idhttp post, can't read response text

Question

I'm sending JSON to a restful service using TidHTTP.Post but having trouble reading the response from idHTTP when an HTTP error 400 occurs. When a 400 occurs, the server provides JSON which describes errors in the data being sent. I get readable JSON results sometimes but most of the time the response contains only a couple of unprintable characters.

procedure TForm1.SendData(const stlACSchedule: TStringList; BatchTimeIn: TDateTime);
var
  TargetURL : String;
  stsJson: TStringStream;
  myResponse : String;
  resp : TMemoryStream;

begin
  TargetURL := 'http://sandbox.xxxxxxxxxxx.com/api/v1/feeds' ;
  stsJson := TStringStream.Create;

  stsJson.WriteString(stlACSchedule.Text);

  resp := TMemoryStream.Create;
  application.ProcessMessages;
  try
    myResponse := IdHTTP1.Post( TargetURL, stsJson );
    WriteStatus( 'Response from Vendor Server:   ' );
    UpdateUploadStatus2( IdHTTP1.ResponseCode, IdHttp1.ResponseText, BatchTimeIn, 'usPending', 'usUploaded' );

  except
    on E: EIdHTTPProtocolException do begin
      WriteStatus( 'HTTP Protocol Error from Vendor Server: ' + #13 + E.ErrorMessage + ' -*- ' + IdHTTP1.ResponseText );
      UpdateUploadStatus2( IdHTTP1.ResponseCode, E.ErrorMessage + ' - ' + IdHTTP1.ResponseText, BatchTimeIn, 'usPending', 'usBatchFail' );
      ShowMessage('Fubar_!: ' + myResponse);
    end;

    on E: Exception do begin
      WriteStatus( 'Unknown Error from Vendor Server:' );
      UpdateUploadStatus2( IdHTTP1.ResponseCode, E.Message + ' - ' + IdHTTP1.ResponseText, BatchTimeIn, 'usPending', 'usBatchFail' );
      ShowMessage('Fubar!: ' + myResponse);
    end;
  end;
  resp.free;
  stsJson.free;

end;  { SendData }

procedure TForm1.WriteStatus(strTextIn : String);
begin
  Memo1.Lines.add('');
  Memo1.Lines.add(strTextIn);
  Memo1.Lines.add(IntToStr(IdHTTP1.ResponseCode));
  Memo1.Lines.add(IdHTTP1.ResponseText);
end;  { WriteStatus }

It appears that the EIdHTTPProtocolException exception handler is catching the error but most of the time I get responses like this (there are 3 unprintable characters below the "HTTP Protocol Error from Vendor Server" line):

HTTP Protocol Error from Vendor Server: 

400
HTTP/1.1 400 Bad Request

but occasionally I get a good response, like this:

HTTP Protocol Error from ReturnJet Server: 
{"errors":[{"code":7,"message":"Invalid departure or destination type for event: 1"}]} -*- HTTP/1.1 400 Bad Request
400
HTTP/1.1 400 Bad Request

It looks like it may have something to do w/ the length of the response but I'm not sure.

What do I need to do to consistently decode the ResponseText?

I'm using: Delphi XE8, Indy ver 10.6

PS - when I Post this data manually using Postman, I always get the full JSON response.

TIA

Answer 1

A 400 response is an error response. By default, TIdHTTP raises an EIdHTTPProtocolException exception when an HTTP error occurs (unless you ask it not to), where the HTTP response headers are available in the TIdHTTP.Response property, and the HTTP response content is available as a string in the exception's ErrorMessage property, so as not to corrupt whatever TStream is used for output (unless you ask for it).

If the exception's ErrorMessage does not contain the JSON you are expecting, then either the server is not sending JSON to begin with, or the JSON is not being transmitted in a format that Indy can decode to a string. But you didn't show what the actual HTTP responses look like, or what the "3 unprintable characters" actually are, so there is no way to know for sure why the ErrorMessage is not being populated as you are expecting.

Answer 2

You have to change some options on IdHTTP in order to get the same response as you get on the browser or programs like Postman.

Use:

IdHTTP1.HTTPOptions := idHTTP1.HTTPOptions + [hoNoProtocolErrorException, hoWantProtocolErrorContent];