GZIP

When generating dynamic responses with a Node.js server, we often may want to compress those responses. Fortunately Node includes zlib, which includes gzip compression.

By calling the pipeline method on a read stream, we can specify a transform. We pass zlib.createGzip as the transform, and the output is then compressed.

Example

This code implements a web server, so when we run it we need to open the localhost server in a browser on port 8080. It always serves a specified file.

Step 1 We call listen() to start the web server we just created with http.createServer. At this point, we can open the web browser.

Step 2 We create a read stream from the file path. This is necessary for the following calls to pipeline() which do the compression.

Step 3 We access the accept-encoding header, which is how browsers tell us whether they accept compressed responses.

Step 4 We see if "gzip" occurs in the accept-encoding header, and if so, we call pipeline with zlib.createGzip to perform compression.

const zlib = require("node:zlib");
const http = require("node:http");
const fs = require("node:fs");
const stream = require("node:stream");
const filePath = "programs/example.txt";

const server = http.createServer((req, res) => {

    // Step 2: create a read stream for the file we want to display.
    const data = fs.createReadStream(filePath);

    // Step 3: get accept-encoding header.
    const acceptEncoding = req.headers["accept-encoding"];

    // Step 4: pipeline the response after testing for "gzip" in accept-encoding header.
    if (/gzip/.test(acceptEncoding)) {
        // If gzip was found, use zlib.createGzip to compress the response.
        res.writeHead(200, { "Content-Encoding": "gzip" });
        stream.pipeline(data, zlib.createGzip(), res, (err) => {
            if (err) {
                res.end();
            }
        });
    } else {
        // If no gzip, write the uncompressed response.
        res.writeHead(200, {});
        stream.pipeline(data, res, (err) => {
            if (err) {
                res.end();
            }
        });
    }
    console.log("Wrote response");
});

// Step 1: start the server.
server.listen(8080, "localhost", () => {
    console.log("Server started");
});Server started
Wrote response

With pipeline() and createReadStream, we use several Node.js modules together to write compressed output. This can speed up real-world use of the server as less data is transmitted.