upstream-command-line

A wrapper around System.CommandLine to allow for large, service-oriented application development. Some of the benefits of this package include:

• Native IOC support: All commands are registered and instantiated via the ServiceProvider .
• Attribute-based command declaration: Commands can be configured via readable, statically typed classes—no more mapping classes to functional configuration methods.
• Leverage System.CommandLine: This is not a fork, but a flexible wrapper around the .NET Foundation sponsored System.CommandLine library. This means that your application will benefit from the continued development/maturity of that project, and can benefit from integrations like dotnet-suggest out of the box. If you wish to switch to a vanilla System.CommandLine implementation down the road, the migration is straightforward.

Setup

Add the package as a dependency to your .NET project via the following command:

dotnet add package Upstream.CommandLine

Usage

Refer to the Sample project for a working example of this package. The following is a simple (non-functional) example of how to configure an Upstream.CommandLine console application that uses dependency injected services, command groups, middleware, and exception handling:

public static class Program
{
    public static Task Main(string[] args)
    {
        return new CommandLineApplication()
            .AddCommand<FooCommandHandler, FooCommand>()
            .AddCommandGroup("gizmo", builder =>
            {
                builder.AddCommand<GadgetCommandHandler, GadgetCommand>();                
            })
            .AddMiddleware<GreetMiddleware>()
            .ConfigureServices(services =>
            {
                services.AddSingleton<IBarService, BarService>();
            })
            .UseExceptionHandler(e =>
            {
                Console.WriteLine($"An exception occured: {e.Message}");
            })
            .InvokeAsync(args);
    }
}

Commands

A command is a class-based representation of the arguments, options, and other tokens that make up a set of command line instructions. Commands are defined by properties decorated with the [Command], [Argument], and/or [Options] attributes.

Example:

[Command("foo")]
public class FooCommand
{
    [Argument(Description = "Drink order at the Bar")]
    public Drink Drink { get; set; }
    
    [Option("-n", "--name")]
    public string Name { get; set; }
    
    [Option("-d", "--double")]
    public bool Double { get; set; }
}

public enum Drink
{
    Whiskey,
    Wine,
    Beer,
}

This following command invocation and class initialization are equivalent:

> foo beer -n Homer --double

new FooCommand
{
    Drink = Drink.Beer,
    Name = "Homer",
    Double = true,
}

Command Groups

Command groups are a feature that allows nested subcommands. The following configuration would enable the subsequent command:

new CommandLineApplication()
    .AddCommandGroup("foo", builder =>
    {
        builder.AddCommandGroup("bar", builder =>
        {
            builder.AddCommandGroup<BazCommandHandler, BazCommand>();
        });
    });

> foo bar baz

Command Handlers

A command handler is a class that implements ICommandHandler and defines the execution of a command. Command handlers are instantiated via dependency injection to enable IoC patterns while developing your command line application.

An ICommandHandler must return an integer representing the exit code of the command. A 0 typically indicates a successful execution, while any other integer indicates an unsuccessful execution.

Example:

public class FooCommandHandler : CommandHandler<FooCommand>
{
    private readonly IBarService _barService;

    public FooCommand(IBarService barService)
    {
        _barService = barService;
    }

    protected override async Task<int> ExecuteAsync(FooCommand command,
        CancellationToken cancellationToken)
    {
        cancellationToken.ThrowIfCancellationRequested();

        Console.WriteLine($"{command.Name} walks into a Bar and orders a {command.Drink}");
        
        await _barService.OrderAsync(command.Drink);

        return 0;
    }
}

Middleware

Middleware can be added to the application pipeline to validate or alter a command. For more information, please refer to the System.CommandLine Middleware Documentation .

Example:

public class GreetMiddleware : ICommandMiddleware
{
    public async Task InvokeAsync(InvocationContext context
        Func<InvocationContext, Task> next)
    {
        Console.WriteLine("Hello!");

        await next(context);
        
        Console.WriteLine("Goodbye!");
    }
}