Refactor to push action to set target sequence number into state which knows what state it's valid for

Author: davidsteiner

crates/hotfix/src/session.rs

@@ -569,22 +569,13 @@ where
                 self.reset_on_next_logon = true;
             }
             AdminRequest::SetNextTargetSeqNum { seq_num, responder } => {
-                let current = self.state.as_status();
-                let response = if matches!(self.state, SessionState::Disconnected(_)) {
-                    self.ctx
-                        .store
-                        .set_target_seq_number(seq_num.get() - 1)
-                        .await
-                        .map_err(SetNextTargetSeqNumError::from)
-                } else {
-                    warn!(
-                        ?current,
-                        seq_num = seq_num.get(),
-                        "rejecting SetNextTargetSeqNum outside Disconnected state"
-                    );
-                    Err(SetNextTargetSeqNumError::InvalidState { current })
-                };
-
+                let response = self
+                    .state
+                    .try_set_next_target_seq_num(&mut self.ctx, seq_num)
+                    .await;
+                if let Err(ref err) = response {
+                    warn!(?err, seq_num = seq_num.get(), "SetNextTargetSeqNum rejected");
+                }
                 if responder.send(response).is_err() {
                     error!("failed to respond to SetNextTargetSeqNum request");
                 }

crates/hotfix/src/session/state.rs

@@ -16,12 +16,15 @@ use crate::message::logon::Logon;
 use crate::message::logout::Logout;
 use crate::message::verification::VerificationFlags;
 use crate::session::ctx::{PreProcessDecision, SessionCtx, TransitionResult, VerificationResult};
-use crate::session::error::{InternalSendError, InternalSendResultExt, SessionOperationError};
+use crate::session::error::{
+    InternalSendError, InternalSendResultExt, SessionOperationError, SetNextTargetSeqNumError,
+};
 use crate::session::event::ScheduleResponse;
 use crate::session::info::Status as SessionInfoStatus;
 use crate::transport::writer::WriterRef;
 use hotfix_message::message::Message;
 use hotfix_store::MessageStore;
+use std::num::NonZeroU64;
 use std::time::Duration;
 use tokio::sync::oneshot;
 use tokio::time::Instant;
@@ -247,6 +250,33 @@ impl SessionState {
         }
     }
 
+    /// Set the next expected target sequence number. Only permitted while
+    /// `Disconnected` — any other state returns `InvalidState`.
+    ///
+    /// The store stores "last seen" (see `inbound::on_sequence_reset` passing
+    /// `end - 1`), so we subtract 1 to make `next_target_seq_number()` return
+    /// `seq_num`. `NonZeroU64` guarantees the subtraction is safe.
+    pub(crate) async fn try_set_next_target_seq_num<A, S>(
+        &self,
+        ctx: &mut SessionCtx<A, S>,
+        seq_num: NonZeroU64,
+    ) -> Result<(), SetNextTargetSeqNumError>
+    where
+        A: Application,
+        S: MessageStore,
+    {
+        match self {
+            SessionState::Disconnected(_) => ctx
+                .store
+                .set_target_seq_number(seq_num.get() - 1)
+                .await
+                .map_err(SetNextTargetSeqNumError::from),
+            _ => Err(SetNextTargetSeqNumError::InvalidState {
+                current: self.as_status(),
+            }),
+        }
+    }
+
     /// Sends a logout message and puts the session state into an [`AwaitingLogout`] state.
     ///
     /// The session waits for a configurable timeout period for the counterparty to