NodeJS Sharp Node Package Memory Consumption Issue

问题

I am working on a NodeJS project that is using sharp node package for resizing JPEG/JPG images.

The problem is Node process keeps adding the processed file in memory and never releases it.

As a result, amount of memory consumed increases with every request & it never gets released.

After debugging the application, I realised that sharp toBuffer API is causing the issue.

I tried using alternative solution by creating a custom writable stream and piping it with sharp Duplex stream but it ends up with the same problem.

I don't understand if I'm missing anything here or it's a bug.

Sharing the code below (I have removed unwanted code to make it compact) -

const { Writable } = require("stream");
const { createServer } = require("http");
const { readFileSync } = require("fs");
const sharp = require("sharp");

async function resizeJpeg(input_buffer) {
    // initialise file, the response object
    const file = { normalisedImage: null, originalImage: null };
    // initialise sharp instance using original image buffer
    let image = sharp(input_buffer);
    // set the original image metadata
    file.originalImage = await image.metadata();
    file.originalImage.quality = 85;

    // generate buffer using sharp resize API with default quality & dimensions.
    // ############### THIS IS WHERE MEMORY CONSUMPTION OCCURS ###############

    // APPROACH 1 (SHARP toBuffer API)
    const buffer = await image.resize(2000, 798).jpeg({ quality: 85 }).toBuffer();
    // APPROACH 1 ENDS 

    // APPROACH 2 (CUSTOM WRITABLE STREAM)
    // const buffer = await sharpToBuffer(image.resize(2000, 798).jpeg({ quality: 85 }));
    // APPROACH 2 ENDS

    // set resized image metadata
    file.normalisedImage = await sharp(buffer).metadata();
    file.normalisedImage.quality = 85;
    return file;
}

// converts sharp readable stream to buffer using custom writable buffer
async function sharpToBuffer(readable) {
    return new Promise((resolve, reject) => {
        const writable = new WriteStream().on("finish", () => resolve(Buffer.concat(writable.bufferChunks)));
        readable.pipe(writable);
    });
}

// simple writable stream
class WriteStream extends Writable {
    constructor() { super(); this.bufferChunks = [] }
    _write(chunk, encoding, next) { this.bufferChunks.push(chunk); next(); }
}

createServer(async (request, response) => {
    // ignore favicon calls
    if (request.url.indexOf("favicon.ico") > -1) { return response.end(); }
    // trigger resize call and pass buffer of original image file
    const { normalisedImage, originalImage } = await resizeJpeg(readFileSync(`${__dirname}/30mb.jpg`));
    // respond stringified json
    response.end(
        JSON.stringify({
            normalisedImage: { size: normalisedImage.size, width: normalisedImage.width, height: normalisedImage.height, quality: normalisedImage.quality },
            originalImage: { size: originalImage.size, width: originalImage.width, height: originalImage.height, quality: originalImage.quality }
        }, null, 4));
}).listen(3000, () => console.log("server started"));

As you can see, resizeJpeg function has both the approaches implemented.

To make this work you just need to make sure 30mb.jpg file exists in same directory.

The image I used is available here

In case you're using linux, following top command can be used to monitor the memory usage assuming file name is so.js -

top ps -ef | grep 'so.js' | awk '{print $2}' | sed 's/.*/-p &/' | xargs echo -c

来源：https://stackoverflow.com/questions/58066655/nodejs-sharp-node-package-memory-consumption-issue