improve security, that no double content is fetched

ReadSharp.Tests/ReadTests.cs

@@ -180,7 +180,10 @@ namespace ReadSharp.Tests
     {
       ReadOptions options = new ReadOptions() { MultipageDownload = true };
 
-      Article result = await reader.Read(new Uri("http://www.anandtech.com/show/7594/samsung-ssd-840-evo-msata-120gb-250gb-500gb-1tb-review"), options);
+      Article result = await reader.Read(new Uri("http://www.maximumpc.com/article/features/modders_toolkit_everything_you_need_make_kick-ass_custom_case_mods"), options);
+      Assert.Equal(result.PageCount, 4);
+
+      result = await reader.Read(new Uri("http://www.anandtech.com/show/7594/samsung-ssd-840-evo-msata-120gb-250gb-500gb-1tb-review"), options);
       Assert.Equal(result.PageCount, 9);
 
       result = await reader.Read(new Uri("http://www.zeit.de/gesellschaft/2014-02/alice-schwarzer-steuerhinterziehung-doppelmoral"), options);

ReadSharp/Reader.cs

@@ -39,6 +39,11 @@ namespace ReadSharp
     /// </summary>
     protected HttpOptions _options;
 
+    /// <summary>
+    /// The current pages
+    /// </summary>
+    protected List<string> _currentPages = new List<string>();
+
     /// <summary>
     /// Redirect faulty mobile URIs to desktop equivalents
     /// </summary>
@@ -118,6 +123,8 @@ namespace ReadSharp
     /// <exception cref="OperationCanceledException"></exception>
     public async Task<Article> Read(Uri uri, ReadOptions options = null, CancellationToken cancellationToken = default(CancellationToken))
     {
+      _currentPages = new List<string>();
+
       Response response;
       string uriString = uri.OriginalString;
 
@@ -274,6 +281,13 @@ namespace ReadSharp
     /// </exception>
     private async Task<Response> Request(Uri uri, ReadOptions options, Response previousResponse, CancellationToken cancellationToken)
     {
+      // URI already fetched
+      if (previousResponse != null && _currentPages.Contains(uri.OriginalString))
+      {
+        return previousResponse;
+      }
+      _currentPages.Add(uri.OriginalString);
+
       HttpResponseMessage response = null;
       TranscodingResult transcodingResult;
       Encoding encoding;
@@ -354,7 +368,7 @@ namespace ReadSharp
 
       // in same special cases their are multiple pages, which are only comments or do not contain new content.
       // if this is the case we will break here and return the first page only.
-      if (previousResponse != null && previousResponse.TranscodingResult.ExtractedContent == transcodingResult.ExtractedContent)
+      if (previousResponse != null && previousResponse.TranscodingResult.ExtractedContent.Contains(transcodingResult.ExtractedContent))
       {
         previousResponse.TranscodingResult.NextPageUrl = null;
         return previousResponse;