SUMMARY

The SMB ioslave asserts in WSDiscoveryClient::sendProbe() if the system does not have IPv6 support or an IPv6 interface configured.  It attempts to use the KDSoapUdpClient to send IPv4 and IPv6 discovery messages, but any error return from either of those is checked with an assert.  This includes when the system does not have IPv6 available, but this is a benign error that should not be fatal.

STEPS TO REPRODUCE
1. Execute the command "kioclient5 ls smb:/" on a system without IPv6.
2. Observe the crash as below.

OBSERVED RESULT

Application: kdeinit5 (kdeinit5), signal: Aborted
Content of s_kcrashErrorMessage: [Current thread is 1 (Thread 0x7f060c539840 (LWP 876210))]
0x00007f060f58226f in poll () from /lib64/libc.so.6

Thread 1 (Thread 0x7f060c539840 (LWP 876210)):
[KCrash Handler]
#8  0x00007f060fac5ac7 in qt_message_fatal (context=..., message=<synthetic pointer>...) at qtbase-everywhere-src-5.15.1/src/corelib/global/qlogging.cpp:1914
#9  QMessageLogger::fatal (this=this@entry=0x7fff8e9bdc90, msg=msg@entry=0x7f060fdd67f8 "ASSERT: \"%s\" in file %s, line %d") at qtbase-everywhere-src-5.15.1/src/corelib/global/qlogging.cpp:893
#10 0x00007f060fac4815 in qt_assert (assertion=assertion@entry=0x7f060ae712e9 "rc", file=file@entry=0x7f060ae73760 "kio-extras/smb/kdsoap-ws-discovery-client/src/wsdiscoveryclient.cpp", line=line@entry=88) at qtbase-everywhere-src-5.15.1/include/QtCore/../../src/corelib/global/qlogging.h:90
#11 0x00007f060ae3a3ae in WSDiscoveryClient::sendProbe (this=this@entry=0x562695317960, typeList=..., scopeList=...) from /usr/lib64/plugins/kf5/kio/smb.so
#12 0x00007f060ae485c2 in WSDiscoverer::start (this=0x56269534dc10) at /usr/lib/gcc/x86_64-pc-linux-gnu/9.3.0/include/g++-v9/initializer_list:79
#13 0x00007f060ae3f984 in SMBSlave::listDir (this=0x7fff8e9be0e0, kurl=...) at kio-extras/smb/kio_smb_browse.cpp:446
#14 0x00007f060abfb2c6 in KIO::SlaveBase::dispatch (this=0x7fff8e9be0f0, command=71, data=...) at kio/src/core/slavebase.cpp:1243
#15 0x00007f060abfbbfe in KIO::SlaveBase::dispatchLoop (this=0x7fff8e9be0f0) at kio/src/core/slavebase.cpp:325
#16 0x00007f060ae3a863 in kdemain (argc=<optimized out>, argv=0x5626952ca6e0) at kio-extras/smb/main.cpp:21

SOFTWARE/OS VERSIONS
KDE Plasma Version: 5.20.80
KDE Frameworks Version: 5.78.0
Qt Version: 5.15.1
kio-extras Git master 003a5ca4

ADDITIONAL INFORMATION

Suggest that the two Q_ASSERT(rc) checks near the end of WSDiscoveryClient::sendProbe() should be changed to qWarning() or qDebug().