getting-started-receiving-eph.md

Get started receiving messages with the EventProcessorHost in .NET Core

What will be accomplished

This tutorial will walk-through how to create the existing solution SampleEphReceiver (inside this folder). You can run the solution as-is replacing the EhConnectionString/EhEntityPath/StorageAccount settings with your Event Hub and storage account values, or follow this tutorial to create your own.

In this tutorial, we will write a .NET Core console application to receive messages from an Event Hub using the EventProcessorHost.

Prerequisites

1. Visual Studio 2015.

2. .NET Core Visual Studio 2015 Tooling.

3. An Azure subscription.

4. An Event Hubs namespace.

Receive messages from the Event Hub

Create a console application

1. Launch Visual Studio and create a new .NET Core console application.

Add the Event Hubs NuGet package

1. Right-click the newly created project and select Manage NuGet Packages.

2. Click the Browse tab, then search for “Microsoft Azure Event Processor Host” and select the Microsoft Azure Event Processor Host item. Click Install to complete the installation, then close this dialog box.

Implement the IEventProcessor interface

1. Create a new class called `SimpleEventProcessor'.

2. Add the following using statements to the top of the SimpleEventProcessor.cs file.

   using Microsoft.Azure.EventHubs;
   using Microsoft.Azure.EventHubs.Processor;

3. Implement the IEventProcessor interface. The class should look like this:

   namespace SampleReceiver
   {
       using System;
       using System.Collections.Generic;
       using System.Text;
       using System.Threading.Tasks;
       using Microsoft.Azure.EventHubs;
       using Microsoft.Azure.EventHubs.Processor;
   
       public class SimpleEventProcessor : IEventProcessor
       {
           public Task CloseAsync(PartitionContext context, CloseReason reason)
           {
               Console.WriteLine($"Processor Shutting Down. Partition '{context.PartitionId}', Reason: '{reason}'.");
               return Task.FromResult<object>(null);
           }
   
           public Task OpenAsync(PartitionContext context)
           {
               Console.WriteLine($"SimpleEventProcessor initialized.  Partition: '{context.PartitionId}'");
               return Task.FromResult<object>(null);
           }
   
           public Task ProcessErrorAsync(PartitionContext context, Exception error)
           {
               Console.WriteLine($"Error on Partition: {context.PartitionId}, Error: {error.Message}");
               return Task.FromResult<object>(null);
           }
   
           public async Task ProcessEventsAsync(PartitionContext context, IEnumerable<EventData> messages)
           {
               foreach (var eventData in messages)
               {
                   var data = Encoding.UTF8.GetString(eventData.Body.Array, eventData.Body.Offset, eventData.Body.Count);
                   Console.WriteLine($"Message received.  Partition: '{context.PartitionId}', Data: '{data}'");
               }
   
               await context.CheckpointAsync();
           }
       }
   }

Write a main console method that uses SimpleEventProcessor to receive messages from an Event Hub

1. Add the following using statements to the top of the Program.cs file.

   using Microsoft.Azure.EventHubs;
   using Microsoft.Azure.EventHubs.Processor;

2. Add constants to the Program class for the Event Hubs connection string, Event Hub path, storage container name, storage account name, and storage account key. Replace placeholders with their corresponding values.

   private const string EhConnectionString = "{Event Hubs connection string}";
   private const string EhEntityPath = "{Event Hub path/name}";
   private const string StorageContainerName = "{Storage account container name}";
   private const string StorageAccountName = "{Storage account name}";
   private const string StorageAccountKey = "{Storage account key}";
   
   private static readonly string StorageConnectionString = string.Format("DefaultEndpointsProtocol=https;AccountName={0};AccountKey={1}", StorageAccountName, StorageAccountKey);

3. Add the following code to the Main method:

   Console.WriteLine("Registering EventProcessor...");
   
   var eventProcessorHost = new EventProcessorHost(
       EhEntityPath,
       PartitionReceiver.DefaultConsumerGroupName,
       EhConnectionString,
       StorageConnectionString,
       StorageContainerName);
   
   // Registers the Event Processor Host and starts receiving messages
   eventProcessorHost.RegisterEventProcessorAsync<SimpleEventProcessor>().Wait();
   
   Console.WriteLine("Receiving. Press enter key to stop worker.");
   Console.ReadLine();
   
   // Disposes of the Event Processor Host
   eventProcessorHost.UnregisterEventProcessorAsync().Wait();

   Here is what your Program.cs file should look like:

   namespace SampleEphReceiver
   {
       using System;
       using Microsoft.Azure.EventHubs;
       using Microsoft.Azure.EventHubs.Processor;
   
       public class Program
       {
           private const string EhConnectionString = "{Event Hubs connection string}";
           private const string EhEntityPath = "{Event Hub path/name}";
           private const string StorageContainerName = "{Storage account container name}";
           private const string StorageAccountName = "{Storage account name}";
           private const string StorageAccountKey = "{Storage account key}";
   
           private static readonly string StorageConnectionString = string.Format("DefaultEndpointsProtocol=https;AccountName={0};AccountKey={1}", StorageAccountName, StorageAccountKey);
   
           public static void Main(string[] args)
           {
               Console.WriteLine("Registering EventProcessor...");
   
               var eventProcessorHost = new EventProcessorHost(
   				EhEntityPath,
                   PartitionReceiver.DefaultConsumerGroupName,
                   EhConnectionString,
                   StorageConnectionString,
                   StorageContainerName);
   
               // Registers the Event Processor Host and starts receiving messages
               eventProcessorHost.RegisterEventProcessorAsync<SimpleEventProcessor>().Wait();
   
               Console.WriteLine("Receiving. Press enter key to stop worker.");
               Console.ReadLine();
   
               // Disposes of the Event Processor Host
               eventProcessorHost.UnregisterEventProcessorAsync().Wait();
           }
       }
   }

4. Run the program, and ensure that there are no errors.

Congratulations! You have now received messages from an Event Hub.