6.2 MqttPublisher.PublishAsync

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/FrameProcessor/Mqtt/MqttPublisher.cs

@@ -1,7 +1,9 @@
 using FrameProcessor.Configuration;
+using FrameProcessor.Domain;
 using Microsoft.Extensions.Options;
 using MQTTnet;
 using MQTTnet.Client;
+using MQTTnet.Protocol;
 
 namespace FrameProcessor.Mqtt;
 
@@ -86,6 +88,43 @@ public sealed class MqttPublisher : BackgroundService
         }
     }
 
+    /// <summary>
+    /// Publish an <c>update</c> notification for the given frame. Returns
+    /// <see cref="PublishResult.Failure"/> on any error (disconnected, broker reject,
+    /// transport fault) — per SPEC.md §3.5, publish failure must not fail the upload,
+    /// so this method never throws on MQTT errors. <see cref="OperationCanceledException"/>
+    /// still propagates so callers can honor cooperative cancellation.
+    /// </summary>
+    public async Task<PublishResult> PublishAsync(MacAddress mac, CancellationToken cancellationToken)
+    {
+        var opts = _options.Value;
+        var topic = $"{opts.BaseTopic}/{mac}";
+        var message = new MqttApplicationMessageBuilder()
+            .WithTopic(topic)
+            .WithPayload("update")
+            .WithQualityOfServiceLevel((MqttQualityOfServiceLevel)opts.PublishQos)
+            .WithRetainFlag(false)
+            .Build();
+
+        try
+        {
+            var result = await _client.PublishAsync(message, cancellationToken).ConfigureAwait(false);
+            if (result.IsSuccess)
+            {
+                _logger.LogInformation("MQTT publish to {Topic} succeeded", topic);
+                return PublishResult.Success;
+            }
+
+            _logger.LogWarning("MQTT publish to {Topic} returned {ReasonCode}", topic, result.ReasonCode);
+            return PublishResult.Failure;
+        }
+        catch (Exception ex) when (!cancellationToken.IsCancellationRequested)
+        {
+            _logger.LogWarning(ex, "MQTT publish to {Topic} failed", topic);
+            return PublishResult.Failure;
+        }
+    }
+
     public override async Task StopAsync(CancellationToken cancellationToken)
     {
         await base.StopAsync(cancellationToken).ConfigureAwait(false);