Question

I’m using WinInet to connect and retrieve information from one of our server. I’m using the following:

indexdata: array of byte[1..5000] of byte;
infoBuffer: array [0..5000] of char;
BufferSize: DWORD;
reserved:   DWORD;
text: string;

BufferSize := Length(infoBuffer);
res := HttpQueryInfo(hHttpRequest, HTTP_QUERY_RAW_HEADERS_CRLF, @infoBuffer, BufferSize, Reserved);

Reserved := 0;
InternetReadFile(hHttpRequest, @indexdata, sizeof(indexdata), Reserved);

SetLength(text, Reserved);
CopyMemory(@text[1], @indexdata[1], Reserved);

The two array of bytes were enough up until now. Things changed. The server can return now information that can be bigger or smaller than 5000; worst yet, in InternetReadFile can return a variable size in the infoBuffer.

So i tried declaring the indexdata and infobuffer as array of byte and then using SetLength to set its length, but 2 things happened.

1) I still don’t know the size of indexdata that the server will return so I cannot properly set it to, say, 100000.

2) I cannot use (as it is now) CopyMemory passing Low(indexdata) to copy indexdata to a simple string variable so I can use the data.

How do I handle this in Delphi? I can do it in C but I can’t seem to be able to do it properly in Delphi.

Code is appreciated

thanks!

Answer 1

You do know that char is a Unicode character since Delphi 2009, but an ANSI character prior to Delphi 2009. In the same way, in Delphi 2009 a string is a UnicodeString, not an AnsiString.

So, when you write SetLength(text, Reserved) you do set the number of characters in text to Reserved. But the number of bytes will be 2*Reserved.

In other words, in Delphi 2009+, one char is not one byte, but two bytes.

You can get back the old behaviour by replacing all char with AnsiChar and all string with AnsiString.

Update

Since you did not post your entire code, I cannot really say what the problem is. Nevertheless, you might find it interesting to read my example usage of InternetReadFile in Delphi. See my answer to this question. It is a fully-working example of how to read a text file from the Internet using Delphi and InternetReadFile.

For your convinience, I paste my code below as well:

To read data from the Internet, use InternetReadFile function. I use the following code to read a small (one-line) text file from the Internet:

function WebGetData(const UserAgent: string; const Server: string; const Resource: string): string;
var
  hInet: HINTERNET;
  hURL: HINTERNET;
  Buffer: array[0..1023] of AnsiChar;
  i, BufferLen: cardinal;
begin
  result := '';
  hInet := InternetOpen(PChar(UserAgent), INTERNET_OPEN_TYPE_PRECONFIG, nil, nil, 0);
  try
    hURL := InternetOpenUrl(hInet, PChar('http://' + Server + Resource), nil, 0, 0, 0);
    try
      repeat
        InternetReadFile(hURL, @Buffer, SizeOf(Buffer), BufferLen);
        if BufferLen = SizeOf(Buffer) then
          result := result + AnsiString(Buffer)
        else if BufferLen > 0 then
          for i := 0 to BufferLen - 1 do
            result := result + Buffer[i];
      until BufferLen = 0;
    finally
      InternetCloseHandle(hURL);
    end;
  finally
    InternetCloseHandle(hInet);
  end;
end;

Sample usage:

WebGetData('My UserAgent', 'www.rejbrand.se', '/MyDir/update/ver.txt')