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Storage

Mount S3-compatible storage buckets (R2, S3, GCS) into the sandbox filesystem for persistent data access. mountBucket() supports R2 binding mounts, local R2 binding sync during development, and remote S3-compatible endpoint mounts.

Methods

mountBucket()

Mount an S3-compatible bucket to a local path in the sandbox.

TypeScript
await sandbox.mountBucket(
  bucket: string,
  mountPath: string,
  options?: MountBucketOptions
): Promise<void>

Parameters:

  • bucket - Bucket identifier
    • When options.endpoint is omitted, pass the Worker R2 binding name (for example, "MY_BUCKET")
    • When options.endpoint is provided, pass the remote bucket name (for example, "my-r2-bucket")
  • mountPath - Local filesystem path to mount at (e.g., "/data")
  • options (optional) - Mount configuration (see MountBucketOptions)
JavaScript
// Mount an R2 bucket by Worker binding name
await sandbox.mountBucket("MY_BUCKET", "/data");


// Read/write files directly
const data = await sandbox.readFile("/data/config.json");
await sandbox.writeFile("/data/results.json", JSON.stringify(data));


// Mount a remote S3-compatible bucket, including explicit R2 endpoints
await sandbox.mountBucket("my-bucket", "/storage", {
  endpoint: "https://s3.amazonaws.com",
  credentials: {
    accessKeyId: env.AWS_ACCESS_KEY_ID,
    secretAccessKey: env.AWS_SECRET_ACCESS_KEY,
  },
});


// Mount an R2 bucket during local development with wrangler dev
await sandbox.mountBucket("MY_BUCKET", "/local-data", {
  localBucket: true,
});


// Mount a prefix from an R2 binding
await sandbox.mountBucket("MY_BUCKET", "/user-data", {
  prefix: "/users/user-123",
  readOnly: true,
});

Throws:

  • InvalidMountPointError - Invalid mount path or conflicts with existing mounts
  • BucketAccessError - Bucket does not exist or insufficient permissions

unmountBucket()

Unmount a previously mounted bucket.

TypeScript
await sandbox.unmountBucket(mountPath: string): Promise<void>

Parameters:

  • mountPath - Path where the bucket is mounted (e.g., "/data")
JavaScript
// Mount, process, unmount
await sandbox.mountBucket("MY_BUCKET", "/data");
await sandbox.exec("python process.py");


// Unmount
await sandbox.unmountBucket("/data");

Types

MountBucketOptions

TypeScript
interface RemoteMountBucketOptions {
  endpoint: string;
  provider?: BucketProvider;
  credentials?: BucketCredentials;
  readOnly?: boolean;
  s3fsOptions?: string[];
  prefix?: string;
}


interface LocalMountBucketOptions {
  localBucket: true;
  prefix?: string;
  readOnly?: boolean;
}


interface R2BindingMountBucketOptions {
  endpoint?: never;
  prefix?: string;
  readOnly?: boolean;
  s3fsOptions?: string[];
}


type MountBucketOptions =
  | RemoteMountBucketOptions
  | LocalMountBucketOptions
  | R2BindingMountBucketOptions;

mountBucket() supports these three modes:

  • R2 binding mount - Omit endpoint to mount by Worker binding name in production

    • Uses credential-less egress interception for R2
    • Supports prefix, readOnly, and s3fsOptions

  • Local R2 binding mount - Set localBucket: true during wrangler dev

    • Uses the Worker R2 binding directly through local synchronization
    • Supports prefix and readOnly

  • Remote endpoint mount - Set endpoint to mount any S3-compatible provider

    • Supports explicit credentials or environment variable auto-detection
    • Supports provider, prefix, readOnly, and s3fsOptions

Field details:

  • endpoint (remote endpoint mode only) - S3-compatible endpoint URL

    • R2: 'https://YOUR_ACCOUNT_ID.r2.cloudflarestorage.com'
    • S3: 'https://s3.amazonaws.com'
    • GCS: 'https://storage.googleapis.com'

  • localBucket (local development mode only) - Mount an R2 bucket using the Worker's R2 binding during local development with wrangler dev

    • When true, the SDK syncs the R2 binding directly instead of using an S3 endpoint

  • provider (remote endpoint mode only) - Storage provider hint

    • Enables provider-specific optimizations
    • Values: 'r2', 's3', 'gcs'

  • credentials (remote endpoint mode only) - API credentials

    • Contains accessKeyId and secretAccessKey
    • If not provided, uses environment variables

  • readOnly (optional) - Mount in read-only mode

    • Default: false

  • prefix (optional) - Subdirectory within the bucket to mount

    • When specified, only contents under this prefix are visible at the mount point
    • Must start with / (for example, /data/uploads or /data/uploads/)
    • Default: Mount entire bucket

  • s3fsOptions (R2 binding and remote endpoint modes only) - Advanced s3fs mount flags

    • Type: string[]
    • Example: ['use_cache=/tmp/cache', 'stat_cache_expire=1']

BucketProvider

Storage provider hint for automatic s3fs flag optimization.

TypeScript
type BucketProvider = "r2" | "s3" | "gcs";
  • 'r2' - Cloudflare R2 (recommended, applies nomixupload flag)
  • 's3' - Amazon S3
  • 'gcs' - Google Cloud Storage