SseStream

Kind: Class

Source: packages/core/router/sse-stream.ts

Part of: Core

Adapted from https://raw.githubusercontent.com/EventSource/node-ssestream Transforms "messages" to W3C event stream content. See https://html.spec.whatwg.org/multipage/server-sent-events.html A message is an object with one or more of the following properties:

• data (String or object, which gets turned into JSON)
• type
• id
• retry
• comment

If constructed with a HTTP Request, it will optimise the socket for streaming. If this stream is piped to an HTTP Response, it will set appropriate headers.

SseStream is a transform stream that converts message objects into W3C Server-Sent Events (SSE) wire-format payloads. It can optimize an incoming HTTP request for streaming and configures appropriate response headers when piped to an HTTP response.

Extends: Transform

Methods

Where it refuses work

• SseStream stops the work with an early return when this._headersCommitted || !this._destination.
• SseStream stops the work with an early return when this._destination.writableEnded.

Diagram

mermaid
graph LR
  A[HTTP Request] --> B[SseStream]
  C[Message objects<br/>data, type, id, retry, comment] --> B
  B -->|Formats as SSE frames| D[HTTP Response]
  D --> E[EventSource client]

AI Coding Instructions

• Write message objects to the stream using standard stream APIs such as stream.write({ data, type, id }).
• Use data for strings or JSON-serializable objects; objects are serialized to JSON before being sent to clients.
• Pipe the stream directly to the HTTP response so SseStream can apply the required SSE response headers.
• Construct the stream with the request when available to enable request socket optimizations for long-lived connections.
• Handle request or response closure and call end() to avoid retaining SSE streams after clients disconnect.