private static async Task SendAndReceiveEvents()
{
var eventBatch = new[]
{
new EventData(Encoding.UTF8.GetBytes("First event data")),
new EventData(Encoding.UTF8.GetBytes("Second event data")),
new EventData(Encoding.UTF8.GetBytes("Third event data"))
};
var index = 0;
var receivedEvents = new List <EventData>();
//Before sending any event, start the receiver
await receiver.ReceiveAsync(1, TimeSpan.Zero);
Console.Write("Ready to send a batch of " + eventBatch.Count().ToString() + " events... ");
await sender.SendAsync(eventBatch);
Console.Write("Sent\n");
Console.Write("Receiving events... ");
while ((receivedEvents.Count < eventBatch.Length) && (++index < 3))
{
receivedEvents.AddRange(await receiver.ReceiveAsync(eventBatch.Length + 10, TimeSpan.FromMilliseconds(25)));
}
if (receivedEvents.Count == 0)
{
throw new Exception(String.Format("Error, No events received."));
}
Console.Write(receivedEvents.Count() + " events received.\n");
if (receivedEvents.Count() < eventBatch.Count())
{
throw new Exception(String.Format($"Error, expecting {eventBatch.Count()} events, but only got {receivedEvents.Count().ToString()}."));
}
Console.WriteLine("done");
}
/// <summary>
/// Runs the sample using the specified Event Hubs connection information.
/// </summary>
///
/// <param name="connectionString">The connection string for the Event Hubs namespace that the sample should target.</param>
/// <param name="eventHubName">The name of the Event Hub, sometimes known as its path, that she sample should run against.</param>
///
public async Task RunAsync(string connectionString,
string eventHubName)
{
// An Event Hub consumer is associated with a specific Event Hub and consumer group. The consumer group is
// a label that identifies one or more consumers as a set. Often, consumer groups are named after the responsibility
// of the consumer in an application, such as "Telemetry" or "OrderProcessing". When an Event Hub is created, a default
// consumer group is created with it, called "$Default."
//
// Each consumer has a unique view of the events in a partition that it reads from, meaning that events are available to all
// consumers and are not removed from the partition when a consumer reads them. This allows for one or more consumers to read and
// process events from the partition at different speeds and beginning with different events without interfering with
// one another.
//
// When events are published, they will continue to exist in the partition and be available for consuming until they
// reach an age where they are older than the retention period.
// (see: https://docs.microsoft.com/en-us/azure/event-hubs/event-hubs-faq#what-is-the-maximum-retention-period-for-events)
//
// Because events are not removed from the partition when consuming, a consumer must specify where in the partition it
// would like to begin reading events. For example, this may be starting from the very beginning of the stream, at an
// offset from the beginning, the next event available after a specific point in time, or at a specific event.
// We will start by creating a client to inspect the Event Hub and select a partition to operate against to ensure that
// events are being published and read from the same partition.
string firstPartition;
await using (var inspectionClient = new EventHubProducerClient(connectionString, eventHubName))
{
// With our client, we can now inspect the partitions and find the identifier
// of the first.
firstPartition = (await inspectionClient.GetPartitionIdsAsync()).First();
}
// In this example, we will create our consumer client for the first partition in the Event Hub, using the default consumer group
// that is created with an Event Hub. Our consumer will begin watching the partition at the very end, reading only new events
// that we will publish for it.
await using (var consumerClient = new EventHubConsumerClient(EventHubConsumerClient.DefaultConsumerGroupName, firstPartition, EventPosition.Latest, connectionString, eventHubName))
await using (var producerClient = new EventHubProducerClient(connectionString, eventHubName, new EventHubProducerClientOptions {
PartitionId = firstPartition
}))
{
// Because our consumer is reading from the latest position, it won't see events that have previously
// been published. Before we can publish the events, we will need to ask the consumer to perform an operation,
// because it opens its connection only when it needs to. The first receive that we ask of it will not see
// any events, but will allow the consumer to start watching the partition.
//
// Because the maximum wait time is specified as zero, this call will return immediately and will not
// have consumed any events.
await consumerClient.ReceiveAsync(1, TimeSpan.Zero);
// Now that the consumer is watching the partition, let's publish the event that we would like to
// receive.
await producerClient.SendAsync(new EventData(Encoding.UTF8.GetBytes("Hello, Event Hubs!")));
Console.WriteLine("The event batch has been published.");
// Because publishing and receiving events is asynchronous, the events that we published may not
// be immediately available for our consumer to see.
//
// We will iterate over the available events in the partition, which should be just the event that we published. Because
// we're expecting only the one event, we will exit the loop when we receive it. To be sure that we do not block forever
// waiting on an event that is not published, we will specify a fairly long time to wait and then cancel waiting.
CancellationTokenSource cancellationSource = new CancellationTokenSource();
cancellationSource.CancelAfter(TimeSpan.FromSeconds(30));
EventData receivedEvent = null;
Stopwatch watch = Stopwatch.StartNew();
await foreach (EventData currentEvent in consumerClient.SubscribeToEvents(cancellationSource.Token))
{
receivedEvent = currentEvent;
watch.Stop();
break;
}
// Print out the events that we received.
Console.WriteLine();
Console.WriteLine($"The following event was consumed in { watch.ElapsedMilliseconds } milliseconds:");
// The body of our event was an encoded string; we'll recover the message by reversing the encoding process.
string message = (receivedEvent == null) ? "No event was received." : Encoding.UTF8.GetString(receivedEvent.Body.ToArray());
Console.WriteLine($"\tMessage: \"{ message }\"");
}
// At this point, our clients have passed their "using" scope and have safely been disposed of. We
// have no further obligations.
Console.WriteLine();
}
public async Task PartitionProcessorCanCreateACheckpointFromPartitionContext()
{
await using (EventHubScope scope = await EventHubScope.CreateAsync(1))
{
var connectionString = TestEnvironment.BuildConnectionStringForEventHub(scope.EventHubName);
await using (var connection = new EventHubConnection(connectionString))
{
// Send some events.
EventData lastEvent;
var dummyEvent = new EventData(Encoding.UTF8.GetBytes("I'm dummy."));
var partitionId = (await connection.GetPartitionIdsAsync(DefaultRetryPolicy)).First();
await using (var producer = new EventHubProducerClient(connection))
await using (var consumer = new EventHubConsumerClient(EventHubConsumerClient.DefaultConsumerGroupName, partitionId, EventPosition.Earliest, connectionString))
{
// Send a few events. We are only interested in the last one of them.
var dummyEventsCount = 10;
for (int i = 0; i < dummyEventsCount; i++)
{
await producer.SendAsync(dummyEvent);
}
// Receive the events; because there is some non-determinism in the messaging flow, the
// sent events may not be immediately available. Allow for a small number of attempts to receive, in order
// to account for availability delays.
var receivedEvents = new List <EventData>();
var index = 0;
while ((receivedEvents.Count < dummyEventsCount) && (++index < ReceiveRetryLimit))
{
receivedEvents.AddRange(await consumer.ReceiveAsync(dummyEventsCount + 10, TimeSpan.FromMilliseconds(25)));
}
Assert.That(receivedEvents.Count, Is.EqualTo(dummyEventsCount));
lastEvent = receivedEvents.Last();
}
// Create a partition manager so we can retrieve the created checkpoint from it.
var partitionManager = new InMemoryPartitionManager();
// Create the event processor manager to manage our event processors.
var eventProcessorManager = new EventProcessorManager
(
EventHubConsumerClient.DefaultConsumerGroupName,
connection,
partitionManager,
onProcessEvents: (partitionContext, events) =>
{
// Make it a list so we can safely enumerate it.
var eventsList = new List <EventData>(events ?? Enumerable.Empty <EventData>());
if (eventsList.Any())
{
partitionContext.UpdateCheckpointAsync(eventsList.Last());
}
}
);
eventProcessorManager.AddEventProcessors(1);
// Start the event processors.
await eventProcessorManager.StartAllAsync();
// Make sure the event processors have enough time to stabilize and receive events.
await eventProcessorManager.WaitStabilization();
// Stop the event processors.
await eventProcessorManager.StopAllAsync();
// Validate results.
IEnumerable <PartitionOwnership> ownershipEnumerable = await partitionManager.ListOwnershipAsync(connection.FullyQualifiedNamespace, connection.EventHubName, EventHubConsumerClient.DefaultConsumerGroupName);
Assert.That(ownershipEnumerable, Is.Not.Null);
Assert.That(ownershipEnumerable.Count, Is.EqualTo(1));
PartitionOwnership ownership = ownershipEnumerable.Single();
Assert.That(ownership.Offset.HasValue, Is.True);
Assert.That(ownership.Offset.Value, Is.EqualTo(lastEvent.Offset));
Assert.That(ownership.SequenceNumber.HasValue, Is.True);
Assert.That(ownership.SequenceNumber.Value, Is.EqualTo(lastEvent.SequenceNumber));
}
}
}
public async Task EventProcessorCanReceiveFromCheckpointedEventPosition()
{
await using (EventHubScope scope = await EventHubScope.CreateAsync(1))
{
var connectionString = TestEnvironment.BuildConnectionStringForEventHub(scope.EventHubName);
await using (var connection = new EventHubConnection(connectionString))
{
int receivedEventsCount = 0;
// Send some events.
var expectedEventsCount = 20;
var dummyEvent = new EventData(Encoding.UTF8.GetBytes("I'm dummy."));
long?checkpointedSequenceNumber = default;
var partitionId = (await connection.GetPartitionIdsAsync(DefaultRetryPolicy)).First();
await using (var producer = new EventHubProducerClient(connectionString))
await using (var consumer = new EventHubConsumerClient(EventHubConsumerClient.DefaultConsumerGroupName, partitionId, EventPosition.Earliest, connection))
{
// Send a few dummy events. We are not expecting to receive these.
var dummyEventsCount = 30;
for (int i = 0; i < dummyEventsCount; i++)
{
await producer.SendAsync(dummyEvent);
}
// Receive the events; because there is some non-determinism in the messaging flow, the
// sent events may not be immediately available. Allow for a small number of attempts to receive, in order
// to account for availability delays.
var receivedEvents = new List <EventData>();
var index = 0;
while ((receivedEvents.Count < dummyEventsCount) && (++index < ReceiveRetryLimit))
{
receivedEvents.AddRange(await consumer.ReceiveAsync(dummyEventsCount + 10, TimeSpan.FromMilliseconds(25)));
}
Assert.That(receivedEvents.Count, Is.EqualTo(dummyEventsCount));
checkpointedSequenceNumber = receivedEvents.Last().SequenceNumber;
// Send the events we expect to receive.
for (int i = 0; i < expectedEventsCount; i++)
{
await producer.SendAsync(dummyEvent);
}
}
// Create a partition manager and add an ownership with a checkpoint in it.
var partitionManager = new InMemoryPartitionManager();
await partitionManager.ClaimOwnershipAsync(new List <PartitionOwnership>()
{
new PartitionOwnership(connection.FullyQualifiedNamespace, connection.EventHubName,
EventHubConsumerClient.DefaultConsumerGroupName, "ownerIdentifier", partitionId,
sequenceNumber: checkpointedSequenceNumber, lastModifiedTime: DateTimeOffset.UtcNow)
});
// Create the event processor manager to manage our event processors.
var eventProcessorManager = new EventProcessorManager
(
EventHubConsumerClient.DefaultConsumerGroupName,
connection,
partitionManager,
onProcessEvents: (partitionContext, events) =>
{
// Make it a list so we can safely enumerate it.
var eventsList = new List <EventData>(events ?? Enumerable.Empty <EventData>());
if (eventsList.Count > 0)
{
Interlocked.Add(ref receivedEventsCount, eventsList.Count);
}
}
);
eventProcessorManager.AddEventProcessors(1);
// Start the event processors.
await eventProcessorManager.StartAllAsync();
// Make sure the event processors have enough time to stabilize and receive events.
await eventProcessorManager.WaitStabilization();
// Stop the event processors.
await eventProcessorManager.StopAllAsync();
// Validate results.
Assert.That(receivedEventsCount, Is.EqualTo(expectedEventsCount));
}
}
}
/// <summary>
/// Runs the sample using the specified Event Hubs connection information.
/// </summary>
///
/// <param name="connectionString">The connection string for the Event Hubs namespace that the sample should target.</param>
/// <param name="eventHubName">The name of the Event Hub, sometimes known as its path, that she sample should run against.</param>
///
public async Task RunAsync(string connectionString,
string eventHubName)
{
// We will start by creating a client to inspect the Event Hub and select a partition to operate against to ensure that
// events are being published and read from the same partition.
string firstPartition;
await using (var inspectionClient = new EventHubProducerClient(connectionString, eventHubName))
{
// With our client, we can now inspect the partitions and find the identifier
// of the first.
firstPartition = (await inspectionClient.GetPartitionIdsAsync()).First();
}
// In this example, we will create our consumer client for the first partition in the Event Hub, using the default consumer group
// that is created with an Event Hub. Our consumer will begin watching the partition at the very end, reading only new events
// that we will publish for it.
await using (var consumerClient = new EventHubConsumerClient(EventHubConsumerClient.DefaultConsumerGroupName, firstPartition, EventPosition.Latest, connectionString, eventHubName))
await using (var producerClient = new EventHubProducerClient(connectionString, eventHubName, new EventHubProducerClientOptions {
PartitionId = firstPartition
}))
{
// Because our consumer client is reading from the latest position, it won't see events that have previously
// been published. Before we can publish the events, we will need to ask the consumer to perform an operation,
// because it opens its connection only when it needs to. The first receive that we ask of it will not see
// any events, but will allow the consumer to start watching the partition.
//
// Because the maximum wait time is specified as zero, this call will return immediately and will not
// have consumed any events.
await consumerClient.ReceiveAsync(1, TimeSpan.Zero);
// Now that the consumer is watching the partition, let's publish a fair sized batch of events
// we would like for it to consume.
int eventBatchSize = 100;
EventData[] eventBatch = new EventData[eventBatchSize];
for (int index = 0; index < eventBatchSize; ++index)
{
eventBatch[index] = new EventData(Encoding.UTF8.GetBytes($"I am event #{ index }"));
}
await producerClient.SendAsync(eventBatch);
Console.WriteLine($"The event batch with { eventBatchSize } events has been published.");
// To allow for throughput in our application, we will process the published events by consuming them in
// small batches with a small wait time. This will allow us to receive and process more quickly than blocking
// to wait on a larger batch size.
//
// The values that are used in this example are intended just for illustration and not intended as guidance for a recommended
// set of defaults. In a real-world application, determining the right balance of batch size and wait time to achieve
// the desired performance will often vary depending on the application and event data being consumed. It is an area
// where some experimentation in the application context may prove helpful.
//
// Our example will attempt to read about 1/5 of the batch at a time, which should result in the need for 5 batches to
// be consumed. Because publishing and receiving events is asynchronous, the events that we published may not be
// immediately available for our consumer to see. To compensate, we will allow for a small number of extra attempts beyond
// the expected 5 to be sure that we don't stop reading before we receive all of our events.
var receivedEvents = new List <EventData>();
int consumeBatchSize = (int)Math.Floor(eventBatchSize / 5.0f);
int maximumAttempts = 15;
int attempts = 0;
while ((receivedEvents.Count < eventBatchSize) && (++attempts < maximumAttempts))
{
// Each receive, we ask for the maximum amount of events that we would like in the batch and
// specify the maximum amount of time that we would like to wait for them.
//
// The batch of events will be returned to us when either we have read our maximum number of events
// or when the time that we asked to wait has elapsed. This means that a batch we receive may have
// between zero and the maximum we asked for, depending on what was available in the partition.
//
// For this attempt, we will ask to receive our computed batch size (1/5 of published events) and wait, at most,
// 25 milliseconds to receive them. We'll then process them and if we haven't gotten all that we published, we'll
// make another attempt until either we have them or we have tried for our maximum number of attempts.
IEnumerable <EventData> receivedBatch = await consumerClient.ReceiveAsync(consumeBatchSize, TimeSpan.FromMilliseconds(25));
receivedEvents.AddRange(receivedBatch);
}
// Print out the events that we received.
Console.WriteLine();
Console.WriteLine($"Events Consumed: { receivedEvents.Count }");
foreach (EventData eventData in receivedEvents)
{
// The body of our event was an encoded string; we'll recover the
// message by reversing the encoding process.
string message = Encoding.UTF8.GetString(eventData.Body.ToArray());
Console.WriteLine($"\tMessage: \"{ message }\"");
}
}
// At this point, our clients have passed their "using" scope and have safely been disposed of. We
// have no further obligations.
Console.WriteLine();
}
/// <summary>
/// Runs the sample using the specified Event Hubs connection information.
/// </summary>
///
/// <param name="connectionString">The connection string for the Event Hubs namespace that the sample should target.</param>
/// <param name="eventHubName">The name of the Event Hub, sometimes known as its path, that she sample should run against.</param>
///
public async Task RunAsync(string connectionString,
string eventHubName)
{
// We will start by creating a client to inspect the Event Hub and select a partition to operate against to ensure that
// events are being published and read from the same partition.
string firstPartition;
await using (var inspectionClient = new EventHubProducerClient(connectionString, eventHubName))
{
// With our client, we can now inspect the partitions and find the identifier
// of the first.
firstPartition = (await inspectionClient.GetPartitionIdsAsync()).First();
}
// In this example, we will make use of multiple clients. Because clients are typically responsible for managing their own connection to the
// Event Hubs service, each will implicitly create their own connection. In this example, we will create a connection that may be shared amongst
// clients in order to illustrate connection sharing. Because we are explicitly creating the connection, we assume responsibility for managing its
// lifespan and ensuring that it is properly closed or disposed when we are done using it.
await using (var eventHubConnection = new EventHubConnection(connectionString, eventHubName))
await using (var producerClient = new EventHubProducerClient(eventHubConnection, new EventHubProducerClientOptions {
PartitionId = firstPartition
}))
{
// Our initial consumer will begin watching the partition at the very end, reading only new events
// that we will publish for it.
//
// Each event that the initial consumer reads will have attributes set that describe the event's place in the
// partition, such as its offset, sequence number, and the date/time that it was enqueued. These attributes can be
// used to create a new consumer that begins consuming at a known position.
//
// With Event Hubs, it is the responsibility of an application consuming events to keep track of those that it has processed,
// and to manage where in the partition the consumer begins reading events. This is done by using the position information to track
// state, commonly known as "creating a checkpoint."
//
// The goal is to preserve the position of an event in some form of durable state, such as writing it to a database, so that if the
// consuming application crashes or is otherwise restarted, it can retrieve that checkpoint information and use it to create a consumer that
// begins reading at the position where it left off.
//
// It is important to note that there is potential for a consumer to process an event and be unable to preserve the checkpoint. A well-designed
// consumer must be able to deal with processing the same event multiple times without it causing data corruption or otherwise creating issues.
// Event Hubs, like most event streaming systems, guarantees "at least once" delivery; even in cases where the consumer does not experience a restart,
// there is a small possibility that the service will return an event multiple times.
//
// In this example, we will publish a batch of events to be received with an initial consumer. The third event that is consumed will be captured
// and another consumer will use its attributes to start reading the event that follows, consuming the same set of events that our initial consumer
// read, skipping over the first three.
int eventBatchSize = 50;
EventData thirdEvent;
await using (var initialConsumerClient = new EventHubConsumerClient(EventHubConsumerClient.DefaultConsumerGroupName, firstPartition, EventPosition.Latest, eventHubConnection))
{
// The first receive that we ask of it will not see any events, but allows the consumer to start watching the partition. Because
// the maximum wait time is specified as zero, this call will return immediately and will not have consumed any events.
await initialConsumerClient.ReceiveAsync(1, TimeSpan.Zero);
// Now that the consumer is watching the partition, let's publish a batch of events.
EventData[] eventBatch = new EventData[eventBatchSize];
for (int index = 0; index < eventBatchSize; ++index)
{
eventBatch[index] = new EventData(Encoding.UTF8.GetBytes($"I am event #{ index }"));
}
await producerClient.SendAsync(eventBatch);
Console.WriteLine($"The event batch with { eventBatchSize } events has been published.");
// We will consume the events until all of the published events have been received.
var receivedEvents = new List <EventData>();
CancellationTokenSource cancellationSource = new CancellationTokenSource();
cancellationSource.CancelAfter(TimeSpan.FromSeconds(30));
await foreach (EventData currentEvent in initialConsumerClient.SubscribeToEvents(cancellationSource.Token))
{
receivedEvents.Add(currentEvent);
if (receivedEvents.Count >= eventBatchSize)
{
break;
}
}
// Print out the events that we received.
Console.WriteLine();
Console.WriteLine($"The initial consumer processed { receivedEvents.Count } events of the { eventBatchSize } that were published. { eventBatchSize } were expected.");
foreach (EventData eventData in receivedEvents)
{
// The body of our event was an encoded string; we'll recover the
// message by reversing the encoding process.
string message = Encoding.UTF8.GetString(eventData.Body.ToArray());
Console.WriteLine($"\tMessage: \"{ message }\"");
}
// Remember the third event that was consumed.
thirdEvent = receivedEvents[2];
}
// At this point, our initial consumer client has passed its "using" scope and has been safely disposed of.
//
// Create a new consumer beginning using the third event as the last sequence number processed; this new consumer will begin reading at the next available
// sequence number, allowing it to read the set of published events beginning with the fourth one.
await using (var newConsumerClient = new EventHubConsumerClient(EventHubConsumerClient.DefaultConsumerGroupName, firstPartition, EventPosition.FromSequenceNumber(thirdEvent.SequenceNumber.Value), eventHubConnection))
{
// We will consume the events using the new consumer until all of the published events have been received.
CancellationTokenSource cancellationSource = new CancellationTokenSource();
cancellationSource.CancelAfter(TimeSpan.FromSeconds(30));
int expectedCount = (eventBatchSize - 3);
var receivedEvents = new List <EventData>();
await foreach (EventData currentEvent in newConsumerClient.SubscribeToEvents(cancellationSource.Token))
{
receivedEvents.Add(currentEvent);
if (receivedEvents.Count >= expectedCount)
{
break;
}
}
// Print out the events that we received.
Console.WriteLine();
Console.WriteLine();
Console.WriteLine($"The new consumer processed { receivedEvents.Count } events of the { eventBatchSize } that were published. { expectedCount } were expected.");
foreach (EventData eventData in receivedEvents)
{
// The body of our event was an encoded string; we'll recover the
// message by reversing the encoding process.
string message = Encoding.UTF8.GetString(eventData.Body.ToArray());
Console.WriteLine($"\tMessage: \"{ message }\"");
}
}
}
// At this point, our clients and connection have passed their "using" scope and have safely been disposed of. We
// have no further obligations.
Console.WriteLine();
}
