCloseHandle(NetHandle);
37.     end
38.   // NetHandle invalid
39.   else
40.     raise Exception.Create('Unable to initialize WinInet');
41. end;
42.  
43.  

Connection timeout is controlled by InternetSetOption: https://stackoverflow.com/questions/28774137/decrease-internetopenurl-timeout

These routines are imported from wininet.dll and depend on Windows. So they are not cross-platform.

[bobonwhidbey]

i get "illegal qualifier" compilation error for the IntPtr.zero argument.

    InternetSetOption(IntPtr.zero, INTERNET_OPTION_CONNECT_TIMEOUT,
                      @dwTimeOut, SizeOf(dwTimeOut));

That routine is being found in WinINet.pp

[bobonwhidbey]

Once I used NetHandle all seems to be working perfectly. Thank you dsiders.

  NetHandle := InternetOpen('Mozilla/5.0(compatible; WinInet)',
    INTERNET_OPEN_TYPE_PRECONFIG, nil, nil, 0);

  dwTimeOut := 5000; // Timeout in milliseconds, so 5 sec.
//  InternetSetOption(IntPtr.zero, INTERNET_OPTION_CONNECT_TIMEOUT,
  InternetSetOption(NetHandle, INTERNET_OPTION_CONNECT_TIMEOUT,
                    @dwTimeOut, SizeOf(dwTimeOut));