strict: a manifest serves one remake, at its base

Review 2, N1: a strict manifest wasn't bound to its base. Any member
could propose an old, legitimately signed one again at the current
heads; nodes would verify it and vote, and every value at a signed
place changed or added since (a ban, a new user, a rotated key, a
changed userSigned or sealed declaration) would be deleted, nothing
after the base being left to replay.

The manifest now names the epoch and the heads it was made at, and a
node takes it (proposing or voting) only for a remake of that epoch
with exactly that base. GET /admin/strict-manifest makes it so;
continuum-signed strict proposes at those heads already.

1 files changed, 50 insertions, 3 deletions

diff --git a/src/access/strict.rs b/src/access/strict.rs
index 0fa6577..0b294f8 100644
--- a/src/access/strict.rs
+++ b/src/access/strict.rs
@@ -27,6 +27,10 @@ pub(crate) const NAMESPACE: &str = "continuum-strict";
 pub(crate) struct Manifest {
     /// The swarm it is for.
     pub(crate) swarm: String,
+    /// The epoch it is for, and the heads it was made at: the base a remake taking it
+    /// must have, so it serves once, for the values it names as they were then.
+    pub(crate) epoch: crate::document::replica::EpochRecord,
+    pub(crate) base: Vec<String>,
     /// The policy the next epoch has (`"values": "signed"`).
     pub(crate) policy: JsonValue,
     /// The values kept at the places values are signed (`envelope::signed_paths`), each
@@ -46,6 +50,29 @@ pub(crate) struct Kept {
 }
 
 impl Manifest {
+    /// Whether it is for a remake of `epoch` at `base` (hex heads): why not, if not.
+    pub(crate) fn for_base(
+        &self,
+        epoch: &crate::document::replica::EpochRecord,
+        base: Option<&[String]>,
+    ) -> Result<(), String> {
+        if &self.epoch != epoch {
+            return Err(format!(
+                "made for epoch {}:{}, not this one",
+                self.epoch.generation, self.epoch.id
+            ));
+        }
+        let sorted = |heads: &[String]| {
+            let mut heads = heads.to_vec();
+            heads.sort();
+            heads
+        };
+        match base {
+            Some(base) if sorted(base) == sorted(&self.base) => Ok(()),
+            _ => Err("made at other heads than the remake's base".to_owned()),
+        }
+    }
+
     /// Whether it keeps `value` at `path`.
     pub(crate) fn keeps(&self, path: &[String], value: &JsonValue) -> bool {
         let digest = digest(value);
@@ -104,17 +131,24 @@ pub(crate) fn held(doc: &impl ReadDoc) -> Vec<(Vec<String>, JsonValue)> {
     out
 }
 
-/// A manifest for `doc` of `swarm`: keeping every value held at a signed place now, the
-/// policy `policy`, for `user` to look over and sign at `at`. Its exact line.
+/// A manifest for `doc` (at heads `base`, of `epoch` of `swarm`): keeping every value
+/// held at a signed place now, the policy `policy`, for `user` to look over and sign at
+/// `at`. Its exact line.
 pub(crate) fn manifest_of(
     doc: &impl ReadDoc,
     swarm: &str,
+    epoch: crate::document::replica::EpochRecord,
+    base: &[crate::document::ChangeHash],
     policy: JsonValue,
     user: &str,
     at: u64,
 ) -> String {
+    let mut base: Vec<String> = base.iter().map(ToString::to_string).collect();
+    base.sort();
     let manifest = Manifest {
         swarm: swarm.to_owned(),
+        epoch,
+        base,
         policy,
         keep: held(doc)
             .into_iter()
@@ -202,7 +236,10 @@ mod tests {
             store::write_path(doc, &path("notes"), &json!(1)).unwrap();
         });
         let policy = json!({"version": 1, "values": "signed"});
-        let line = manifest_of(&doc, "s", policy, "alice", 1);
+        let epoch =
+            crate::document::replica::EpochRecord::from(crate::document::replica::Epoch::GENESIS);
+        let heads = doc.get_heads();
+        let line = manifest_of(&doc, "s", epoch.clone(), &heads, policy, "alice", 1);
         let key = SigningKey::from_bytes(&[3; 32]);
         let public = sshsig::PublicKey(key.verifying_key().to_bytes());
         let text = format!("{line}\n{}", sshsig::sign(&key, NAMESPACE, line.as_bytes()));
@@ -229,5 +266,15 @@ mod tests {
         assert!(verify(&elsewhere, std::slice::from_ref(&public), "s").is_err());
         let tampered = text.replacen("alice", "mallory", 1);
         assert!(verify(&tampered, std::slice::from_ref(&public), "s").is_err());
+        // For its epoch and base only.
+        let base: Vec<String> = heads.iter().map(ToString::to_string).collect();
+        assert!(manifest.for_base(&epoch, Some(&base)).is_ok());
+        assert!(manifest.for_base(&epoch, None).is_err());
+        assert!(manifest.for_base(&epoch, Some(&[])).is_err());
+        let later = crate::document::replica::EpochRecord {
+            generation: 1,
+            id: "ab".to_owned(),
+        };
+        assert!(manifest.for_base(&later, Some(&base)).is_err());
     }
 }