Fix Redis session expiration entry deletion

Closes gh-585

Author: swurzinger

spring-session-data-redis/src/main/java/org/springframework/session/data/redis/RedisSessionExpirationPolicy.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2019 the original author or authors.
+ * Copyright 2014-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -50,6 +50,8 @@ final class RedisSessionExpirationPolicy {
 
 	private static final Log logger = LogFactory.getLog(RedisSessionExpirationPolicy.class);
 
+	private static final String SESSION_EXPIRES_PREFIX = "expires:";
+
 	private final RedisOperations<Object, Object> redis;
 
 	private final Function<Long, String> lookupExpirationKey;
@@ -67,11 +69,12 @@ final class RedisSessionExpirationPolicy {
 	void onDelete(Session session) {
 		long toExpire = roundUpToNextMinute(expiresInMillis(session));
 		String expireKey = getExpirationKey(toExpire);
-		this.redis.boundSetOps(expireKey).remove(session.getId());
+		String entryToRemove = SESSION_EXPIRES_PREFIX + session.getId();
+		this.redis.boundSetOps(expireKey).remove(entryToRemove);
 	}
 
 	void onExpirationUpdated(Long originalExpirationTimeInMilli, Session session) {
-		String keyToExpire = "expires:" + session.getId();
+		String keyToExpire = SESSION_EXPIRES_PREFIX + session.getId();
 		long toExpire = roundUpToNextMinute(expiresInMillis(session));
 
 		if (originalExpirationTimeInMilli != null) {

spring-session-data-redis/src/test/java/org/springframework/session/data/redis/RedisSessionExpirationPolicyTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2019 the original author or authors.
+ * Copyright 2014-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -164,4 +164,11 @@ void onExpirationUpdatedPersistOnNegativeExpiration() {
 		verify(this.hashOperations).persist();
 	}
 
+	@Test
+	void onDeleteRemoveExpirationEntry() {
+		this.policy.onDelete(this.session);
+
+		verify(this.setOperations).remove("expires:" + this.session.getId());
+	}
+
 }