Handle 404 exceptions in StatusAggregator (#10430)

Author: advay26

src/StatusAggregator/Messages/MessageFactory.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Threading.Tasks;
+using Azure;
 using Microsoft.Extensions.Logging;
 using NuGet.Services.Status;
 using NuGet.Services.Status.Table;
@@ -36,7 +37,17 @@ public async Task CreateMessageAsync(EventEntity eventEntity, DateTime time, Mes
         {
             _logger.LogInformation("Creating new message of type {Type} for event {EventRowKey} at {Timestamp} affecting {ComponentPath} with status {ComponentStatus}.",
                 type, eventEntity.RowKey, time, component.Path, status);
-            var existingMessage = await _table.RetrieveAsync<MessageEntity>(MessageEntity.GetRowKey(eventEntity, time));
+
+            MessageEntity existingMessage = null;
+            try
+            {
+                existingMessage = await _table.RetrieveAsync<MessageEntity>(MessageEntity.GetRowKey(eventEntity, time));
+            }
+            catch (RequestFailedException e) when (e.Status == 404)
+            {
+                _logger.LogInformation("No existing message found.");
+            }
+
             if (existingMessage != null)
             {
                 _logger.LogInformation("Message already exists, will not recreate.");
@@ -83,4 +94,4 @@ public async Task UpdateMessageAsync(EventEntity eventEntity, DateTime time, Mes
             await _table.ReplaceAsync(existingMessage);
         }
     }
-}
+}

tests/StatusAggregator.Tests/Messages/MessageFactoryTests.cs

@@ -1,8 +1,9 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
 using System.Threading.Tasks;
+using Azure;
 using Azure.Data.Tables;
 using Microsoft.Extensions.Logging;
 using Moq;
@@ -101,10 +102,10 @@ public async Task CreatesNewMessage()
                 Builder
                     .Setup(x => x.Build(type, component, expectedStatus))
                     .Returns(contents);
-                
+
                 Table
                     .Setup(x => x.RetrieveAsync<MessageEntity>(MessageEntity.GetRowKey(EventEntity, Time)))
-                    .ReturnsAsync((MessageEntity)null)
+                    .ThrowsAsync(new RequestFailedException(404, "Not Found"))
                     .Verifiable();
 
                 Table