Convert a URL to a valid win32 filename in Delphi - delphi

Question

As part of a Delphi application I'm wanting to convert a URL to a filename. What I'm doing is caching QR-Codes. The QR-Code represents a URL, and I want to store the QR-Code image with a filename that represents that URL. For example http://myurl.com/bla might become http___myrul.com_bla.png - here I've just replaced any non alpha-numeric characters with underscores (and added the .png extension).
I was wondering if there was a simple/standard way of doing this (preferably in Delphi) or should I code up the algorithm mentioned above.

Answer 1

try encoding the URL (the returned string will be always a valid filename) and then add the extention. also the process is reversable so you can obtain the original url from the filename.
{$APPTYPE CONSOLE}
uses
SysUtils;
function URLEncode(const AUrl: string): string;
var
Index: Integer;
begin
Result := '';
for Index := 1 to Length(AUrl) do
begin
case AUrl[Index] of
'A'..'Z', 'a'..'z', '0'..'9', '-', '_', '.': Result := Result + AUrl[Index];
' ' : Result := Result + '%20';
else
Result := Result + '%' + IntToHex(Ord(AUrl[Index]), 2);
end;
end;
end;
function UrlToFileName(const AUrl,Ext : string) : TFileName;
begin
Result := Format('%s.%s',[URLEncode(AUrl),Ext]);
end;
begin
try
Writeln(UrlToFileName('http://stackoverflow.com/questions/5784218/convert-a-url-to-a-valid-win32-filename-in-delphi','png'));
except
on E:Exception do
Writeln(E.Classname, ': ', E.Message);
end;
Readln;
end.
this will return
http%3A%2F%2Fstackoverflow.com%2Fquestions%2F5784218%2Fconvert-a-url-to-a-valid-
win32-filename-in-delphi.png
for additional info read the Naming Files, Paths, and Namespaces article.

Answer 2

You can also use PathGetCharType function from the Windows API.
uses ShLwApi;
...
var s: string;
i: integer;
begin
s := 'http://stackoverflow.com/questions/5784218/convert-a-url-to-a-valid-win32-filename-in-delphi';
for i := 1 to Length(s) do
if PathGetCharType(s[i]) in [GCT_INVALID, GCT_SEPARATOR] then
s[i] := '_';
Writeln(s);
end;
This will return
http___stackoverflow.com_questions_5784218_convert-a-url-to-a-valid-win32-filename-in-delphi
Anyway, I was wondering how many functions exists for path handling. Maybe PathCreateFromUrl do what you want (except extension addition of course), I haven't tested it yet.