| | | 1 | | // Copyright (c) Microsoft Corporation. All rights reserved. |
| | | 2 | | // Licensed under the MIT License. |
| | | 3 | | |
| | | 4 | | using System; |
| | | 5 | | using System.Collections.Generic; |
| | | 6 | | using System.Text; |
| | | 7 | | using System.Threading; |
| | | 8 | | using System.Threading.Tasks; |
| | | 9 | | using Azure.Messaging.EventHubs.Consumer; |
| | | 10 | | using Azure.Messaging.EventHubs.Producer; |
| | | 11 | | using Azure.Messaging.EventHubs.Samples.Infrastructure; |
| | | 12 | | |
| | | 13 | | namespace Azure.Messaging.EventHubs.Samples |
| | | 14 | | { |
| | | 15 | | /// <summary> |
| | | 16 | | /// An example of reading events, beginning with only those newly available from an Event Hub. |
| | | 17 | | /// </summary> |
| | | 18 | | /// |
| | | 19 | | public class Sample09_ReadOnlyNewEvents : IEventHubsSample |
| | | 20 | | { |
| | | 21 | | /// <summary> |
| | | 22 | | /// The name of the sample. |
| | | 23 | | /// </summary> |
| | | 24 | | /// |
| | 0 | 25 | | public string Name => nameof(Sample09_ReadOnlyNewEvents); |
| | | 26 | | |
| | | 27 | | /// <summary> |
| | | 28 | | /// A short description of the sample. |
| | | 29 | | /// </summary> |
| | | 30 | | /// |
| | 0 | 31 | | public string Description => "An example of reading events, beginning with only those newly available from an Ev |
| | | 32 | | |
| | | 33 | | /// <summary> |
| | | 34 | | /// Runs the sample using the specified Event Hubs connection information. |
| | | 35 | | /// </summary> |
| | | 36 | | /// |
| | | 37 | | /// <param name="connectionString">The connection string for the Event Hubs namespace that the sample should tar |
| | | 38 | | /// <param name="eventHubName">The name of the Event Hub, sometimes known as its path, that she sample should ru |
| | | 39 | | /// |
| | | 40 | | public async Task RunAsync(string connectionString, |
| | | 41 | | string eventHubName) |
| | | 42 | | { |
| | | 43 | | // In this example, our consumer will read from the latest position instead of the earliest. As a result, i |
| | | 44 | | // have previously been published. Before we can publish the events and have them observed, we will need to |
| | | 45 | | // to perform a read operation in order for it to begin observing the Event Hub partitions. |
| | | 46 | | // |
| | | 47 | | // Each partition of an Event Hub represents potentially infinite stream of events. When a consumer is read |
| | | 48 | | // point where it can assess that all events have been read and no more will be available. As a result, whe |
| | | 49 | | // the available events for a partition, it will continue to wait for new events to arrive so that it can su |
| | | 50 | | // time, the iterator will block. |
| | | 51 | | // |
| | | 52 | | // In order to prevent the consumer from waiting forever for events, and blocking other code, there are two |
| | | 53 | | // control this behavior. First, signaling the cancellation token passed when reading will cause the consum |
| | | 54 | | // immediately. This is desirable when you have decided that you are done reading and do not wish to contin |
| | | 55 | | // you would like control returned to your code momentarily to perform some action and then to continue read |
| | | 56 | | // |
| | | 57 | | // In that scenario, you may specify a maximum wait time which is applied to each iteration of the enumerato |
| | | 58 | | // event being available to read, the enumerator will emit an empty event in order to return control to the |
| | | 59 | | // such as sending a heartbeat, emitting telemetry, or simply exiting the loop. |
| | | 60 | | // |
| | | 61 | | // For our loop, we'll specify a small wait time when we begin reading, which will allow control to return t |
| | | 62 | | // the events after we ensure the consumer is observing the partition. |
| | | 63 | | |
| | 0 | 64 | | await using (var consumerClient = new EventHubConsumerClient(EventHubConsumerClient.DefaultConsumerGroupName |
| | | 65 | | { |
| | 0 | 66 | | bool wereEventsPublished = false; |
| | 0 | 67 | | int eventBatchCount = 0; |
| | 0 | 68 | | List<EventData> receivedEvents = new List<EventData>(); |
| | | 69 | | |
| | | 70 | | // Each time the consumer looks to read events, we'll ask that it waits only a short time before emittin |
| | | 71 | | // an empty event, so that our code has the chance to run without indefinite blocking. |
| | | 72 | | |
| | 0 | 73 | | ReadEventOptions readOptions = new ReadEventOptions |
| | 0 | 74 | | { |
| | 0 | 75 | | MaximumWaitTime = TimeSpan.FromMilliseconds(150) |
| | 0 | 76 | | }; |
| | | 77 | | |
| | | 78 | | // As a preventative measure, we'll also specify that cancellation should occur after 2 minutes, so that |
| | | 79 | | // in the event of a service error where the events we've published cannot be read. |
| | | 80 | | |
| | 0 | 81 | | using CancellationTokenSource cancellationSource = new CancellationTokenSource(); |
| | 0 | 82 | | cancellationSource.CancelAfter(TimeSpan.FromMinutes(2)); |
| | | 83 | | |
| | | 84 | | // The reading of all events will default to the earliest events available in each partition; in order t |
| | | 85 | | // latest event, we'll need to specify that reading should not start at earliest. |
| | | 86 | | |
| | 0 | 87 | | await foreach (PartitionEvent currentEvent in consumerClient.ReadEventsAsync(startReadingAtEarliestEvent |
| | | 88 | | { |
| | 0 | 89 | | if (!wereEventsPublished) |
| | | 90 | | { |
| | 0 | 91 | | await using (var producerClient = new EventHubProducerClient(connectionString, eventHubName)) |
| | | 92 | | { |
| | 0 | 93 | | using EventDataBatch eventBatch = await producerClient.CreateBatchAsync(); |
| | 0 | 94 | | eventBatch.TryAdd(new EventData(Encoding.UTF8.GetBytes("Hello, Event Hubs!"))); |
| | 0 | 95 | | eventBatch.TryAdd(new EventData(Encoding.UTF8.GetBytes("Goodbye, Event Hubs!"))); |
| | | 96 | | |
| | 0 | 97 | | await producerClient.SendAsync(eventBatch); |
| | 0 | 98 | | wereEventsPublished = true; |
| | 0 | 99 | | eventBatchCount = eventBatch.Count; |
| | | 100 | | |
| | 0 | 101 | | await Task.Delay(250); |
| | 0 | 102 | | Console.WriteLine("The event batch has been published."); |
| | 0 | 103 | | } |
| | | 104 | | |
| | | 105 | | // Since we know that there was no event to observe for this iteration, |
| | | 106 | | // we'll just skip to the next one. |
| | | 107 | | |
| | 0 | 108 | | continue; |
| | | 109 | | } |
| | | 110 | | |
| | | 111 | | // Because publishing and receiving events is asynchronous, the events that we published may not |
| | | 112 | | // be immediately available for our consumer to see, so we'll have to guard against an empty event b |
| | | 113 | | // if our wait time interval has elapsed before the consumer observed the events that we published. |
| | | 114 | | |
| | 0 | 115 | | if (currentEvent.Data != null) |
| | | 116 | | { |
| | 0 | 117 | | receivedEvents.Add(currentEvent.Data); |
| | | 118 | | |
| | 0 | 119 | | if (receivedEvents.Count >= eventBatchCount) |
| | | 120 | | { |
| | | 121 | | break; |
| | | 122 | | } |
| | | 123 | | } |
| | | 124 | | } |
| | | 125 | | |
| | | 126 | | // Print out the events that we received; the body is an encoded string; we'll recover the message by re |
| | | 127 | | |
| | 0 | 128 | | Console.WriteLine(); |
| | | 129 | | |
| | 0 | 130 | | foreach (EventData currentEvent in receivedEvents) |
| | | 131 | | { |
| | 0 | 132 | | string message = Encoding.UTF8.GetString(currentEvent.Body.ToArray()); |
| | 0 | 133 | | Console.WriteLine($"\tEvent Message: \"{ message }\""); |
| | | 134 | | } |
| | 0 | 135 | | } |
| | | 136 | | |
| | | 137 | | // At this point, our clients have passed their "using" scope and have safely been disposed of. We |
| | | 138 | | // have no further obligations. |
| | | 139 | | |
| | 0 | 140 | | Console.WriteLine(); |
| | 0 | 141 | | } |
| | | 142 | | } |
| | | 143 | | } |