nostr: add NIP-C7 support

Pull-Request: #1067

Author: SubatomicPlanets

README.md

@@ -129,7 +129,7 @@ Learn more about `rust-nostr` at <https://rust-nostr.org>.
 |     ❌     | [B0 - Web Bookmarks](https://github.com/nostr-protocol/nips/blob/master/B0.md)                                  |
 |     ✅     | [B7 - Blossom](https://github.com/nostr-protocol/nips/blob/master/B7.md)                                        |
 |     ✅     | [C0 - Code Snippets](https://github.com/nostr-protocol/nips/blob/master/C0.md)                                  |
-|     ❌     | [C7 - Chats](https://github.com/nostr-protocol/nips/blob/master/C7.md)                                          |
+|     ✅     | [C7 - Chats](https://github.com/nostr-protocol/nips/blob/master/C7.md)                                          |
 |     ✅     | [EE - Messaging using the MLS Protocol](https://github.com/nostr-protocol/nips/blob/master/EE.md)               |
 
 ## State

crates/nostr/CHANGELOG.md

@@ -35,6 +35,7 @@
 
 ### Added
 
+- Add NIP-C7 support (https://github.com/rust-nostr/nostr/pull/1067)
 - Implement `ToBech32` trait for `Nip21`
 - Add nip47 holdinvoice methods and notification (https://github.com/rust-nostr/nostr/pull/1019)
 - Add `TransactionState` to `LookupInvoiceResponse` and `PaymentNotification` (https://github.com/rust-nostr/nostr/pull/1045)

crates/nostr/src/event/builder.rs

@@ -49,6 +49,8 @@ pub enum Error {
     /// NIP04 error
     #[cfg(feature = "nip04")]
     NIP04(nip04::Error),
+    /// NIP21 error
+    NIP21(nip21::Error),
     /// NIP44 error
     #[cfg(all(feature = "std", feature = "nip44"))]
     NIP44(nip44::Error),
@@ -80,6 +82,7 @@ impl fmt::Display for Error {
             Self::NIP03(e) => e.fmt(f),
             #[cfg(feature = "nip04")]
             Self::NIP04(e) => e.fmt(f),
+            Self::NIP21(e) => e.fmt(f),
             #[cfg(all(feature = "std", feature = "nip44"))]
             Self::NIP44(e) => e.fmt(f),
             Self::NIP58(e) => e.fmt(f),
@@ -125,6 +128,12 @@ impl From<nip04::Error> for Error {
     }
 }
 
+impl From<nip21::Error> for Error {
+    fn from(e: nip21::Error) -> Self {
+        Self::NIP21(e)
+    }
+}
+
 #[cfg(all(feature = "std", feature = "nip44"))]
 impl From<nip44::Error> for Error {
     fn from(e: nip44::Error) -> Self {
@@ -1706,6 +1715,67 @@ impl EventBuilder {
     pub fn poll_response(response: PollResponse) -> Self {
         response.to_event_builder()
     }
+
+    /// Chat message
+    ///
+    /// <https://github.com/nostr-protocol/nips/blob/master/C7.md>
+    #[inline]
+    pub fn chat_message<S>(content: S) -> Self
+    where
+        S: Into<String>,
+    {
+        Self::new(Kind::ChatMessage, content)
+    }
+
+    /// Chat message reply
+    ///
+    /// <https://github.com/nostr-protocol/nips/blob/master/C7.md>
+    pub fn chat_message_reply<S>(
+        content: S,
+        reply_to: &Event,
+        relay_url: Option<RelayUrl>,
+    ) -> Result<Self, Error>
+    where
+        S: Into<String>,
+    {
+        let mut content = content.into();
+
+        if !has_nostr_event_uri(&content, &reply_to.id) {
+            let nevent = Nip19Event {
+                event_id: reply_to.id,
+                author: None,
+                kind: None,
+                relays: relay_url.clone().into_iter().collect(),
+            };
+            content = format!("{}\n{content}", nevent.to_nostr_uri()?);
+        }
+
+        Ok(
+            Self::new(Kind::ChatMessage, content).tag(Tag::from_standardized_without_cell(
+                TagStandard::Quote {
+                    event_id: reply_to.id,
+                    relay_url,
+                    public_key: Some(reply_to.pubkey),
+                },
+            )),
+        )
+    }
+}
+
+fn has_nostr_event_uri(content: &str, event_id: &EventId) -> bool {
+    const OPTS: NostrParserOptions = NostrParserOptions::disable_all().nostr_uris(true);
+
+    let parser = NostrParser::new().parse(content).opts(OPTS);
+
+    for token in parser.into_iter() {
+        if let Token::Nostr(nip21) = token {
+            if nip21.event_id().as_ref() == Some(event_id) {
+                return true;
+            }
+        }
+    }
+
+    false
 }
 
 #[cfg(test)]

crates/nostr/src/event/kind.rs

@@ -163,6 +163,7 @@ kind_variants! {
     CodeSnippet => 1337, "Code Snippets", "<https://github.com/nostr-protocol/nips/blob/master/C0.md>",
     Poll => 1068, "Poll", "<https://github.com/nostr-protocol/nips/blob/master/88.md>",
     PollResponse => 1018, "Poll response", "<https://github.com/nostr-protocol/nips/blob/master/88.md>",
+    ChatMessage => 9, "Chat Message", "<https://github.com/nostr-protocol/nips/blob/master/C7.md>",
 }
 
 impl PartialEq for Kind {