feat: Add MLDv2 Listener Query response support

This add support for responding to MLDv2 Listener Queries. Both general
queries and multicast specific queries are supported.

src/iface/interface/ipv6.rs

@@ -422,6 +422,16 @@ impl InterfaceInner {
                 #[cfg(feature = "medium-ip")]
                 Medium::Ip => None,
             },
+            #[cfg(feature = "multicast")]
+            Icmpv6Repr::Mld(repr) => match repr {
+                // [RFC 3810 § 6.2], reception checks
+                MldRepr::Query { .. }
+                    if ip_repr.hop_limit == 1 && ip_repr.src_addr.is_link_local() =>
+                {
+                    self.process_mldv2(ip_repr, repr)
+                }
+                _ => None,
+            },
 
             // Don't report an error if a packet with unknown type
             // has been handled by an ICMP socket

src/iface/interface/multicast.rs

@@ -34,6 +34,18 @@ pub(crate) enum IgmpReportState {
     },
 }
 
+#[cfg(feature = "proto-ipv6")]
+pub(crate) enum MldReportState {
+    Inactive,
+    ToGeneralQuery {
+        timeout: crate::time::Instant,
+    },
+    ToSpecificQuery {
+        group: Ipv6Address,
+        timeout: crate::time::Instant,
+    },
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 enum GroupState {
     /// Joining group, we have to send the join packet.
@@ -49,6 +61,8 @@ pub(crate) struct State {
     /// When to report for (all or) the next multicast group membership via IGMP
     #[cfg(feature = "proto-ipv4")]
     igmp_report_state: IgmpReportState,
+    #[cfg(feature = "proto-ipv6")]
+    mld_report_state: MldReportState,
 }
 
 impl State {
@@ -57,6 +71,8 @@ impl State {
             groups: LinearMap::new(),
             #[cfg(feature = "proto-ipv4")]
             igmp_report_state: IgmpReportState::Inactive,
+            #[cfg(feature = "proto-ipv6")]
+            mld_report_state: MldReportState::Inactive,
         }
     }
 
@@ -306,6 +322,46 @@ impl Interface {
             }
             _ => {}
         }
+        #[cfg(feature = "proto-ipv6")]
+        match self.inner.multicast.mld_report_state {
+            MldReportState::ToGeneralQuery { timeout } if self.inner.now >= timeout => {
+                let records = self
+                    .inner
+                    .multicast
+                    .groups
+                    .iter()
+                    .filter_map(|(addr, _)| match addr {
+                        IpAddress::Ipv6(addr) => Some(MldAddressRecordRepr::new(
+                            MldRecordType::ModeIsExclude,
+                            *addr,
+                        )),
+                        #[allow(unreachable_patterns)]
+                        _ => None,
+                    })
+                    .collect::<heapless::Vec<_, IFACE_MAX_MULTICAST_GROUP_COUNT>>();
+                if let Some(pkt) = self.inner.mldv2_report_packet(&records) {
+                    if let Some(tx_token) = device.transmit(self.inner.now) {
+                        self.inner
+                            .dispatch_ip(tx_token, PacketMeta::default(), pkt, &mut self.fragmenter)
+                            .unwrap();
+                    };
+                };
+                self.inner.multicast.mld_report_state = MldReportState::Inactive;
+            }
+            MldReportState::ToSpecificQuery { group, timeout } if self.inner.now >= timeout => {
+                let record = MldAddressRecordRepr::new(MldRecordType::ModeIsExclude, group);
+                if let Some(pkt) = self.inner.mldv2_report_packet(&[record]) {
+                    if let Some(tx_token) = device.transmit(self.inner.now) {
+                        // NOTE(unwrap): packet destination is multicast, which is always routable and doesn't require neighbor discovery.
+                        self.inner
+                            .dispatch_ip(tx_token, PacketMeta::default(), pkt, &mut self.fragmenter)
+                            .unwrap();
+                    }
+                }
+                self.inner.multicast.mld_report_state = MldReportState::Inactive;
+            }
+            _ => {}
+        }
     }
 }
 
@@ -425,4 +481,53 @@ impl InterfaceInner {
             )
         })
     }
+
+    /// Host duties of the **MLDv2** protocol.
+    ///
+    /// Sets up `mld_report_state` for responding to MLD general/specific membership queries.
+    /// Membership must not be reported immediately in order to avoid flooding the network
+    /// after a query is broadcasted by a router; Currently the delay is fixed and not randomized.
+    #[cfg(feature = "proto-ipv6")]
+    pub(super) fn process_mldv2<'frame>(
+        &mut self,
+        ip_repr: Ipv6Repr,
+        repr: MldRepr<'frame>,
+    ) -> Option<Packet<'frame>> {
+        match repr {
+            MldRepr::Query {
+                mcast_addr,
+                max_resp_code,
+                ..
+            } => {
+                // Do not respont immediately to the query
+                let delay = crate::time::Duration::from_millis(max_resp_code.into()) / 3;
+                // General query
+                if mcast_addr.is_unspecified()
+                    && (ip_repr.dst_addr == IPV6_LINK_LOCAL_ALL_NODES
+                        || self.has_ip_addr(ip_repr.dst_addr))
+                {
+                    let ipv6_multicast_group_count = self
+                        .multicast
+                        .groups
+                        .keys()
+                        .filter(|a| matches!(a, IpAddress::Ipv6(_)))
+                        .count();
+                    if ipv6_multicast_group_count != 0 {
+                        self.multicast.mld_report_state = MldReportState::ToGeneralQuery {
+                            timeout: self.now + delay,
+                        };
+                    }
+                }
+                if self.has_multicast_group(mcast_addr) && ip_repr.dst_addr == mcast_addr {
+                    self.multicast.mld_report_state = MldReportState::ToSpecificQuery {
+                        group: mcast_addr,
+                        timeout: self.now + delay,
+                    };
+                }
+                None
+            }
+            MldRepr::Report { .. } => None,
+            MldRepr::ReportRecordReprs { .. } => None,
+        }
+    }
 }