ZeroConf/Bonjour Code that works in Delphi 7 not working in 2009

Question

I have the following declaration for DNSServiceRegister:

  function DNSServiceRegister
      (
      var sdRef: TDNSServiceRef;
      const flags: TDNSServic         


        

Answer 1

I can't find the declaration instruction for the vars "ServiceName" and "ServiceType" in your code sample.

Assuming a String type (thus a unicode string), I guess (yes... no D2009 available to test this) lazy typecasting could be an issue:

name  := ServiceName;

Why not use the following?

name  := PAnsiChar(AnsiString(ServiceName)) 

Anyhow... just my 2 cts.

BTW: I always use the pre defined "EmptyStr", "EmptyWideStr" ... so the test would look like:

if (ServiceName <> EmptyStr) then

which should be safe and avoid the confusion of types.

On the other side, Delphi may interpret the '' as an ANSIChar like the following declaration do:

const
  MyParagraphChar = '§';

Not sure... I'm confused - should go home now ;)

Answer 2

The answer to this is mind boggling. On the one hand I made a completely stupid, very simple mistake, but on the other hand it should never - as far as I can see - have worked in ANY version of Delphi!

The problem was nothing what-so-ever to do with the Unicode/non-unicodeness of any strings, but was actually due to a type mismatch in the PORT parameter.

I was passing in the result of ReverseBytes(Port) - that parameter expected a uint16_t, i.e. a Word value. My Port property was however declared (lazily) as an Integer!!

Once I fixed this and had Port declared as a Word, it now works on both D2007- and D2009+ versions of Delphi.

Very weird.

I can only think that some other edge-case behaviour of the compiler that might have somehow affected this was changed when Unicode support was introduced.

Answer 3

Based on the information that we have available here, the situation is this:

• When calling the DLL with your code in Delphi 2007, it gives one result.
• When calling the same DLL with your code in Delphi 2009, it gives another result.
• The suspicion is, that it is related to the Delphi 2009 compiler.

Logically, the difference must therefore be, that Delphi 2009 sends different values as parameters. In order to make the debugging truly Delphi-independent, you therefore need to create a dummy DLL, which reports the values it gets. Other Delphi-dependent methods may be applied, like looking at the disassembly of the function-call into the DLL, and debugging it so that we know exactly what values are passed, and how, to the DLL, in both compilers.

Answer 4

If the DLL is not written using Delphi 2009, you may want to use something else than PUTF8String. The Delphi 2009 Utf8String type is different from Delphi 2007's UTF8String type.

If the DLL was written using C/C++, I strongly suggest to use PAnsiChar() instead of PUtf8String.