1 files changed, 100 insertions, 0 deletions
diff --git a/src/swarm/dissemination.rs b/src/swarm/dissemination.rs
index 1d92b06..93ad4e9 100644
--- a/src/swarm/dissemination.rs
+++ b/src/swarm/dissemination.rs
@@ -10,6 +10,7 @@
 //! first, and so how soon.
 
 use async_trait::async_trait;
+use tracing::trace;
 
 use crate::document::ChangeHash;
 use crate::state::AppState;
@@ -48,4 +49,103 @@ pub(crate) trait Dissemination: Send + Sync + 'static {
         carried: bool,
         authors: &[(String, Vec<ChangeHash>)],
     );
+
+    /// `peer` asks us to send it `writer`'s changes at once (`eager`, a GRAFT) or to
+    /// leave them to announcements (a PRUNE), for a way that keeps such links
+    /// (PlumTree). By default nothing.
+    async fn linked(&self, state: &AppState, peer: &str, writer: u64, eager: bool) {
+        let _ = (state, peer, writer, eager);
+    }
+
+    /// `peer` told us of `heads` we lack (a STATUS: an announcement, or its keepalive's),
+    /// for a way that minds which neighbour has changes first (PlumTree). By default
+    /// nothing.
+    fn announced(&self, peer: &str, heads: &[ChangeHash]) {
+        let _ = (peer, heads);
+    }
+
+    /// The neighbours whose links are lazy, for a way that keeps such links (PlumTree),
+    /// for the benchmark to report. By default none.
+    #[cfg(test)]
+    fn lazy(&self) -> Option<std::collections::HashSet<String>> {
+        None
+    }
+}
+
+/// What every way does with its `plan` for `writer`'s `changes` from `from` (none: we
+/// had them already): those it leaves to others (`Plan::covered`) count as having them
+/// (`SyncSession::known_to_peer`): else, with writers in turn, each change coming along
+/// another way, the next message we pass on to one would carry all we got since our
+/// last to it, mostly what its other parents brought it; should one lack them after
+/// all, it asks, and gets them (`resend_if_needed`). Those it sends to
+/// (`Plan::children`, but `from`) get them at once, with those of them that `changes`
+/// build on, if they were counted so lately (`SyncSession::with_predecessors`).
+pub(crate) async fn pass_on(
+    state: &AppState,
+    writer: u64,
+    from: &str,
+    changes: &[ChangeHash],
+    mut plan: Plan,
+) -> Plan {
+    if !changes.is_empty() {
+        for neighbour in &plan.covered {
+            if let Some(peer_state) = state.get_peer_state(neighbour).await {
+                peer_state
+                    .lock()
+                    .await
+                    .sync
+                    .known_to_peer(changes, tokio::time::Instant::now());
+            }
+        }
+    }
+    plan.children.retain(|child| child != from);
+    let children = &plan.children;
+    let replica = if changes.is_empty() {
+        None
+    } else {
+        Some(state.doc.read().await)
+    };
+    for child in children {
+        if let Some(peer_state) = state.get_peer_state(child).await {
+            let mut peer_state = peer_state.lock().await;
+            peer_state.tree_writer = Some(writer);
+            if let Some(replica) = &replica {
+                peer_state.sync.with_predecessors(
+                    &replica.doc,
+                    changes,
+                    tokio::time::Instant::now(),
+                );
+            }
+        }
+        state.stats.tree_forward();
+        state.request_sync(child);
+    }
+    if !children.is_empty() {
+        trace!(
+            writer,
+            children = children.len(),
+            "Passing a change on along the writer's tree"
+        );
+    }
+    plan
+}
+
+/// The ways to choose from (`--dissemination`); one per swarm.
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
+#[serde(rename_all = "kebab-case")]
+pub(crate) enum Kind {
+    /// Writers' trees (`swarm::tree`).
+    #[default]
+    WritersTrees,
+    /// PlumTree (`swarm::plumtree`).
+    Plumtree,
+}
+
+impl Kind {
+    pub(crate) fn make(self) -> std::sync::Arc<dyn Dissemination> {
+        match self {
+            Kind::WritersTrees => std::sync::Arc::new(crate::swarm::tree::WritersTrees),
+            Kind::Plumtree => std::sync::Arc::new(crate::swarm::plumtree::PlumTree::default()),
+        }
+    }
 }