Express & Plain Node

Bridge Node's req/res to the Web-standard handler - streaming included, so SSE works.

Express and plain Node's http module predate the Web Request/Response types, so they need a small bridge. Streaming the response body is what makes /stream (SSE) work - don't buffer it.

Express

import express from "express";
import { chat } from "./chat";

const app = express();
const chatHandler = chat.handler();

app.use("/api/chat", async (req, res) => {
  // req.originalUrl matters under Express mounts
  const url = `http://${req.headers.host}${req.originalUrl}`;
  const chunks = [];
  for await (const c of req) chunks.push(c);
  const request = new Request(url, {
    method: req.method,
    headers: Object.entries(req.headers).flatMap(([k, v]) =>
      v === undefined ? [] : Array.isArray(v) ? v.map((x) => [k, x]) : [[k, v]],
    ),
    body: chunks.length ? new Uint8Array(Buffer.concat(chunks)) : null,
  });

  const response = await chatHandler.fetch(request);

  res.writeHead(response.status, Object.fromEntries(response.headers.entries()));
  if (response.body) {
    const reader = response.body.getReader();
    req.on("close", () => void reader.cancel().catch(() => {}));
    for (;;) {
      const { done, value } = await reader.read();
      if (done) break;
      res.write(value);
    }
  }
  res.end();
});

app.listen(3000);

The pieces that matter:

req.originalUrl - under an Express mount (app.use("/api/chat", ...)), req.url has the prefix stripped; originalUrl keeps the full path the handler needs for routing.
Streaming the body with a reader loop - res.write(value) per chunk is what lets SSE events flow as they happen.
req.on("close") → reader.cancel() - cleans up the server-side stream when the client disconnects.

Plain Node

A complete, runnable plain-Node version - including in-memory or Postgres storage and a full curl walkthrough with SSE reconnect - lives at examples/node-server.

Node 18+ has Request/Response globals built in - no polyfill needed (the repo requires Node >= 18).

Express & Plain Node

Express

Plain Node

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