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This doc is a WIP: It was extracted from the API docs for file uploads so it's a bit out of context. We intend to re-write this as a general guide on file uploads.

Most of the time, you'll probably want to proxy the file to a file host.

Example:

import type {
  ActionArgs,
  UploadHandler,
} from "@remix-run/node"; // or cloudflare/deno
import {
  unstable_composeUploadHandlers,
  unstable_createMemoryUploadHandler,
  unstable_parseMultipartFormData,
} from "@remix-run/node"; // or cloudflare/deno
import { writeAsyncIterableToWritable } from "@remix-run/node"; // `writeAsyncIterableToWritable` is a Node-only utility
import type {
  UploadApiOptions,
  UploadApiResponse,
  UploadStream,
} from "cloudinary";
import cloudinary from "cloudinary";

async function uploadImageToCloudinary(
  data: AsyncIterable<Uint8Array>
) {
  const uploadPromise = new Promise<UploadApiResponse>(
    async (resolve, reject) => {
      const uploadStream =
        cloudinary.v2.uploader.upload_stream(
          {
            folder: "remix",
          },
          (error, result) => {
            if (error) {
              reject(error);
              return;
            }
            resolve(result);
          }
        );
      await writeAsyncIterableToWritable(
        data,
        uploadStream
      );
    }
  );

  return uploadPromise;
}

export const action = async ({ request }: ActionArgs) => {
  const userId = getUserId(request);

  const uploadHandler = unstable_composeUploadHandlers(
    // our custom upload handler
    async ({ name, contentType, data, filename }) => {
      if (name !== "img") {
        return undefined;
      }
      const uploadedImage = await uploadImageToCloudinary(
        data
      );
      return uploadedImage.secure_url;
    },
    // fallback to memory for everything else
    unstable_createMemoryUploadHandler()
  );

  const formData = await unstable_parseMultipartFormData(
    request,
    uploadHandler
  );

  const imageUrl = formData.get("avatar");

  // because our uploadHandler returns a string, that's what the imageUrl will be.
  // ... etc
};

The UploadHandler function accepts a number of parameters about the file:

Property Type Description
name string The field name (comes from your HTML form field "name" value)
data AsyncIterable The iterable of the file bytes
filename string The name of the file that the user selected for upload (like rickroll.mp4)
contentType string The content type of the file (like videomp4)

Your job is to do whatever you need with the data and return a value that's a valid [FormData][form-data] value: [File][the-browser-file-api], string, or undefined to skip adding it to the resulting FormData.

Upload Handler Composition

We have the built-in unstable_createFileUploadHandler and unstable_createMemoryUploadHandler and we also expect more upload handler utilities to be developed in the future. If you have a form that needs to use different upload handlers, you can compose them together with a custom handler, here's a theoretical example:

import type { UploadHandler } from "@remix-run/node"; // or cloudflare/deno
import { unstable_createFileUploadHandler } from "@remix-run/node"; // or cloudflare/deno
import { createCloudinaryUploadHandler } from "some-handy-remix-util";

export const standardFileUploadHandler =
  unstable_createFileUploadHandler({
    directory: "public/calendar-events",
  });

export const cloudinaryUploadHandler =
  createCloudinaryUploadHandler({
    folder: "/my-site/avatars",
  });

export const fileUploadHandler: UploadHandler = (args) => {
  if (args.name === "calendarEvent") {
    return standardFileUploadHandler(args);
  } else if (args.name === "eventBanner") {
    return cloudinaryUploadHandler(args);
  }
  return undefined;
};