api, webui: Clear cache usage limits when changing assigned limits

When changing the usage limits of a user via the web UI clear the cached
usage limits. This makes sure the newly assigned limits are loaded at
the time of the next API call. This means regular loading of usage data
from the database is no longer necessary for applying newly assigned
limits, so the time for reloading can be increased (or even reloading
completely removed). Note this only works when the api and the webui
backend share the same memcached instance.

Author: MKleusberg

api/limiter.go

@@ -16,8 +16,8 @@ const cacheTime int = 0
 
 // Interval for flushing the cached data of a user and reloading it from the database
 // Reloading the data from database also reloads the assigned usage limits. So this is also the maximum
-// time a user has to wait until a newly assigned limit is active.
-const reloadInterval time.Duration = 1 * time.Hour
+// time a user has to wait until a newly assigned limit is active unless the cache is cleared.
+const reloadInterval time.Duration = 24 * time.Hour
 
 type rateLimitCacheData struct {
 	// These values reflect the applied settings from the usage_limits table

common/memcache.go

@@ -7,6 +7,7 @@ import (
 	"crypto/tls"
 	"encoding/gob"
 	"encoding/hex"
+	"errors"
 	"fmt"
 	"io"
 	"log"
@@ -80,6 +81,18 @@ func ConnectCache() (err error) {
 	return nil
 }
 
+// DeleteCacheItem deletes the cached item with the given key if it exists
+func DeleteCacheItem(cacheKey string) (error) {
+	err := memCache.Delete(cacheKey)
+
+	// We don't care about cache misses
+	if errors.Is(err, memcache.ErrCacheMiss) {
+		return nil
+	}
+
+	return err
+}
+
 // GetCachedData retrieves cached data from Memcached
 func GetCachedData(cacheKey string, cacheData interface{}) (bool, error) {
 	cacheItem, err := memCache.Get(cacheKey)

webui/main.go

@@ -3992,6 +3992,13 @@ func saveLimitsHandler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Flush cached limits for user so they are applied immediately
+	err = com.DeleteCacheItem("limits-" + username)
+	if err != nil {
+		w.WriteHeader(http.StatusInternalServerError)
+		return
+	}
+
 	return
 }