Subscribers

Subscribers are responsible for receiving messages from RabbitMQ and dispatching them to application logic.

They form the consumer side of the messaging infrastructure.

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Overview

Subscribers receive messages from RabbitMQ and perform the following operations:

1. Receive payload.
2. Deserialize payload.
3. Execute application logic.
4. Complete processing.

graph LR

    RabbitMQ --> Subscriber

    Subscriber --> Formatter

    Subscriber --> Handler

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Architecture

The subscriber implementation is descriptor-driven.

graph TD

    SubscriberBoundDescriptor

    IDataFormatter

    Subscriber

    RabbitMQ

    SubscriberBoundDescriptor --> Subscriber

    IDataFormatter --> Subscriber

    RabbitMQ --> Subscriber

Subscriber behavior is primarily controlled through descriptors.

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Subscriber Responsibilities

Subscribers are responsible for:

• message reception;
• payload deserialization;
• handler execution;
• acknowledgement management;
• retry participation;
• runtime start and stop lifecycle.

Subscribers are not responsible for:

• topology definition;
• exchange design;
• routing strategy design.

Those concerns belong to descriptors.

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Low-Level Construction

The following diagram illustrates the required dependencies.

RabbitMQ.Client v6

graph LR

    IModel --> Subscriber

    IDataFormatter --> Subscriber

    SubscriberBoundDescriptor --> Subscriber

Primary channel abstraction:

IModel

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RabbitMQ.Client v7

graph LR

    IChannel --> Subscriber

    IDataFormatter --> Subscriber

    SubscriberBoundDescriptor --> Subscriber

Primary channel abstraction:

IChannel

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Consumption Flow

The subscriber processing workflow is shown below.

sequenceDiagram

    participant RabbitMQ

    participant Subscriber

    participant Formatter

    participant Handler

    RabbitMQ->>Subscriber: Deliver Message

    Subscriber->>Formatter: Deserialize()

    Formatter-->>Subscriber: Message

    Subscriber->>Handler: Execute()

    Handler-->>Subscriber: Result

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Message Acknowledgement

Successful processing generally results in message acknowledgement.

sequenceDiagram

    participant Subscriber

    participant RabbitMQ

    Subscriber->>RabbitMQ: Ack

Acknowledgements prevent messages from being redelivered.

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Retry Participation

Subscribers are typically involved in retry workflows.

graph TD

    Message

    Process

    Success

    Failure

    Retry

    DeadLetter

    Message --> Process

    Process --> Success

    Process --> Failure

    Failure --> Retry

    Retry --> Process

    Failure --> DeadLetter

Retry behavior is configured through descriptors.

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Descriptor Integration

Common descriptor settings include:

• queue information;
• exchange bindings;
• retry behavior;
• dead-letter configuration;
• consumer settings.

The descriptor model centralizes infrastructure concerns and keeps handlers focused on business logic.

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Lifecycle

Subscribers implement IAsyncRunnable.

public interface IAsyncRunnable
{
    bool IsRunning { get; }

    Task Start();

    Task Stop();
}

The subscriber is explicitly started and stopped.

await subscriber.Start();

await subscriber.Stop();

The current runtime state can be inspected through IsRunning.

if (subscriber.IsRunning)
{
    Console.WriteLine("Subscriber is running.");
}

stateDiagram-v2

    [*] --> Created

    Created --> Running : Start()

    Running --> Stopped : Stop()

    Stopped --> Running : Start()

Implementations should handle repeated calls to Start() and Stop() gracefully.

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Error Handling

Subscriber failures may be caused by:

• invalid payloads;
• deserialization issues;
• business exceptions;
• infrastructure failures.

Handling strategies typically involve:

• retries;
• dead-letter queues;
• operational monitoring.

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v6 vs v7

Capability	RabbitMQ.Client v6	RabbitMQ.Client v7
Channel Type	IModel	IChannel
Subscriber API	Supported	Supported
Descriptor Model	Same	Same
Formatter Model	Same	Same

The framework maintains a consistent programming model across both RabbitMQ client versions.