Basket service

Basket holds each shopper’s cart in Redis. When a cart is saved, it applies coupons from the Discount service over gRPC. At checkout, it publishes an integration event to RabbitMQ and clears the cart.

Source	src/Services/Basket
Store	Redis, through IDistributedCache (key = user name, value = JSON ShoppingCart)
Calls	Discount over gRPC (GrpcSettings:DiscountUrl)
Publishes	BasketCheckoutEvent (v1), BasketCheckoutEventV2 (v2)
Local port	8001 (container port 80)

Layers

Project	What is in it
src/Services/Basket/Basket.API	v1 and v2 BasketController, and Program.cs (versioned Swagger, gRPC client, Redis, MassTransit)
src/Services/Basket/Basket.Application	Commands, queries and handlers, DiscountGrpcService, BasketMapper; compiles discount.proto as a gRPC client
src/Services/Basket/Basket.Core	ShoppingCart, ShoppingCartItem, BasketCheckout, BasketCheckoutV2, IBasketRepository
src/Services/Basket/Basket.Infrastructure	BasketRepository over IDistributedCache

Endpoints

Method	Route	Handler	Notes
GET	api/v1/Basket/GetBasket/{userName}	GetBasketByUserNameQuery
POST	api/v1/Basket/CreateBasket	CreateShoppingCartCommand	Upserts the whole cart; applies discounts
DELETE	api/v1/Basket/DeleteBasket/{userName}	DeleteBasketByUserNameCommand
POST	api/v1/Basket/Checkout	inline in controller	Publishes BasketCheckoutEvent, deletes the cart, returns 202 Accepted
POST	api/v2/Basket/Checkout	inline in controller	Same flow with the slimmer BasketCheckoutEventV2 (user name and total only)

Controllers: src/Services/Basket/Basket.API/Controllers/BasketController.cs and src/Services/Basket/Basket.API/Controllers/V2/BasketController.cs. Swagger publishes separate v1 and v2 documents, and a DocInclusionPredicate assigns each action by the [ApiVersion] on its controller.

Data model

classDiagram
  class ShoppingCart {
    +string UserName
    +List~ShoppingCartItem~ Items
  }
  class ShoppingCartItem {
    +int Quantity
    +decimal Price
    +decimal OriginalPrice
    +decimal DiscountAmount
    +string ProductId
    +string ProductName
    +string ImageFile
    +decimal FinalPrice()
  }
  class ShoppingCartResponse {
    +string UserName
    +List Items
    +decimal TotalPrice()
  }
  ShoppingCart "1" *-- "many" ShoppingCartItem
  ShoppingCart ..> ShoppingCartResponse : BasketMapper

In Redis, the cart is serialized with System.Text.Json. BasketRepository reads it with PropertyNameCaseInsensitive = true, a comment notes, to match the old Newtonsoft behaviour, so carts cached before the migration still deserialize (src/Services/Basket/Basket.Infrastructure/Repositories/BasketRepository.cs). Carts are stored with no expiry.

TotalPrice is computed in the response as sum(Price * Quantity), where Price is already the discounted unit price (src/Services/Basket/Basket.Application/Responses/ShoppingCartResponse.cs).

Discount application

CreateShoppingCartCommandHandler (src/Services/Basket/Basket.Application/Handlers/CreateShoppingCartCommandHandler.cs) walks every item:

1. If OriginalPrice is not set, it copies Price into it.
2. If discounts are not bypassed (BypassDiscount:Enabled), the item has no discount yet, and Price == OriginalPrice, it calls DiscountGrpcService.GetDiscount(ProductName).
3. It sets DiscountAmount = coupon.Amount and Price = OriginalPrice - DiscountAmount.

The “not yet discounted” check makes the operation idempotent: re-saving a cart does not apply the same coupon twice. The calls run sequentially, one gRPC round trip per undiscounted item.

DiscountGrpcService (src/Services/Basket/Basket.Application/GrpcService/DiscountGrpcService.cs) catches RpcException. For Unavailable it logs a warning, and for other codes it logs an error. Either way it returns a zero-amount coupon, so the cart saves at full price rather than failing.

The gRPC client is registered with AddGrpcClient<DiscountProtoService.DiscountProtoServiceClient> and a plain HttpClientHandler, and talks cleartext HTTP/2 (h2c) to Discount on port 8080 (GrpcSettings__DiscountUrl=http://discount.api:8080 in docker-compose.override.yml). OpenTelemetry’s AddGrpcClientInstrumentation() creates spans for these calls.

Checkout

flowchart LR
  req["POST /Checkout"] --> get["GetBasketByUserNameQuery"]
  get -->|"null"| bad["400 Bad Request"]
  get -->|cart| map["BasketMapper: BasketCheckout to BasketCheckoutEvent"]
  map --> total["TotalPrice = cart.TotalPrice (server side)"]
  total --> pub["IPublishEndpoint.Publish"]
  pub --> del["DeleteBasketByUserNameCommand"]
  del --> ok["202 Accepted"]

The total price in the event comes from the stored cart, not the request body, which prevents the client from under-reporting the total. Item prices themselves are client-supplied, though, as noted on the architecture page.

Known issues

• Publish and delete are two independent steps with no outbox. If the process dies after the publish, the cart survives and a retry re-publishes; Ordering’s consumer is idempotent on the event’s CorrelationId, so this cannot create a duplicate order. The request is validated before anything is published, so an invalid checkout returns 400 and keeps the cart.
• The v1 event carries card number, expiry and CVV in clear text through RabbitMQ, and Ordering stores them. A real system would tokenize payment data before it reaches the backend.
• Discount calls have a gRPC deadline, so a hung Discount service cannot hang basket creation; on failure the cart is priced without a discount.
• The gateway rate-limits checkout to one request per 3-second window (see API Gateway).

Configuration

Key	Example	Purpose
CacheSettings:ConnectionString	basketdb:6379	Redis
GrpcSettings:DiscountUrl	http://discount.api:8080	Discount gRPC endpoint
EventBusSettings:HostAddress	amqp://guest:guest@rabbitmq:5672	RabbitMQ; the full URI (host, port, vhost, credentials) is passed to MassTransit
BypassDiscount:Enabled	false (default)	Skip gRPC discount lookup, useful for load tests
ElasticConfiguration:Uri, Otlp:Endpoint		Logging and tracing