Fix event hub partition keys bug that cause events to be routed to non-existent partitions

src/Spotflow.InMemory.Azure.EventHubs/Resources/InMemoryEventHub.cs

@@ -33,6 +33,11 @@ public InMemoryEventHub(
         _partitions = CreatePartitions(Properties.PartitionIds, options, this);
     }
 
+    public IReadOnlyDictionary<string, PartitionProperties> GetPartitionProperties()
+    {
+        return _partitions.ToDictionary(kv => kv.Key, kv => kv.Value.GetProperties(), StringComparer.Ordinal);
+    }
+
     public long GetInitialSequenceNumber(string partitionId)
     {
         if (!_partitions.TryGetValue(partitionId, out var partition))
@@ -45,7 +50,7 @@ public long GetInitialSequenceNumber(string partitionId)
 
     private static IReadOnlyDictionary<string, InMemoryPartition> CreatePartitions(string[] partitionIds, InMemoryEventHubOptions options, InMemoryEventHub parent)
     {
-        var result = new Dictionary<string, InMemoryPartition>();
+        var result = new Dictionary<string, InMemoryPartition>(StringComparer.Ordinal);
 
         Random? random = null;
 
@@ -123,13 +128,13 @@ internal bool TryGetPartition(string partitionId, [NotNullWhen(true)] out InMemo
 
     internal InMemoryPartition GetPartitionByKey(string partitionKey)
     {
-        var hashBytes = MD5.HashData(Encoding.UTF8.GetBytes(partitionKey));
+        var hashBytes = SHA384.HashData(Encoding.UTF8.GetBytes(partitionKey));
 
         var hashCode = BinaryPrimitives.ReadInt32BigEndian(hashBytes.AsSpan(0, 4));
 
-        hashCode -= int.MinValue;
+        var mod = Properties.PartitionIds.Length;
 
-        var partitionId = hashCode % Properties.PartitionIds.Length;
+        var partitionId = ((hashCode % mod) + mod) % mod;
 
         return GetPartition(PartitionIdFromInt(partitionId));
     }

tests/Tests/EventHub/EventHubProducerClientTests.cs

@@ -50,4 +50,68 @@ public async Task SystemProperties_ShouldBeSent()
 
     }
 
+    [TestMethod]
+    [DataRow(1)]
+    [DataRow(2)]
+    [DataRow(3)]
+    [DataRow(1024)]
+    [DataRow(1237)]
+    public async Task Send_With_Partition_Key_Should_Provide_Distribution_Properties(int partitionCount)
+    {
+        var eventHub = new InMemoryEventHubProvider().AddNamespace().AddEventHub("test-eh", partitionCount);
+
+        await using var producer = InMemoryEventHubProducerClient.FromEventHub(eventHub);
+
+        foreach (var i in Enumerable.Range(0, 100_000))
+        {
+            var options = new CreateBatchOptions { PartitionKey = $"test-pk-{i:D10}" };
+
+            var batch = await producer.CreateBatchAsync(options);
+
+            batch.TryAdd(new EventData());
+
+            await producer.SendAsync(batch);
+        }
+
+        var lastSequenceNumbers = eventHub.GetPartitionProperties().Select(kv => kv.Value.LastEnqueuedSequenceNumber).ToList();
+
+        var averageLastSequenceNumber = (long) lastSequenceNumbers.Average();
+
+        var delta = (ulong) (averageLastSequenceNumber * 0.4);
+
+        foreach (var sequenceNumber in lastSequenceNumbers)
+        {
+            sequenceNumber.Should().BeCloseTo(averageLastSequenceNumber, delta);
+        }
+    }
+
+    [TestMethod]
+    [DataRow(1)]
+    [DataRow(2)]
+    [DataRow(3)]
+    [DataRow(1024)]
+    [DataRow(1237)]
+    public async Task Send_With_Partition_Key_Should_Respect_Partitioning_Invariant(int partitionCount)
+    {
+        var eventHub = new InMemoryEventHubProvider().AddNamespace().AddEventHub("test-eh", partitionCount);
+
+        await using var producer = InMemoryEventHubProducerClient.FromEventHub(eventHub);
+
+        foreach (var i in Enumerable.Range(0, 10_000))
+        {
+            var options = new CreateBatchOptions { PartitionKey = $"test-pk" };
+
+            var batch = await producer.CreateBatchAsync(options);
+
+            batch.TryAdd(new EventData());
+
+            await producer.SendAsync(batch);
+        }
+
+        var lastSequenceNumbers = eventHub.GetPartitionProperties().Select(kv => kv.Value.LastEnqueuedSequenceNumber).ToList();
+
+        lastSequenceNumbers.Where(n => n >= 0).Should().HaveCount(1);
+        lastSequenceNumbers.Where(n => n == -1).Should().HaveCount(partitionCount - 1);
+    }
+
 }