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 features are implemented based on JetStream, so JetStream must be explicitly enabled on the server.

You must enable JetStream by specifying the --jetstream parameter when starting the NATS server to use CAP properly.

Configuration

To use NATS as a 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	Optional NATS.Client connection configuration; if omitted, the client library defaults are used.	NATS.Client.Options	Client defaults
Servers	Server URL or URLs.	string	nats://127.0.0.1:4222
ConnectionPoolSize	Number of pooled connections.	int	10
EnableSubscriberClientStreamAndSubjectCreation	Allow consumer clients to create streams and subjects.	bool	true
StreamOptions	🆕 Stream configuration	Action	NULL
ConsumerOptions	🆕 Consumer configuration	Action	NULL
CustomHeadersBuilder	Custom subscribe headers	See the blow	NULL
NormalizeStreamName	Converts a topic name to its stream name.	Func<string, string>	First segment before .

NATS Configuration Options

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

services.AddCap(capOptions => 
{
    capOptions.UseNATS(natsOptions=>
    {
        // NATS options.
        natsOptions.Options = NATS.Client.ConnectionFactory.GetDefaultOptions();
        natsOptions.Options.Url = "nats://127.0.0.1:4222";
    });
});

Options is a NATS.Client ConfigurationOptions. You can find more details at this link.

Custom Headers Builder Option

When messages are sent from 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.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)
    ];
});