Implemented unicast responses to direct unicast, unicast questions and legacy unicast queries.

Cargo.toml

@@ -22,6 +22,7 @@ if-addrs = { version = "0.10", features = ["link-local"] } # get local IP addres
 log = { version = "0.4", optional = true }             # logging
 polling = "2.1"                                        # select/poll sockets
 socket2 = { version = "0.5.5", features = ["all"] }      # socket APIs
+socket-pktinfo = { version = "0.2.1" }                  # socket packet info extension
 
 [dev-dependencies]
 fastrand = "1.8"

README.md

@@ -28,9 +28,6 @@ This implementation is based on the following RFCs:
 
 This is still beta software. We focus on the common use cases at hand. And we tested with some existing common tools (e.g. `Avahi` on Linux, `dns-sd` on MacOS, and `Bonjour` library on iOS) to verify the basic compatibility.
 
-Currently this library has the following limitations:
-- Only support multicast, no unicast send/recv.
-
 ## License
 
 Licensed under either of

src/dns_parser.rs

@@ -31,7 +31,8 @@ pub(crate) const TYPE_ANY: u16 = 255;
 
 pub(crate) const CLASS_IN: u16 = 1;
 pub(crate) const CLASS_MASK: u16 = 0x7FFF;
-pub(crate) const CLASS_UNIQUE: u16 = 0x8000;
+pub(crate) const CLASS_CACHE_FLUSH: u16 = 0x8000;
+pub(crate) const CLASS_UNICAST_RESPONSE: u16 = 0x8000;
 
 /// Max size of UDP datagram payload: 9000 bytes - IP header 20 bytes - UDP header 8 bytes.
 /// Reference: RFC6762: https://datatracker.ietf.org/doc/html/rfc6762#section-17
@@ -66,7 +67,7 @@ impl DnsEntry {
             name,
             ty,
             class: class & CLASS_MASK,
-            unique: (class & CLASS_UNIQUE) != 0,
+            unique: (class & CLASS_CACHE_FLUSH) != 0,
         }
     }
 }
@@ -77,6 +78,12 @@ pub(crate) struct DnsQuestion {
     pub(crate) entry: DnsEntry,
 }
 
+impl DnsQuestion {
+    pub fn is_unicast_response_requested(&self) -> bool {
+        self.entry.class & CLASS_UNICAST_RESPONSE == CLASS_UNICAST_RESPONSE
+    }
+}
+
 /// A DNS Resource Record - like a DNS entry, but has a TTL.
 /// RFC: https://www.rfc-editor.org/rfc/rfc1035#section-3.2.1
 ///      https://www.rfc-editor.org/rfc/rfc1035#section-4.1.3
@@ -548,7 +555,7 @@ impl DnsOutPacket {
         self.write_short(record.entry.ty);
         if record.entry.unique {
             // check "multicast"
-            self.write_short(record.entry.class | CLASS_UNIQUE);
+            self.write_short(record.entry.class | CLASS_CACHE_FLUSH);
         } else {
             self.write_short(record.entry.class);
         }
@@ -825,7 +832,7 @@ impl DnsOutgoing {
         // https://tools.ietf.org/html/rfc6763#section-12.1.
         self.add_additional_answer(Box::new(DnsSrv::new(
             service.get_fullname(),
-            CLASS_IN | CLASS_UNIQUE,
+            CLASS_IN | CLASS_CACHE_FLUSH,
             service.get_host_ttl(),
             service.get_priority(),
             service.get_weight(),
@@ -836,7 +843,7 @@ impl DnsOutgoing {
         self.add_additional_answer(Box::new(DnsTxt::new(
             service.get_fullname(),
             TYPE_TXT,
-            CLASS_IN | CLASS_UNIQUE,
+            CLASS_IN | CLASS_CACHE_FLUSH,
             service.get_host_ttl(),
             service.generate_txt(),
         )));
@@ -850,7 +857,7 @@ impl DnsOutgoing {
             self.add_additional_answer(Box::new(DnsAddress::new(
                 service.get_hostname(),
                 t,
-                CLASS_IN | CLASS_UNIQUE,
+                CLASS_IN | CLASS_CACHE_FLUSH,
                 service.get_host_ttl(),
                 address,
             )));
@@ -1331,7 +1338,7 @@ mod tests {
     use crate::dns_parser::{TYPE_A, TYPE_AAAA};
 
     use super::{
-        DnsIncoming, DnsNSec, DnsOutgoing, DnsSrv, CLASS_IN, CLASS_UNIQUE, FLAGS_QR_QUERY,
+        DnsIncoming, DnsNSec, DnsOutgoing, DnsSrv, CLASS_CACHE_FLUSH, CLASS_IN, FLAGS_QR_QUERY,
         FLAGS_QR_RESPONSE, TYPE_PTR,
     };
 
@@ -1379,7 +1386,7 @@ mod tests {
         let mut response = DnsOutgoing::new(FLAGS_QR_RESPONSE);
         response.add_additional_answer(Box::new(DnsSrv::new(
             name,
-            CLASS_IN | CLASS_UNIQUE,
+            CLASS_IN | CLASS_CACHE_FLUSH,
             1,
             1,
             1,
@@ -1407,7 +1414,13 @@ mod tests {
         let name = "instance1._nsec_test._udp.local.";
         let next_domain = name.to_string();
         let type_bitmap = vec![64, 0, 0, 8]; // Two bits set to '1': bit 1 and bit 28.
-        let nsec = DnsNSec::new(name, CLASS_IN | CLASS_UNIQUE, 1, next_domain, type_bitmap);
+        let nsec = DnsNSec::new(
+            name,
+            CLASS_IN | CLASS_CACHE_FLUSH,
+            1,
+            next_domain,
+            type_bitmap,
+        );
         let absent_types = nsec._types();
         assert_eq!(absent_types.len(), 2);
         assert_eq!(absent_types[0], TYPE_A);