Multipart Strategy

Multipart uploads are resumable and ideal for large files. Parts are signed per request by your backend, 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 multipart strategy tracks progress using a cursor that is 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 is uploaded individually using signed URLs from your backend
• Cursor updates are persisted after each completed part, enabling resumability
• The completed flag prevents double completion on resume
• The strategy handles basic part retries internally
• Abort signals are checked between parts for pause and cancel support

When to Use

Use multipart for files where:

• The file size exceeds your POST strategy limits
• Resumability is important (large files, unreliable connections)
• You want concurrent part uploads for better throughput