blossom/buds/04.md

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# BUD-04
## Mirroring blobs
`draft` `optional`
Defines the `/mirror` endpoint
## PUT /mirror - Mirror Blob
A server may expose a `PUT /mirror` endpoint to allow users to copy a blob from a URL instead of uploading it
Clients MUST pass the URL of the remote blob as a stringified JSON object in the request body
```json
// request body
{
"url": "https://cdn.satellite.earth/b1674191a88ec5cdd733e4240a81803105dc412d6c6708d53ab94fc248f4f553.pdf"
}
```
Clients MUST set the `Authorization` header to an upload authorization event defined in [BUD-02](./02.md#upload-authorization-required)
The `/mirror` endpoint MUST download the blob from the specified URL and verify that there is at least one `x` tag in the authorization event matching the sha256 hash of the download blob
**Multiple `x` tags MUST NOT be interpreted as the user requesting a bulk mirror.**
The endpoint MUST return a [Blob Descriptor](#blob-descriptor) if the mirroring was successful or an error object if it was not
Servers should re-use the `Content-Type` header returned from the URL to discover the mime type of the blob. if none is returned it may use the file extension in the URL
Servers MAY reject a mirror request for any reason and should respond with the appropriate HTTP `4xx` status code and an error message explaining the reason for the rejection
## Example Flow
1. Client signs authorization event and uploads blob to Server A
1. Server A returns blob descriptor with `url`
1. Client sends the `url` to Server B `/mirror` using the original authorization event
1. Server B downloads blob from Server A using the url
1. Server B verifies downloaded blob hash matches `x` tag in authorization event
1. Server B returns [Blob Descriptor](./02.md#blob-descriptor)