RequestContextHost

Kind: Class

Source: packages/microservices/context/request-context-host.ts

Part of: Microservices

RequestContextHost is a lightweight implementation of the microservices RequestContext interface. It stores a message pattern, payload data, and transport-specific context, exposing them through typed getter methods for use in message handlers and interceptors.

Implements: RequestContext

Methods

Diagram

mermaid
graph LR
  A[Incoming microservice message] --> B[RequestContextHost]
  B --> C[getPattern()]
  B --> D[getData()]
  B --> E[getContext()]
  C --> F[Message routing metadata]
  D --> G[Payload]
  E --> H[Transport-specific context]

Usage

ts
import { RequestContextHost } from '@nestjs/microservices';

interface CreateUserPayload {
  email: string;
  name: string;
}

const context = RequestContextHost.create<CreateUserPayload, { requestId: string }>(
  { cmd: 'create_user' },
  {
    email: 'ada@example.com',
    name: 'Ada Lovelace',
  },
  {
    requestId: 'req_123',
  },
);

console.log(context.getPattern()); // { cmd: 'create_user' }
console.log(context.getData().email); // ada@example.com
console.log(context.getContext().requestId); // req_123

AI Coding Instructions

• Preserve the generic TData and TContext types so payload and transport context remain type-safe.
• Use RequestContextHost.create() when constructing a context outside the normal microservice request pipeline.
• Treat the context as a read-only request snapshot; access values through getData(), getPattern(), and getContext().
• Support both string and object message patterns when consuming the value returned by getPattern().
• Keep transport-specific metadata in TContext; do not mix it into the message payload data.

How it works

RequestContextHost<TData, TContext> is an exported public class that implements the RequestContext<TData> shape and represents a request as a pattern, data payload, and RPC context. Its context type is constrained to BaseRpcContext; both generic types default to any. [packages/microservices/context/request-context-host.ts:4-10]

• Its constructor requires pattern, data, and context, then exposes each as a public readonly property. pattern may be a string or record; data has type TData; context has type TContext. [packages/microservices/context/request-context-host.ts:11-15]
• getData(), getPattern(), and getContext() return those stored properties directly. [packages/microservices/context/request-context-host.ts:26-36]
• create() constructs a new host from the same three inputs and returns it typed as RequestContext<TData, TContext>. [packages/microservices/context/request-context-host.ts:17-24]
• The class contains no runtime input validation, transformation, explicit error handling, or mutation after construction. [packages/microservices/context/request-context-host.ts:11-36]

The stored context can expose its handler arguments through BaseRpcContext.getArgs() and a single indexed argument through getArgByIndex(). [packages/microservices/ctx-host/base-rpc.context.ts:4-20]

In microservice listener dispatch, request-scoped handlers recognize a RequestContextHost passed as their first argument, derive a context ID from it, and remove it before invoking the handler proxy. [packages/microservices/listeners-controller.ts:238-245] When no host is first, the listener creates one from the matched pattern, incoming data, and RPC context before deriving the context ID. [packages/microservices/listeners-controller.ts:246-255] During that context-ID derivation, the listener may attach a non-enumerable request-context ID property to the host and register a request-provider value with the container. [packages/microservices/listeners-controller.ts:302-320]