feat(messaging): recognise ANSRVR's relayed group messages and notices

docs/design/messaging.md

@@ -126,7 +126,7 @@ no acks, repeated on a `BulletinSchedule` (#272): doubling waits from 1 minute t
 ## Out of scope
 
 - The email gateway and auto-reply rules (A11-AA): AprsMap builds them on `Send` and `MessageReceived`. ANSRVR's
-  message forms are `AnsrvrCommand` (#272). An
+  message forms are `AnsrvrCommand` (#272), and its relays and notices are `AnsrvrMessage` (#281). An
   auto-reply has no message ID and no retries, which `Send` allows with `RetryProfile.None` and `withId: false`.
 - ITEM-in-MSG and the 1.2 message servers (A12-MSG-01, 02).
 - Gating messages between APRS-IS and RF: that is the two-way IGate's job, `InternetToRfGate` in `AprsNet.IGate`

src/AprsNet.Messaging/AnsrvrMessage.cs

@@ -0,0 +1,129 @@
+using System.Diagnostics.CodeAnalysis;
+using AprsNet.Packets;
+
+namespace AprsNet.Messaging;
+
+/// <summary>What kind of group traffic an <see cref="AnsrvrMessage"/> is.</summary>
+public enum AnsrvrMessageKind
+{
+    /// <summary>A member's post, relayed to this station by ANSRVR in the member's name.</summary>
+    Relay,
+
+    /// <summary>ANSRVR's own reply about a group, such as <c>N:NZEVENT 2 Messages Sent</c>.</summary>
+    Notice,
+}
+
+/// <summary>
+/// A message from a group on ANSRVR, the APRS announcement server: a member's post relayed to this station, or
+/// ANSRVR's notice about a group. Both read <c>N:GROUP text</c>; <see cref="TryParse(IncomingMessage, out AnsrvrMessage?)"/>
+/// tells them apart by who sent them.
+/// </summary>
+/// <remarks>
+/// <para>
+/// A relay comes from the member who posted, not from ANSRVR: ANSRVR's host sends it in their name (on APRS-IS with
+/// the destination <c>APWW11</c> and <c>qAO</c>), with the poster's <c>CQ GROUP</c> replaced by <c>N:GROUP</c> and no
+/// message ID, so it isn't acked. For example, when N1KXJ-14 sends <c>CQ NEDR Pretty quiet</c>, each other member gets
+/// <c>N1KXJ-14&gt;APWW11,qAO,KJ4ERJ-15::N1KXJ-10 :N:NEDR Pretty quiet</c>.
+/// </para>
+/// <para>
+/// A notice comes from <see cref="AnsrvrCommand.Ansrvr"/> with a message ID, and is acked like any message: the answer
+/// to a join (<c>N:C4FM Now Monitoring with 2 Members</c>), a post (<c>N:NEDR 2 Messages Sent</c>) or a leave
+/// (<c>N:HOTG Removed From Group</c>). ANSRVR's replies that name no group, such as <c>No Memberships</c>, aren't
+/// recognised.
+/// </para>
+/// <para>
+/// A message with a message ID from any other station is never a relay, even if it starts with <c>N:</c>: a person
+/// typed it.
+/// </para>
+/// </remarks>
+/// <example>
+/// <code>
+/// station.MessageReceived += (_, e) =>
+/// {
+///     if (AnsrvrMessage.TryParse(e.Message, out var group))
+///     {
+///         ShowInGroup(group.Group, group.From, group.Text);
+///     }
+/// };
+/// </code>
+/// </example>
+public sealed class AnsrvrMessage
+{
+    private const string Prefix = "N:";
+
+    private AnsrvrMessage(AnsrvrMessageKind kind, string group, Callsign from, string text)
+    {
+        Kind = kind;
+        Group = group;
+        From = from;
+        Text = text;
+    }
+
+    /// <summary>A member's post, or ANSRVR's notice.</summary>
+    public AnsrvrMessageKind Kind { get; }
+
+    /// <summary>The group, as written, such as <c>NEDR</c>.</summary>
+    public string Group { get; }
+
+    /// <summary>
+    /// For a <see cref="AnsrvrMessageKind.Relay"/>, the member who posted; for a notice, <see cref="AnsrvrCommand.Ansrvr"/>.
+    /// </summary>
+    public Callsign From { get; }
+
+    /// <summary>The text after the group, such as <c>Pretty quiet</c> or <c>2 Messages Sent</c>; empty when there is none.</summary>
+    public string Text { get; }
+
+    /// <summary>Recognises a message <see cref="MessagingStation.MessageReceived"/> gave.</summary>
+    /// <returns><see langword="false"/> if <paramref name="message"/> isn't a relay or notice from a group.</returns>
+    public static bool TryParse(IncomingMessage message, [NotNullWhen(true)] out AnsrvrMessage? ansrvr)
+    {
+        ArgumentNullException.ThrowIfNull(message);
+        return TryParse(message.From, message.Text, message.MessageId, out ansrvr);
+    }
+
+    /// <summary>Recognises a message from <paramref name="from"/> with <paramref name="text"/> and its message ID.</summary>
+    /// <param name="from">The station it came from.</param>
+    /// <param name="text">The message text, without the message ID.</param>
+    /// <param name="messageId">Its message ID, or <see langword="null"/> when it has none.</param>
+    /// <param name="ansrvr">The relay or notice.</param>
+    /// <returns><see langword="false"/> if it isn't a relay or notice from a group.</returns>
+    public static bool TryParse(
+        Callsign from,
+        string? text,
+        string? messageId,
+        [NotNullWhen(true)] out AnsrvrMessage? ansrvr
+    )
+    {
+        ArgumentNullException.ThrowIfNull(from);
+        ansrvr = null;
+        if (text is null || !text.StartsWith(Prefix, StringComparison.Ordinal))
+        {
+            return false;
+        }
+
+        var rest = text[Prefix.Length..];
+        var space = rest.IndexOf(' ', StringComparison.Ordinal);
+        var group = space < 0 ? rest : rest[..space];
+        if (group.Length == 0 || group.Any(char.IsControl))
+        {
+            return false;
+        }
+
+        var fromAnsrvr = string.Equals(from.Value, AnsrvrCommand.Ansrvr.Value, StringComparison.OrdinalIgnoreCase);
+        if (!fromAnsrvr && messageId is not null)
+        {
+            return false;
+        }
+
+        ansrvr = new AnsrvrMessage(
+            fromAnsrvr ? AnsrvrMessageKind.Notice : AnsrvrMessageKind.Relay,
+            group,
+            from,
+            space < 0 ? string.Empty : rest[(space + 1)..]
+        );
+        return true;
+    }
+
+    /// <inheritdoc />
+    public override string ToString() => $"{From.Value} {Prefix}{Group} {Text}".TrimEnd();
+}

src/AprsNet.Messaging/PublicAPI.Unshipped.txt

@@ -245,3 +245,14 @@ AprsNet.Messaging.QueryState.Status.get -> AprsNet.Packets.StatusReport?
 AprsNet.Messaging.QueryState.Status.init -> void
 AprsNet.Messaging.QueryState.Weather.get -> AprsNet.Packets.AprsPayload?
 AprsNet.Messaging.QueryState.Weather.init -> void
+AprsNet.Messaging.AnsrvrMessage
+AprsNet.Messaging.AnsrvrMessage.From.get -> AprsNet.Packets.Callsign!
+AprsNet.Messaging.AnsrvrMessage.Group.get -> string!
+AprsNet.Messaging.AnsrvrMessage.Kind.get -> AprsNet.Messaging.AnsrvrMessageKind
+AprsNet.Messaging.AnsrvrMessage.Text.get -> string!
+AprsNet.Messaging.AnsrvrMessageKind
+AprsNet.Messaging.AnsrvrMessageKind.Notice = 1 -> AprsNet.Messaging.AnsrvrMessageKind
+AprsNet.Messaging.AnsrvrMessageKind.Relay = 0 -> AprsNet.Messaging.AnsrvrMessageKind
+override AprsNet.Messaging.AnsrvrMessage.ToString() -> string!
+static AprsNet.Messaging.AnsrvrMessage.TryParse(AprsNet.Messaging.IncomingMessage! message, out AprsNet.Messaging.AnsrvrMessage? ansrvr) -> bool
+static AprsNet.Messaging.AnsrvrMessage.TryParse(AprsNet.Packets.Callsign! from, string? text, string? messageId, out AprsNet.Messaging.AnsrvrMessage? ansrvr) -> bool

src/AprsNet.Messaging/README.md

@@ -59,6 +59,20 @@ drops a member after 12 hours without one.
 station.Send(AnsrvrCommand.Ansrvr, AnsrvrCommand.Join("NZEVENT").Text);
 ```
 
+`AnsrvrMessage` recognises what comes back from a group. Both forms read `N:GROUP text`:
+- **A relay** is another member's post. It arrives from that member, not from ANSRVR, and has no message ID.
+- **A notice** is ANSRVR's own reply, such as `N:NZEVENT 2 Messages Sent`.
+
+```csharp
+station.MessageReceived += (_, e) =>
+{
+    if (AnsrvrMessage.TryParse(e.Message, out var group) && group.Kind == AnsrvrMessageKind.Relay)
+    {
+        ShowInGroup(group.Group, group.From, group.Text);
+    }
+};
+```
+
 `QueryResponder` answers the queries of APRS101 ch. 15 from what the app gives it in a `QueryState`: its position and
 status, weather, IGate capabilities, objects, the stations it has heard and the messages waiting. It does no I/O; it
 returns the payloads to send and how long to wait first. Directed queries (`?APRSP`, `?APRSD`, `?PING?` …) are answered

tests/AprsNet.Messaging.Tests/AnsrvrMessageTests.cs

@@ -0,0 +1,135 @@
+using AprsNet.Packets;
+
+namespace AprsNet.Messaging.Tests;
+
+/// <summary>
+/// ANSRVR's group traffic as captured on APRS-IS on 2026-10-18 and 2026-10-27 (#272, #281): relays come from the
+/// member who posted with no message ID, notices from ANSRVR with one.
+/// </summary>
+public sealed class AnsrvrMessageTests
+{
+    private static IncomingMessage Received(string line)
+    {
+        var packet = AprsPacket.Parse(line);
+        if (packet.Payload is ThirdPartyPayload { Packet: { } inner })
+        {
+            packet = inner;
+        }
+
+        var message = Assert.IsType<MessagePayload>(packet.Payload);
+        return new IncomingMessage(
+            packet.Source!,
+            message.Text,
+            message.MessageId,
+            DateTimeOffset.UnixEpoch,
+            "aprs-is",
+            packet
+        );
+    }
+
+    [Theory]
+    [InlineData(
+        "N1KXJ-14>APWW11,qAO,KJ4ERJ-15::N1KXJ-10 :N:NEDR Pretty quiet ot here...",
+        "N1KXJ-14",
+        "NEDR",
+        "Pretty quiet ot here..."
+    )]
+    [InlineData(
+        "9M2PJU>APWW11,qAO,KJ4ERJ-15::K7XYG-7  :N:HOTG PSE JOIN #APRSMY Net https://aprsmy.hamradio.my",
+        "9M2PJU",
+        "HOTG",
+        "PSE JOIN #APRSMY Net https://aprsmy.hamradio.my"
+    )]
+    // Gated to RF by a two-way IGate: the same text, another path.
+    [InlineData(
+        "N0CALL-10>APZNET,WIDE1-1:}N1KXJ-14>APWW11,TCPIP,N0CALL-10*::N0CALL-9 :N:NEDR Hi",
+        "N1KXJ-14",
+        "NEDR",
+        "Hi"
+    )]
+    public void ARelayIsAMembersPost(string line, string from, string group, string text)
+    {
+        var received = Received(line);
+
+        Assert.True(AnsrvrMessage.TryParse(received, out var relay));
+
+        Assert.Equal(AnsrvrMessageKind.Relay, relay.Kind);
+        Assert.Equal(from, relay.From.Value);
+        Assert.Equal(group, relay.Group);
+        Assert.Equal(text, relay.Text);
+    }
+
+    [Theory]
+    [InlineData(
+        "ANSRVR>APWW11,KJ4ERJ-15*,TCPIP*,qAS,KJ4ERJ-15::N1KXJ-14 :N:NEDR 2 Messages Sent{HV}",
+        "NEDR",
+        "2 Messages Sent"
+    )]
+    [InlineData(
+        "ANSRVR>APWW11,KJ4ERJ-15*,TCPIP*,qAS,KJ4ERJ-15::NZ0P-3   :N:C4FM Now Monitoring with 2 Members{AB}",
+        "C4FM",
+        "Now Monitoring with 2 Members"
+    )]
+    [InlineData(
+        "ANSRVR>APWW11,KJ4ERJ-15*,TCPIP*,qAS,KJ4ERJ-15::NZ0P-3   :N:APRSNETTEST2 Send D APRSNETTEST2 <Description>{BI}",
+        "APRSNETTEST2",
+        "Send D APRSNETTEST2 <Description>"
+    )]
+    [InlineData(
+        "ANSRVR>APWW11,KJ4ERJ-15*,TCPIP*,qAS,KJ4ERJ-15::NZ0P-3   :N:HOTG Removed From Group, Left OwnerLess!{BK}",
+        "HOTG",
+        "Removed From Group, Left OwnerLess!"
+    )]
+    public void ANoticeIsAnsrvrsOwn(string line, string group, string text)
+    {
+        Assert.True(AnsrvrMessage.TryParse(Received(line), out var notice));
+
+        Assert.Equal(AnsrvrMessageKind.Notice, notice.Kind);
+        Assert.Equal(AnsrvrCommand.Ansrvr, notice.From);
+        Assert.Equal(group, notice.Group);
+        Assert.Equal(text, notice.Text);
+    }
+
+    [Theory]
+    // A person's message that starts with N: has a message ID.
+    [InlineData("W1AW>APRS,TCPIP*,qAC,T2TEST::N0CALL-9 :N:NEDR not a relay{01")]
+    // ANSRVR's replies with no group.
+    [InlineData("ANSRVR>APWW11,KJ4ERJ-15*,TCPIP*,qAS,KJ4ERJ-15::NZ0P-3   :No Memberships{BL}")]
+    [InlineData("ANSRVR>APWW11,KJ4ERJ-15*,TCPIP*,qAS,KJ4ERJ-15::NZ0P-3   :Duplicate (retry?) request suppressed")]
+    [InlineData("ANSRVR>APWW11,KJ4ERJ-15*,TCPIP*,qAS,KJ4ERJ-15::NZ0P-3   :N: no group{BM}")]
+    // A post to ANSRVR, and ordinary messages.
+    [InlineData("N1KXJ-14>APSTKA,TCPIP*,qAS,N1KXJ-W3::ANSRVR   :CQ NEDR Pretty quiet{9W")]
+    [InlineData("W1AW>APRS,TCPIP*,qAC,T2TEST::N0CALL-9 :Net at 7pm")]
+    [InlineData("W1AW>APRS,TCPIP*,qAC,T2TEST::N0CALL-9 :n:NEDR lower case")]
+    public void OtherMessagesAreNotGroupTraffic(string line)
+    {
+        Assert.False(AnsrvrMessage.TryParse(Received(line), out var ansrvr));
+        Assert.Null(ansrvr);
+    }
+
+    [Fact]
+    public void AGroupWithNoTextHasEmptyText()
+    {
+        Assert.True(AnsrvrMessage.TryParse(Callsign.Parse("N1KXJ-14"), "N:NEDR", null, out var relay));
+
+        Assert.Equal("NEDR", relay.Group);
+        Assert.Equal("", relay.Text);
+        Assert.Equal("N1KXJ-14 N:NEDR", relay.ToString());
+    }
+
+    [Fact]
+    public void ANoticeIsFromAnsrvrInAnyCase()
+    {
+        Assert.True(AnsrvrMessage.TryParse(Callsign.Parse("ansrvr"), "N:NEDR 2 Messages Sent", "HV", out var notice));
+        Assert.Equal(AnsrvrMessageKind.Notice, notice.Kind);
+    }
+
+    [Fact]
+    public void ARelayIsNotAMessageFromAnsrvrsOtherStations()
+    {
+        // An SSID of ANSRVR's is another station; with a message ID it's a person's message, without one a relay.
+        Assert.False(AnsrvrMessage.TryParse(Callsign.Parse("ANSRVR-1"), "N:NEDR 2 Messages Sent", "HV", out _));
+        Assert.True(AnsrvrMessage.TryParse(Callsign.Parse("ANSRVR-1"), "N:NEDR hi", null, out var relay));
+        Assert.Equal(AnsrvrMessageKind.Relay, relay.Kind);
+    }
+}