How to cut out a part from a stream in Delphi7

Question

I have an incoming soap message wich form is TStream (Delphi7), server that send this soap is in development mode and adds a html header to the message for debugging purposes. Now i need to cut out the html header part from it before i can pass it to soap converter. It starts from the beginning with 'pre' tag and ends with '/pre' tag. Im thinking it should be fairly easy to but i havent done it before in Delphi7, so can someone help me?

Answer 1

Make a new TStream (use TMemoryStream) and move any stuff you want to keep over from one stream to the other with TStream.CopyFrom or the TStream.ReadBuffer/WriteBuffer methods.

Answer 2

I think the following code would do what you want, assuming you only have one <pre> block in your document.

function DepreStream(Stm : tStream):tStream;
var
  sTemp : String;
  oStrStm : tStringStream;
  i : integer;
begin
  oStrStm := tStringStream.create('');
  try
    Stm.Seek(0,soFromBeginning);
    oStrStm.copyfrom(Stm,Stm.Size);
    sTemp := oStrStm.DataString;
    if (Pos('<pre>',sTemp) > 0) and (Pos('</pre>',sTemp) > 0) then
      begin
        delete(sTemp,Pos('<pre>',sTemp),(Pos('</pre>',sTemp)-Pos('<pre>',sTemp))+6);
        oStrStm.free;
        oStrStm := tStringStream.Create(sTemp);
      end;
    Result := tMemoryStream.create;
    oStrStm.Seek(0,soFromBeginning);
    Result.CopyFrom(oStrStm,oStrStm.Size);
    Result.Seek(0,soFromBeginning);
  finally
    oStrStm.free;
  end;
end;

Another option I believe would be to use an xml transform to remove the unwanted tags, but I don't do much in the way of transforms so if anyone else wants that torch...

EDIT: Corrected code so that it works. Teaches me for coding directly into SO rather than into the IDE first.

Answer 3

An XPath expression of "//pre[1][1]" will haul out the first node of the first <pre> tag in the XML message: from your description, that should contain the SOAP message you want.

It's been many years since I last used it, but I think Dieter Koehler's OpenXML library supports XPath.

Answer 4

Another solution, more in line with Lars' suggestion and somehow more worked out.
It's faster, especially when the size of the Stream is above 100, and even more so on really big ones. It avoids copying to an intermediate string.
FilterBeginStream is simpler and follows the "specs" in removing everything up until the end of the header.
FilterMiddleStream does the same as DepreStream, leaving what's before and after the header.

Warning: this code is for Delphi up to D2007, not D2009.

// returns position of a string token (its 1st char) into a Stream. 0 if not found
function StreamPos(Token: string; AStream: TStream): Int64;
var
  TokenLength: Integer;
  StringToMatch: string;
begin
  Result := 0;
  TokenLength := Length(Token);
  if TokenLength > 0 then
  begin
    SetLength(StringToMatch, TokenLength);
    while AStream.Read(StringToMatch[1], 1) > 0 do
    begin
      if (StringToMatch[1] = Token[1]) and
         ((TokenLength = 1) or
          ((AStream.Read(StringToMatch[2], Length(Token)-1) = Length(Token)-1) and
           (Token = StringToMatch))) then
      begin
        Result := AStream.Seek(0, soCurrent) - (Length(Token) - 1); // i.e. AStream.Position - (Length(Token) - 1);
        Break;
      end;
    end;
  end;
end;

// Returns portion of a stream after the end of a tag delimited header. Works for 1st header.
// Everything preceding the header is removed too. Returns same stream if no valid header detected.
// Result is True if valid header found and stream has been filtered.
function FilterBeginStream(const AStartTag, AEndTag: string; const AStreamIn, AStreamOut: TStream): Boolean;
begin
  AStreamIn.Seek(0, soBeginning); // i.e. AStreamIn.Position := 0;
  Result := (StreamPos(AStartTag, TStream(AStreamIn)) > 0) and (StreamPos(AEndTag, AStreamIn) > 0);
  if Result then
    AStreamOut.CopyFrom(AStreamIn, AStreamIn.Size - AStreamIn.Position)
  else
    AStreamOut.CopyFrom(AStreamIn, 0);
end;

// Returns a stream after removal of a tag delimited portion. Works for 1st encountered tag.
// Returns same stream if no valid tag detected.
// Result is True if valid tag found and stream has been filtered.
function FilterMiddleStream(const AStartTag, AEndTag: string; const AStreamIn, AStreamOut: TStream): Boolean;
var
  StartPos, EndPos: Int64;
begin
  Result := False;
  AStreamIn.Seek(0, soBeginning); // i.e. AStreamIn.Position := 0;
  StartPos := StreamPos(AStartTag, TStream(AStreamIn));
  if StartPos > 0 then
  begin
    EndPos := StreamPos(AEndTag, AStreamIn);
    Result := EndPos > 0;
  end;
  if Result then
  begin
    if StartPos > 1 then
    begin
      AStreamIn.Seek(0, soBeginning); // i.e. AStreamIn.Position := 0;
      AStreamOut.CopyFrom(AStreamIn, StartPos - 1);
      AStreamIn.Seek(EndPos - StartPos + Length(AEndTag), soCurrent);
    end;
    AStreamOut.CopyFrom(AStreamIn, AStreamIn.Size - AStreamIn.Position);
  end
  else
    AStreamOut.CopyFrom(AStreamIn, 0);
end;