Streaming — Courier Docs

Backend — SSE Endpoint

Express sends Server-Sent Events with 500ms intervals. The proxy forwards the stream to the client.

// Express SSE endpoint
router.get("/stream", (_req, res) => {
  res.setHeader("Content-Type", "text/event-stream")
  res.setHeader("Cache-Control", "no-cache")
  res.setHeader("Connection", "keep-alive")

  const items = ["Hello", "from", "the", "streaming", "endpoint!"]
  let index = 0

  const interval = setInterval(() => {
    if (index < items.length) {
      res.write(`data: ${JSON.stringify({ chunk: items[index], index })}\n\n`)
      index++
    } else {
      res.write("data: [DONE]\n\n")
      clearInterval(interval)
      res.end()
    }
  }, 500)
})

The backend sends 5 chunks at 500ms intervals, then a [DONE] signal. The courier proxy passes the ReadableStream through transparently.

Streaming docs

Progressive Rendering

Watch chunks arrive in real time. Each chunk appears as the server sends it.

// Endpoint definition — return type is ReadableStream
const misc = defineGroup({
  prefix: "misc",
  endpoints: {
    stream: endpoint.get("stream").response<ReadableStream>(),
  },
})

// Call with stream: true via .with() — returns raw Response instead of parsed JSON
const response = await caller.misc.with({ stream: true }).stream()

// Read the stream
const reader = response.body.getReader()
const decoder = new TextDecoder()

while (true) {
  const { done, value } = await reader.read()
  if (done) break

  const text = decoder.decode(value, { stream: true })
  // Parse SSE: "data: {...}\n\n"
}

caller.misc.with({ stream: true }).stream()SANDBOX

idle