NextJS S3 object download API endpoint

download.ts

import { NextApiRequest, NextApiResponse } from "next";
import { middleware } from "@lib/middleware";
import { S3Client, GetObjectCommand } from "@aws-sdk/client-s3";
import { logMessage } from "@lib/logger";

const FILE_ATTACHMENT_BUCKET = process.env.VAULT_FILE_STORAGE as string;

const s3Client = new S3Client({
    endpoint: process.env.LOCAL_AWS_ENDPOINT ?? undefined,
    forcePathStyle: process.env.LOCAL_AWS_ENDPOINT ? true : undefined,
    region: process.env.AWS_REGION ?? "ca-central-1",
});

/**
 * Download an S3 object with a give `key` query param
 * @param req 
 * @param res 
 */
const handler = async (req: NextApiRequest, res: NextApiResponse) => {
    let maxMemory = 0;
    let previousUsed = getMemory();
    const objectKey = req.query.key as string;

    // Get the S3 object
    const s3Object = await s3Client.send(
        new GetObjectCommand({
            Bucket: FILE_ATTACHMENT_BUCKET,
            Key: objectKey,
        })
    );

    // Stream the object back to the response
    if (s3Object.Body) {
        res.setHeader("Content-Type", "application/octet-stream");
        res.setHeader("Content-Disposition", "attachment; filename=download.img");

        const s3ObjectStream = s3Object.Body as NodeJS.ReadableStream;
        s3ObjectStream
            .on("data", () => {
                const used = getMemory();
                logMessage.info(`${objectKey}: streaming memory ${formatNumber(used)} MB (delta ${formatNumber(used - previousUsed)} MB)`);
                maxMemory = Math.max(maxMemory, used);
                previousUsed = used;
            })
            .on("end", () => {
                logMessage.info(`${objectKey}: max memory ${formatNumber(maxMemory)} MB`);   
            });
         
        s3ObjectStream.pipe(res);
    }
};

const formatNumber = (num: number): string => {
    return num.toLocaleString("en-CA");
}

const getMemory = (): number => {
    return process.memoryUsage().heapUsed / 1024 / 1024;
}

export default middleware([], handler);