NATS

NATS is a simple, secure and performant communications system for digital systems, services and devices. NATS is part of the Cloud Native Computing Foundation (CNCF).

Warning

Since version 5.2+, CAP's relevant features have been implemented based on JetStream, so it needs to be explicitly enabled on the server.

You need to enable JetStream by specifying the --jetstream parameter when starting the NATS Server in order to use CAP properly.

Configuration

To use NATS transporter, you need to install the following package from NuGet:

PM> Install-Package DotNetCore.CAP.NATS

Then you can add configuration items to the ConfigureServices method of Startup.cs.

public void ConfigureServices(IServiceCollection services)
{
    services.AddCap(capOptions =>
    {
        capOptions.UseNATS(natsOptions=>{
            //NATS Options
        });
    });
}

NATS Options

NATS configuration parameters provided directly by the CAP:

NAME	DESCRIPTION	TYPE	DEFAULT
Options	NATS client configuration	Options	Options
Servers	Server url/urls used to connect to the NATs server.	string	NULL
ConnectionPoolSize	number of connections pool	uint	10
DeliverPolicy	The point in the stream to receive messages from (⚠️ Removed from version 8.1.0, use ConsumerOptions instead.)	enum	DeliverPolicy.New
StreamOptions	🆕 Stream configuration	Action	NULL
ConsumerOptions	🆕 Consumer configuration	Action	NULL
CustomHeadersBuilder	Custom subscribe headers	See the blow	NULL

NATS ConfigurationOptions

If you need more native NATS related configuration options, you can set them in the Options option:

services.AddCap(capOptions => 
{
    capOptions.UseNATS(natsOptions=>
    {
        // NATS options.
        natsOptions.Options.Url="";
    });
});

Options is a NATS.Client ConfigurationOptions , you can find more details through this link

CustomHeadersBuilder Option

When the message sent from a heterogeneous system, because of the CAP needs to define additional headers, so an exception will occur at this time. By providing this parameter to set the custom headersn to make the subscriber works.

You can find the description of Header Information here.

Example：

x.UseNATS(aa =>
{
    aa.CustomHeadersBuilder = (e, sp) =>
    [
        new(DotNetCore.CAP.Messages.Headers.MessageId, sp.GetRequiredService<ISnowflakeId>().NextId().ToString()),
        new(DotNetCore.CAP.Messages.Headers.MessageName, e.Message.Subject)
    ];
});