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

There are two types of middleware that are supported by this library.

System.CommandLine Middleware

Classes that implement ICommandInvocationMiddleware can be added to the application pipeline to validate or alter a command. For more information, please refer to the System.CommandLine Middleware Documentation. These classes are invoked during parsing and model binding. Therefore, you cannot access the Command class that is available in command handlers.

Example:

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

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

Upstream.CommandLine Middleware

Classes that implement ICommandHandlerMiddleware can be registered with the service provider to alter or supplement command handling. These classes are invoked after model binding but before the matching ICommandHandler<TCommand> is executed.

Example:

public class CommandTypeMiddleware : ICommandHandlerMiddleware
{
    public async Task InvokeAsync<TCommand>(TCommand command, Func<TCommand, Task> next, CancellationToken cancellationToken)
        where TCommand : class
    {
        Console.WriteLine($"Before executing command: {command.GetType().Name}");
        
        if (command is TestCommand testCommand)
        {
            Console.WriteLine($"Looks like this is a test!: {testCommand.Reason}");
        }

        await next(command);
        
        Console.WriteLine($"After executing command: {command.GetType().Name}");
    }
}