update concord bcakend

crates/concord/src/cords/cord01.rs

@@ -17,8 +17,8 @@ pub const KIND_SEAL_PLAINTEXT: u16 = 20014;
 pub const NIP44_MAX_PLAINTEXT: usize = 65_535;
 
 const TAG_MS: &str = "ms";
-const TAG_CHANNEL: &str = "channel";
-const TAG_EPOCH: &str = "epoch";
+pub(crate) const TAG_CHANNEL: &str = "channel";
+pub(crate) const TAG_EPOCH: &str = "epoch";
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum SealForm {
@@ -420,7 +420,10 @@ fn check_plaintext_cap(len: usize) -> Result<(), StreamError> {
     Ok(())
 }
 
-fn unique_tag(rumor: &UnsignedEvent, name: &'static str) -> Result<Option<String>, StreamError> {
+pub(crate) fn unique_tag(
+    rumor: &UnsignedEvent,
+    name: &'static str,
+) -> Result<Option<String>, StreamError> {
     let mut found: Option<String> = None;
 
     for tag in rumor.tags.iter() {

crates/concord/src/cords/cord03.rs

@@ -5,8 +5,9 @@ use anyhow::Result;
 use nostr_sdk::prelude::*;
 
 use crate::cord01::{
-    KIND_WRAP, KIND_WRAP_EPHEMERAL, OpenedStream, SealForm, build_rumor_ms, build_seal,
-    channel_binding_tags, check_channel_binding, open_wrap, resolve_ms_strict, wrap_seal,
+    KIND_WRAP, KIND_WRAP_EPHEMERAL, OpenedStream, SealForm, TAG_CHANNEL, TAG_EPOCH, build_rumor_ms,
+    build_seal, channel_binding_tags, check_channel_binding, open_wrap, resolve_ms_strict,
+    unique_tag, wrap_seal,
 };
 use crate::cord04::{AuthorityCitation, canonical_decimal, citation_tag};
 pub use crate::cords::rumor::RumorError as ChatError;
@@ -313,6 +314,20 @@ pub fn open(
     Ok((opened, chat))
 }
 
+/// Rebuild a rumor from a locally-cached copy: the binding tags name its channel and epoch.
+pub fn parse_rumor(rumor: &UnsignedEvent) -> Result<ChatRumor, ChatError> {
+    let channel: ChannelId = unique_tag(rumor, TAG_CHANNEL)?
+        .ok_or(ChatError::MissingTag(TAG_CHANNEL))?
+        .parse()
+        .map_err(|_| ChatError::BadTag(TAG_CHANNEL))?;
+
+    let epoch = unique_tag(rumor, TAG_EPOCH)?
+        .ok_or(ChatError::MissingTag(TAG_EPOCH))
+        .and_then(|raw| canonical_decimal(&raw).ok_or(ChatError::BadTag(TAG_EPOCH)))?;
+
+    typed(rumor, &channel, Epoch(epoch))
+}
+
 /// `secret` is the `community_root` for a public channel, its own key for a private one.
 pub fn plane_keys(
     held: &[(Epoch, [u8; 32])],