add HEAD /sha256 endpoint for checking blobs

Nostr.md

@@ -6,7 +6,7 @@ See [Authorization events](./Server.md#authorization-events)
 
 ## User Server Discovery
 
-Users should publish a kind `10063` event with a list of `r` tags indicating servers that others users should use when getting their blobs
+Users should publish a kind `10063` event with a list of ordered `r` tags indicating servers that others users should use when getting their blobs
 
 ### Example
 

README.md

@@ -15,6 +15,7 @@ Blobs are packs of binary data addressed by their sha256 hash
 Blossom Servers expose four endpoints for managing blobs
 
 - `GET /<sha256>` (optional file `.ext`)
+- `HEAD /<sha256>` (optional file `.ext`)
 - `PUT /upload`
   - `Authentication`: Signed [nostr event](./Server.md#upload-authorization-required)
   - Return a blob descriptor

Server.md

@@ -105,6 +105,12 @@ Example Authorization event:
 }
 ```
 
+### HEAD /sha256 - Has Blob
+
+The `HEAD /<sha256>` endpoint MUST respond with either a `200` or `404` status code
+
+The endpoint MUST accept an optional file extension in the URL similar to the `GET /<sha256>` endpoint. ie. `.pdf`, `.png`, etc
+
 ### 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.