Multipart Strategy

Multipart uploads are resumable and suit large files. The backend signs each part on demand, enabling S3/MinIO-style chunked uploads.

Intent Shape

Your backend's createIntent should return this shape for multipart uploads:

type MultipartIntent = {
  strategy: 'multipart'
  fileId: string
  uploadId: string
  partSize: number
  partCount: number
  parts?: Array<{
    partNumber: number
    url: string
    headers?: Record<string, string>
  }>
}

type MultipartIntent = {
  strategy: 'multipart'
  fileId: string
  uploadId: string
  partSize: number
  partCount: number
  parts?: Array<{
    partNumber: number
    url: string
    headers?: Record<string, string>
  }>
}

Cursor Shape

The strategy tracks progress with a cursor persisted after each part:

type MultipartCursor = {
  done: Array<{
    partNumber: number
    etag: string
    size: number
  }>
  completed?: true
}

type MultipartCursor = {
  done: Array<{
    partNumber: number
    etag: string
    size: number
  }>
  completed?: true
}

Behavior

• Each part uploads individually using signed URLs from the backend.
• The cursor persists after each part, so uploads resume.
• The completed flag prevents double completion on resume.
• The strategy handles basic per-part retries internally.
• Abort signals check between parts for pause and cancel.

When to Use

Use multipart when:

• File size exceeds the POST strategy limit.
• Resumability matters (large files, unreliable connections).
• Concurrent part uploads improve throughput.