Linkr 1.0.0

Linkr

Linkr is a powerful request/response mediation library designed to provide clean separation of concerns, extensibility, and maintainability for complex business applications.

Introduction 👋

Linkr is a modern .NET-based mediation library built for clean, scalable request/response handling. Inspired by Mediator patterns, Linkr enables you to encapsulate business logic into handlers, enforce validation and authorization policies, monitor requests with diagnostics, and orchestrate advanced pipelines via behaviors—all using a modular and pluggable architecture.

With Linkr, developers can focus on domain logic while seamlessly integrating cross-cutting concerns like logging, validation, timeouts, and authorization. Whether you're building microservices, monoliths, or APIs, Linkr empowers you to keep your application maintainable, testable, and aligned with clean architecture principles

Authors

• @Khaled Harby

Features

• Request/Response Pattern
• Authorization Policies
• Validation Policies
• Cancellation Policy
• Timeout Policy
• Diagnostics (Logging)
• Custom Authorization Attributes
• Pipeline Behavior

Usage/Examples

1- Request/Response Pattern Examples

Query Example

-- Example - Query:

public class GetUserQuery : IRequest<UserDto> 
{
    public string UserId { get; set; }
}

public class GetUserQueryHandler : IRequestHandler<GetUserQuery, UserDto>
{
    public Task<UserDto> Handle(GetUserQuery request, CancellationToken cancellationToken)
    {
        return Task.FromResult(new UserDto { Id = request.UserId, Name = "John Doe" });
    }
}

Command Example

public class CreateUserCommand : IRequest<bool>
{
    public string Email { get; set; }
    public string Name { get; set; }
}

public class CreateUserCommandHandler : IRequestHandler<CreateUserCommand, bool>
{
    public Task<bool> Handle(CreateUserCommand request, CancellationToken cancellationToken)
    {
        // Save user to DB
        return Task.FromResult(true);
    }
}

2- Pipeline Behaviors

Add cross-cutting concerns (logging, validation, etc.)

Example

public class LoggingBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
{
    public async Task<TResponse> Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate<TResponse> next)
    {
        Console.WriteLine($"Handling {typeof(TRequest).Name}");
        var response = await next();
        Console.WriteLine($"Handled {typeof(TResponse).Name}");
        return response;
    }
}

3- Validation Behaviors

Ensure requests are valid before execution.

Example

public class CreateUserValidator : IValidator<CreateUserCommand>
{
    public void Validate(CreateUserCommand request)
    {
        if (string.IsNullOrWhiteSpace(request.Email))
            throw new ValidationException("Email is required");
    }
}

4- Authorization Behaviors

Enforce role or claim-based access to request handlers.

Example

[Authorize(Roles = "Admin")]
public class DeleteUserCommand : IRequest<bool> 
{
    public string UserId { get; set; }
}

5- Custom Authorization Attributes

You can customize security checks using user context.

Example

[OnlySelf]
public class UpdateUserProfileCommand : IRequest<bool>
{
    public string UserId { get; set; }
    public string NewName { get; set; }
}


public class OnlySelfAttribute : Attribute, IAuthorizationRequirement
{
    public bool IsAuthorized(IUserContext userContext, object request)
    {
        if (request is UpdateUserProfileCommand cmd)
            return userContext.UserId == cmd.UserId;

        return false;
    }
}

6- Custom Authorization Attributes

Automatically handle timeout and cancellation tokens in long-running tasks.

Example

public class TimeoutBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
{
    public async Task<TResponse> Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate<TResponse> next)
    {
        using var cts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
        cts.CancelAfter(TimeSpan.FromSeconds(10));
        return await next();
    }
}

-- To reigster into DI 
services.AddTransient(typeof(IPipelineBehavior<,>), typeof(TimeoutBehavior<,>));

7- Custom Authorization Attributes

Diagnostics Support.

Example

public class DiagnosticBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
{
    public async Task<TResponse> Handle(TRequest request, CancellationToken cancellationToken, RequestHandlerDelegate<TResponse> next)
    {
        var stopwatch = Stopwatch.StartNew();
        var response = await next();
        stopwatch.Stop();
        Console.WriteLine($"Request {typeof(TRequest).Name} took {stopwatch.ElapsedMilliseconds}ms");
        return response;
    }
}


-- To register into DI 
services.AddTransient(typeof(IPipelineBehavior<,>), typeof(DiagnosticBehavior<,>));