[avahi] Follow-up: Bonjour compatibility layer - no results from DNSServiceBrowse

[Joshua Foster]

Following up on this for a third time because I have received no responses.  Has anyone on the list had a chance to look at this issue?

I have an app that uses Bonjour to detect other services of its type on the network.  It works as expected with Bonjour under Win32, however I need it to work on Linux as well.  It's not feasible to rewrite the code with the Avahi API because I need it to work primarily on Win32.  So I'm trying to use the Bonjour compatibility layer in Avahi, but having problems with the most basic of operations: Browsing.

Sample code is provided below.  It's just a simple service discovery.

-------------------------------------

/**
 * Spends 5 seconds browsing for services of the given regtype. If any are
 * found, their names are output.
 *
 * Build: g++ AvahiBonjourTest.cpp -o AvahiBonjourTest -ldns_sd
 *
 * Run: ./AvahiBonjourTest [regType]
 *  - If no regtype is given, _ipp._tcp" is used.
 */

#ifndef WIN32
#include <sys/select.h>
#endif // ndef WIN32

#include <dns_sd.h>
#include <stdio.h>
#include <iostream>
using namespace std;

void DNSSD_API ProcessBrowseResult( DNSServiceRef sdRef, DNSServiceFlags flags,
	uint32_t interfaceIndex, DNSServiceErrorType errorCode,
	const char *serviceName, const char *regtype, const char *replyDomain,
	void *context )
{
	if( errorCode == kDNSServiceErr_NoError )
	{
		cout << " * Found a " << regtype << " service at \"" << serviceName
			 << "\"!" << endl;
	}
	else
	{
		cout << " * ProcessBrowseResult(): Bonjour error " << errorCode << endl;
	}
}

int main( int argc, const char* argv[] )
{
	const char* regType = ( argc > 1 ? argv[1] : "_ipp._tcp" );
	DNSServiceRef browseSvc = 0;
	
	cout << "Looking for services of type " << regType << "..." << endl;
	
	// Start the browse operation
	int errorCode = DNSServiceBrowse( &browseSvc, 0, 0, regType, 0,
		ProcessBrowseResult, 0 );
	
	if( errorCode != kDNSServiceErr_NoError )
	{
		cout << " * DNSServiceBrowse(): Bonjour error " << errorCode << endl;
		DNSServiceRefDeallocate( browseSvc );
		return 0;
	}
	
	fd_set readfds;
	FD_ZERO( &readfds );
	FD_SET( DNSServiceRefSockFD( browseSvc ), &readfds );
	
	timeval tv;
	tv.tv_sec = 5;
	tv.tv_usec = 0;
	
	// Wait for a response from mDNSResponder, or until timeout, whichever is
	// first
	int result = select( 1, &readfds, NULL, NULL, &tv );
	if( result == -1 )
	{
		perror( " * select() threw an error" );
		
	}
	else if( result > 0 )
	{
		cout << " * Got a result!  processing..." << endl;
		// Read the response and call ProcessBrowseResult()
		errorCode = DNSServiceProcessResult( browseSvc );
	}
	else
	{
		cout << " * select() timed out" << endl;
	}
	
	DNSServiceRefDeallocate( browseSvc );
	return 0;
}

-------------------------------------

There are 4 printers on the network.  On Windows with Bonjour a service is found immediately:

  Looking for services of type _ipp._tcp...
   * Got a result!  processing...
   * Found a _ipp._tcp. service at "Dell Laser Printer 1720dn"!

On Linux with Avahi, no browse results are received and select() times out:

  Looking for services of type _ipp._tcp...
  *** WARNING *** The program 'AvahiBonjourTest' uses the Apple Bonjour compatibility layer   of Avahi.
  *** WARNING *** Please fix your application to use the native API of Avahi!
  *** WARNING *** For more information see <http://0pointer.de/avahiompat?s=libdns_sd&e=AvahiBonjourTest>
   * select() timed out

But I know Avahi is working, because avahi-discover shows 4 services of type _ipp._tcp".  So... why does the browse socket not returning anything?  What am I missing?

Thanks again for your help!


________________________________________

Joshua Foster
Sr. Computer Programmer
2721 X-Ray Drive
Gastonia, NC 28054
(704) 824-0199 x217
(704) 824-0241 Fax

jfoster at dtiweb.net
www.dtiweb.net
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