Handling Streams

import { createReadStream } from "node:fs";
app.get("/files/report.csv", (req, res) => {
  res.type("text/csv").attachment("report.csv");
  createReadStream("./reports/report.csv").pipe(res);
});

createReadStream("./big.bin", { highWaterMark: 1024 * 1024 }).pipe(res);  // 1 MB chunks

app.get("/users.ndjson", async (req, res) => {
  res.type("application/x-ndjson");
  for await (const user of db.users.cursor()) {
    if (!res.write(JSON.stringify(user) + "\n")) {
      await new Promise(r => res.once("drain", r));
    }
  }
  res.end();
});

import { pipeline } from "node:stream/promises";
app.get("/download", async (req, res, next) => {
  try {
    await pipeline(createReadStream("./big.bin"), res);
  } catch (err) { next(err); }
});

import { createGzip } from "node:zlib";
app.get("/big.json.gz", (req, res) => {
  res.set({ "Content-Type": "application/json", "Content-Encoding": "gzip" });
  pipeline(createReadStream("./big.json"), createGzip(), res).catch(err => res.destroy(err));
});

function emit(res, chunk) {
  if (!res.write(chunk)) {
    return new Promise(r => res.once("drain", r));
  }
}

import busboy from "busboy";
import { Upload } from "@aws-sdk/lib-storage";

app.post("/upload", (req, res, next) => {
  const bb = busboy({ headers: req.headers, limits: { fileSize: 100 * 1024 * 1024 } });
  bb.on("file", (name, file, info) => {
    const upload = new Upload({
      client: s3,
      params: { Bucket: "uploads", Key: info.filename, Body: file, ContentType: info.mimeType }
    });
    upload.done().then(() => res.json({ ok: true })).catch(next);
  });
  req.pipe(bb);
});

import { pipeline } from "node:stream/promises";
import { createReadStream, createWriteStream } from "node:fs";
import { createBrotliCompress } from "node:zlib";

await pipeline(createReadStream("in.txt"), createBrotliCompress(), createWriteStream("out.txt.br"));

app.get("/events", (req, res) => {
  res.set({
    "Content-Type":  "text/event-stream",
    "Cache-Control": "no-cache, no-transform",
    "Connection":    "keep-alive"
  });
  res.flushHeaders();

  const tick = setInterval(() => res.write(`data: ${Date.now()}\n\n`), 1000);
  req.on("close", () => clearInterval(tick));
});