Snippet in node.js to download a file from an Azure Files SMB Share using the REST API

azure-file-download.js

'use strict';

// Uses request: npm install --save request
const request = require('request');
const fs = require('fs');
const crypto = require('crypto');

const dummyLog = function (s) {
  console.log(s);
}
const debug = dummyLog, info = dummyLog, error = dummyLog;

const x_ms_version = '2018-03-28';

function downloadFromStorage(storageName, storageKey, shareName, filePath, outFilePath, callback) {
    debug(`downloadFromStorage(${shareName}, ${filePath})`);

    const mediaPath = `${shareName}${filePath}`;
    const mediaUri = `https://${storageName}.file.core.windows.net/${mediaPath}`;

    const x_ms_date = (new Date()).toUTCString();
    const canonicalizedResource = `/${storageName}/${mediaPath}`;

    const headers = {
        'x-ms-date': x_ms_date,
        'x-ms-version': x_ms_version
    };
    const canonicalizedHeaders = makeCanonicalizedHeaders(headers);

    // SharedKeyLite
    const stringToSign = `GET\n\n\n\n${canonicalizedHeaders}${canonicalizedResource}`;
    debug(stringToSign);

    const secret = Buffer.from(storageKey, 'base64');
    const hmac256 = crypto.createHmac('sha256', secret);
    hmac256.update(stringToSign, 'utf-8');
    const sig = hmac256.digest('base64');

    headers.Authorization = `SharedKeyLite ${storageName}:${sig}`;

    request.get({
        uri: mediaUri,
        headers: headers
    })
        .on('response', function (res) {
            debug(`GET ${mediaPath} responding with ${res.statusCode}, Content-Type ${res.headers['content-type']}`);
            if (res.statusCode === 200) {
                res.pipe(fs.createWriteStream(outFilePath))
                    .on('finish', function () {
                        info(`Downloaded ${mediaPath} on the fly.`);
                        return callback(null);
                    });
            } else {
                return callback(makeError(res.statusCode, `Could not download ${mediaPath} (status code ${res.statusCode})`));
            }
        })
        .on('error', function (err) {
            error(err);
            return callback(makeError(500, `An error occurred while downloading ${mediaPath}`));
        });
}

function makeCanonicalizedHeaders(headers) {
    let first = true;
    let c = '';
    for (let h in headers) {
        if (!h.startsWith('x-ms-'))
            continue;
        c += `${h}:${headers[h]}\n`;
    }
    return c;
}

function makeError(status, message, innerError) {
    const err = new Error(message);
    err.status = status;
    if (innerError)
        err.innerError = innerError;
    return err;
}