chinenual
commented
4 years ago To recap: I'm trying to fix behavior in the current library that causes a LookupType() to not see some services that have already registered themselves with mDNS prior to my application startup. I've observed another application that appears to solve this by sending out a _services._dns-sd._udp query at startup - and gets answers for everything on the network.
.... actually I think my proposed solution may not be sufficient (see below for how it behaves):
I am using wireshark to try to understand how a general bonjour browser works (Discovery on macos). I see it send out a QU query for _services._dns-sd._udp.local and gets Answers for everything on the network.
I've made a local copy of the dnssd module with the proposed fix:
func LookupTypeUnicast(ctx context.Context, service string, add AddServiceFunc, rmv RmvServiceFunc) (err error) {
conn, err := newMDNSConn()
if err != nil {
return err
}
defer conn.close()
return lookupType(ctx, service, conn, add, rmv, true)
}
func lookupType(ctx context.Context, service string, conn MDNSConn, add AddServiceFunc, rmv RmvServiceFunc, unicast bool) (err error) {
...
if unicast {
setQuestionUnicast(&m.Question[0])
}
and call it like this from my application:
serviceType := "_services._dns-sd._udp.local."
logger.Infof("ZEROCONF: serviceDiscovery %s\n", serviceType)
if err = dnssd.LookupTypeUnicast(ctx, serviceType, addFn, rmvFn); err != nil {
if strings.Contains(err.Error(), "context deadline exceeded") {
logger.Debugf("ZEROCONF: ListenFor %s %v\n", serviceType, err)
} else {
logger.Errorf("ZEROCONF: ListenFor %s %v\n", serviceType, err)
}
return
}I can see the query via wireshark and it looks identical to the one I see from Discovery -- however mine has no answers. Is there something else I need to do ?
brutella
I'm trying to send out a unicast QU for service discovery at startup of my application. I can't find a way to use the library to do that. LookupType() does not expose a way to set the unicast bit and unconditionally sends out a QM query.
I tried to copy and paste the browse.go functions into my app and adapt them, but got stuck since I can't create a Query struct (all fields are unexported) and I can't find a public constructor function.
Ideas?
(if you agree that this is a reasonable use case and adding a call to setQuestionUnicast() in lookupType is the fix, I could create a pull request. Perhaps create a new func LookupTypeUnicast() that passes in a boolean to tell lookupType() to set the bit?)