From 732ffc7739fb487cd8e6d4ad558f1622c8163a1f Mon Sep 17 00:00:00 2001
From: debspencer <debspencer@gmail.com>
Date: Tue, 10 Aug 2021 22:33:43 -0400
Subject: [PATCH] Add a SetAndGet method to return previous value when setting
 a new one (#101)

---
 cache.go      | 19 +++++++++++++++++++
 cache_test.go | 20 ++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/cache.go b/cache.go
index df76d50..8fdd55b 100644
--- a/cache.go
+++ b/cache.go
@@ -117,6 +117,25 @@ func (cache *Cache) GetOrSet(key, value []byte, expireSeconds int) (retValue []b
 	return
 }
 
+// SetAndGet sets a key, value and expiration for a cache entry and stores it in the cache.
+// If the key is larger than 65535 or value is larger than 1/1024 of the cache size,
+// the entry will not be written to the cache. expireSeconds <= 0 means no expire,
+// but it can be evicted when cache is full.  Returns existing value if record exists
+// with a bool value to indicate whether an existing record was found
+func (cache *Cache) SetAndGet(key, value []byte, expireSeconds int) (retValue []byte, found bool, err error) {
+	hashVal := hashFunc(key)
+	segID := hashVal & segmentAndOpVal
+	cache.locks[segID].Lock()
+	defer cache.locks[segID].Unlock()
+
+	retValue, _, err = cache.segments[segID].get(key, nil, hashVal, false)
+	if err == nil {
+		found = true
+	}
+	err = cache.segments[segID].set(key, value, hashVal, expireSeconds)
+	return
+}
+
 // Peek returns the value or not found error, without updating access time or counters.
 func (cache *Cache) Peek(key []byte) (value []byte, err error) {
 	hashVal := hashFunc(key)
diff --git a/cache_test.go b/cache_test.go
index c12eebf..161f0a4 100644
--- a/cache_test.go
+++ b/cache_test.go
@@ -824,3 +824,23 @@ func TestConcurrentGetTTL(t *testing.T) {
 		t.Fatalf("Failed to get the TTL with an error: %+v", err)
 	}
 }
+
+func TestSetAndGet(t *testing.T) {
+	cache := NewCache(1024)
+	key := []byte("abcd")
+	val1 := []byte("efgh")
+
+	_, found, _ := cache.SetAndGet(key, val1, 0)
+	if found == true {
+		t.Fatalf("SetAndGet unexpected found data")
+	}
+
+	val2 := []byte("ijkl")
+	rval, found, _ := cache.SetAndGet(key, val2, 0)
+	if found == false {
+		t.Fatalf("SetAndGet expected found data")
+	}
+	if string(val1) != string(rval) {
+		t.Fatalf("SetAndGet expected SetAndGet %s: got %s", string(val1), string(rval))
+	}
+}