Application Contracts Clients

Overview

The Intent.Application.Contracts.Clients module generates client-side service contracts for consuming your application services from other applications. This is particularly useful for microservices architectures, integration projects, and creating client SDKs.

Module: Intent.Application.Contracts.ClientsVersion: 5.1.6+Dependencies:

Intent.Common.CSharp
Intent.Modelers.Services
Intent.Modelers.Services.CQRS
Intent.Modelers.Types.ServiceProxies

Key Features

Client DTOs: Generate client-side DTO contracts
Service Proxies: Interface definitions for service clients
Paginated Results: Client-side pagination support
Type Safety: Strongly-typed contracts
Enum Contracts: Client-side enum definitions
Separation of Concerns: Keep client contracts separate from server implementation

Use Cases

Microservices

Service A consumes Service B’s contracts

Client SDKs

Distribute client libraries for your API

Integration Projects

Connect to external services

BFF Pattern

Backend-for-Frontend service integration

Installation

intent install Intent.Application.Contracts.Clients

Architecture

Typical Setup

YourSolution/
├── OrderService.Api/              # Service provider
│   ├── Application/
│   │   ├── Interfaces/           # Server contracts
│   │   │   └── IOrderService.cs
│   │   └── Orders/
│   │       └── OrderDto.cs
│   └── ...
│
├── Warehouse.Api/                 # Service consumer
│   ├── Application/
│   │   └── IntegrationServices/  # Client contracts
│   │       ├── Contracts/        # Client DTOs
│   │       │   ├── OrderDto.cs
│   │       │   └── OrderStatus.cs
│   │       └── IOrderServiceClient.cs
│   └── ...
│
└── Shared.Contracts/              # Alternative: Shared library
    └── Orders/
        ├── OrderDto.cs
        └── IOrderService.cs

Generated Components

Client DTO Contracts

// In OrderService.Api
namespace OrderService.Application.Orders
{
    public class OrderDto
    {
        public Guid Id { get; set; }
        public string OrderNumber { get; set; }
        public OrderStatus Status { get; set; }
        public decimal TotalAmount { get; set; }
        public List<OrderItemDto> Items { get; set; }
    }
}

Client Service Contract

Generated Client Interface

namespace Warehouse.Application.IntegrationServices
{
    public interface IOrderServiceClient
    {
        Task<OrderDto> GetOrderAsync(
            Guid id,
            CancellationToken cancellationToken = default);

        Task<PagedResult<OrderDto>> GetOrdersAsync(
            int pageNo,
            int pageSize,
            CancellationToken cancellationToken = default);

        Task<Guid> CreateOrderAsync(
            CreateOrderDto dto,
            CancellationToken cancellationToken = default);

        Task UpdateOrderStatusAsync(
            Guid id,
            OrderStatus status,
            CancellationToken cancellationToken = default);
    }
}

Client Enum Contracts

Generated Enum

namespace Warehouse.Application.IntegrationServices.Contracts
{
    public enum OrderStatus
    {
        Pending = 0,
        Confirmed = 1,
        Shipped = 2,
        Delivered = 3,
        Cancelled = 4
    }
}

Paginated Results

The module generates client-side pagination types:

Client PagedResult

namespace Warehouse.Application.IntegrationServices.Contracts
{
    public class PagedResult<T>
    {
        public int TotalCount { get; set; }
        public int PageCount { get; set; }
        public int PageSize { get; set; }
        public int PageNumber { get; set; }
        public IEnumerable<T> Data { get; set; }
    }
}

Configuration in Designer

Creating a Service Proxy

Add Service Proxy

In the Service Proxies Designer, add a new Service Proxy

Reference Source Service

Point to the source service in the external application

Select Operations

Choose which operations to expose in the client contract

Generate

Run Software Factory to generate client contracts

Implementation Examples

HTTP Client Implementation

Implement the client interface using HttpClient:

OrderServiceClient.cs

using System.Net.Http.Json;
using Warehouse.Application.IntegrationServices;
using Warehouse.Application.IntegrationServices.Contracts;

public class OrderServiceClient : IOrderServiceClient
{
    private readonly HttpClient _httpClient;
    private readonly ILogger<OrderServiceClient> _logger;

    public OrderServiceClient(
        HttpClient httpClient,
        ILogger<OrderServiceClient> logger)
    {
        _httpClient = httpClient;
        _logger = logger;
    }

    public async Task<OrderDto> GetOrderAsync(
        Guid id,
        CancellationToken cancellationToken)
    {
        var response = await _httpClient.GetAsync(
            $"api/orders/{id}",
            cancellationToken);

        response.EnsureSuccessStatusCode();

        return await response.Content.ReadFromJsonAsync<OrderDto>(
            cancellationToken: cancellationToken)
            ?? throw new InvalidOperationException("Failed to deserialize order");
    }

    public async Task<PagedResult<OrderDto>> GetOrdersAsync(
        int pageNo,
        int pageSize,
        CancellationToken cancellationToken)
    {
        var response = await _httpClient.GetAsync(
            $"api/orders?pageNo={pageNo}&pageSize={pageSize}",
            cancellationToken);

        response.EnsureSuccessStatusCode();

        return await response.Content.ReadFromJsonAsync<PagedResult<OrderDto>>(
            cancellationToken: cancellationToken)
            ?? throw new InvalidOperationException("Failed to deserialize orders");
    }

    public async Task<Guid> CreateOrderAsync(
        CreateOrderDto dto,
        CancellationToken cancellationToken)
    {
        var response = await _httpClient.PostAsJsonAsync(
            "api/orders",
            dto,
            cancellationToken);

        response.EnsureSuccessStatusCode();

        return await response.Content.ReadFromJsonAsync<Guid>(
            cancellationToken: cancellationToken);
    }

    public async Task UpdateOrderStatusAsync(
        Guid id,
        OrderStatus status,
        CancellationToken cancellationToken)
    {
        var response = await _httpClient.PutAsJsonAsync(
            $"api/orders/{id}/status",
            new { Status = status },
            cancellationToken);

        response.EnsureSuccessStatusCode();
    }
}

Dependency Injection Setup

Startup.cs / Program.cs

services.AddHttpClient<IOrderServiceClient, OrderServiceClient>(client =>
{
    client.BaseAddress = new Uri("https://orderservice.example.com");
    client.Timeout = TimeSpan.FromSeconds(30);
});

// With Polly for resilience
services.AddHttpClient<IOrderServiceClient, OrderServiceClient>(client =>
{
    client.BaseAddress = new Uri("https://orderservice.example.com");
})
.AddTransientHttpErrorPolicy(policy =>
    policy.WaitAndRetryAsync(3, retryAttempt =>
        TimeSpan.FromSeconds(Math.Pow(2, retryAttempt))))
.AddTransientHttpErrorPolicy(policy =>
    policy.CircuitBreakerAsync(5, TimeSpan.FromSeconds(30)));

Using the Client

WarehouseService.cs

public class WarehouseService : IWarehouseService
{
    private readonly IOrderServiceClient _orderServiceClient;
    private readonly IWarehouseRepository _repository;

    public WarehouseService(
        IOrderServiceClient orderServiceClient,
        IWarehouseRepository repository)
    {
        _orderServiceClient = orderServiceClient;
        _repository = repository;
    }

    public async Task ProcessShipmentAsync(
        Guid orderId,
        CancellationToken cancellationToken)
    {
        // Get order details from Order Service
        var order = await _orderServiceClient.GetOrderAsync(
            orderId,
            cancellationToken);

        // Process shipment
        var shipment = await _repository.CreateShipmentAsync(
            order,
            cancellationToken);

        // Update order status in Order Service
        await _orderServiceClient.UpdateOrderStatusAsync(
            orderId,
            OrderStatus.Shipped,
            cancellationToken);
    }
}

gRPC Client Support

For gRPC services, implement the client differently:

gRPC Client

using Grpc.Net.Client;
using OrderService.Grpc;

public class OrderServiceGrpcClient : IOrderServiceClient
{
    private readonly OrderService.OrderServiceClient _grpcClient;

    public OrderServiceGrpcClient(GrpcChannel channel)
    {
        _grpcClient = new OrderService.OrderServiceClient(channel);
    }

    public async Task<OrderDto> GetOrderAsync(
        Guid id,
        CancellationToken cancellationToken)
    {
        var request = new GetOrderRequest { Id = id.ToString() };
        var response = await _grpcClient.GetOrderAsync(request, cancellationToken: cancellationToken);

        return new OrderDto
        {
            Id = Guid.Parse(response.Id),
            OrderNumber = response.OrderNumber,
            Status = (OrderStatus)response.Status,
            TotalAmount = response.TotalAmount
        };
    }

    // ... other methods
}

Advanced Scenarios

Authentication & Authorization

Add authentication to client calls:

Authenticated Client

public class AuthenticatedOrderServiceClient : IOrderServiceClient
{
    private readonly HttpClient _httpClient;
    private readonly ITokenProvider _tokenProvider;

    public AuthenticatedOrderServiceClient(
        HttpClient httpClient,
        ITokenProvider tokenProvider)
    {
        _httpClient = httpClient;
        _tokenProvider = tokenProvider;
    }

    public async Task<OrderDto> GetOrderAsync(
        Guid id,
        CancellationToken cancellationToken)
    {
        var token = await _tokenProvider.GetAccessTokenAsync(cancellationToken);
        
        using var request = new HttpRequestMessage(HttpMethod.Get, $"api/orders/{id}");
        request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", token);

        var response = await _httpClient.SendAsync(request, cancellationToken);
        response.EnsureSuccessStatusCode();

        return await response.Content.ReadFromJsonAsync<OrderDto>(
            cancellationToken: cancellationToken)
            ?? throw new InvalidOperationException();
    }
}

Circuit Breaker Pattern

Resilient Client

services.AddHttpClient<IOrderServiceClient, OrderServiceClient>(client =>
{
    client.BaseAddress = new Uri("https://orderservice.example.com");
})
.AddPolicyHandler(Policy<HttpResponseMessage>
    .Handle<HttpRequestException>()
    .OrResult(msg => !msg.IsSuccessStatusCode)
    .CircuitBreakerAsync(
        handledEventsAllowedBeforeBreaking: 3,
        durationOfBreak: TimeSpan.FromSeconds(30),
        onBreak: (result, duration) =>
        {
            Log.Warning("Circuit breaker opened for {Duration}s", duration.TotalSeconds);
        },
        onReset: () =>
        {
            Log.Information("Circuit breaker reset");
        }));

Caching

Add caching to reduce service calls:

Cached Client

public class CachedOrderServiceClient : IOrderServiceClient
{
    private readonly IOrderServiceClient _inner;
    private readonly IMemoryCache _cache;

    public CachedOrderServiceClient(
        IOrderServiceClient inner,
        IMemoryCache cache)
    {
        _inner = inner;
        _cache = cache;
    }

    public async Task<OrderDto> GetOrderAsync(
        Guid id,
        CancellationToken cancellationToken)
    {
        var cacheKey = $"order_{id}";

        if (_cache.TryGetValue<OrderDto>(cacheKey, out var cachedOrder))
        {
            return cachedOrder!;
        }

        var order = await _inner.GetOrderAsync(id, cancellationToken);

        _cache.Set(cacheKey, order, TimeSpan.FromMinutes(5));

        return order;
    }

    // ... other methods
}

Testing

Mocking Client Contracts

Unit Test

public class WarehouseServiceTests
{
    private readonly Mock<IOrderServiceClient> _mockOrderClient;
    private readonly WarehouseService _service;

    public WarehouseServiceTests()
    {
        _mockOrderClient = new Mock<IOrderServiceClient>();
        _service = new WarehouseService(_mockOrderClient.Object, ...);
    }

    [Fact]
    public async Task ProcessShipment_ValidOrder_UpdatesStatus()
    {
        // Arrange
        var orderId = Guid.NewGuid();
        var order = new OrderDto
        {
            Id = orderId,
            OrderNumber = "ORD-001",
            Status = OrderStatus.Confirmed
        };

        _mockOrderClient
            .Setup(c => c.GetOrderAsync(orderId, It.IsAny<CancellationToken>()))
            .ReturnsAsync(order);

        _mockOrderClient
            .Setup(c => c.UpdateOrderStatusAsync(
                orderId,
                OrderStatus.Shipped,
                It.IsAny<CancellationToken>()))
            .Returns(Task.CompletedTask);

        // Act
        await _service.ProcessShipmentAsync(orderId, CancellationToken.None);

        // Assert
        _mockOrderClient.Verify(
            c => c.UpdateOrderStatusAsync(
                orderId,
                OrderStatus.Shipped,
                It.IsAny<CancellationToken>()),
            Times.Once);
    }
}

Best Practices

Use Interface Segregation

Create focused client interfaces that only expose the operations a particular client needs:

// ✅ Good - Focused client
public interface IOrderQueryClient
{
    Task<OrderDto> GetOrderAsync(...);
    Task<List<OrderDto>> GetOrdersAsync(...);
}

public interface IOrderCommandClient
{
    Task<Guid> CreateOrderAsync(...);
    Task UpdateOrderAsync(...);
}

// ❌ Bad - Exposing everything
public interface IOrderServiceClient
{
    // 20+ methods
}

Version Your Contracts

Use versioned namespaces or separate packages for different API versions:

namespace Warehouse.Application.IntegrationServices.V1.Contracts
namespace Warehouse.Application.IntegrationServices.V2.Contracts

Implement Resilience

Always add retry logic, circuit breakers, and timeouts:

services.AddHttpClient<IOrderServiceClient, OrderServiceClient>()
    .AddTransientHttpErrorPolicy(p => p.WaitAndRetryAsync(3, _ => TimeSpan.FromSeconds(2)))
    .AddTransientHttpErrorPolicy(p => p.CircuitBreakerAsync(5, TimeSpan.FromSeconds(30)));

Handle Failures Gracefully

Always handle potential failures:

try
{
    var order = await _orderClient.GetOrderAsync(id, ct);
}
catch (HttpRequestException ex)
{
    _logger.LogError(ex, "Failed to retrieve order {OrderId}", id);
    // Return cached data, default, or rethrow
}

Default Output Location

Generated client contracts are placed in:

YourProject.Application/IntegrationServices/
├── Contracts/           # Client DTOs and enums
│   ├── OrderDto.cs
│   ├── OrderStatus.cs
│   └── PagedResult.cs
└── IOrderServiceClient.cs

Application Contracts - Server-side contracts
DTOs - Data transfer objects
HTTP Clients - HTTP client infrastructure
Service Proxies - Service proxy modeling

Troubleshooting

Contracts Not Generated

Issue: Client contracts aren’t being created.Solution:

Verify Intent.Application.Contracts.Clients is installed
Check that Service Proxy is properly configured in the designer
Ensure source service is correctly referenced
Run Software Factory

Type Mismatches

Issue: Client DTOs don’t match server DTOs.Solution:

Ensure both applications use the same source designer files
Regenerate both server and client contracts
Check for designer synchronization issues

CQRS & MediatR

Data Transfer Objects

Validation

Contracts & Clients

Overview

Key Features

Use Cases

Microservices

Client SDKs

Integration Projects

BFF Pattern

Installation

Architecture

Typical Setup

Generated Components

Client DTO Contracts

Client Service Contract

Client Enum Contracts

Paginated Results

Configuration in Designer

Creating a Service Proxy

Implementation Examples

HTTP Client Implementation

Dependency Injection Setup

Using the Client

gRPC Client Support

Advanced Scenarios

Authentication & Authorization

Circuit Breaker Pattern

Caching

Testing

Mocking Client Contracts

Best Practices

Default Output Location

Troubleshooting

External Resources

Build docs developers (and LLMs) love

CQRS & MediatR

Data Transfer Objects

Validation

Contracts & Clients

​Overview

​Key Features

​Use Cases

Microservices

Client SDKs

Integration Projects

BFF Pattern

​Installation

​Architecture

​Typical Setup

​Generated Components

​Client DTO Contracts

​Client Service Contract

​Client Enum Contracts

​Paginated Results

​Configuration in Designer

​Creating a Service Proxy

​Implementation Examples

​HTTP Client Implementation

​Dependency Injection Setup

​Using the Client

​gRPC Client Support

​Advanced Scenarios

​Authentication & Authorization

​Circuit Breaker Pattern

​Caching

​Testing

​Mocking Client Contracts

​Best Practices

​Default Output Location

​Related Modules

​Troubleshooting

​External Resources

Build docs developers (and LLMs) love

Overview

Key Features

Use Cases

Installation

Architecture

Typical Setup

Generated Components

Client DTO Contracts

Client Service Contract

Client Enum Contracts

Paginated Results

Configuration in Designer

Creating a Service Proxy

Implementation Examples

HTTP Client Implementation

Dependency Injection Setup

Using the Client

gRPC Client Support

Advanced Scenarios

Authentication & Authorization

Circuit Breaker Pattern

Caching

Testing

Mocking Client Contracts

Best Practices

Default Output Location

Related Modules

Troubleshooting

External Resources