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typespec-asyncapi

Reusable Components

AsyncAPI 3.1’s components.* slots let you define an operation trait, message trait, parameter, correlation ID, or binding once and reference it everywhere. The emitter populates all of them.

Operation and message traits

Section titled “Operation and message traits”
namespace MyAPI;


@operationTrait("standardHeaders", #{
  bindings: #{ http: #{ method: "POST" } }
  description: "Standard HTTP operation behavior"
})
@messageTrait("commonHeaders", #{
  headers: #{
    type: "object"
    properties: #{ traceId: #{ type: "string" } }
  }
})
@channel("orders")
@useOperationTrait("standardHeaders")
@publish
op placeOrder(): Order;

@operationTrait extracts security, tags, bindings (plus summary/description); @messageTrait extracts headers, correlationId, summary, tags, bindings (plus name/description). The @use* reference decorators attach them via $ref.

Channel address parameters

Section titled “Channel address parameters”
@parameter("tenantId", #{
  location: "$message.payload#/tenantId"
  description: "Tenant identifier"
})
@channel("{tenantId}/events")
@subscribe
op onEvent(): Event;

A channel address parameter ({tenantId}) auto-upgrades to a $ref under channels.address when a matching @parameter exists. The location, when present, must start with $message. and contain a # JSON-pointer separator.

Correlation IDs

Section titled “Correlation IDs”
@reusableCorrelationId("traceId", "$message.header#/traceid")
namespace MyAPI;


@useCorrelationId("traceId")
model Event { id: string; }

Inline @correlationId(location) on a model still works without populating components.correlationIds.

Reusable bindings

Section titled “Reusable bindings”
@reusableBinding("prodKafka", #{
  kafka: #{ topic: "orders", partitions: 6 }
})
namespace MyAPI;


@channel("orders")
@useChannelBinding("prodKafka")
@publish
op publishOrder(): Order;

The 7 slots

Section titled “The 7 slots”
Slot Definition decorator Reference decorator
components.operationTraits @operationTrait (Namespace) @useOperationTrait (Operation)
components.messageTraits @messageTrait (Namespace) @useMessageTrait (Model)
components.parameters @parameter (Namespace) channel address {param}
components.correlationIds @reusableCorrelationId (Namespace) @useCorrelationId (Model)
components.operationBindings @reusableBinding (Namespace) @useBinding (Operation/Model/Namespace)
components.messageBindings @reusableBinding (Namespace) @useBinding
components.channelBindings @reusableBinding (Namespace) @useChannelBinding (Operation)

Where to go next

Section titled “Where to go next”