dotnet add package Azure.Messaging.ServiceBus
dotnet add package Azure.Identity

AZURE_SERVICEBUS_FULLY_QUALIFIED_NAMESPACE=<namespace>.servicebus.windows.net
# Or connection string (less secure)
AZURE_SERVICEBUS_CONNECTION_STRING=Endpoint=sb://...

using Azure.Identity;
using Azure.Messaging.ServiceBus;

string fullyQualifiedNamespace = "<namespace>.servicebus.windows.net";
await using ServiceBusClient client = new(fullyQualifiedNamespace, new DefaultAzureCredential());

string connectionString = "<connection_string>";
await using ServiceBusClient client = new(connectionString);

services.AddAzureClients(builder =>
{
    builder.AddServiceBusClientWithNamespace("<namespace>.servicebus.windows.net");
    builder.UseCredential(new DefaultAzureCredential());
});

ServiceBusClient
├── CreateSender(queueOrTopicName)      → ServiceBusSender
├── CreateReceiver(queueName)           → ServiceBusReceiver
├── CreateReceiver(topicName, subName)  → ServiceBusReceiver
├── AcceptNextSessionAsync(queueName)   → ServiceBusSessionReceiver
├── CreateProcessor(queueName)          → ServiceBusProcessor
└── CreateSessionProcessor(queueName)   → ServiceBusSessionProcessor

ServiceBusAdministrationClient (separate client for CRUD)

await using ServiceBusClient client = new(fullyQualifiedNamespace, new DefaultAzureCredential());
ServiceBusSender sender = client.CreateSender("my-queue");

// Single message
ServiceBusMessage message = new("Hello world!");
await sender.SendMessageAsync(message);

// Safe batching (recommended)
using ServiceBusMessageBatch batch = await sender.CreateMessageBatchAsync();
if (batch.TryAddMessage(new ServiceBusMessage("Message 1")))
{
    // Message added successfully
}
if (batch.TryAddMessage(new ServiceBusMessage("Message 2")))
{
    // Message added successfully
}
await sender.SendMessagesAsync(batch);

ServiceBusReceiver receiver = client.CreateReceiver("my-queue");

// Single message
ServiceBusReceivedMessage message = await receiver.ReceiveMessageAsync();
string body = message.Body.ToString();
Console.WriteLine(body);

// Complete the message (removes from queue)
await receiver.CompleteMessageAsync(message);

// Batch receive
IReadOnlyList<ServiceBusReceivedMessage> messages = await receiver.ReceiveMessagesAsync(maxMessages: 10);
foreach (var msg in messages)
{
    Console.WriteLine(msg.Body.ToString());
    await receiver.CompleteMessageAsync(msg);
}

// Complete - removes message from queue
await receiver.CompleteMessageAsync(message);

// Abandon - releases lock, message can be received again
await receiver.AbandonMessageAsync(message);

// Defer - prevents normal receive, use ReceiveDeferredMessageAsync
await receiver.DeferMessageAsync(message);

// Dead Letter - moves to dead letter subqueue
await receiver.DeadLetterMessageAsync(message, "InvalidFormat", "Message body was not valid JSON");

ServiceBusProcessor processor = client.CreateProcessor("my-queue", new ServiceBusProcessorOptions
{
    AutoCompleteMessages = false,
    MaxConcurrentCalls = 2
});

processor.ProcessMessageAsync += async (args) =>
{
    try
    {
        string body = args.Message.Body.ToString();
        Console.WriteLine($"Received: {body}");
        await args.CompleteMessageAsync(args.Message);
    }
    catch (Exception ex)
    {
        Console.WriteLine($"Error processing: {ex.Message}");
        await args.AbandonMessageAsync(args.Message);
    }
};

processor.ProcessErrorAsync += (args) =>
{
    Console.WriteLine($"Error source: {args.ErrorSource}");
    Console.WriteLine($"Entity: {args.EntityPath}");
    Console.WriteLine($"Exception: {args.Exception}");
    return Task.CompletedTask;
};

await processor.StartProcessingAsync();
// ... application runs
await processor.StopProcessingAsync();

// Send session message
ServiceBusMessage message = new("Hello")
{
    SessionId = "order-123"
};
await sender.SendMessageAsync(message);

// Receive from next available session
ServiceBusSessionReceiver receiver = await client.AcceptNextSessionAsync("my-queue");

// Or receive from specific session
ServiceBusSessionReceiver receiver = await client.AcceptSessionAsync("my-queue", "order-123");

// Session state management
await receiver.SetSessionStateAsync(new BinaryData("processing"));
BinaryData state = await receiver.GetSessionStateAsync();

// Renew ses