BUD-04
======

Efficiently mirroring blobs
---------------------

`draft` `optional`

If a server supports the `/upload` endpoint defined in [BUD-02](./02.md) it MAY also support an optional `url` query parameter in the URL ( eg. `/upload?url=https://cdn.satellite.earth/b1674191a88ec5cdd733e4240a81803105dc412d6c6708d53ab94fc248f4f553.pdf` )

If the `url` query parameter is specified the server MUST ignore the body and `Content-Type` of the request and download the raw binary blob data from the URL

The server MUST verify the sha256 hash of the downloaded blob matches the `x` tag in the upload [authorization event](./02.md#upload-authorization-required)

The server should re-use the `Content-Type` header returned from the URL to know the mime type of the blob. if none is returned it may use the file extension in the URL

The endpoint MUST return a [Blob Descriptor](#blob-descriptor) if the mirroring was successful or an error object if it was not

If no `url` query parameter is specified the server MUST follow the rules layed out in [BUD-02](./02.md)

## Example Flow

1. Client requests lists of blobs from Server A
1. Client signs an upload auth event for X
1. Client makes request `https://cdn.server-b.com/upload?url=https://cdn.server-a.com/<sha256>.png` with authorization header
1. Server B receives request
1. Server B downloads blob from Server A using url query parameter
1. Server B verifies downloaded blob hash matches `x` tag in authorization header
1. Server B returns [Blob Descriptor](./02.md#blob-descriptor)