IdHTTP异常导致分段错误

Question

I have run the code below as an Android App. The lHttp sends an request to a WebService that i made, where the IP (URL) and Port are defined by the user. However, if the webservice is not active in that URL the App is crashed. While debugging, it gives me the following errors while trying to catch an exception.

raised exception class EIdHTTPProtocolException with message 'HTTP/1.1 500 Internal Server Error'.

raised exception class Segmentation fault (11).

raised exception class EAccessViolation with message 'Access violation at address B6FBD7CE, accessing address 000000A8'.

Does someone know how to catch this exception whithout crashing the App?

  Path:= 'http://'+ Conf.IP + ':' + Conf.Port +'/services/MyWebService.dll/GetQuestions';

  lHTTP:= TIdHTTP.Create(nil);

  Stream:= TStringStream.Create;
  Stream.WriteString(Requisition);

  try
    Result := lHTTP.Post(Path, Stream);
  except
    on E:EIdException do
      Result:= E.Message;

    on E:EIdSocketError do
      Result:= E.Message;

    on E:EIdConnClosedGracefully do
      Result:= E.Message;

    on E:EIdHTTPProtocolException do
      Result:= E.Message;

    on E:Exception do
      Result:= E.Message;
  end;

  Stream.Free;

  FreeAndNil(lHTTP);

Answer 1

I'm not sure of what you are actually asking for: solving 500 ISE or catching the exception, but I'm going with:

Does someone know how to catch this exception whithout crashing the App?

Answer: You can create a global exception handler.

1- Declare your custom exception handler in your form's "public declarations" section. For example, if your form is named "Form1:"

{ Public declarations }
procedure MyExceptionHandler(Sender : TObject; E : Exception );

2 - Define your exception handler in the "implementation" section:

procedure TForm1.MyExceptionHandler(Sender : TObject; E : Exception );
begin

    if E.Message.Contains('HTTP/1.1 500 Internal Server Error') then
    begin
    // Do Something
    end;

    {
    // Default App Exception
    Application.ShowException( E );
    }

        end;

3 - Finally, assign the newly created exception handler to your application's OnException event.

procedure
  TForm1.FormCreate(Sender: TObject);
begin
  { begin new code }
  Application.OnException :=
    MyExceptionHandler;
  { end new code }
end;

Answer 2

It seems that you have two problems. The 500 error is a server side an it should have nothing to do with the client side. The problem with the delphi code is that is not handling the access violation. You should try to do a catch exception to get more details of the exception. I don't have the rest of the code so is hard to test. Also what kind of request are you trying? get, post....

lHTTP := TIdHTTP.Create; //Try with out NIL

  try 
    Result := lHTTP.Post(path, Stream);
    lHTTP.Destroy;  // Try destroying the TiDHTTP
  finally
    Stream.Free;
  except on e:Exception do
    ShowMessage (e.Message +' '+ Result); 
  end;

to see each exception add a showmessage plus the result on every exception on your code to get more info on the exceptions.

ShowMessage (result); //if result is a string

Answer 3

EIdHTTPProtocolException means the server sent an error response. That should be the only exception being raised by Post() . Your except block is trying to handle it, but won't actually see it since you have an earlier case for EIdException . All Indy exceptions derive from EIdException , and an except block matches on the first compatible case found. Your EIdException case should be near the bottom of the except block, not the top:

  try
    Result := lHTTP.Post(Path, Stream);
  except
    on E:EIdHTTPProtocolException do
      Result:= E.Message;

    on E:EIdConnClosedGracefully do
      Result:= E.Message;

    on E:EIdSocketError do
      Result:= E.Message;

    on E:EIdException do
      Result:= E.Message;

    on E:Exception do
      Result:= E.Message;
  end;

Which can be simplified to the following, as all exceptions derive from Exception , and you are not doing anything different for specific exception types:

  try
    Result := lHTTP.Post(Path, Stream);
  except
    on E:Exception do
      Result:= E.Message;
  end;

That being said, you will have to debug your app and look at the call stack to figure out where the segfault is actually occuring. It is likely occuring outside of the code you have shown. Segfault(11) is equivalent to an access violation. The EAccessViolation appears to be due to a nil pointer being accessed somewhere.