MMR tag: add merkle mountain range tag

crates/nostr/Cargo.toml

@@ -25,6 +25,7 @@ nip19 = ["dep:bech32"]
 nip21 = ["nip19"]
 nip46 = ["nip04"]
 nip47 = ["nip04"]
+mmr = []
 
 [dependencies]
 aes = { version = "0.8", optional = true }

crates/nostr/src/event/builder.rs

@@ -3,14 +3,15 @@
 
 //! Event builder
 
+#[cfg(feature = "mmr")]
+use bitcoin_hashes::sha256::Hash;
 use core::fmt;
-#[cfg(not(target_arch = "wasm32"))]
-use std::time::Instant;
-
 #[cfg(target_arch = "wasm32")]
 use instant::Instant;
 use secp256k1::XOnlyPublicKey;
 use serde_json::{json, Value};
+#[cfg(not(target_arch = "wasm32"))]
+use std::time::Instant;
 use url::Url;
 
 pub use super::kind::Kind;
@@ -169,6 +170,49 @@ impl EventBuilder {
             tags.pop();
         }
     }
+
+    /// Build MMR [`Event`]
+    #[cfg(feature = "mmr")]
+    pub fn to_mmr_event(
+        self,
+        keys: &Keys,
+        prev_event_hash: Hash,
+        prev_mmr_root: Hash,
+        prev_event_pos: i64,
+    ) -> Result<Event, Error> {
+        let pubkey: XOnlyPublicKey = keys.public_key();
+        Ok(self
+            .to_unsigned_mmr_event(pubkey, prev_event_hash, prev_mmr_root, prev_event_pos)
+            .sign(keys)?)
+    }
+
+    /// Build unsigned MMR [`Event`]
+    #[cfg(feature = "mmr")]
+    pub fn to_unsigned_mmr_event(
+        self,
+        pubkey: XOnlyPublicKey,
+        prev_event_id: Hash,
+        prev_mmr_root: Hash,
+        prev_event_pos: i64,
+    ) -> UnsignedEvent {
+        let mut tags: Vec<Tag> = self.tags;
+        tags.push(Tag::Mmr {
+            prev_event_id,
+            prev_mmr_root,
+            prev_event_pos,
+        });
+        let created_at: Timestamp = Timestamp::now();
+        let id = EventId::new(&pubkey, created_at, &self.kind, &tags, &self.content);
+        // TODO verify if valid MMR append operation for vector commitment
+        UnsignedEvent {
+            id,
+            pubkey,
+            created_at,
+            kind: self.kind,
+            tags,
+            content: self.content,
+        }
+    }
 }
 
 impl EventBuilder {

crates/nostr/src/event/tag.rs

@@ -7,6 +7,8 @@ use core::fmt;
 use core::num::ParseIntError;
 use core::str::FromStr;
 
+#[cfg(feature = "mmr")]
+use bitcoin_hashes::sha256::Hash;
 use secp256k1::schnorr::Signature;
 use secp256k1::XOnlyPublicKey;
 use serde::de::Error as DeserializerError;
@@ -242,6 +244,9 @@ pub enum TagKind {
     Lnurl,
     /// Name tag
     Name,
+    #[cfg(feature = "mmr")]
+    /// Merkle mountain range
+    Mmr,
     /// Custom tag kind
     Custom(String),
 }
@@ -275,6 +280,8 @@ impl fmt::Display for TagKind {
             Self::Amount => write!(f, "amount"),
             Self::Lnurl => write!(f, "lnurl"),
             Self::Name => write!(f, "name"),
+            #[cfg(feature = "mmr")]
+            Self::Mmr => write!(f, "mmr"),
             Self::Custom(tag) => write!(f, "{tag}"),
         }
     }
@@ -313,6 +320,8 @@ where
             "amount" => Self::Amount,
             "lnurl" => Self::Lnurl,
             "name" => Self::Name,
+            #[cfg(feature = "mmr")]
+            "mmr" => Self::Mmr,
             tag => Self::Custom(tag.to_string()),
         }
     }
@@ -370,6 +379,12 @@ pub enum Tag {
     Lnurl(String),
     Name(String),
     PublishedAt(Timestamp),
+    #[cfg(feature = "mmr")]
+    Mmr {
+        prev_event_id: Hash,
+        prev_mmr_root: Hash,
+        prev_event_pos: i64,
+    },
 }
 
 impl Tag {
@@ -420,6 +435,8 @@ impl Tag {
             Tag::Amount(..) => TagKind::Amount,
             Tag::Name(..) => TagKind::Name,
             Tag::Lnurl(..) => TagKind::Lnurl,
+            #[cfg(feature = "mmr")]
+            Tag::Mmr { .. } => TagKind::Mmr,
         }
     }
 }
@@ -581,6 +598,12 @@ where
                     conditions: Conditions::from_str(&tag[2])?,
                     sig: Signature::from_str(&tag[3])?,
                 }),
+                #[cfg(feature = "mmr")]
+                TagKind::Mmr => Ok(Self::Mmr {
+                    prev_event_id: Hash::from_str(tag[1].as_str())?,
+                    prev_mmr_root: Hash::from_str(tag[2].as_str())?,
+                    prev_event_pos: i64::from_str(tag[3].as_str())?,
+                }),
                 _ => Ok(Self::Generic(tag_kind, tag[1..].to_vec())),
             }
         } else {
@@ -726,6 +749,19 @@ impl From<Tag> for Vec<String> {
             Tag::Lnurl(lnurl) => {
                 vec![TagKind::Lnurl.to_string(), lnurl]
             }
+            #[cfg(feature = "mmr")]
+            Tag::Mmr {
+                prev_event_id,
+                prev_mmr_root,
+                prev_event_pos,
+            } => {
+                vec![
+                    TagKind::Mmr.to_string(),
+                    prev_event_id.to_string(),
+                    prev_mmr_root.to_string(),
+                    prev_event_pos.to_string(),
+                ]
+            }
         }
     }
 }