feat(mqtt): Sparkplug primary-host STATE publishing, Primary-gated (#511)
`ActAsPrimaryHost` was accepted by config and by the AdminUI form and did nothing but
log a warning. It now delivers the whole three-part contract or none of it: a retained
`ONLINE` on `spBv1.0/STATE/{hostId}`, a matching retained `OFFLINE` armed as the MQTT
Last Will, and an explicit `OFFLINE` on a clean stand-down.
**The claim is a dedicated connection, not a message.** A Will can only be registered in
the CONNECT packet — it cannot be added to a live session, changed, or withdrawn. So a
claim that is acquired and released at runtime cannot ride the long-lived ingest session.
`SparkplugPrimaryHost` opens its own connection (client id `{clientId}-spbhost`, forced
clean-session) when the node gains Primary and closes it when the node loses Primary; the
connection's lifetime *is* the claim, so every leg follows from its lifecycle. Ingest is
untouched by a role change — no dropped subscriptions, no lost birth cache, no data gap at
the Secondary->Primary transition.
**Primary-gated** (owner decision, recorded on the issue). Both pair nodes subscribe
independently, so an ungated claim means both claim the same host id — and the sharp
failure is not the two fighting over the retained STATE, it is that the SECONDARY's death
fires its Will and publishes OFFLINE while the Primary is healthy, stopping every edge node
in the group. Registering the Will only on whichever node is Primary at connect time fails
the other way: a node that later gains Primary would publish ONLINE with no Will behind it.
New seam: `IDriverPrimaryRoleSource` (`Core.Abstractions`) carrying the *data-plane* verdict
(`PrimaryGatePolicy.ShouldServiceAsPrimary`), not the alarm-drain verdict — an unknown role
with a driver peer present must deny. Registered unconditionally by `AddOtOpcUaRuntime`,
deliberately NOT alongside `IRedundancyRoleView`, which `AddAlarmHistorian` registers only
when that section is enabled: piggybacking would leave a pair with no alarm historian
falling back to "claim unconditionally". Polled on a 1s timer rather than evented — a
process singleton raising events at per-instance drivers outlives every driver it holds.
Accepted trade: a brief edge-visible OFFLINE window during failover. That is a genuine
state transition, not a glitch to hide.
Live-gated 5/5 against the Mosquitto fixture, including the Will leg — `AbandonForTests`
drops the socket with no DISCONNECT, because a clean disconnect makes the broker discard
the Will by protocol rule, so a test driven through `StopAsync` would observe the
stand-down OFFLINE and pass against an implementation that never armed a Will. Falsified:
removing the Will turns that leg and only that leg red.
Also corrects two stale claims found en route: the AdminUI form still said MQTT tags are
read-only (#508 shipped), and the driver doc still said nothing consumes `IRediscoverable`.
Claude-Session: https://claude.ai/code/session_015p7wGqy3YpZNCpDzTpGMKo
This commit is contained in:
Joseph Doherty
+30
-14
@@ -225,7 +225,7 @@
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<div class="col-md-3">
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<label class="form-label" for="mqtt-spb-host">Host ID (optional)</label>
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<InputText id="mqtt-spb-host" @bind-Value="_form.SparkplugHostId" @bind-Value:after="EmitAsync" class="form-control form-control-sm mono" placeholder="scada-primary" />
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<div class="form-text">Sparkplug Host Application identity. Receive-only in this version.</div>
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<div class="form-text">Sparkplug Host Application identity — the <code class="mono">spBv1.0/STATE/{hostId}</code> topic. Required to act as Primary Host.</div>
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</div>
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<div class="col-md-3 d-flex flex-column justify-content-center">
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<div class="form-check form-switch">
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@@ -237,25 +237,42 @@
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<InputCheckbox id="mqtt-spb-primary" @bind-Value="_form.SparkplugActAsPrimaryHost" @bind-Value:after="EmitAsync" class="form-check-input" />
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<label class="form-check-label" for="mqtt-spb-primary">
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Act as Primary Host
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<span class="badge text-bg-warning">not implemented</span>
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</label>
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</div>
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</div>
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@if (_form.SparkplugActAsPrimaryHost)
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{
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@* Shown rather than the flag being hidden: an operator who needs a primary host must
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learn it is absent HERE, not from a plant that never sees a STATE message. The
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driver logs the same warning at startup so the two cannot drift. *@
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<div class="col-12">
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<div class="alert alert-warning py-2 px-3 mb-0 small" role="alert">
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<strong>Primary-host STATE publishing is not implemented.</strong> This driver is
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receive-only: it will not publish <code class="mono">spBv1.0/STATE/@(string.IsNullOrWhiteSpace(_form.SparkplugHostId) ? "{HostId}" : _form.SparkplugHostId)</code>,
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so edge nodes will not treat it as their primary host. The driver logs a warning at
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startup rather than being silently inert. Leave this off unless you are staging
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configuration ahead of that feature.
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@* Two distinct messages, and which one shows is decided by SparkplugPrimaryHostAdvice —
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a plain static, not markup logic, because this repo has no bUnit and a Razor-only rule
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is untestable. A blank host id is a REFUSAL (there is no topic to publish on) and must
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not read like the ordinary case; the driver logs the same distinction at startup so the
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two surfaces cannot drift. *@
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@if (SparkplugPrimaryHostAdvice.DescribeBlockingProblem(_form.SparkplugHostId) is { } problem)
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{
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<div class="col-12">
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<div class="alert alert-warning py-2 px-3 mb-0 small" role="alert">
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<strong>This host claim cannot be made.</strong> @problem
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</div>
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</div>
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</div>
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}
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else
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{
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<div class="col-12">
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<div class="alert alert-info py-2 px-3 mb-0 small" role="alert">
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This node will publish a retained <code class="mono">ONLINE</code> on
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<code class="mono">spBv1.0/STATE/@_form.SparkplugHostId.Trim()</code> and arm a matching
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<code class="mono">OFFLINE</code> as its MQTT Last Will, so edge nodes learn promptly
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whether the host is alive — including after a crash.
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<strong>Only the node holding the redundancy Primary role claims it.</strong>
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Two nodes claiming one host id would let a <em>Secondary's</em> death publish
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<code class="mono">OFFLINE</code> over a healthy Primary and stop the whole group, so a
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failover leaves a brief window in which edge nodes correctly see no host.
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At most one primary host may exist per host id per broker — do not set this on two
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separate deployments pointing at the same broker.
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</div>
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</div>
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}
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}
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<div class="col-12">
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@@ -263,7 +280,6 @@
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Sparkplug tags bind by the <code class="mono">group / edge node / device / metric</code>
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tuple, not by topic — author them with <strong>Browse device…</strong> on a device under
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this driver, which builds its tree from observed birth certificates.
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<strong>MQTT tags are read-only</strong> (write-through is not implemented).
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</div>
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</div>
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}
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+12
-6
@@ -142,17 +142,23 @@ public sealed class MqttDriverFormModel
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public string SparkplugGroupId { get; set; } = "";
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/// <summary>
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/// Sparkplug mode: the Host Application identity. Optional, and <b>receive-only</b> in this
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/// version — see <see cref="SparkplugActAsPrimaryHost"/>.
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/// Sparkplug mode: the Host Application identity — the <c>spBv1.0/STATE/{hostId}</c> topic the
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/// driver observes, and publishes on when <see cref="SparkplugActAsPrimaryHost"/> is set.
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/// Optional for observation; <b>required</b> to claim.
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/// </summary>
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public string SparkplugHostId { get; set; } = "";
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/// <summary>
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/// Sparkplug mode: claim the Primary Host Application role. <b>Not implemented</b> — STATE
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/// publishing is out of scope, and the driver logs a warning rather than being silently inert
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/// when this is set. Surfaced (rather than hidden) so an operator who needs it learns that from
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/// the form instead of from a quiet plant.
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/// Sparkplug mode: claim the Primary Host Application role (Gitea #511) — a retained
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/// <c>ONLINE</c>, a matching <c>OFFLINE</c> armed as the MQTT Last Will, and an explicit
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/// <c>OFFLINE</c> on clean shutdown.
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/// </summary>
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/// <remarks>
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/// <b>Primary-gated:</b> only the node holding the redundancy Primary role claims it, so the two
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/// nodes of a pair cannot fight over one host id. At most one primary host may exist per host id
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/// per broker, which the form states — it is not enforceable from here, since a second
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/// deployment pointing at the same broker is invisible to this one.
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/// </remarks>
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public bool SparkplugActAsPrimaryHost { get; set; }
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/// <summary>Sparkplug mode: answer a detected sequence-number gap with a rebirth request (NCMD).</summary>
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+35
@@ -0,0 +1,35 @@
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namespace ZB.MOM.WW.OtOpcUa.AdminUI.Components.Shared.Drivers.Forms;
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/// <summary>
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/// The rule deciding which primary-host advisory <c>MqttDriverForm</c> shows when
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/// <c>Act as Primary Host</c> is on (Gitea #511).
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/// </summary>
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/// <remarks>
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/// <para>
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/// <b>A plain static rather than markup logic, because this repo has no bUnit.</b> A condition
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/// written inline in a <c>.razor</c> file is unreachable from any test, and the failure mode
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/// here is specific: an operator who ticks the box with a blank host id must see a
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/// <i>refusal</i>, not the ordinary "here is what will happen" note. Getting that backwards
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/// tells them a claim is being made when the driver is in fact declining to make one.
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/// </para>
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/// <para>
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/// Deliberately mirrors <c>SparkplugPrimaryHost.DescribeUnusable</c>'s blank-host-id arm. The
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/// mode arm is not duplicated: this panel only renders inside the SparkplugB branch of the
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/// form, so mode cannot be wrong here.
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/// </para>
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/// </remarks>
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public static class SparkplugPrimaryHostAdvice
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{
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/// <summary>
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/// Describes why a primary-host claim cannot be made for <paramref name="hostId"/>, or
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/// <see langword="null"/> when it can.
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/// </summary>
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/// <param name="hostId">The Sparkplug host id as typed into the form.</param>
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/// <returns>An operator-facing reason, or <see langword="null"/>.</returns>
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public static string? DescribeBlockingProblem(string? hostId) =>
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string.IsNullOrWhiteSpace(hostId)
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? "A Sparkplug host claim is published on spBv1.0/STATE/{hostId}, so it needs a Host ID. "
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+ "Set one above, or turn this off — the driver will otherwise log a warning at startup "
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+ "and publish nothing."
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: null;
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}
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