feat(NIP-26): allow searches for delegated public keys

Implements core NIP-26 delegated event functionality.  Events can
include a `delegation` tag that provides a signature and restrictions
on which events can be delegated.

Notable points on the implementation so far:

* Schema has been upgraded to include an index and new column.
* Basic rune parsing/evaluation to implement the example event in the
  NIP, but no more.
* No special logic for deletion.
* No migration logic for determining delegated authors for
  already-stored events.

Cargo.lock

@@ -1042,6 +1042,7 @@ dependencies = [
  "r2d2",
  "r2d2_sqlite",
  "rand 0.8.5",
+ "regex",
  "rusqlite",
  "secp256k1",
  "serde",

Cargo.toml

@@ -32,6 +32,7 @@ http = { version = "0.2" }
 parse_duration = "2"
 rand = "0.8"
 const_format = "0.2.28"
+regex = "1"
 
 [dev-dependencies]
 anyhow = "1"

README.md

@@ -27,6 +27,7 @@ mirrored on [GitHub](https://github.com/scsibug/nostr-rs-relay).
 - [x] NIP-15: [End of Stored Events Notice](https://github.com/nostr-protocol/nips/blob/master/15.md)
 - [x] NIP-16: [Event Treatment](https://github.com/nostr-protocol/nips/blob/master/16.md)
 - [x] NIP-22: [Event `created_at` limits](https://github.com/nostr-protocol/nips/blob/master/22.md) (_future-dated events only_)
+- [x] NIP-26: [Event Delegation](https://github.com/nostr-protocol/nips/blob/master/26.md)
 
 ## Quick Start
 

src/db.rs

@@ -142,12 +142,15 @@ pub async fn db_writer(
             if next_event.is_none() {
                 break;
             }
+            // track if an event write occurred; this is used to
+            // update the rate limiter
             let mut event_write = false;
             let subm_event = next_event.unwrap();
             let event = subm_event.event;
             let notice_tx = subm_event.notice_tx;
             // check if this event is authorized.
             if let Some(allowed_addrs) = whitelist {
+                // TODO: incorporate delegated pubkeys
                 // if the event address is not in allowed_addrs.
                 if !allowed_addrs.contains(&event.pubkey) {
                     info!(
@@ -284,12 +287,13 @@ pub fn write_event(conn: &mut PooledConnection, e: &Event) -> Result<usize> {
     let tx = conn.transaction()?;
     // get relevant fields from event and convert to blobs.
     let id_blob = hex::decode(&e.id).ok();
-    let pubkey_blob = hex::decode(&e.pubkey).ok();
+    let pubkey_blob: Option<Vec<u8>> = hex::decode(&e.pubkey).ok();
+    let delegator_blob: Option<Vec<u8>> = e.delegated_by.as_ref().and_then(|d| hex::decode(d).ok());
     let event_str = serde_json::to_string(&e).ok();
     // ignore if the event hash is a duplicate.
     let mut ins_count = tx.execute(
-        "INSERT OR IGNORE INTO event (event_hash, created_at, kind, author, content, first_seen, hidden) VALUES (?1, ?2, ?3, ?4, ?5, strftime('%s','now'), FALSE);",
+        "INSERT OR IGNORE INTO event (event_hash, created_at, kind, author, delegated_by, content, first_seen, hidden) VALUES (?1, ?2, ?3, ?4, ?5, ?6, strftime('%s','now'), FALSE);",
-        params![id_blob, e.created_at, e.kind, pubkey_blob, event_str]
+        params![id_blob, e.created_at, e.kind, pubkey_blob, delegator_blob, event_str]
     )?;
     if ins_count == 0 {
         // if the event was a duplicate, no need to insert event or
@@ -439,16 +443,22 @@ fn query_from_filter(f: &ReqFilter) -> (String, Vec<Box<dyn ToSql>>) {
         for auth in authvec {
             match hex_range(auth) {
                 Some(HexSearch::Exact(ex)) => {
-                    auth_searches.push("author=?".to_owned());
+                    auth_searches.push("author=? OR delegated_by=?".to_owned());
+                    params.push(Box::new(ex.clone()));
                     params.push(Box::new(ex));
                 }
                 Some(HexSearch::Range(lower, upper)) => {
-                    auth_searches.push("(author>? AND author<?)".to_owned());
+                    auth_searches.push(
+                        "(author>? AND author<?) OR (delegated_by>? AND delegated_by<?)".to_owned(),
+                    );
+                    params.push(Box::new(lower.clone()));
+                    params.push(Box::new(upper.clone()));
                     params.push(Box::new(lower));
                     params.push(Box::new(upper));
                 }
                 Some(HexSearch::LowerOnly(lower)) => {
-                    auth_searches.push("author>?".to_owned());
+                    auth_searches.push("author>? OR delegated_by>?".to_owned());
+                    params.push(Box::new(lower.clone()));
                     params.push(Box::new(lower));
                 }
                 None => {

src/delegation.rs

@@ -0,0 +1,416 @@
+//! Event parsing and validation
+use crate::error::Error;
+use crate::error::Result;
+use crate::event::Event;
+use bitcoin_hashes::{sha256, Hash};
+use lazy_static::lazy_static;
+use regex::Regex;
+use secp256k1::{schnorr, Secp256k1, VerifyOnly, XOnlyPublicKey};
+use serde::{Deserialize, Serialize};
+use std::str::FromStr;
+use tracing::{debug, info};
+
+// This handles everything related to delegation, in particular the
+// condition/rune parsing and logic.
+
+// Conditions are poorly specified, so we will implement the minimum
+// necessary for now.
+
+// fields MUST be either "kind" or "created_at".
+// operators supported are ">", "<", "=", "!".
+// no operations on 'content' are supported.
+
+// this allows constraints for:
+// valid date ranges (valid from X->Y dates).
+// specific kinds (publish kind=1,5)
+// kind ranges (publish ephemeral events, kind>19999&kind<30001)
+
+// for more complex scenarios (allow delegatee to publish ephemeral
+// AND replacement events), it may be necessary to generate and use
+// different condition strings, since we do not support grouping or
+// "OR" logic.
+
+lazy_static! {
+    /// Secp256k1 verification instance.
+    pub static ref SECP: Secp256k1<VerifyOnly> = Secp256k1::verification_only();
+}
+
+#[derive(Serialize, Deserialize, PartialEq, Eq, Debug, Clone)]
+pub enum Field {
+    Kind,
+    CreatedAt,
+}
+
+impl FromStr for Field {
+    type Err = Error;
+    fn from_str(value: &str) -> Result<Self, Self::Err> {
+        if value == "kind" {
+            Ok(Field::Kind)
+        } else if value == "created_at" {
+            Ok(Field::CreatedAt)
+        } else {
+            Err(Error::DelegationParseError)
+        }
+    }
+}
+
+#[derive(Serialize, Deserialize, PartialEq, Eq, Debug, Clone)]
+pub enum Operator {
+    LessThan,
+    GreaterThan,
+    Equals,
+    NotEquals,
+}
+impl FromStr for Operator {
+    type Err = Error;
+    fn from_str(value: &str) -> Result<Self, Self::Err> {
+        if value == "<" {
+            Ok(Operator::LessThan)
+        } else if value == ">" {
+            Ok(Operator::GreaterThan)
+        } else if value == "=" {
+            Ok(Operator::Equals)
+        } else if value == "!" {
+            Ok(Operator::NotEquals)
+        } else {
+            Err(Error::DelegationParseError)
+        }
+    }
+}
+
+#[derive(Serialize, Deserialize, PartialEq, Eq, Debug, Clone)]
+pub struct ConditionQuery {
+    pub(crate) conditions: Vec<Condition>,
+}
+
+impl ConditionQuery {
+    pub fn allows_event(&self, event: &Event) -> bool {
+        // check each condition, to ensure that the event complies
+        // with the restriction.
+        for c in &self.conditions {
+            if !c.allows_event(event) {
+                // any failing conditions invalidates the delegation
+                // on this event
+                return false;
+            }
+        }
+        // delegation was permitted unconditionally, or all conditions
+        // were true
+        true
+    }
+}
+
+// Verify that the delegator approved the delegation; return a ConditionQuery if so.
+pub fn validate_delegation(
+    delegator: &str,
+    delegatee: &str,
+    cond_query: &str,
+    sigstr: &str,
+) -> Option<ConditionQuery> {
+    // form the token
+    let tok = format!("nostr:delegation:{}:{}", delegatee, cond_query);
+    // form SHA256 hash
+    let digest: sha256::Hash = sha256::Hash::hash(tok.as_bytes());
+    let sig = schnorr::Signature::from_str(sigstr).unwrap();
+    if let Ok(msg) = secp256k1::Message::from_slice(digest.as_ref()) {
+        if let Ok(pubkey) = XOnlyPublicKey::from_str(delegator) {
+            let verify = SECP.verify_schnorr(&sig, &msg, &pubkey);
+            if verify.is_ok() {
+                // return the parsed condition query
+                cond_query.parse::<ConditionQuery>().ok()
+            } else {
+                debug!("client sent an delegation signature that did not validate");
+                None
+            }
+        } else {
+            debug!("client sent malformed delegation pubkey");
+            None
+        }
+    } else {
+        info!("error converting delegation digest to secp256k1 message");
+        None
+    }
+}
+
+/// Parsed delegation condition
+/// see https://github.com/nostr-protocol/nips/pull/28#pullrequestreview-1084903800
+/// An example complex condition would be:  kind=1,2,3&created_at<1665265999
+#[derive(Serialize, Deserialize, PartialEq, Eq, Debug, Clone)]
+pub struct Condition {
+    pub(crate) field: Field,
+    pub(crate) operator: Operator,
+    pub(crate) values: Vec<u64>,
+}
+
+impl Condition {
+    /// Check if this condition allows the given event to be delegated
+    pub fn allows_event(&self, event: &Event) -> bool {
+        // determine what the right-hand side of the operator is
+        let resolved_field = match &self.field {
+            Field::Kind => event.kind,
+            Field::CreatedAt => event.created_at,
+        };
+        match &self.operator {
+            Operator::LessThan => {
+                // the less-than operator is only valid for single values.
+                if self.values.len() == 1 {
+                    if let Some(v) = self.values.first() {
+                        return resolved_field < *v;
+                    }
+                }
+            }
+            Operator::GreaterThan => {
+                // the greater-than operator is only valid for single values.
+                if self.values.len() == 1 {
+                    if let Some(v) = self.values.first() {
+                        return resolved_field > *v;
+                    }
+                }
+            }
+            Operator::Equals => {
+                // equals is interpreted as "must be equal to at least one provided value"
+                return self.values.iter().any(|&x| resolved_field == x);
+            }
+            Operator::NotEquals => {
+                // not-equals is interpreted as "must not be equal to any provided value"
+                // this is the one case where an empty list of values could be allowed; even though it is a pointless restriction.
+                return self.values.iter().all(|&x| resolved_field != x);
+            }
+        }
+        false
+    }
+}
+
+fn str_to_condition(cs: &str) -> Option<Condition> {
+    // a condition is a string (alphanum+underscore), an operator (<>=!), and values (num+comma)
+    lazy_static! {
+        static ref RE: Regex = Regex::new("([[:word:]]+)([<>=!]+)([,[[:digit:]]]*)").unwrap();
+    }
+    // match against the regex
+    let caps = RE.captures(cs)?;
+    let field = caps.get(1)?.as_str().parse::<Field>().ok()?;
+    let operator = caps.get(2)?.as_str().parse::<Operator>().ok()?;
+    // values are just comma separated numbers, but all must be parsed
+    let rawvals = caps.get(3)?.as_str();
+    let values = rawvals
+        .split_terminator(',')
+        .map(|n| n.parse::<u64>().ok())
+        .collect::<Option<Vec<_>>>()?;
+    // convert field string into Field
+    Some(Condition {
+        field,
+        operator,
+        values,
+    })
+}
+
+/// Parse a condition query from a string slice
+impl FromStr for ConditionQuery {
+    type Err = Error;
+    fn from_str(value: &str) -> Result<Self, Self::Err> {
+        // split the string with '&'
+        let mut conditions = vec![];
+        let condstrs = value.split_terminator('&');
+        // parse each individual condition
+        for c in condstrs {
+            conditions.push(str_to_condition(c).ok_or(Error::DelegationParseError)?);
+        }
+        Ok(ConditionQuery { conditions })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // parse condition strings
+    #[test]
+    fn parse_empty() -> Result<()> {
+        // given an empty condition query, produce an empty vector
+        let empty_cq = ConditionQuery { conditions: vec![] };
+        let parsed = "".parse::<ConditionQuery>()?;
+        assert_eq!(parsed, empty_cq);
+        Ok(())
+    }
+
+    // parse field 'kind'
+    #[test]
+    fn test_kind_field_parse() -> Result<()> {
+        let field = "kind".parse::<Field>()?;
+        assert_eq!(field, Field::Kind);
+        Ok(())
+    }
+    // parse field 'created_at'
+    #[test]
+    fn test_created_at_field_parse() -> Result<()> {
+        let field = "created_at".parse::<Field>()?;
+        assert_eq!(field, Field::CreatedAt);
+        Ok(())
+    }
+    // parse unknown field
+    #[test]
+    fn unknown_field_parse() {
+        let field = "unk".parse::<Field>();
+        assert!(field.is_err());
+    }
+
+    // parse a full conditional query with an empty array
+    #[test]
+    fn parse_kind_equals_empty() -> Result<()> {
+        // given an empty condition query, produce an empty vector
+        let kind_cq = ConditionQuery {
+            conditions: vec![Condition {
+                field: Field::Kind,
+                operator: Operator::Equals,
+                values: vec![],
+            }],
+        };
+        let parsed = "kind=".parse::<ConditionQuery>()?;
+        assert_eq!(parsed, kind_cq);
+        Ok(())
+    }
+    // parse a full conditional query with a single value
+    #[test]
+    fn parse_kind_equals_singleval() -> Result<()> {
+        // given an empty condition query, produce an empty vector
+        let kind_cq = ConditionQuery {
+            conditions: vec![Condition {
+                field: Field::Kind,
+                operator: Operator::Equals,
+                values: vec![1],
+            }],
+        };
+        let parsed = "kind=1".parse::<ConditionQuery>()?;
+        assert_eq!(parsed, kind_cq);
+        Ok(())
+    }
+    // parse a full conditional query with multiple values
+    #[test]
+    fn parse_kind_equals_multival() -> Result<()> {
+        // given an empty condition query, produce an empty vector
+        let kind_cq = ConditionQuery {
+            conditions: vec![Condition {
+                field: Field::Kind,
+                operator: Operator::Equals,
+                values: vec![1, 2, 4],
+            }],
+        };
+        let parsed = "kind=1,2,4".parse::<ConditionQuery>()?;
+        assert_eq!(parsed, kind_cq);
+        Ok(())
+    }
+    // parse multiple conditions
+    #[test]
+    fn parse_multi_conditions() -> Result<()> {
+        // given an empty condition query, produce an empty vector
+        let cq = ConditionQuery {
+            conditions: vec![
+                Condition {
+                    field: Field::Kind,
+                    operator: Operator::GreaterThan,
+                    values: vec![10000],
+                },
+                Condition {
+                    field: Field::Kind,
+                    operator: Operator::LessThan,
+                    values: vec![20000],
+                },
+                Condition {
+                    field: Field::Kind,
+                    operator: Operator::NotEquals,
+                    values: vec![10001],
+                },
+                Condition {
+                    field: Field::CreatedAt,
+                    operator: Operator::LessThan,
+                    values: vec![1665867123],
+                },
+            ],
+        };
+        let parsed =
+            "kind>10000&kind<20000&kind!10001&created_at<1665867123".parse::<ConditionQuery>()?;
+        assert_eq!(parsed, cq);
+        Ok(())
+    }
+    fn simple_event() -> Event {
+        Event {
+            id: "0".to_owned(),
+            pubkey: "0".to_owned(),
+            delegated_by: None,
+            created_at: 0,
+            kind: 0,
+            tags: vec![],
+            content: "".to_owned(),
+            sig: "0".to_owned(),
+            tagidx: None,
+        }
+    }
+    // Check for condition logic on event w/ empty values
+    #[test]
+    fn condition_with_empty_values() {
+        let mut c = Condition {
+            field: Field::Kind,
+            operator: Operator::GreaterThan,
+            values: vec![],
+        };
+        let e = simple_event();
+        assert!(!c.allows_event(&e));
+        c.operator = Operator::LessThan;
+        assert!(!c.allows_event(&e));
+        c.operator = Operator::Equals;
+        assert!(!c.allows_event(&e));
+        // Not Equals applied to an empty list *is* allowed
+        // (pointless, but logically valid).
+        c.operator = Operator::NotEquals;
+        assert!(c.allows_event(&e));
+    }
+
+    // Check for condition logic on event w/ single value
+    #[test]
+    fn condition_kind_gt_event_single() {
+        let c = Condition {
+            field: Field::Kind,
+            operator: Operator::GreaterThan,
+            values: vec![10],
+        };
+        let mut e = simple_event();
+        // kind is not greater than 10, not allowed
+        e.kind = 1;
+        assert!(!c.allows_event(&e));
+        // kind is greater than 10, allowed
+        e.kind = 100;
+        assert!(c.allows_event(&e));
+        // kind is 10, not allowed
+        e.kind = 10;
+        assert!(!c.allows_event(&e));
+    }
+    // Check for condition logic on event w/ multi values
+    #[test]
+    fn condition_with_multi_values() {
+        let mut c = Condition {
+            field: Field::Kind,
+            operator: Operator::Equals,
+            values: vec![0, 10, 20],
+        };
+        let mut e = simple_event();
+        // Allow if event kind is in list for Equals
+        e.kind = 10;
+        assert!(c.allows_event(&e));
+        // Deny if event kind is not in list for Equals
+        e.kind = 11;
+        assert!(!c.allows_event(&e));
+        // Deny if event kind is in list for NotEquals
+        e.kind = 10;
+        c.operator = Operator::NotEquals;
+        assert!(!c.allows_event(&e));
+        // Allow if event kind is not in list for NotEquals
+        e.kind = 99;
+        c.operator = Operator::NotEquals;
+        assert!(c.allows_event(&e));
+        // Always deny if GreaterThan/LessThan for a list
+        c.operator = Operator::LessThan;
+        assert!(!c.allows_event(&e));
+        c.operator = Operator::GreaterThan;
+        assert!(!c.allows_event(&e));
+    }
+}

src/error.rs

@@ -50,6 +50,8 @@ pub enum Error {
     HyperError(hyper::Error),
     #[error("Hex encoding error")]
     HexError(hex::FromHexError),
+    #[error("Delegation parse error")]
+    DelegationParseError,
     #[error("Unknown/Undocumented")]
     UnknownError,
 }

src/event.rs

@@ -1,4 +1,5 @@
 //! Event parsing and validation
+use crate::delegation::validate_delegation;
 use crate::error::Error::*;
 use crate::error::Result;
 use crate::nip05;
@@ -31,6 +32,8 @@ pub struct EventCmd {
 pub struct Event {
     pub id: String,
     pub(crate) pubkey: String,
+    #[serde(skip)]
+    pub(crate) delegated_by: Option<String>,
     pub(crate) created_at: u64,
     pub(crate) kind: u64,
     #[serde(deserialize_with = "tag_from_string")]
@@ -83,6 +86,7 @@ impl From<EventCmd> for Result<Event> {
         } else if ec.event.is_valid() {
             let mut e = ec.event;
             e.build_index();
+            e.update_delegation();
             Ok(e)
         } else {
             Err(EventInvalid)
@@ -110,6 +114,50 @@ impl Event {
         None
     }
 
+    // is this event delegated (properly)?
+    // does the signature match, and are conditions valid?
+    // if so, return an alternate author for the event
+    pub fn delegated_author(&self) -> Option<String> {
+        // is there a delegation tag?
+        let delegation_tag: Vec<String> = self
+            .tags
+            .iter()
+            .filter(|x| x.len() == 4)
+            .filter(|x| x.get(0).unwrap() == "delegation")
+            .take(1)
+            .next()?
+            .to_vec(); // get first tag
+
+        //let delegation_tag = self.tag_values_by_name("delegation");
+        // delegation tags should have exactly 3 elements after the name (pubkey, condition, sig)
+        // the event is signed by the delagatee
+        let delegatee = &self.pubkey;
+        // the delegation tag references the claimed delagator
+        let delegator: &str = delegation_tag.get(1)?;
+        let querystr: &str = delegation_tag.get(2)?;
+        let sig: &str = delegation_tag.get(3)?;
+
+        // attempt to get a condition query; this requires the delegation to have a valid signature.
+        if let Some(cond_query) = validate_delegation(delegator, delegatee, querystr, sig) {
+            // The signature was valid, now we ensure the delegation
+            // condition is valid for this event:
+            if cond_query.allows_event(self) {
+                // since this is allowed, we will provide the delegatee
+                Some(delegator.into())
+            } else {
+                debug!("an event failed to satisfy delegation conditions");
+                None
+            }
+        } else {
+            debug!("event had had invalid delegation signature");
+            None
+        }
+    }
+
+    /// Update delegation status
+    fn update_delegation(&mut self) {
+        self.delegated_by = self.delegated_author();
+    }
     /// Build an event tag index
     fn build_index(&mut self) {
         // if there are no tags; just leave the index as None
@@ -145,7 +193,7 @@ impl Event {
         self.pubkey.chars().take(8).collect()
     }
 
-    /// Retrieve tag values
+    /// Retrieve tag initial values across all tags matching the name
     pub fn tag_values_by_name(&self, tag_name: &str) -> Vec<String> {
         self.tags
             .iter()
@@ -269,6 +317,7 @@ mod tests {
         Event {
             id: "0".to_owned(),
             pubkey: "0".to_owned(),
+            delegated_by: None,
             created_at: 0,
             kind: 0,
             tags: vec![],
@@ -350,6 +399,7 @@ mod tests {
         let e = Event {
             id: "999".to_owned(),
             pubkey: "012345".to_owned(),
+            delegated_by: None,
             created_at: 501234,
             kind: 1,
             tags: vec![],
@@ -367,6 +417,7 @@ mod tests {
         let e = Event {
             id: "999".to_owned(),
             pubkey: "012345".to_owned(),
+            delegated_by: None,
             created_at: 501234,
             kind: 1,
             tags: vec![
@@ -388,11 +439,39 @@ mod tests {
         assert_eq!(v, vec!["foo", "bar", "baz"]);
     }
 
+    #[test]
+    fn event_no_tag_select() {
+        let e = Event {
+            id: "999".to_owned(),
+            pubkey: "012345".to_owned(),
+            delegated_by: None,
+            created_at: 501234,
+            kind: 1,
+            tags: vec![
+                vec!["j".to_owned(), "abc".to_owned()],
+                vec!["e".to_owned(), "foo".to_owned()],
+                vec!["e".to_owned(), "baz".to_owned()],
+                vec![
+                    "p".to_owned(),
+                    "aaaa".to_owned(),
+                    "ws://example.com".to_owned(),
+                ],
+            ],
+            content: "this is a test".to_owned(),
+            sig: "abcde".to_owned(),
+            tagidx: None,
+        };
+        let v = e.tag_values_by_name("x");
+        // asking for tags that don't exist just returns zero-length vector
+        assert_eq!(v.len(), 0);
+    }
+
     #[test]
     fn event_canonical_with_tags() {
         let e = Event {
             id: "999".to_owned(),
             pubkey: "012345".to_owned(),
+            delegated_by: None,
             created_at: 501234,
             kind: 1,
             tags: vec![

src/info.rs

@@ -35,7 +35,7 @@ impl From<config::Info> for RelayInfo {
             description: i.description,
             pubkey: i.pubkey,
             contact: i.contact,
-            supported_nips: Some(vec![1, 2, 9, 11, 12, 15, 16, 22]),
+            supported_nips: Some(vec![1, 2, 9, 11, 12, 15, 16, 22, 26]),
             software: Some("https://git.sr.ht/~gheartsfield/nostr-rs-relay".to_owned()),
             version: CARGO_PKG_VERSION.map(|x| x.to_owned()),
         }

src/lib.rs

@@ -2,6 +2,7 @@ pub mod close;
 pub mod config;
 pub mod conn;
 pub mod db;
+pub mod delegation;
 pub mod error;
 pub mod event;
 pub mod hexrange;

src/schema.rs

@@ -20,7 +20,7 @@ pragma mmap_size = 536870912; -- 512MB of mmap
 "##;
 
 /// Latest database version
-pub const DB_VERSION: usize = 6;
+pub const DB_VERSION: usize = 7;
 
 /// Schema definition
 const INIT_SQL: &str = formatcp!(
@@ -40,6 +40,7 @@ event_hash BLOB NOT NULL, -- 4-byte hash
 first_seen INTEGER NOT NULL, -- when the event was first seen (not authored!) (seconds since 1970)
 created_at INTEGER NOT NULL, -- when the event was authored
 author BLOB NOT NULL, -- author pubkey
+delegated_by BLOB, -- delegator pubkey (NIP-26)
 kind INTEGER NOT NULL, -- event kind
 hidden INTEGER, -- relevant for queries
 content TEXT NOT NULL -- serialized json of event object
@@ -49,6 +50,7 @@ content TEXT NOT NULL -- serialized json of event object
 CREATE UNIQUE INDEX IF NOT EXISTS event_hash_index ON event(event_hash);
 CREATE INDEX IF NOT EXISTS created_at_index ON event(created_at);
 CREATE INDEX IF NOT EXISTS author_index ON event(author);
+CREATE INDEX IF NOT EXISTS delegated_by_index ON event(delegated_by);
 CREATE INDEX IF NOT EXISTS kind_index ON event(kind);
 
 -- Tag Table
@@ -152,6 +154,9 @@ pub fn upgrade_db(conn: &mut PooledConnection) -> Result<()> {
             if curr_version == 5 {
                 curr_version = mig_5_to_6(conn)?;
             }
+            if curr_version == 6 {
+                curr_version = mig_6_to_7(conn)?;
+            }
             if curr_version == DB_VERSION {
                 info!(
                     "All migration scripts completed successfully.  Welcome to v{}.",
@@ -348,3 +353,23 @@ fn mig_5_to_6(conn: &mut PooledConnection) -> Result<usize> {
     info!("vacuumed DB after tags rebuild in {:?}", start.elapsed());
     Ok(6)
 }
+
+fn mig_6_to_7(conn: &mut PooledConnection) -> Result<usize> {
+    info!("database schema needs update from 6->7");
+    // only change is adding a hidden column to events.
+    let upgrade_sql = r##"
+ALTER TABLE event ADD delegated_by BLOB;
+CREATE INDEX IF NOT EXISTS delegated_by_index ON event(delegated_by);
+PRAGMA user_version = 7;
+"##;
+    match conn.execute_batch(upgrade_sql) {
+        Ok(()) => {
+            info!("database schema upgraded v6 -> v7");
+        }
+        Err(err) => {
+            error!("update failed: {}", err);
+            panic!("database could not be upgraded");
+        }
+    }
+    Ok(7)
+}

src/subscription.rs

@@ -217,6 +217,17 @@ impl ReqFilter {
             .unwrap_or(true)
     }
 
+    fn delegated_authors_match(&self, event: &Event) -> bool {
+        if let Some(delegated_pubkey) = &event.delegated_by {
+            self.authors
+                .as_ref()
+                .map(|vs| prefix_match(vs, delegated_pubkey))
+                .unwrap_or(true)
+        } else {
+            false
+        }
+    }
+
     fn tag_match(&self, event: &Event) -> bool {
         // get the hashset from the filter.
         if let Some(map) = &self.tags {
@@ -248,7 +259,7 @@ impl ReqFilter {
             && self.since.map(|t| event.created_at > t).unwrap_or(true)
             && self.until.map(|t| event.created_at < t).unwrap_or(true)
             && self.kind_match(event.kind)
-            && self.authors_match(event)
+            && (self.authors_match(event) || self.delegated_authors_match(event))
             && self.tag_match(event)
             && !self.force_no_match
     }
@@ -308,6 +319,7 @@ mod tests {
         let e = Event {
             id: "foo".to_owned(),
             pubkey: "abcd".to_owned(),
+            delegated_by: None,
             created_at: 0,
             kind: 0,
             tags: Vec::new(),
@@ -326,6 +338,7 @@ mod tests {
         let e = Event {
             id: "abcd".to_owned(),
             pubkey: "".to_owned(),
+            delegated_by: None,
             created_at: 0,
             kind: 0,
             tags: Vec::new(),
@@ -344,6 +357,7 @@ mod tests {
         let e = Event {
             id: "abcde".to_owned(),
             pubkey: "".to_owned(),
+            delegated_by: None,
             created_at: 0,
             kind: 0,
             tags: Vec::new(),
@@ -363,6 +377,7 @@ mod tests {
         let e = Event {
             id: "abc".to_owned(),
             pubkey: "".to_owned(),
+            delegated_by: None,
             created_at: 50,
             kind: 0,
             tags: Vec::new(),
@@ -386,6 +401,7 @@ mod tests {
         let e = Event {
             id: "abc".to_owned(),
             pubkey: "".to_owned(),
+            delegated_by: None,
             created_at: 150,
             kind: 0,
             tags: Vec::new(),
@@ -407,6 +423,7 @@ mod tests {
         let e = Event {
             id: "abc".to_owned(),
             pubkey: "".to_owned(),
+            delegated_by: None,
             created_at: 50,
             kind: 0,
             tags: Vec::new(),
@@ -425,6 +442,7 @@ mod tests {
         let e = Event {
             id: "abc".to_owned(),
             pubkey: "".to_owned(),
+            delegated_by: None,
             created_at: 1001,
             kind: 0,
             tags: Vec::new(),
@@ -443,6 +461,7 @@ mod tests {
         let e = Event {
             id: "abc".to_owned(),
             pubkey: "".to_owned(),
+            delegated_by: None,
             created_at: 0,
             kind: 0,
             tags: Vec::new(),
@@ -461,6 +480,7 @@ mod tests {
         let e = Event {
             id: "123".to_owned(),
             pubkey: "abc".to_owned(),
+            delegated_by: None,
             created_at: 0,
             kind: 0,
             tags: Vec::new(),
@@ -479,6 +499,7 @@ mod tests {
         let e = Event {
             id: "123".to_owned(),
             pubkey: "bcd".to_owned(),
+            delegated_by: None,
             created_at: 0,
             kind: 0,
             tags: Vec::new(),
@@ -497,6 +518,7 @@ mod tests {
         let e = Event {
             id: "123".to_owned(),
             pubkey: "xyz".to_owned(),
+            delegated_by: None,
             created_at: 0,
             kind: 0,
             tags: Vec::new(),