Extend expire time of cached link preview data to a week

There's no need to invalidate cache and send request again frequently

api/post.go

@@ -14,7 +14,10 @@ import (
 	"github.com/mattermost/platform/utils"
 )
 
-const OPEN_GRAPH_METADATA_CACHE_SIZE = 10000
+const (
+	OPEN_GRAPH_METADATA_CACHE_SIZE = 10000
+	openGraphDataCacheExpireTime   = 604800
+)
 
 var openGraphDataCache = utils.NewLru(OPEN_GRAPH_METADATA_CACHE_SIZE)
 
@@ -470,7 +473,7 @@ func getOpenGraphMetadata(c *Context, w http.ResponseWriter, r *http.Request) {
 	og := app.GetOpenGraphMetadata(url)
 
 	ogJSON, err := og.ToJSON()
-	openGraphDataCache.AddWithExpiresInSecs(props["url"], ogJSON, 3600) // Cache would expire after 1 hour
+	openGraphDataCache.AddWithExpiresInSecs(props["url"], ogJSON, openGraphDataCacheExpireTime) // Cache would expire after 1 week
 	if err != nil {
 		w.Write([]byte(`{"url": ""}`))
 		return