Remix upload to S3

Last updated: 
Upload files to S3 compatible API - I'm using Backblaze B2 - with Remix and parseMultipartFormData

Please make sure you're on Remix v1.2.2 as you're otherwise going to run into issue which limits file size to pretty small files like 100kb 🤏

Table of contents

Required environment variables



import {
  type RouteHandle,
  type LoaderFunction,
  type ActionFunction,
} from "remix";
import cuid from "cuid";

Custom uploadHandler

const uploadHandler: UploadHandler = async ({ name, filename, mimetype, encoding, stream }) => {
  if (name !== "files") {

  const key = cuid(); // or filename or whatever fits your usecase 😉;

  const params: PutObjectCommandInput = {
    Bucket: process.env.S3_BUCKET ?? "",
    Key: key,
    Body: stream,
    ContentType: mimetype,
    ContentEncoding: encoding,
    Metadata: {
      filename: filename,

  try {
    const { S3Client } = await import("@aws-sdk/client-s3");
    const { Upload } = await import("@aws-sdk/lib-storage");
    const { getApplyMd5BodyChecksumPlugin } = await import(

    const client = new S3Client({
      endpoint: process.env.S3_ENDPOINT ?? "",
      region: process.env.S3_REGION ?? "",
      credentials: {
        accessKeyId: process.env.S3_ACCESS_KEY_ID ?? "",
        secretAccessKey: process.env.S3_SECRET_ACCESS_KEY ?? "",


    const upload = new Upload({ client, params });

    upload.on("httpUploadProgress", (progress) => {
      console.log({ progress });

    await upload.done();
  } catch (e) {

  return JSON.stringify({ filename, key });

You could also import the aws-sdk modules in parallel changing the following code from the last code block from:

const { S3Client } = await import("@aws-sdk/client-s3");
const { Upload } = await import("@aws-sdk/lib-storage");
const { getApplyMd5BodyChecksumPlugin } = await import("@aws-sdk/middleware-apply-body-checksum");


const [{ S3Client }, { Upload }, { getApplyMd5BodyChecksumPlugin }] = await Promise.all([

Note that type UploadHandler only "allows" to return a string a File or undefined, I "complained" about it in #1139

File has the following shape and so requires more data than I need 🤷🏻‍♂️

interface File extends Blob {
  readonly lastModified: number;
  readonly name: string;
  readonly webkitRelativePath: string;

That's why I have to kinda awkwardly JSON.parse it using .map in my ActionFunction as it returns file by file so it'll return an array of JSON.stringifyed strings 🥲


type CustomFile = {
  key: string;
  filename: string;

export const action: ActionFunction = async ({ request }) => {
  const form = await unstable_parseMultipartFormData(request, uploadHandler);
  const fileJsons = form.getAll("files");
  const files =
    (str) => JSON.parse((str as unknown as string) ?? "{}") as CustomFile,
  console.log({ files });
  return { files };

The React component

Then I get the data via useActionData in my client-component and render for example a list of the uploaded files, like in this very compact example.

const actionData = useActionData<ActionData>();

return (
  {/* Upload Form etc */}
    {actionData?.files?.length > 0 &&
      actionData?.files?.map((f) => <li>{f.filename}</li>)}

Alright, that's it for now.

Soonish I plan on sharing more details about Backblaze integration and the CMS I'm building as I advance.

Let me know (e.g. via Twitter) if you have any questions.

Saludos from Perú 🙋🏻‍♂️

Below a little "bonus" for future me and just in case someone else stumbles upon this error and could need a hint 😉

Fixing TypeError: Cannot read properties of undefined (reading '#text')

Full Error stack trace
TypeError: Cannot read properties of undefined (reading '#text')
    at [..]/node_modules/@aws-sdk/client-s3/dist-cjs/protocols/Aws_restXml.js:12897:30
    at runMicrotasks (<anonymous>)
    at processTicksAndRejections (node:internal/process/task_queues:96:5)
    at async deserializeAws_restXmlPutObjectCommandError ([..]/node_modules/@aws-sdk/client-s3/dist-cjs/protocols/Aws_restXml.js:8246:15)
    at async [..]/node_modules/@aws-sdk/middleware-serde/dist-cjs/deserializerMiddleware.js:7:24
    at async [..]/node_modules/@aws-sdk/middleware-signing/dist-cjs/middleware.js:11:20
    at async StandardRetryStrategy.retry ([..]/node_modules/@aws-sdk/middleware-retry/dist-cjs/StandardRetryStrategy.js:51:46)
    at async [..]/node_modules/@aws-sdk/middleware-logger/dist-cjs/loggerMiddleware.js:6:22
    at async Upload.__uploadUsingPut ([..]/node_modules/@aws-sdk/lib-storage/dist-cjs/Upload.js:45:27)
    at async Upload.__doConcurrentUpload ([..]/node_modules/@aws-sdk/lib-storage/dist-cjs/Upload.js:74:28)
    at async Promise.all (index 0)
    at async Upload.__doMultipartUpload ([..]/node_modules/@aws-sdk/lib-storage/dist-cjs/Upload.js:120:9)
    at async Upload.done ([..]/node_modules/@aws-sdk/lib-storage/dist-cjs/Upload.js:36:16)
    at async uploadHandler ([..]/build/index.js:3487:26)
    at async [..]/node_modules/@remix-run/node/parseMultipartFormData.js:63:25
    at async Promise.all (index 0) {
  '$response': HttpResponse {
    statusCode: 500,
    headers: {
      'cache-control': 'max-age=0, no-cache, no-store',
      'content-type': 'application/json;charset=utf-8',
      'content-length': '105',
      date: 'Sat, 12 Feb 2022 00:09:33 GMT',
      connection: 'close'
    body: IncomingMessage {
      _readableState: [ReadableState],
      _events: [Object: null prototype],
      _eventsCount: 2,
      _maxListeners: undefined,
      socket: [TLSSocket],
      httpVersionMajor: 1,
      httpVersionMinor: 1,
      httpVersion: '1.1',
      complete: true,
      rawHeaders: [Array],
      rawTrailers: [],
      aborted: false,
      upgrade: false,
      url: '',
      method: null,
      statusCode: 500,
      statusMessage: '',
      client: [TLSSocket],
      _consuming: false,
      _dumped: false,
      req: [ClientRequest],
      [Symbol(kCapture)]: false,
      [Symbol(kHeaders)]: [Object],
      [Symbol(kHeadersCount)]: 10,
      [Symbol(kTrailers)]: null,
      [Symbol(kTrailersCount)]: 0,
      [Symbol(RequestTimeout)]: undefined
  '$metadata': { attempts: 1, totalRetryDelay: 0 }

Most of he time, at least lately thanks to all the avancements in dev, error messages and stack traces are pretty accurate pointing (almost) exactly at line and column of the file in question. While in other cases you get something like the error above which is pretty hard to debug, especially if your preferred search-engine isn't showing useful results 😢

Anyway, at least in my case it was a stupid 🙊 comma in my .env file as I copied the credentials from some JS/JSON object and forgot to delete the commas and even changing : to =, which doesn't seem to make a difference though.


TypeError: Cannot read property '#text' of undefined - PublishCommand (@aws-sdk/client-sns) #2161

Can Rau
Can Rau

Doing web-development since around 2000, building my digital garden with a mix of back-to-the-roots-use-the-platform and modern edge-rendered-client-side-magic tech 📻🚀

Living and working in Cusco, Perú 🦙