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: TDNSServiceFlags;
      const interfaceIndex: uint32_t;
      const name: PUTF8String;                    //* may be NULL */
      const regType: PUTF8String;
      const domain: PUTF8String;                  //* may be NULL */
      const host: PUTF8String;                    //* may be NULL */
      const port: uint16_t;
      const txtLen: uint16_t;
      const txtRecord: Pointer;                 //* may be NULL */
      const callBack: TDNSServiceRegisterReply; //* may be NULL */
      const context: Pointer                    //* may be NULL */
      ): TDNSServiceErrorType; stdcall; external DNSSD_DLL;

In my Bonjour framework I have the following response to an announced service being made active (i.e. to actually start announcing itself, via Bonjour):

  procedure TAnnouncedService.Activate;
  var
    flags: Cardinal;
    name: UTF8String;
    svc: UTF8String;
    pn: PUTF8String;
    ps: PUTF8String;
  begin
    fPreAnnouncedServiceName := ServiceName;

    inherited;

    if AutoRename then
      flags := 0
    else
      flags := kDNSServiceFlagsNoAutoRename;  { - do not auto-rename }

    if (ServiceName <> '') then
    begin
      name  := ServiceName;
      pn    := PUTF8String(name);
    end
    else
      pn := NIL;

    svc := ServiceType;
    ps  := PUTF8String(svc);

    CheckAPIResult(DNSServiceRegister(fHandle,
                                      flags,
                                      0 { interfaceID - register on all interfaces },
                                      pn,
                                      ps,
                                      NIL { domain - register in all available },
                                      NIL { hostname - use default },
                                      ReverseBytes(Port),
                                      0   { txtLen },
                                      NIL { txtRecord },
                                      DNSServiceRegisterReply,
                                      self));
    TBonjourEventHandler.Create(fHandle);
  end;

This is more verbose than I think it strictly needs to be, certainly it was working perfectly well in Delphi 7 in a much less verbose form. I have expanded a lot of operations into explicit steps to facilitate debugging, e.g. to be able to identify any implicit transforms of string payloads that may be occuring "under the hood" in Delphi 2009.

Even in this untidy expanded form this code compiles and works perfectly well in Delphi 7, but if I compile and run with Delphi 2009 I get no announcement of my service.

For example, if I run this code as part of a Delphi 7 application to register a _daap._tcp service (an iTunes shared library) I see it pop-up in a running instance of iTunes. If I recompile the exact same application without modification in Delphi 2009 and run it, I do not see my service appearing in iTunes.

I get the same behaviour when monitoring with the dns-sd command line utility. That is, service code compiled with Delphi 7 behaves as I expect, compiled in Delphi 2009 - nothing.

I am not getting any errors from the Bonjour API - the DNSServiceRegisterReply callback is being called with an ErrorCode of 0 (zero), i.e. success, and if I supply a NIL name parameter with AutoRename specified in the flags then my service is allocated the correct default name. But still the service does not show up in iTunes.

I am at a loss as to what is going on.

As you might be able to tell from the expansion of the code, I have been chasing potential errors being introduced by the Unicode implementation in Delphi 2009, but this seems to be leading me nowhere.

The code was originally developed against version 1.0.3 of the Bonjour API/SDK. I've since updated to 1.0.6 in case that was somehow involved, without any success. afaict 1.0.6 merely added a new function for obtaining "properties", which currently supports only a "DaemonVersion" property for obtaining the Bonjour version - this is working perfectly.

NOTE: I'm aware that the code as it stands is not technically UTF8-safe in Delphi 7 - I have eliminated explicit conversions as far as possible so as to keep things as simple as possible for the automatic conversions that Delphi 2009 applies. My aim now is to get this working in Delphi 2009 then work backward from that solution to hopefully find a compatible approach for earlier versions of Delphi.

NOTE ALSO: I originally also had problems with browsing for advertised services, i.e. identifying an actual iTunes shared library on the network. Those issues were caused by the Unicode handling in Delphi 2009 and have been resolved. My Delphi 2009 code is just as capable of identifying an actual iTunes shared library and querying it's TXT records. It's only this service registration that isn't working.

I must be missing something stupid and obvious.

Does anyone have any ideas?!

UPDATE

Having returned to this problem I have now discovered the following:

If I have a pre-D2009 and a D2009+ IDE open (e.g D2006 and D2010) with the same project loaded into both IDE's concurrently:

• Build and run under 2006: It works - my service announcement is picked up by iTunes
• Switch to D2010 and run (without building): It does a minimal compile, runs and works.

• Do a full build in D2010: It stops working

• Switch back to D2006 and run (without building): It doesn't work

• Do a full build in D2006: It works again

Does this give anyone any other ideas?

Answer 1

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 2

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 3

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 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.