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Network interface selection for outgoing UDP multicast datagrams

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Default  selection  is  the  loop-back interface.  Users  who  require
interoperation  between  WSJT-X   instances  cooperating  applications
running on different hosts should  select a suitable network interface
and  carefully choose  a multicast  group address,  and TTL,  that has
minimal scope covering the necessary  network(s). Using 224.0.0.1 is a
reasonable    strategy    if   all    hosts    are    on   the    same
subnet. Administratively  scoped multicast group addresses  like those
within 239.255.0.0/16  can cover larger  boundaries, but care  must be
taken if the local subnet has access to a multicast enabled router.

The  IPv4  broadcast  address  (255.255.255.255) may  be  used  as  an
alternative  to multicast  UDP, but  note that  WSJT-X will  only send
broadcast UDP datagrams  on the loop-back interface,  so all recipient
applications must be running on the same host system.

The reference UDP Message protocol  applications are being extended to
be configurable  with a list of  interfaces to join a  multicast group
address on. By default they will only join on the loop-back interface,
which is also  recommended for any applications designed  to take part
in the WSJT-X  UDP Message Protocol. This allows full  user control of
the  scope of  multicast  group membership  with  a very  conservative
default  mode  that will  work  with  all interoperating  applications
running on the same host system.
This commit is contained in:
Bill Somerville
2020-11-02 15:33:44 +00:00
parent 9e71d07075
commit 662ed0fa7a
11 changed files with 510 additions and 139 deletions
Download Patch File Download Diff File Expand all files Collapse all files
UDPExamples/MessageServer.cpp
+37 -48
View File
@@ -32,7 +32,6 @@ public:
: self_ {self}
, version_ {version}
, revision_ {revision}
, port_ {0u}
, clock_ {new QTimer {this}}
{
// register the required types with Qt
@@ -78,8 +77,8 @@ public:
MessageServer * self_;
QString version_;
QString revision_;
port_type port_;
QHostAddress multicast_group_address_;
QStringList network_interfaces_;
static BindMode constexpr bind_mode_ = ShareAddress | ReuseAddressHint;
struct Client
{
@@ -109,56 +108,39 @@ MessageServer::impl::BindMode constexpr MessageServer::impl::bind_mode_;
void MessageServer::impl::leave_multicast_group ()
{
if (!multicast_group_address_.isNull () && BoundState == state ()
#if QT_VERSION >= 0x050600
&& multicast_group_address_.isMulticast ()
#endif
)
if (BoundState == state () && is_multicast_address (multicast_group_address_))
{
for (auto const& interface : QNetworkInterface::allInterfaces ())
for (auto const& if_name : network_interfaces_)
{
if (QNetworkInterface::CanMulticast & interface.flags ())
{
leaveMulticastGroup (multicast_group_address_, interface);
}
leaveMulticastGroup (multicast_group_address_, QNetworkInterface::interfaceFromName (if_name));
}
}
}
void MessageServer::impl::join_multicast_group ()
{
if (BoundState == state ()
&& !multicast_group_address_.isNull ()
#if QT_VERSION >= 0x050600
&& multicast_group_address_.isMulticast ()
#endif
)
if (BoundState == state () && is_multicast_address (multicast_group_address_))
{
auto mcast_iface = multicastInterface ();
if (IPv4Protocol == multicast_group_address_.protocol ()
&& IPv4Protocol != localAddress ().protocol ())
if (network_interfaces_.size ())
{
close ();
bind (QHostAddress::AnyIPv4, port_, bind_mode_);
}
bool joined {false};
for (auto const& interface : QNetworkInterface::allInterfaces ())
{
if (QNetworkInterface::CanMulticast & interface.flags ())
for (auto const& if_name : network_interfaces_)
{
// Windows requires outgoing interface to match
// interface to be joined while joining, at least for
// IPv4 it seems to
setMulticastInterface (interface);
joined |= joinMulticastGroup (multicast_group_address_, interface);
joinMulticastGroup (multicast_group_address_, QNetworkInterface::interfaceFromName (if_name));
}
}
if (!joined)
else
{
multicast_group_address_.clear ();
// find the loop-back interface and join on that
for (auto const& net_if : QNetworkInterface::allInterfaces ())
{
auto flags = QNetworkInterface::IsUp | QNetworkInterface::IsLoopBack | QNetworkInterface::CanMulticast;
if ((net_if.flags () & flags) == flags)
{
joinMulticastGroup (multicast_group_address_, net_if);
break;
}
}
}
setMulticastInterface (mcast_iface);
}
}
@@ -448,27 +430,34 @@ MessageServer::MessageServer (QObject * parent, QString const& version, QString
{
}
void MessageServer::start (port_type port, QHostAddress const& multicast_group_address)
void MessageServer::start (port_type port, QHostAddress const& multicast_group_address
, QStringList const& network_interface_names)
{
if (port != m_->port_
|| multicast_group_address != m_->multicast_group_address_)
if (port != m_->localPort () || multicast_group_address != m_->multicast_group_address_)
{
m_->leave_multicast_group ();
if (impl::BoundState == m_->state ())
if (impl::UnconnectedState != m_->state ())
{
m_->close ();
}
m_->multicast_group_address_ = multicast_group_address;
auto address = m_->multicast_group_address_.isNull ()
|| impl::IPv4Protocol != m_->multicast_group_address_.protocol () ? QHostAddress::Any : QHostAddress::AnyIPv4;
if (port && m_->bind (address, port, m_->bind_mode_))
if (!(multicast_group_address.isNull () || is_multicast_address (multicast_group_address)))
{
m_->port_ = port;
m_->join_multicast_group ();
Q_EMIT error ("Invalid multicast group address");
}
else if (is_MAC_ambiguous_multicast_address (multicast_group_address))
{
Q_EMIT error ("MAC-ambiguous IPv4 multicast group address not supported");
}
else
{
m_->port_ = 0;
m_->multicast_group_address_ = multicast_group_address;
m_->network_interfaces_ = network_interface_names;
QHostAddress local_addr {is_multicast_address (multicast_group_address)
&& impl::IPv4Protocol == multicast_group_address.protocol () ? QHostAddress::AnyIPv4 : QHostAddress::Any};
if (port && m_->bind (local_addr, port, m_->bind_mode_))
{
m_->join_multicast_group ();
}
}
}
}