Upstash Blob JS

@upstash/blob SDK

S3-compatible object storage. Bucket runs on your server; uploadHandler plus React hooks upload from the browser straight to storage so the bytes never pass through your app.

Bundled docs and source

The @upstash/blob npm package includes docs in node_modules/@upstash/blob/docs/ and readable TypeScript source in node_modules/@upstash/blob/src/. Before writing or debugging SDK code, read and search the relevant docs and source.

Install & Setup

npm install @upstash/blob

Create a bucket in the console and set UPSTASH_BLOB_TOKEN. The token is a bearer secret for the whole bucket — keep it server side, never in NEXT_PUBLIC_ or any bundler-inlined variable.

A bucket is public (every object has a URL) or private (no URL; reads go through signedReadUrl). That is a console setting, not a client option — the SDK learns it from the backend.

import { Bucket } from "@upstash/blob"

export const bucket = Bucket.fromEnv()                          // reads UPSTASH_BLOB_TOKEN
Bucket.fromEnv({ cache: "immutable" })                        // default variable, plus options
Bucket.fromEnv("MEDIA_TOKEN", { cache: "immutable" })           // another variable, plus options
new Bucket({ token: env.UPSTASH_BLOB_TOKEN })                   // Workers: no process.env

Writing

const blob = await bucket.put("reports/q3.pdf", pdf, { contentType: "application/pdf" })
blob.url            // public URL, undefined on a private bucket
blob.versionedUrl   // url + ?v=<etag>, changes whenever the bytes do
blob.etag           // what ifUnchanged takes

Bodies: Request, Blob/File, ArrayBuffer, typed array, string, ReadableStream. A stream carries no length — pass size (exact, streams through) or maxSize (buffers up to the cap), or put throws length_required.

Sizes are decimal: '20mb' is 20,000,000 bytes. '5mib' throws.

import { uniquePath } from "@upstash/blob"

uniquePath`${user.id}/${file.name}`   // 'u7/holiday-pic-3xK9mBqR.png'

Use uniquePath for any value you don't control. Each ${} becomes one slugged filename that can never add a directory, and the finished path gets a random suffix — so two uploads of photo.png never collide. The literal parts of the template are passed through as written, so keep . and .. out of them yourself: a path with those segments is refused later, by the call that uses it, with a TypeError rather than a BlobError.

bucket.copy(from, to, { contentType, cache, metadata }) and bucket.move(from, to, options) preserve source properties you omit. bucket.updateJson(path, fn, { maxAttempts: 6 }) retries a read-modify-write on conflict with backoff.

Reading

const res = await bucket.get("reports/q3.pdf")   // record + body: ReadableStream
const info = await bucket.info("reports/q3.pdf") // same record, no bytes (HEAD)
await bucket.exists("avatars/u7.png")            // boolean instead of a throw
const page = await bucket.list({ prefix: "avatars/", limit: 1000 })

get/info throw not_found. Nothing is buffered — wrap the stream to read it:

await new Response((await bucket.get("notes/1.md")).body).text()

list pages with page.cursor (set only while more remains) and carries no contentType or metadata. prefix is the only filter — keep your own table as the index and treat the bucket as storage, not a queryable store.

const { url, expiresAt } = await bucket.signedReadUrl("private/report.pdf", {
  expiresIn: "2m",
  downloadAs: "Report Q3.pdf",   // save under this name instead of rendering inline
})

Cache the link until expiresAt, never a deadline you compute — a link cannot outlive the credential that signed it, so you may get less than you asked for. await bucket.publicUrl(path) returns the public URL, undefined on a private bucket.

Deleting

await bucket.del("avatars/me.png")            // one path
await bucket.del(["a.png", "b.png"])          // an array, batched by 1000
await bucket.del({ prefix: "tmp/" })          // everything under a prefix

Already-gone counts as success, so deletes are safe to retry. An array or prefix delete where objects survive throws partial_delete with them in e.failed. del({ prefix: '' }) is refused unless you pass all: true.

Browser uploads

The handler authorizes and records; the bytes go browser → storage, so platform request body caps don't apply. Supply your application's getUser and db.files.upsert implementations below.

// lib/uploads.ts
import "server-only"
import { BlobError, uniquePath, uploadHandler } from "@upstash/blob"
import { getUser } from "@/lib/auth"
import { db } from "@/lib/db"

export const uploads = uploadHandler({
  constraints: { maxSize: "20mb", contentTypes: ["image/*", "application/pdf"] },

  onBeforeUpload: async ({ request, file }) => {
    const user = await getUser(request)
    if (!user) throw new BlobError("unauthorized")     // nothing is signed
    return { path: uniquePath`${user.id}/${file.name}`, metadata: { owner: user.id } }
  },

  onUploadComplete: async ({ uploadId, path, url, metadata }) => {
    if (!metadata.owner) throw new BlobError("unauthorized")
    await db.files.upsert({ id: uploadId, owner: metadata.owner, path, url })
    return { path }                                    // becomes upload.blob.data
  },
})

// app/api/upload/route.ts
import { uploads } from "@/lib/uploads"

export const { GET, POST } = uploads

// lib/upload-hooks.ts
"use client"
import { uploadHooks } from "@upstash/blob/react"
import type { uploads } from "./uploads"

export const { useUpload } = uploadHooks<typeof uploads>()

"use client"
import { useUpload } from "@/lib/upload-hooks"

export function UploadForm() {
  const { start, upload, accept } = useUpload()

  return <>
    <input type="file" accept={accept} onChange={(e) => start({ file: e.target.files?.[0] })} />
    {upload?.pending && <progress value={upload.percent} max={100} />}
    {upload?.status === "done" && <a href={upload.blob.url}>{upload.blob.data.path}</a>}
    {upload?.status === "error" && <p>{upload.error.message}</p>}
  </>
}

GET serves the route's constraints, so accept fills the file dialog and an oversized file is refused before any request leaves the browser. uploadHooks<typeof uploads>() types route names and completion data at compile time; import type keeps server code out of the bundle.

This example assumes a public bucket. On a private one url is undefined, so store path instead and hand the client a bucket.signedReadUrl(path) when it needs to read.

Two rules that bite:

• onUploadComplete can run more than once. The browser retries it, so upsert on uploadId rather than inserting.

• A throw out of onUploadComplete deletes the object. That is right for a refusal and wrong for a transient database error — catch your own storage errors.

Files over 16 MB go up in parts, which is what gives pause(), resume(), per-part retry, and resume-after-reload when the user picks the same file again. percent caps at 99 until status is done; drive UI off upload.pending.

Use multipart: true on the handler to make every upload multipart. Then a closed tab leaves incomplete parts rather than a stored object nobody recorded, and one cron cleans up:

await bucket.abortStaleMultipartUploads({ olderThan: "1d" })

For routes where the bytes must pass through your app, write an ordinary route calling bucket.put and drive it with useServerUpload from @upstash/blob/react.

Caching

cache is written once, at upload, and stored with the object — changing it means writing the object again.

immutable needs a path that changes when the bytes do — either uniquePath per upload, or a stable path served through versionedUrl. On a private bucket private replaces public.

Errors

import { BlobError } from "@upstash/blob"

if (BlobError.is(e) && e.code === "not_found") return null

Use BlobError.is(), never instanceof — an ESM and a CJS copy are different classes. Codes: not_found, already_exists, conflict, content_type_not_allowed, invalid_input, too_large, empty_body, length_required, signature_mismatch, unauthorized, forbidden, rate_limited, not_ready, partial_delete, move_left_a_copy, invalid_content_type_pattern, mint_backoff, request_failed.

A refusal keeps its code all the way to the browser, so hooks switch on error.code rather than status numbers. Bad option values ('5mib', a missing token) throw a TypeError where they are written, not a BlobError per request.

S3 clients

import { GetObjectCommand, S3Client } from "@aws-sdk/client-s3"

const config = bucket.s3()
const s3 = new S3Client(config)   // endpoint and credentials are async providers

// config.bucket is the underlying bucket id, available nowhere else
await s3.send(new GetObjectCommand({ Bucket: config.bucket, Key: "reports/q3.pdf" }))

Buckets are S3-compatible. Use this for what the SDK doesn't wrap — byte ranges, conditional GETs, tagging. Pass the providers through as they come so the AWS SDK can refresh an expired credential.