Ensure memcache TTL cannot be over 30 days (#14592)

Memcached TTL cannot be > 30 days and if it is attempted the TTL is interpreted as
a unix timestamp.

This PR ensures that the TTL is switched to a unix timestamp in those cases.

Fix #14571

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/setting/cache.go

@@ -49,6 +49,9 @@ var (
 	}
 )
 
+// MemcacheMaxTTL represents the maximum memcache TTL
+const MemcacheMaxTTL = 30 * 24 * time.Hour
+
 func newCacheService() {
 	sec := Cfg.Section("cache")
 	if err := sec.MapTo(&CacheService); err != nil {
@@ -85,3 +88,19 @@ func newCacheService() {
 		log.Info("Last Commit Cache Service Enabled")
 	}
 }
+
+// TTLSeconds returns the TTLSeconds or unix timestamp for memcache
+func (c Cache) TTLSeconds() int64 {
+	if c.Adapter == "memcache" && c.TTL > MemcacheMaxTTL {
+		return time.Now().Add(c.TTL).Unix()
+	}
+	return int64(c.TTL.Seconds())
+}
+
+// LastCommitCacheTTLSeconds returns the TTLSeconds or unix timestamp for memcache
+func LastCommitCacheTTLSeconds() int64 {
+	if CacheService.Adapter == "memcache" && CacheService.LastCommit.TTL > MemcacheMaxTTL {
+		return time.Now().Add(CacheService.LastCommit.TTL).Unix()
+	}
+	return int64(CacheService.LastCommit.TTL.Seconds())
+}