1 files changed, 39 insertions, 6 deletions

diff --git a/src/access/envelope.rs b/src/access/envelope.rs
index 7244a3b..1804b98 100644
--- a/src/access/envelope.rs
+++ b/src/access/envelope.rs
@@ -72,15 +72,39 @@ pub(crate) fn signed_paths(doc: &impl ReadDoc) -> Vec<Vec<String>> {
 /// its `*` segments as `path` has them.
 pub(crate) fn signed_path(signed: &[Vec<String>], path: &[String]) -> Option<Vec<String>> {
     signed.iter().find_map(|pattern| {
-        (path.len() >= pattern.len()
-            && pattern
-                .iter()
-                .zip(path)
-                .all(|(segment, key)| segment == "*" || segment == key))
-        .then(|| path[..pattern.len()].to_vec())
+        (path.len() >= pattern.len() && agree(pattern, path))
+            .then(|| path[..pattern.len()].to_vec())
     })
 }
 
+/// Whether `path` is where a user-signed value goes, of `signed` (`signed_paths`).
+pub(crate) fn is_signed(signed: &[Vec<String>], path: &[String]) -> bool {
+    signed
+        .iter()
+        .any(|pattern| pattern.len() == path.len() && agree(pattern, path))
+}
+
+/// Whether a user-signed value of `signed` may be below `path` (`signed_paths`).
+pub(crate) fn above_signed(signed: &[Vec<String>], path: &[String]) -> bool {
+    signed
+        .iter()
+        .any(|pattern| pattern.len() > path.len() && agree(pattern, path))
+}
+
+/// Whether a write at `path` reaches a user-signed value of `signed` (`signed_paths`):
+/// at one, within one, or above one.
+pub(crate) fn reaches_signed(signed: &[Vec<String>], path: &[String]) -> bool {
+    signed.iter().any(|pattern| agree(pattern, path))
+}
+
+/// Whether `pattern` and `path` agree as far as both go (`*`: any key).
+fn agree(pattern: &[String], path: &[String]) -> bool {
+    pattern
+        .iter()
+        .zip(path)
+        .all(|(segment, key)| segment == "*" || segment == key)
+}
+
 /// A signed value's payload.
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 pub(crate) struct Payload {
@@ -280,5 +304,14 @@ mod tests {
             signed_path(&signed, &path("_continuum/access/policy")),
             Some(path("_continuum/access/policy"))
         );
+        assert!(is_signed(&signed, &path("_continuum/users/alice")));
+        assert!(!is_signed(&signed, &path("_continuum/users/alice/caps")));
+        assert!(above_signed(&signed, &path("_continuum/users")));
+        assert!(above_signed(&signed, &path("a")));
+        assert!(!above_signed(&signed, &path("a/b")));
+        assert!(reaches_signed(&signed, &path("a")));
+        assert!(reaches_signed(&signed, &path("a/b/c")));
+        assert!(!reaches_signed(&signed, &path("a/c")));
+        assert!(!reaches_signed(&signed, &path("_continuum/members/x")));
     }
 }