add client implementation details

buds/03.md

@@ -10,9 +10,9 @@ Defines a replaceable event using `kind:10063` to advertise the blossom servers
 
 The event MUST include at least one `server` tag containing the full server URL including the `http://` or `https://`.
 
-The order of these tags is important and should be arranged with the users most "reliable" or "trusted" servers coming first.
+The order of these tags is important and should be arranged with the users most "reliable" or "trusted" servers being first.
 
-The `.content` is not used.
+The `.content` field is not used.
 
 ```json
 {
@@ -29,12 +29,50 @@ The `.content` is not used.
 }
 ```
 
-## Client Integration
+## Client Upload Implementation
 
-When uploading blobs clients should attempt to upload the blob to all or at least the top 3 server on the list event.
+When uploading blobs clients MUST attempt to upload the blob to at least the first `server` listed in the users server list.
+
+Optionally clients MAY upload the blob to all the servers or mirror the blob to the other servers if they support [BUD-04](./04.md)
 
 This ensures that the blob is available in multiple locations in the case one of the servers goes offline.
 
-## Server Integration
+## Client Retrieval Implementation
 
-Servers may use this event kind to discover other servers that a user is uploading to in order to download specific blobs from.
+When extracting the SHA256 hash from the URL clients MUST use the last occurrence of a 64 char hex string. This allows clients to extract hashes from blossom URLs and SOME non-blossom URLs.
+
+In all the following examples, the hash `b1674191a88ec5cdd733e4240a81803105dc412d6c6708d53ab94fc248f4f553` should be selected
+
+- Blossom URLs
+  - `https://blossom.example.com/b1674191a88ec5cdd733e4240a81803105dc412d6c6708d53ab94fc248f4f553.pdf`
+  - `https://cdn.example.com/b1674191a88ec5cdd733e4240a81803105dc412d6c6708d53ab94fc248f4f553`
+- Non Blossom URLs
+  - `https://cdn.example.com/user/ec4425ff5e9446080d2f70440188e3ca5d6da8713db7bdeef73d0ed54d9093f0/media/b1674191a88ec5cdd733e4240a81803105dc412d6c6708d53ab94fc248f4f553.pdf`
+  - `https://cdn.example.com/media/user-name/documents/b1674191a88ec5cdd733e4240a81803105dc412d6c6708d53ab94fc248f4f553.pdf`
+  - `http://download.example.com/downloads/b1674191a88ec5cdd733e4240a81803105dc412d6c6708d53ab94fc248f4f553`
+  - `http://media.example.com/documents/b1/67/b1674191a88ec5cdd733e4240a81803105dc412d6c6708d53ab94fc248f4f553.pdf`
+
+In the context of nostr events, clients SHOULD use the author's server list when looking for blobs that are no longer available at the original URL.
+
+Take the following event as an example
+
+```json
+{
+  "id": "834185269f4ab72539193105060dbb1c8b2efd702d14481cea345c47beefe6eb",
+  "pubkey": "ec4425ff5e9446080d2f70440188e3ca5d6da8713db7bdeef73d0ed54d9093f0",
+  "content": "I've developed a new open source P2P e-cash system called Bitcoin. check it out\nhttps://cdn.broken-domain.com/b1674191a88ec5cdd733e4240a81803105dc412d6c6708d53ab94fc248f4f553.pdf",
+  "kind": 1,
+  "created_at": 1297484820,
+  "tags": [],
+  "sig": "bd4bb200bdd5f7ffe5dbc3e539052e27b05d6f9f528e255b1bc4261cc16b8f2ad85c89eef990c5f2eee756ef71b4c571ecf6a88ad12f7338e321dd60c6a903b5"
+}
+```
+
+Once the client discovers that the URL `https://cdn.broken-domain.com/b1674191a88ec5cdd733e4240a81803105dc412d6c6708d53ab94fc248f4f553.pdf` is no longer available. It should perform the following steps to find the blob:
+
+1. Get the SHA256 has from the URL
+2. Look for the authors server list `kind:10063`
+3. If found, Attempt to retrieve the blob from each `server` listed started with the first
+3. If not found, the client MAY fallback to using a well-known popular blossom server to retrieve the blob
+
+This ensures clients can quickly find missing blobs using the users list of trusted servers.