blossom/Server.md

Blossom Server Implementation

All pubkeys MUST be in hex format

CORS

Servers MUST set Access-Control-Allow-Origin: *, Access-Control-Allow-Headers: Authorization,* and Access-Control-Allow-Methods: GET, PUT, DELETE headers on all endpoint to ensure compatibility with apps hosted on other domains

Authorization events

Authorization events are used to identify the users pubkey with the server

Authorization events must be generic and must NOT be scoped to specific servers. This allows pubkeys to sign a single event and interact the same way with multiple servers.

Events must be kind 24242 and have a t tag with a verb of get, upload, list, or delete

Events must have the content set to a human readable string explaining to the user what the events inteded use is. For example Upload Blob, Delete dog-picture.png, List Images, etc

All events must have a NIP-40 expiration tag set to a unix timestamp at which the event should be considered expired.

Example event:

{
  "id": "65c72db0c3b82ffcb395589d01f3e2849c28753e9e7156ceb88e5dd937ca845f",
  "pubkey": "6ea2ab6f206844b1fe48bd8a7eb22ed6e4114a5b2a5252700a729a88142b2bc3",
  "kind": 24242,
  "content": "Upload bitcoin.pdf",
  "created_at": 1708773959,
  "tags": [
    ["t", "upload"],
    ["size", "184292"],
    ["expiration", "1708858680"]
  ],
  "sig": "df099ecaeadb7ebcd7ec8247eb57eb6720d39f64a024be3ef1ed9b5d51087b0e866bd08fd317d5167f9bdb9cdae4e593539b86678c4d922db17d0463e0f9e0e3"
}

Servers must perform the following checks in order to validate the event

1. The kind must be 24242
2. created_at must be in the past
3. The expiration tag must be set to a Unix timespamp in the future
4. The t tag must have a verb matching the intended action of the endpoint
5. Additional checks for specific endpoints. /upload, /delete, etc

Using the Authorization HTTP header, the kind 24242 event MUST be base64 encoded and use the Authorization scheme Nostr

Example HTTP Authorization header:

Authorization: Nostr 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

Endpoints

All endpoints MUST be served from the root path (eg. https://cdn.example.com/upload, etc). This allows clients to talk to servers interchangeably when uploading or fetching blobs

Servers MUST repond with Content-Type: application/json and a JSON object containing message for all error responses

The message field MUST be human readable and should explain the reason for the error. Optionally servers may include other fields for the client with more information about the error.

Example Error response

HTTP/2 401
content-type: application/json; charset=utf-8
content-length: 32
access-control-allow-origin: *
access-control-expose-headers: *

{"message":"Missing Auth event"}

GET /sha256 - Get Blob

The GET /<sha256> endpoint MUST return the contents of the blob with the Content-Type header set to the appropriate MIME type

The endpoint MUST accept an optional file extension in the URL. ie. .pdf, .png, etc

Get Authorization (optional)

The server may optionally require authorization when fetching blobs from the GET /<sha256> endpoint

In this case the server MUST perform additional checks on the authorization event

1. The t tag must be set to get

If the client did not send an Authorization header the server must respond with the appropriate HTTP status code 401 (Unauthorized)

Example Authorization event:

{
  "id": "3a2c0a58f88f86ab81ce7d111df57096e8cd9f41a75731a021e06e07c6df9d0e",
  "pubkey": "96ddb0e7c4a5786a842094fee014d4c6cbb1f1627a8d75ef6fb601baeb6c5054",
  "kind": 24242,
  "content": "Get Blobs",
  "created_at": 1708771927,
  "tags": [
    ["t", "get"],
    ["expiration", "1708857340"]
  ],
  "sig": "2f279b2ac0a5d5f7551f5612b69a111e038ab6b31233a78bfc98f63bd5e38ae8cb5929cf7427f0b7b2dd5eff29e769df23d93926326b0d059dc475701a41d6d3"
}

PUT /upload - Upload Blob

The PUT /upload endpoint should expect the Content-Type header of the request to be set to the MIME type of the blob and the body of the request to the raw data of the blob.

The endpoint MUST return a Blob Descriptor if the upload was successful or an error object if not.

Servers may reject an upload for any reason and should respond with the appropiate HTTP 4xx status code and an error message explaining the reason for the rejection

Upload Authorization (required)

Servers must accept an authorization event when uploading blobs and should perform additional checks

1. The t tag must be set to upload
2. A size tag must be present and set to the total size of the uploaded blob

Example Authorization event:

{
  "id": "65c72db0c3b82ffcb395589d01f3e2849c28753e9e7156ceb88e5dd937ca845f",
  "pubkey": "6ea2ab6f206844b1fe48bd8a7eb22ed6e4114a5b2a5252700a729a88142b2bc3",
  "kind": 24242,
  "content": "Upload bitcoin.pdf",
  "created_at": 1708773959,
  "tags": [
    ["t", "upload"],
    ["size", "184292"],
    ["expiration", "1708858680"]
  ],
  "sig": "df099ecaeadb7ebcd7ec8247eb57eb6720d39f64a024be3ef1ed9b5d51087b0e866bd08fd317d5167f9bdb9cdae4e593539b86678c4d922db17d0463e0f9e0e3"
}

GET /list/pubkey - List Blobs

The /list/<pubkey> endpoint must return a JSON array of Blob Descriptor that where uploaded by the specified pubkey

The endpoint must support a since and until query parameter to limit the returned blob descriptors by the created field

Servers may reject an upload for any reason and MUST respond with the appropriate HTTP 4xx status code and an error message explaining the reason for the rejection

List Authorization (optional)

The server may optionally require Authorization when listing blobs uploaded by the pubkey

In this case the server must perform additional checks on the authorization event

1. The t tag must be set to list

Example Authorization event:

{
  "id": "cbb1cab9566355bfdf04e1f1fc1e655fe903ecc193e8a750092ee53beec2a0e8",
  "pubkey": "a5fc3654296e6de3cda6ba3e8eba7224fac8b150fd035d66b4c3c1dc2888b8fc",
  "kind": 24242,
  "content": "List Blobs",
  "created_at": 1708772350,
  "tags": [
    ["t", "list"],
    ["expiration", "1708858680"]
  ],
  "sig": "ff9c716f8de0f633738036472be553ce4b58dc71d423a0ef403f95f64ef28582ef82129b41d4d0ef64d2338eb4aeeb66dbc03f8b3a3ed405054ea8ecb14fa36c"
}

DELETE /sha256 - Delete Blob

Servers MUST accept DELETE requests to the /<sha256> endpoint

Servers may reject a delete request for any reason and should respond with the aproperate HTTP 4xx status code and an error message explaining the reason for the rejection

Delete Authorization (required)

Servers must accept an authorization event when deleting blobs

Servers should perform additional checks on the authorization event

1. The t tag must be set to delete
2. A x tag must be present and set to the sha256 hash of the blob being deleted

Example Authorization event:

{
  "id": "a92868bd8ea740706d931f5d205308eaa0e6698e5f8026a990e78ee34ce47fe8",
  "pubkey": "ae0063dd2c81ec469f2291ac029a19f39268bfc40aea7ab4136d7a858c3a06de",
  "kind": 24242,
  "content": "Delete bitcoin.pdf",
  "created_at": 1708774469,
  "tags": [
    ["t", "delete"],
    ["x", "b1674191a88ec5cdd733e4240a81803105dc412d6c6708d53ab94fc248f4f553 "],
    ["expiration", "1708858680"]
  ],
  "sig": "2ba9af680505583e3eb289a1624a08661a2f6fa2e5566a5ee0036333d517f965e0ffba7f5f7a57c2de37e00a2e85fd7999076468e52bdbcfad8abb76b37a94b0"
}