Client Uploads with Vercel Blob

In this guide, you'll learn how to do the following:

• Use the Vercel dashboard to create a Blob store connected to a project
• Upload a file using the Blob SDK from a browser

Vercel Blob works with any frontend framework. First, install the package:

pnpm i @vercel/blob

1. Create a Blob store

   Navigate to the Project you'd like to add the blob store to. Select the Storage tab, then select the Connect Database button.

   Under the Create New tab, select Blob and then the Continue button.

   Use the name "Images" and select Create a new Blob store. Select the environments where you would like the read-write token to be included. You can also update the prefix of the Environment Variable in Advanced Options

   Once created, you are taken to the Vercel Blob store page.

2. Prepare your local project

   Since you created the Blob store in a project, we automatically created and added the following Environment Variable to the project for you.

   • BLOB_READ_WRITE_TOKEN

   To use this Environment Variable locally, we recommend pulling it with the Vercel CLI:

   vercel env pull

When you need to upload files larger than 4.5 MB, you can use client uploads. In this case, the file is sent directly from the client (a browser in this example) to Vercel Blob. This transfer is done securely as to not expose your Vercel Blob store to anonymous uploads. The security mechanism is based on a token exchange between your server and Vercel Blob.

1. Create a client upload page

   This page allows to upload files to Vercel Blob. The files will go directly from the browser to Vercel Blob without going through your server.

   Behind the scenes, the upload is done securely by exchanging a token with your server before uploading the file.

   Next.js (/app)Next.js (/pages)Other frameworks

   src/app/avatar/upload/page.tsx

   TypeScript

   TypeScriptJavaScript

   'use client';
    
   import { type PutBlobResult } from '@vercel/blob';
   import { upload } from '@vercel/blob/client';
   import { useState, useRef } from 'react';
    
   export default function AvatarUploadPage() {
     const inputFileRef = useRef<HTMLInputElement>(null);
     const [blob, setBlob] = useState<PutBlobResult | null>(null);
     return (
       <>
         <h1>Upload Your Avatar</h1>
    
         <form
           onSubmit={async (event) => {
             event.preventDefault();
    
             if (!inputFileRef.current?.files) {
               throw new Error('No file selected');
             }
    
             const file = inputFileRef.current.files[0];
    
             const newBlob = await upload(file.name, file, {
               access: 'public',
               handleUploadUrl: '/api/avatar/upload',
             });
    
             setBlob(newBlob);
           }}
         >
           <input name="file" ref={inputFileRef} type="file" required />
           <button type="submit">Upload</button>
         </form>
         {blob && (
           <div>
             Blob url: <a href={blob.url}>{blob.url}</a>
           </div>
         )}
       </>
     );
   }

2. Create a client upload route

   The responsibility of this client upload route is to:

   1. Generate tokens for client uploads
   2. Listen for completed client uploads, so you can update your database with the URL of the uploaded file for example

   The @vercel/blob npm package exposes a helper to implement said responsibilities.

   Next.js (/app)Next.js (/pages)Other frameworks

   src/app/api/avatar/upload/route.ts

   TypeScript

   TypeScriptJavaScript

   import { handleUpload, type HandleUploadBody } from '@vercel/blob/client';
   import { NextResponse } from 'next/server';
    
   export async function POST(request: Request): Promise<NextResponse> {
     const body = (await request.json()) as HandleUploadBody;
    
     try {
       const jsonResponse = await handleUpload({
         body,
         request,
         onBeforeGenerateToken: async (
           pathname,
           /* clientPayload */
         ) => {
           // Generate a client token for the browser to upload the file
           // Make sure to authenticate and authorize users before generating the token.
           // Otherwise, you're allowing anonymous uploads.
    
           return {
             allowedContentTypes: ['image/jpeg', 'image/png', 'image/webp'],
             addRandomSuffix: true,
             // callbackUrl: 'https://example.com/api/avatar/upload',
             // optional, `callbackUrl` is automatically computed when hosted on Vercel
             tokenPayload: JSON.stringify({
               // optional, sent to your server on upload completion
               // you could pass a user id from auth, or a value from clientPayload
             }),
           };
         },
         onUploadCompleted: async ({ blob, tokenPayload }) => {
           // Called by Vercel API on client upload completion
           // Use tools like ngrok if you want this to work locally
    
           console.log('blob upload completed', blob, tokenPayload);
    
           try {
             // Run any logic after the file upload completed
             // const { userId } = JSON.parse(tokenPayload);
             // await db.update({ avatar: blob.url, userId });
           } catch (error) {
             throw new Error('Could not update user');
           }
         },
       });
    
       return NextResponse.json(jsonResponse);
     } catch (error) {
       return NextResponse.json(
         { error: (error as Error).message },
         { status: 400 }, // The webhook will retry 5 times waiting for a 200
       );
     }
   }

1. Run your application locally

   Run your application locally and visit /avatar/upload to upload the file to your store. The browser will display the unique URL created for the file.

2. Review the Blob object metadata

   • Go to the Vercel Project where you created the store
   • Select the Storage tab and select your new store
   • Paste the blob object URL returned in the previous step in the Blob URL input box in the Browser section and select Lookup
   • The following blob object metadata will be displayed: file name, path, size, uploaded date, content type and HTTP headers
   • You also have the option to download and delete the file from this page

You have successfully uploaded an object to your Vercel Blob store and are able to review it's metadata, download, and delete it from your Vercel Storage Dashboard.

The onUploadCompleted callback is called by Vercel API when a client upload completes. For this to work, @vercel/blob computes the correct callback URL to call based on the environment variables of your project.

We use the following environment variables to compute the callback URL:

• VERCEL_BRANCH_URL in preview environments
• VERCEL_URL in preview environments where VERCEL_BRANCH_URL is not set
• VERCEL_PROJECT_PRODUCTION_URL in production environments

These variables are automatically set by Vercel through System Environment Variables. If you're not using System Environment Variables, use the callbackUrl option at the onBeforeGenerateToken step in handleUpload.

When running your application locally, the onUploadCompleted callback will not work as Vercel Blob cannot contact your localhost. Instead, we recommend you run your local application through a tunneling service like ngrok, so you can experience the full Vercel Blob development flow locally.

When using ngrok in local development, you can configure the domain to call for onUploadCompleted by using the VERCEL_BLOB_CALLBACK_URL environment variable in your .env.local file when using Next.js:

VERCEL_BLOB_CALLBACK_URL=https://abc123.ngrok-free.app

• Learn how to use the methods available with the @vercel/blob package