RabbitMQ

RabbitMQ is an open-source message broker software that implements the Advanced Message Queuing Protocol (AMQP) and has been extended with a plug-in architecture to support additional protocols such as Streaming Text Oriented Messaging Protocol (STOMP), Message Queuing Telemetry Transport (MQTT), and others.

RabbitMQ can be used in CAP as a message transporter.

Important Notes

When using RabbitMQ, the consumer integrated with the CAP application will automatically create a persistent queue after it starts for the first time. Subsequent messages will be normally transmitted to the queue and consumed.

However, if you have never started the consumer, the queue will not be created. In this case, if you publish messages first, the RabbitMQ exchange will discard the messages until the consumer is started and the queue is created.

Configuration

To use RabbitMQ as a transporter, you need to install the following package from NuGet:

PM> Install-Package DotNetCore.CAP.RabbitMQ

Next, add configuration items to the ConfigureServices method of Startup.cs.

public void ConfigureServices(IServiceCollection services)
{
    // ...

    services.AddCap(x =>
    {
        x.UseRabbitMQ(opt=>
        {
            //RabbitMQOptions
        });
        // x.UseXXX ...
    });
}

RabbitMQ Options

The RabbitMQ configuration parameters provided directly by CAP:

NAME	DESCRIPTION	TYPE	DEFAULT
HostName	Broker host address	string	localhost
UserName	Broker user name	string	guest
Password	Broker password	string	guest
VirtualHost	Broker virtual host	string	/
Port	Port	int	-1
ExchangeName	Default exchange name	string	cap.default.topic
QueueArguments	Extra queue x-arguments	QueueArgumentsOptions	N/A
QueueOptions	Change Options for created queue	QueueRabbitOptions	{ Durable=true, Exclusive=false, AutoDelete=false }
ConnectionFactoryOptions	RabbitMQClient native connection options	ConnectionFactory	N/A
CustomHeadersBuilder	Custom subscribe headers	See the blow	N/A
PublishConfirms	Enable publish confirms	bool	false
BasicQosOptions	Specify Qos of message prefetch	BasicQos	N/A

ConnectionFactory Option

If you need more native ConnectionFactory configuration options, you can set it by 'ConnectionFactoryOptions' option:

services.AddCap(x =>
{
    x.UseRabbitMQ(o =>
    {
        o.HostName = "localhost";
        o.ConnectionFactoryOptions = opt => { 
            //rabbitmq client ConnectionFactory config
        };
    });
});

CustomHeadersBuilder Option

When the message is sent from the RabbitMQ management console or a heterogeneous system, CAP requires additional headers to be defined. By providing this parameter, you can set custom headers to ensure the subscriber works correctly.

You can find the description of Header Information here.

Example：

x.UseRabbitMQ(aa =>
{
    aa.CustomHeadersBuilder = (msg, sp) =>
    [
        new(DotNetCore.CAP.Messages.Headers.MessageId, sp.GetRequiredService<ISnowflakeId>().NextId().ToString()),
        new(DotNetCore.CAP.Messages.Headers.MessageName, msg.RoutingKey)
    ];
});

How to Connect to a Cluster

Use a comma-separated connection string like this:

x=> x.UseRabbitMQ("localhost:5672,localhost:5673,localhost:5674")