NIP-25: Reactions

Signed-off-by: William Casarin <jb55@jb55.com>

25.md

@@ -0,0 +1,43 @@
+
+NIP-25
+======
+
+Reactions
+---------
+
+`draft` `optional` `author:jb55`
+
+A reaction is a `kind 7` note that is used to react to `kind 1` text notes.
+
+The generic reaction, represented by an empty string, SHOULD be interpreted as
+a "like".
+
+The `content` MAY be an emoji, in this case it MAY be interpreted as a "like",
+or the client MAY display this emoji reaction on the post.
+
+Tags
+----
+
+The reaction event SHOULD include `e` and `p` tags from the note the user is
+reacting to. This allows users to be notified of reactions to posts they were
+mentioned in. Including the `e` tags enables clients to pull all the reactions
+associated with individual posts or all the posts in a thread.
+
+The last `e` tag MUST be the `id` of the note that is being reacted to. 
+
+The last `p` tag MUST be the `pubkey` of the event being reacted to.
+
+Example code
+
+```swift
+func make_like_event(pubkey: String, privkey: String, liked: NostrEvent) -> NostrEvent {
+    var tags: [[String]] = liked.tags.filter { 
+    	tag in tag.count >= 2 && (tag[0] == "e" || tag[0] == "p") 
+    }
+    tags.append(["e", liked.id])
+    tags.append(["p", liked.pubkey])
+    let ev = NostrEvent(content: "", pubkey: pubkey, kind: 7, tags: tags)
+    ev.calculate_id()
+    ev.sign(privkey: privkey)
+    return ev
+}

README.md

@@ -18,6 +18,7 @@ NIPs stand for **Nostr Implementation Possibilities**. They exist to document wh
 - [NIP-14: Subject tag in text events.](14.md)
 - [NIP-15: End of Stored Events Notice](15.md)
 - [NIP-16: Event Treatment](16.md)
+- [NIP-25: Reactions](25.md)
 
 ## Event Kinds
 
@@ -29,6 +30,7 @@ NIPs stand for **Nostr Implementation Possibilities**. They exist to document wh
 | 3    | Contacts                  | 2    |
 | 4    | Encrypted Direct Messages | 4    |
 | 5    | Event Deletion            | 9    |
+| 7    | Reaction                  | 25   |
 
 Please update this list when proposing NIPs introducing new event kinds.