Add test case for resend request without begin sequence number

Author: davidsteiner

crates/hotfix/src/session.rs

@@ -370,6 +370,7 @@ impl<A: Application<M>, M: FixMessage, S: MessageStore> Session<A, M, S> {
             Err(_) => {
                 let reject = Reject::new(
                     message
+                        .header()
                         .get(fix44::MSG_SEQ_NUM)
                         .map_err(|_| anyhow!("failed to get seq number"))?,
                 )
@@ -392,6 +393,7 @@ impl<A: Application<M>, M: FixMessage, S: MessageStore> Session<A, M, S> {
             Err(_) => {
                 let reject = Reject::new(
                     message
+                        .header()
                         .get(fix44::MSG_SEQ_NUM)
                         .map_err(|_| anyhow!("failed to get seq number"))?,
                 )

crates/hotfix/tests/common/test_messages.rs

@@ -373,3 +373,16 @@ pub fn replace_field_value(raw_message: &mut Vec<u8>, tag: u32, new_value: &[u8]
         }
     }
 }
+
+/// Builds a resend request message without the required BeginSeqNo field.
+pub fn build_resend_request_without_begin_seq_no(msg_seq_num: u64) -> Vec<u8> {
+    let mut msg = Message::new("FIX.4.4", "2"); // MsgType 2 = ResendRequest
+    msg.set(fix44::SENDER_COMP_ID, COUNTERPARTY_COMP_ID);
+    msg.set(fix44::TARGET_COMP_ID, OUR_COMP_ID);
+    msg.set(fix44::MSG_SEQ_NUM, msg_seq_num);
+    msg.set(fix44::SENDING_TIME, Timestamp::utc_now());
+    // Intentionally omit BeginSeqNo (tag 7)
+    msg.set(fix44::END_SEQ_NO, 2);
+
+    msg.encode(&Config::default()).unwrap()
+}

crates/hotfix/tests/session_test_cases/resend_tests.rs

@@ -3,6 +3,7 @@ use crate::common::assertions::{assert_msg_type, then};
 use crate::common::setup::given_an_active_session;
 use crate::common::test_messages::{
     TestMessage, build_execution_report_with_incorrect_body_length,
+    build_resend_request_without_begin_seq_no,
 };
 use hotfix::message::FixMessage;
 use hotfix::session::Status;
@@ -142,3 +143,25 @@ async fn test_resent_message_previously_received_is_ignored() {
     when(&session).requests_disconnect().await;
     then(&mut counterparty).gets_disconnected().await;
 }
+
+/// Tests that when a counterparty sends a resend request without the required BeginSeqNo field,
+/// the session rejects the malformed message.
+#[tokio::test]
+async fn test_resend_request_without_begin_seq_no_is_rejected() {
+    let (session, mut counterparty) = given_an_active_session().await;
+
+    // build a resend request message missing the required BeginSeqNo (tag 7)
+    let seq_num = counterparty.next_target_sequence_number();
+    let invalid_resend_request = build_resend_request_without_begin_seq_no(seq_num);
+    when(&mut counterparty)
+        .sends_raw_message(invalid_resend_request)
+        .await;
+
+    // the session should reject this invalid resend request
+    then(&mut counterparty)
+        .receives(|msg| assert_msg_type(msg, MsgType::Reject))
+        .await;
+
+    when(&session).requests_disconnect().await;
+    then(&mut counterparty).gets_disconnected().await;
+}