[SOLVED] How to clear TFPHTTPClient cache?
lazarus / 38-Networking and Web Programming

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senglit · 2022-03-03 15:55

hi all,

I got a simple example code to read an xml file from a web page like
this:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.Button1Click(Sender: TObject);var  http: TFPHTTPClient; 
Response: TMemoryStream;  res: string;begin  http :=
TFPHTTPClient.Create(nil);  Response := TMemoryStream.Create; 
http.AddHeader('Accept',
'text/html,application/xhtml+xml,application/xml'); 
http.AddHeader('Accept-Encoding', 'dflate');  http.AddHeader('Cache-
Control', 'max-age=0');  http.AddHeader('Connection', 'keep-alive'); 
http.KeepConnection := True;  while updating do begin   
http.Get('http://127.0.0.1/ajax/F_refresh.asp?Mode=RT', Response);   
Response.Seek(0, soFromBeginning);    res := StreamToString(Response);
         // <------  this is what I want    sleep(1000); 
end;end; function TForm1.StreamToString(aStream: TStream): string;var 
SS: TStringStream;begin  if aStream <> nil then begin    SS :=
TStringStream.Create('');    try      SS.CopyFrom(aStream, 0);     
Result := SS.DataString;    finally      SS.Free;    end;  end else
begin    Result := '';  end;end;           
I'm sure the server will refresh the page every 0.5 sec. And there is
a timestamp in the returned xml text. It can be confirmed by a
webbrowser.

But with this code, I got the same value in 'res' everytime. If I free
the httpclient and create it before I send the GET request then I can
get the correct value in 'res'. I think there must be a cache
somewhere with TFPHTTPClient and I didn't find the way to clear it. I
just want to save the cpu resources and don't want to recreate it
every time. how should I do?

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lainz · 2022-03-03 15:59

Hi, I had the same problem and finally the best was to recreate the
FPHTTPClient.

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senglit · 2022-03-03 17:14

haha~~~

After digging a little bit into the source code of TFPHTTPClient.Get,
I found a way to solve this problem.

Do not use TFPHTTPClient.Get
This works:
     TFPHTTPClient.HTTPMethod('GET',url,Response,[200]);

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Leledumbo · 2022-03-03 18:18

Quote from: senglit on March 03, 2022, 06:14:19 pmhaha~~~

After digging a little bit into the source code of TFPHTTPClient.Get,
I found a way to solve this problem.

Do not use TFPHTTPClient.Get
This works:
     TFPHTTPClient.HTTPMethod('GET',url,Response,[200]);
 
Funny because if you look at Get implementation, it actually just
wraps the call to HTTPMethod.
ResetResponse is called on the start of every call to HTTPMethod,
which cleans up the response. I think what you actually need is to
call:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
Response.Seek(0, soFromBeginning);again after StreamToString. The
ReadResponse method which is responsible to write the response to
stream parameter does not do anything to the passed stream except
calling Write, so it's your responsibility to ensure that its internal
pointer is at the beginning. Otherwise, you just keep appending. You
can prove this by printing out the stream's Size on each iteration,
you'll see it getting bigger and bigger.

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Thaddy · 2022-03-03 18:44

And that is the correct answer...

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senglit · 2022-03-04 01:56

You are right. What actually worked is not recreate fphttpclient, but
recreate response.
I need to do Response.Clear every time before http.get

Quote from: Leledumbo on March 03, 2022, 07:18:04 pmQuote from:
senglit on March 03, 2022, 06:14:19 pmhaha~~~

After digging a little bit into the source code of TFPHTTPClient.Get,
I found a way to solve this problem.

Do not use TFPHTTPClient.Get
This works:
     TFPHTTPClient.HTTPMethod('GET',url,Response,[200]);
 
Funny because if you look at Get implementation, it actually just
wraps the call to HTTPMethod.
ResetResponse is called on the start of every call to HTTPMethod,
which cleans up the response. I think what you actually need is to
call:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
Response.Seek(0, soFromBeginning);again after StreamToString. The
ReadResponse method which is responsible to write the response to
stream parameter does not do anything to the passed stream except
calling Write, so it's your responsibility to ensure that its internal
pointer is at the beginning. Otherwise, you just keep appending. You
can prove this by printing out the stream's Size on each iteration,
you'll see it getting bigger and bigger.