Backblaze B2

Backblaze B2 uses the S3 API with AWS Signature V4 against https://s3.<region>.backblazeb2.com. MIRAGE derives this endpoint from your region automatically. Credentials (B2 application key, the keyID is the access key and the applicationKey is the secret) are created the same way in both runtimes, see Backblaze B2 Credentials.

Node (server-side)

pnpm add @struktoai/mirage-node

import { BackblazeVFS, MountMode, Workspace } from '@struktoai/mirage-node'

const b2 = new BackblazeVFS({
  bucket: process.env.B2_BUCKET!,
  region: process.env.B2_REGION!,
  accessKeyId: process.env.B2_ACCESS_KEY_ID!,
  secretAccessKey: process.env.B2_SECRET_ACCESS_KEY!,
})

const ws = new Workspace({ '/bucket/': b2 }, { mode: MountMode.READ })
const res = await ws.shell('ls /bucket/')
console.log(res.stdoutText)

Config

Field	Description
`bucket` required	Name of the bucket to mount.
`accessKeyId` secret	Access key ID; set it with `secretAccessKey`. Unset uses the AWS SDK credential chain.
`secretAccessKey` secret	Secret access key paired with `accessKeyId`.
`sessionToken` secret	Session token for temporary credentials, sent with the access key pair.
`profile`	Named profile in the shared AWS config and credentials files that supplies credentials when no access key pair is given.
`forcePathStyle`	Address the bucket in the URL path (`<endpoint>/<bucket>/<key>`) instead of as a subdomain of the endpoint.
`keyPrefix`	Key prefix inside the bucket that the mount treats as its root; keys outside it are not visible. Leading slashes are dropped and a trailing `/` is added.
`timeout` default `DEFAULT_TIMEOUT`	Seconds a request may wait to connect, or between two reads of its answer, before it fails; a download that keeps flowing is never cut off.
`proxy` secret	Proxy URL for every HTTP and HTTPS request to the endpoint.
`region` required	Provider region every request is signed for. Most providers also build their endpoint URL from it unless `endpoint` is set.
`endpoint`	Endpoint URL that replaces the one the provider derives.

Fields marked secret are redacted in snapshots.

Browser (presigned URLs)

pnpm add @struktoai/mirage-browser

The browser BackblazeVFS is secret-free, your backend signs each operation using your B2 application key and returns a URL. B2 accepts AWS Signature V4, so @aws-sdk/s3-request-presigner works, pointed at the B2 endpoint.

Config

Field	Description
`bucket` required	Name of the bucket to mount.
`presignedUrlProvider` required, secret	Function `(path, operation, options)` that returns a signed URL for each S3 operation; your server signs it, so the browser holds no keys.
`region`	Region of the bucket. Most providers derive the endpoint from it; requests go to the host each presigned URL names.
`endpoint`	Endpoint URL that replaces the one the provider derives. Requests go to the host each presigned URL names; the mount uses it to name its storage location.
`defaultContentType` default `'application/octet-stream'`	`Content-Type` stored with every object the mount writes.
`keyPrefix`	Key prefix the mount treats as its root. The browser can change it before a URL is signed, so enforce the prefix on the signing server.
`timeout` default `DEFAULT_TIMEOUT`	Seconds a request may wait to connect, or between two reads of its answer, before it fails; a download that keeps flowing is never cut off.

Fields marked secret are redacted in snapshots.

1. Server: sign URLs with the B2 endpoint

import {
  CopyObjectCommand,
  DeleteObjectCommand,
  GetObjectCommand,
  HeadObjectCommand,
  ListObjectsV2Command,
  PutObjectCommand,
  S3Client,
} from '@aws-sdk/client-s3'
import { getSignedUrl } from '@aws-sdk/s3-request-presigner'

const REGION = process.env.B2_REGION!

const client = new S3Client({
  region: REGION,
  endpoint: `https://s3.${REGION}.backblazeb2.com`,
  credentials: {
    accessKeyId: process.env.B2_ACCESS_KEY_ID!,
    secretAccessKey: process.env.B2_SECRET_ACCESS_KEY!,
  },
})
const BUCKET = process.env.B2_BUCKET!

app.post('/presign/b2', async (req, res) => {
  const { path, op, opts } = req.body
  const key = path.replace(/^\/+/, '')
  const ttl = typeof opts?.ttlSec === 'number' ? opts.ttlSec : 300
  let cmd
  switch (op) {
    case 'GET':    cmd = new GetObjectCommand({ Bucket: BUCKET, Key: key }); break
    case 'PUT':    cmd = new PutObjectCommand({ Bucket: BUCKET, Key: key, ContentType: opts?.contentType }); break
    case 'HEAD':   cmd = new HeadObjectCommand({ Bucket: BUCKET, Key: key }); break
    case 'DELETE': cmd = new DeleteObjectCommand({ Bucket: BUCKET, Key: key }); break
    case 'LIST':   cmd = new ListObjectsV2Command({
      Bucket: BUCKET,
      Prefix: opts?.listPrefix,
      Delimiter: opts?.listDelimiter,
      ContinuationToken: opts?.listContinuationToken,
    }); break
    case 'COPY':   cmd = new CopyObjectCommand({
      Bucket: BUCKET,
      Key: key,
      CopySource: `${BUCKET}/${opts?.copySource}`,
    }); break
  }
  res.json({ url: await getSignedUrl(client, cmd, { expiresIn: ttl }) })
})

2. Browser: wire it up

import { BackblazeVFS, MountMode, Workspace } from '@struktoai/mirage-browser'

const b2 = new BackblazeVFS({
  bucket: 'my-bucket',
  region: 'us-west-004',
  presignedUrlProvider: async (path, op, opts) => {
    const r = await fetch('/presign/b2', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ path, op, opts }),
    })
    const { url } = await r.json()
    return url
  },
})

const ws = new Workspace({ '/bucket/': b2 }, { mode: MountMode.READ })

region on the browser config is only used for display/logging; the actual endpoint is baked into the presigned URLs your backend returns.

3. CORS

B2 manages CORS through its native API, not the S3 PutBucketCors call. Set CORS rules in the Backblaze web console (Bucket Settings -> CORS Rules) or with the b2 CLI:

b2 bucket update my-bucket \
  --cors-rules '[{"corsRuleName":"mirage","allowedOrigins":["http://localhost:5173","https://app.example.com"],"allowedOperations":["s3_get","s3_put","s3_head","s3_delete","s3_post"],"allowedHeaders":["*"],"exposeHeaders":["etag","content-length","content-type","last-modified"],"maxAgeSeconds":3000}]'

See the Backblaze VFS docs for the equivalent Python wiring. For write: conditional on this provider, see S3-compatible stores.

VFS.md

The VFS.md an agent reads with Backblaze B2 mounted at /<path>.

Rendered
Raw

Virtual Filesystem

Path	Description
`/<path>`	`backblaze`, write

Supported Unix Commands for VFS

Unix commands work on each path as on a local filesystem, as far as the path supports them:

Path	Supported
`/<path>`	Almost all Unix commands.

Limitations of Unix Commands for VFS

Where a path differs from a local filesystem:

Path	Limitations
`/<path>`	`grep -r`, `find` and `du` stop after 1000 files; a glob matching more, `tar -c`, `cp -r` and `rm -r` are refused.

Run man <cmd> or <cmd> --help for one command’s usage.

---
name: workspace-filesystem
description: The virtual filesystem layout of this workspace.
---

# Virtual Filesystem

| Path | Description |
| --- | --- |
| `/<path>` | `backblaze`, write |

## Supported Unix Commands for VFS

Unix commands work on each path as on a local filesystem, as far as the path supports them:

| Path | Supported |
| --- | --- |
| `/<path>` | Almost all Unix commands. |

## Limitations of Unix Commands for VFS

Where a path differs from a local filesystem:

| Path | Limitations |
| --- | --- |
| `/<path>` | `grep -r`, `find` and `du` stop after 1000 files; a glob matching more, `tar -c`, `cp -r` and `rm -r` are refused. |

Run `man <cmd>` or `<cmd> --help` for one command's usage.

Integration

What Backblaze B2 answers through its own API, so fewer files are read. Integration explains each command.

Command	On Backblaze B2
`find`, `du`, `ls -R`, `tree`	One recursive listing

Getting Started

Access

AI Agents

VFS

CLIs

Runtimes

Node (server-side)

Config

Browser (presigned URLs)

Config

1. Server: sign URLs with the B2 endpoint

2. Browser: wire it up

3. CORS

VFS.md

Virtual Filesystem

Supported Unix Commands for VFS

Limitations of Unix Commands for VFS

Integration

​Node (server-side)

​Config

​Browser (presigned URLs)

​Config

​1. Server: sign URLs with the B2 endpoint

​2. Browser: wire it up

​3. CORS

​VFS.md

​Virtual Filesystem

​Supported Unix Commands for VFS

​Limitations of Unix Commands for VFS

​Integration

Node (server-side)

Config

Browser (presigned URLs)

Config

1. Server: sign URLs with the B2 endpoint

2. Browser: wire it up

3. CORS

VFS.md

Virtual Filesystem

Supported Unix Commands for VFS

Limitations of Unix Commands for VFS

Integration