Clean way to specify options for a service when doing DI - asp.net-core

Question

So I have a service lets say for example it's an email service on ASPNET Core.
When I add my service to the ASPNET DI container I would like to apply the following pattern on my IServiceCollection to setup my service.
public interface IEmailService
{
void SendMail(string recipient, string message);
}
public void ConfigureServices(IServiceCollection services)
{
//configures my service
services.AddEmailService<MyEmailService>(options => options.UseEmailServer(sender, smtpHost, smtpPort, smtpPassword));
}
I would like to know whats the best way to do this if possible. I am sure I would need to make an extension method for the .AddEmailService() method on IServiceCollection however anything beyond that I am not sure where to start or look.

Answer 1

Here's an example application with comments to let you know what the different things are doing:
public class Startup
{
public void ConfigureServices(IServiceCollection services)
{
// Add the options stuff. This will allow you to inject IOptions<T>.
services.AddOptions();
// This will take care of adding and configuring the email service.
services.AddEmailService<MyEmailService>(options =>
{
options.Host = "some-host.com";
options.Port = 25;
options.Sender = "firstname#lastname.com";
options.Username = "email";
options.Password = "sup4r-secr3t!";
});
}
public void Configure(IApplicationBuilder app, ILoggerFactory loggerFactory)
{
// Make sure we add the console logger.
loggerFactory.AddConsole();
app.Use(async (context, next) =>
{
// Retrieve the email service from the services.
var emailService = context.RequestServices.GetRequiredService<IEmailService>();
// Send the email
await emailService.SendMail("hello#recipient.com", "Hello World!");
});
}
public static void Main(string[] args)
{
WebApplication.Run<Startup>(args);
}
}
public interface IEmailService
{
Task SendMail(string recipient, string message);
}
public class EmailOptions
{
public string Sender { get; set; }
public string Host { get; set; }
public int Port { get; set; }
public string Username { get; set; }
public string Password { get; set; }
}
public class MyEmailService : IEmailService
{
public MyEmailService(IOptions<EmailOptions> options, ILogger<MyEmailService> logger)
{
Options = options; // This contains the instance we configured.
Logger = logger;
}
private IOptions<EmailOptions> Options { get; }
private ILogger<MyEmailService> Logger { get; }
public Task SendMail(string recipient, string message)
{
// Send the email
var builder = new StringBuilder();
builder.AppendLine($"Host: {Options.Value.Host}");
builder.AppendLine($"Port: {Options.Value.Port}");
builder.AppendLine($"Username: {Options.Value.Username}");
builder.AppendLine($"Password: {Options.Value.Password}");
builder.AppendLine("---------------------");
builder.AppendLine($"From: {Options.Value.Sender}");
builder.AppendLine($"To: {recipient}");
builder.AppendLine("---------------------");
builder.AppendLine($"Message: {message}");
Logger.LogInformation(builder.ToString());
return Task.FromResult(0);
}
}
public static class ServiceCollectionExtensions
{
public static IServiceCollection AddEmailService<TEmailService>(this IServiceCollection services, Action<EmailOptions> configure)
where TEmailService : class, IEmailService
{
// Configure the EmailOptions and register it in the service collection, as IOptions<EmailOptions>.
services.Configure(configure);
// Add the service itself to the collection.
return services.AddSingleton<IEmailService, TEmailService>();
}
}
And here's the application running in the console:
As you can see, the application is pulling some information from the configured EmailOptions, and some information form the arguments passed in.
EDIT: These are the required packages:
"Microsoft.AspNet.Server.Kestrel": "1.0.0-rc1-final",
"Microsoft.Extensions.OptionsModel": "1.0.0-rc1-final",
"Microsoft.Extensions.Logging.Console": "1.0.0-rc1-final"