[Solved] Check if URL is ok?

[Fred vS]

Hello.

How to check if a url is available and ok?

For example, this site is not available at the moment:
http://server1.harmonyradio.be:8000/harmonyradio.mp3

Trying to access it via firefox, after a +- short time there is a message "This is site is not accessible".

But with the pre-check to only get the header, the application crash and I have to reboot the system.
This to get the header:
 

Code: Pascal  [Select][+][-]

1. Http.RequestHeaders.Clear;
2. Http.KeepConnection := False;
3. Http.HTTPMethod('HEAD', URL, Nil, [200, 204, 301, 302, 303, 307, 308, 400]);
4. SL.Assign(http.ResponseHeaders);

What can be used to do a pre-check that will not crash the system if the url is not available?

Thanks.

[Fred vS]

Yep, thanks to my friend Gork, here the solution, create a independent http call and use it before to call the "heavy" http:

Code: Pascal  [Select][+][-]

1. { Pre-check URL accessibility }
2. function IsURLAccessible(const URL: string): Boolean;
3. var
4.   Http: TFPHTTPClient;
5. begin
6.   Result := False;
7.   if (URL = '') or (Pos('http', LowerCase(URL)) <> 1) then
8.     Exit;
9.  
10.   Http := TFPHTTPClient.Create(nil);
11.   try
12.     Http.AllowRedirect := True;
13.     Http.IOTimeout := 5000; // 5-second timeout
14.     Http.ConnectTimeout := 5000;
15.     Http.RequestHeaders.Clear;
16.     try
17.       Http.HTTPMethod('HEAD', URL, nil, [200, 204, 301, 302, 303, 307, 308]);
18.       Result := True; // URL is accessible
19.     except
20.       on E: Exception do
21.       begin
22.         // Optional: Log error for debugging
23.         // Writeln('URL check failed: ', E.Message);
24.       end;
25.     end;
26.   finally
27.     Http.Free;
28.   end;
29. end;

Thanks Gork (and tell your boss to be cooler).

[Remy Lebeau]

How to check if a url is available and ok?

The only way is to actually request the url and handle any failures that may occur.

But with the pre-check to only get the header, the application crash and I have to reboot the system.
...
What can be used to do a pre-check that will not crash the system if the url is not available?

An unavailable url should not crash the whole system. It should not even crash your app, unless you are not doing adequate error handling to begin with. Even if the url were available, you still have to be prepared to handle server errors, transmission errors, memory errors, file errors, etc. So things can still go wrong that you need to handle. So a precheck isn't really that useful anyway, especially when an actual download would at least report the same server errors that a precheck would report.

[Fred vS]

Hello Remy and thanks for the advice.

Indeed it would be more logic to have the check done in the audio-thread but, after long nights to try to do it with the correct http.head(), it crash the app and sometimes all the system.

And the solution to first check the url with a independent check, outside the TThreadHttpGetter = class(TThread) of audio web streaming and before to create it works like charm.

[d2010]

Yep, thanks to my friend Gork, here the solution, create a independent http call and use it before to call the "heavy" http:

If you add your-routine inside cozipinc.dll, then you can avoid Exception
message, because , using value elseDoExcep<-100.
If you are inside mainprogram.exe with Debugger, then you cannot display errorException-> in this case you return wrong-error-number.
Perhaps, You scan too much the memory-of-EXE, with Pos('http:'),
i copied only first 15characters inside small-memory.(avoid memory-leaks)

Code: Pascal  [Select][+][-]

1. Function cozipinc_urlacces(const curl:string;elseDoExcep:integer):integer;exports;
2. var Http: TFPHTTPClient;
3.     Buf3:array[0..15] of char;
4. begin
5.   Result := RTCAN;
6.   fillchar(buf3,sizeof(Buf3),0);
7.   if (length(curl)>=high(Buf3)) then copymemory(@Buf3[0],@curl[1],15)  else
8.      if (length(curl)>5) then  copymemory(@Buf3[0],@curl[01],length(Curl));
9.   Result:=RTINPUTTRUNCATED;
10.   if (length(curl)>4094) then exit;  //url is to large
11.   if (Buf3[5]=#00) then exit;
12.   Result := RTFAIL;
13.   if (Pos('://',Buf3) < 5) then Exit;
14.     Http := TFPHTTPClient.Create(nil);
15.     try
16.       Http.AllowRedirect := True;
17.       Http.IOTimeout := 5000; // 5-second timeout
18.       Http.ConnectTimeout := 5000;
19.       Http.RequestHeaders.Clear;
20.       try
21.         Http.HTTPMethod('HEAD',curl, nil, [200, 204, 301, 302, 303, 307, 308]);
22.         Result := RTNORM; // URL is accessible
23.       except
24.         ON E: Exception do
25.           if (-100>elseDoExcep) then result:=elseDoExcep else
26.              if (elseDoExcep>00)and(elseDoExcep<256) then
27.                Writeln('URL check failed: ', E.Message);
28.       end;
29.     finally
30.       Http.Free;
31.     end;
32. end;
33.