Uploading files using GCF. The following example uses the busboy npm module, but you can use any valid multipart parser module that takes a Buffer as input.

upload.js

/**
 * Copyright 2017, Google, Inc.
 * Licensed under the Apache License, Version 2.0 (the "License")
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
'use strict';

const path = require('path');
const os = require('os');
const fs = require('fs');
const Busboy = require('busboy');

exports.uploadFile = (req, res) => {
    if (req.method === 'POST') {
        const busboy = new Busboy({ headers: req.headers });
        // This object will accumulate all the uploaded files, keyed by their name.
        const uploads = {}
        const tmpdir = os.tmpdir();

        // This callback will be invoked for each file uploaded.
        busboy.on('file', (fieldname, file, filename, encoding, mimetype) => {
            // Note that os.tmpdir() is an in-memory file system, so should only 
            // be used for files small enough to fit in memory.
            const filepath = path.join(tmpdir, filename)
            uploads[fieldname] = filepath;
            file.pipe(fs.createWriteStream(filepath));
        });

        // This callback will be invoked after all uploaded files are saved.
        busboy.on('finish', () => {

            // *** Process uploaded files here ***

            for (const name in uploads) {
                const file = uploads[name];
                fs.unlinkSync(file);
            }
            res.end();
        });

        // The raw bytes of the upload will be in req.rawBody.  Send it to busboy, and get
        // a callback when it's finished.
        busboy.end(req.rawBody);
    } else {
        // Client error - only support POST.
        res.status(405).end();
    }
}