#1964 The speed of loading user agents was increased and memory usage was reduced

Author: skoshelev

src/Libraries/Nop.Services/Helpers/BrowscapXmlParser.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Text;
 using System.Text.RegularExpressions;
 using System.Xml.Linq;
 using Nop.Core;
@@ -14,7 +15,7 @@ namespace Nop.Services.Helpers
     public class BrowscapXmlHelper
     {
         private readonly List<string> _crawlerUserAgentsRegexp;
-
+       
         public BrowscapXmlHelper(string filePath)
         {
             _crawlerUserAgentsRegexp = new List<string>();
@@ -26,9 +27,7 @@ private void Initialize(string filePath)
         {
             using (var sr = new StreamReader(filePath))
             {
-                var text = sr.ReadToEnd().Replace("&", "&amp;");
-
-                var browsercapItems = XDocument.Parse(text).Root.Return(x => x.Element("browsercapitems"), null);
+                var browsercapItems = XDocument.Load(sr).Root.Return(x => x.Element("browsercapitems"), null);
 
                 if (browsercapItems == null)
                     throw new Exception("Incorrect file format");
@@ -37,8 +36,9 @@ private void Initialize(string filePath)
                     //only crawlers
                     .Where(IsBrowscapItemIsCrawler)
                     //get only user agent names
-                    .Select(e => e.Attribute("name").Return(a => a.Value.Replace("&amp;", "&"), ""))
-                    .Where(s => !string.IsNullOrEmpty(s))
+                    .Select(e => e.Attribute("name"))
+                    .Where(e => e != null && !string.IsNullOrEmpty(e.Value))
+                    .Select(e => e.Value)
                     .Select(ToRegexp));
             }
         }
@@ -47,13 +47,14 @@ private static bool IsBrowscapItemIsCrawler(XElement browscapItem)
         {
             var el = browscapItem.Elements("item").FirstOrDefault(e => e.Attribute("name").Return(a => a.Value, "") == "Crawler");
 
-            return el == null ? false : el.Attribute("value").Return(a => a.Value.ToLower() == "true", false);
+            return el != null && el.Attribute("value").Return(a => a.Value.ToLower() == "true", false);
         }
 
-        private string ToRegexp(string str)
+        private static string ToRegexp(string str)
         {
-            str = String.Format("^{0}$", Regex.Escape(str));
-            return str.Replace("\\?", ".").Replace("\\*", ".*?");
+            var sb = new StringBuilder(Regex.Escape(str));
+            sb.Replace("&amp;", "&").Replace("\\?", ".").Replace("\\*", ".*?");
+            return string.Format("^{0}$", sb);
         }
 
         /// <summary>

src/Libraries/Nop.Services/Helpers/UserAgentHelper.cs

@@ -15,6 +15,7 @@ public partial class UserAgentHelper : IUserAgentHelper
     {
         private readonly NopConfig _config;
         private readonly HttpContextBase _httpContext;
+        private static readonly object _locker = new object();
 
         /// <summary>
         /// Ctor
@@ -37,11 +38,19 @@ protected virtual BrowscapXmlHelper GetBrowscapXmlHelper()
             if (String.IsNullOrEmpty(_config.UserAgentStringsPath))
                 return null;
 
-            var filePath = CommonHelper.MapPath(_config.UserAgentStringsPath);
-            var bowscapXmlHelper = new BrowscapXmlHelper(filePath);
-            
-            Singleton<BrowscapXmlHelper>.Instance = bowscapXmlHelper;
-            return Singleton<BrowscapXmlHelper>.Instance;
+            //prevent multi loading data
+            lock (_locker)
+            {
+                //data can be loaded while we waited
+                if (Singleton<BrowscapXmlHelper>.Instance != null)
+                    return Singleton<BrowscapXmlHelper>.Instance;
+
+                var filePath = CommonHelper.MapPath(_config.UserAgentStringsPath);
+                var browscapXmlHelper = new BrowscapXmlHelper(filePath);
+                Singleton<BrowscapXmlHelper>.Instance = browscapXmlHelper;
+
+                return Singleton<BrowscapXmlHelper>.Instance;
+            }
         }
 
         /// <summary>