enforce correct api use

patch-db/src/locker.rs

@@ -1,6 +1,6 @@
 use std::collections::{BTreeMap, VecDeque};
 
-use imbl::{ordset, OrdSet};
+use imbl::{ordmap, ordset, OrdMap, OrdSet};
 use json_ptr::{JsonPointer, SegList};
 #[cfg(test)]
 use proptest::prelude::*;
@@ -27,6 +27,8 @@ impl Locker {
             let mut cancellations = vec![dummy_recv];
 
             let mut request_queue = VecDeque::<(Request, OrdSet<HandleId>)>::new();
+            let mut lock_order_enforcer = LockOrderEnforcer::new();
+
             while let Some(action) =
                 get_action(&mut new_requests, &mut locks_on_lease, &mut cancellations).await
             {
@@ -110,21 +112,26 @@ impl Locker {
                     Action::HandleRequest(mut req) => {
                         #[cfg(feature = "tracing")]
                         tracing::debug!("New lock request");
-                        cancellations.extend(req.cancel.take());
-                        let hot_seat = request_queue.pop_front();
-                        process_new_req(
-                            hot_seat.as_ref(),
-                            req,
-                            &mut trie,
-                            &mut locks_on_lease,
-                            &mut request_queue,
-                        );
-                        if let Some(hot_seat) = hot_seat {
-                            request_queue.push_front(hot_seat);
+                        if let Err(e) = lock_order_enforcer.try_insert(&req.lock_info) {
+                            req.reject(e)
+                        } else {
+                            cancellations.extend(req.cancel.take());
+                            let hot_seat = request_queue.pop_front();
+                            process_new_req(
+                                hot_seat.as_ref(),
+                                req,
+                                &mut trie,
+                                &mut locks_on_lease,
+                                &mut request_queue,
+                            );
+                            if let Some(hot_seat) = hot_seat {
+                                request_queue.push_front(hot_seat);
+                            }
                         }
                     }
                     Action::HandleRelease(lock_info) => {
                         // release actual lock
+                        lock_order_enforcer.remove(&lock_info);
                         trie.unlock(&lock_info);
                         #[cfg(feature = "tracing")]
                         {
@@ -176,7 +183,7 @@ impl Locker {
                         }
                     }
                     Action::HandleCancel(lock_info) => {
-                        // trie.handle_cancel(lock_info, &mut locks_on_lease)
+                        lock_order_enforcer.remove(&lock_info);
                         let entry = request_queue
                             .iter()
                             .enumerate()
@@ -218,7 +225,7 @@ impl Locker {
         struct CancelGuard {
             lock_info: Option<LockInfo>,
             channel: Option<oneshot::Sender<LockInfo>>,
-            recv: oneshot::Receiver<Guard>,
+            recv: oneshot::Receiver<Result<Guard, LockError>>,
         }
         impl Drop for CancelGuard {
             fn drop(&mut self) {
@@ -251,7 +258,7 @@ impl Locker {
             .unwrap();
         let res = (&mut cancel_guard.recv).await.unwrap();
         cancel_guard.channel.take();
-        Ok(res)
+        res
     }
 }
 
@@ -297,6 +304,115 @@ async fn get_action(
     }
 }
 
+struct LockOrderEnforcer {
+    locks_held: OrdMap<HandleId, OrdMap<(JsonPointer, LockType), usize>>,
+}
+impl LockOrderEnforcer {
+    fn new() -> Self {
+        LockOrderEnforcer {
+            locks_held: ordmap! {},
+        }
+    }
+    // locks must be acquired in lexicographic order for the pointer, and reverse order for type
+    fn validate(&self, req: &LockInfo) -> Result<(), LockError> {
+        match self.locks_held.get(&req.handle_id) {
+            None => Ok(()),
+            Some(m) => {
+                // quick accept
+                for (ptr, ty) in m.keys() {
+                    let tmp = LockInfo {
+                        ptr: ptr.clone(),
+                        ty: *ty,
+                        handle_id: req.handle_id.clone(),
+                    };
+                    if tmp.implicitly_grants(req) {
+                        return Ok(());
+                    }
+                }
+                let err = m.keys().find_map(|(ptr, ty)| {
+                    match ptr.cmp(&req.ptr) {
+                        std::cmp::Ordering::Less => None, // this is OK
+                        std::cmp::Ordering::Equal => {
+                            if req.ty > *ty {
+                                Some(LockError::LockTypeEscalation {
+                                    session: req.handle_id.clone(),
+                                    ptr: ptr.clone(),
+                                    first: *ty,
+                                    second: req.ty,
+                                })
+                            } else {
+                                None
+                            }
+                        }
+                        std::cmp::Ordering::Greater => Some(if ptr.starts_with(&req.ptr) {
+                            LockError::LockTaxonomyEscalation {
+                                session: req.handle_id.clone(),
+                                first: ptr.clone(),
+                                second: req.ptr.clone(),
+                            }
+                        } else {
+                            LockError::NonCanonicalOrdering {
+                                session: req.handle_id.clone(),
+                                first: ptr.clone(),
+                                second: req.ptr.clone(),
+                            }
+                        }),
+                    }
+                });
+                err.map_or(Ok(()), Err)
+            }
+        }
+    }
+    fn try_insert(&mut self, req: &LockInfo) -> Result<(), LockError> {
+        self.validate(req)?;
+        match self.locks_held.get_mut(&req.handle_id) {
+            None => {
+                self.locks_held.insert(
+                    req.handle_id.clone(),
+                    ordmap![(req.ptr.clone(), req.ty) => 1],
+                );
+            }
+            Some(locks) => {
+                let k = (req.ptr.clone(), req.ty);
+                match locks.get_mut(&k) {
+                    None => {
+                        locks.insert(k, 1);
+                    }
+                    Some(n) => {
+                        *n += 1;
+                    }
+                }
+            }
+        }
+        Ok(())
+    }
+    fn remove(&mut self, req: &LockInfo) {
+        match self.locks_held.remove_with_key(&req.handle_id) {
+            None => {
+                #[cfg(feature = "tracing")]
+                tracing::warn!("Invalid removal from session manager: {}", req);
+            }
+            Some((hdl, mut locks)) => {
+                let k = (req.ptr.clone(), req.ty);
+                match locks.remove_with_key(&k) {
+                    None => {
+                        #[cfg(feature = "tracing")]
+                        tracing::warn!("Invalid removal from session manager: {}", req);
+                    }
+                    Some((k, n)) => {
+                        if n - 1 > 0 {
+                            locks.insert(k, n - 1);
+                        }
+                    }
+                }
+                if !locks.is_empty() {
+                    self.locks_held.insert(hdl, locks);
+                }
+            }
+        }
+    }
+}
+
 #[derive(Debug, Default)]
 struct Trie {
     state: LockState,
@@ -891,6 +1007,24 @@ impl LockInfo {
                 }
             }
     }
+    fn implicitly_grants(&self, other: &LockInfo) -> bool {
+        self.handle_id == other.handle_id
+            && match self.ty {
+                LockType::Exist => other.ty == LockType::Exist && self.ptr.starts_with(&other.ptr),
+                LockType::Read => {
+                    // E's in the ancestry
+                    other.ty == LockType::Exist && self.ptr.starts_with(&other.ptr)
+                    // nonexclusive locks in the subtree
+                        || other.ty != LockType::Write && other.ptr.starts_with(&self.ptr)
+                }
+                LockType::Write => {
+                    // E's in the ancestry
+                    other.ty == LockType::Exist && self.ptr.starts_with(&other.ptr)
+                    // anything in the subtree
+                        || other.ptr.starts_with(&self.ptr)
+                }
+            }
+    }
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
@@ -944,20 +1078,26 @@ pub enum LockError {
 struct Request {
     lock_info: LockInfo,
     cancel: Option<oneshot::Receiver<LockInfo>>,
-    completion: oneshot::Sender<Guard>,
+    completion: oneshot::Sender<Result<Guard, LockError>>,
 }
 impl Request {
     fn complete(self) -> oneshot::Receiver<LockInfo> {
         let (sender, receiver) = oneshot::channel();
-        if let Err(_) = self.completion.send(Guard {
+        if let Err(_) = self.completion.send(Ok(Guard {
             lock_info: self.lock_info,
             sender: Some(sender),
-        }) {
+        })) {
             #[cfg(feature = "tracing")]
             tracing::warn!("Completion sent to closed channel.")
         }
         receiver
     }
+    fn reject(self, err: LockError) {
+        if let Err(_) = self.completion.send(Err(err)) {
+            #[cfg(feature = "tracing")]
+            tracing::warn!("Rejection sent to closed channel.")
+        }
+    }
 }
 
 #[derive(Debug)]