Download Session File - BlobHub

Download the bytes of a file session object, along with its envelope.

POST `/revisions/:id/data/query` (Command: `download_session_file`)

This is a binary response: pass Accept: application/octet-stream and the bytes come back as the response body, with the JSON envelope serialized into the X-Response-Body header instead of the body. Access-Control-Expose-Headers names X-Response-Body, so a browser client can read it.

Request Body

Parameter	Type	Required	Description
`engine`	string	Yes	Must be `workflow_blobhub`.
`command`	string	Yes	Must be `download_session_file`.
`session_id`	string	Yes	The ID of the session.
`alias`	string	Yes	Alias of the file object to download.

Response

The bytes themselves, as application/octet-stream — there is no presigned URL to follow. The JSON envelope travels in the X-Response-Body header instead of the body:

Header	Value
`Content-Type`	`application/octet-stream`
`X-Response-Body`	`{"status": "success", "object": {...}}` — the file object’s full envelope.

Errors

forbidden (403) — the alias does not exist, belongs to another revision, or its bytes are gone; a missing and an inaccessible file are deliberately indistinguishable, matching the platform’s read-access convention for session objects.
invalid_file_object — the alias names a session object that exists and is not a file.

Example

curl -X POST https://api.blobhub.io/v1/revisions/rev_001/data/query \
  -H "X-API-Key: $BLOB_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Accept: application/octet-stream" \
  -d '{"engine":"workflow_blobhub","command":"download_session_file","session_id":"sess_001","alias":"report"}' \
  -o report.pdf -D -

{
  "status": "success",
  "object": {
    "revision_id": "rev_001",
    "session_id": "sess_001",
    "alias": "report",
    "updated_at": "2026-07-12T10:00:00.000000Z",
    "value": {
      "type": "file",
      "file": {
        "name": "report.pdf",
        "content_type": "application/pdf",
        "size": 154829,
        "sha256": "bc3863f758932818eedbdaa783c4f7b62e5119c87cbd94725e2ce483c5623fe7"
      }
    }
  }
}

The bytes land in report.pdf; the JSON above is what -D - prints as the X-Response-Body header.

See also

File session object — envelope shape and limits.
Upload Session File — create or replace the file.