Add base class for response filters to safely modify intercepted files

Core/Handling/Filters/ResponseFilterBase.cs

@@ -0,0 +1,72 @@
+using System;
+using System.IO;
+using System.Text;
+using CefSharp;
+
+namespace TweetDuck.Core.Handling.Filters{
+    abstract class ResponseFilterBase : IResponseFilter{
+        private enum State{
+            Reading, Writing, Done
+        }
+
+        private readonly Encoding encoding;
+        private byte[] responseData;
+
+        private State state;
+        private int offset;
+
+        protected ResponseFilterBase(int totalBytes, Encoding encoding){
+            this.responseData = new byte[totalBytes];
+            this.encoding = encoding;
+            this.state = State.Reading;
+        }
+        
+        FilterStatus IResponseFilter.Filter(Stream dataIn, out long dataInRead, Stream dataOut, out long dataOutWritten){
+            int responseLength = responseData.Length;
+
+            if (state == State.Reading){
+                int bytesToRead = Math.Min(responseLength-offset, (int)Math.Min(dataIn.Length, int.MaxValue));
+                
+                dataIn.Read(responseData, offset, bytesToRead);
+                offset += bytesToRead;
+                
+                dataInRead = bytesToRead;
+                dataOutWritten = 0;
+                
+                if (offset >= responseLength){
+                    responseData = encoding.GetBytes(ProcessResponse(encoding.GetString(responseData)));
+                    state = State.Writing;
+                    offset = 0;
+                }
+
+                return FilterStatus.NeedMoreData;
+            }
+            else if (state == State.Writing){
+                int bytesToWrite = Math.Min(responseLength-offset, (int)Math.Min(dataOut.Length, int.MaxValue));
+
+                if (bytesToWrite > 0){
+                    dataOut.Write(responseData, offset, bytesToWrite);
+                    offset += bytesToWrite;
+                }
+
+                dataOutWritten = bytesToWrite;
+                dataInRead = 0;
+
+                if (offset < responseLength){
+                    return FilterStatus.NeedMoreData;
+                }
+                else{
+                    state = State.Done;
+                    return FilterStatus.Done;
+                }
+            }
+            else{
+                throw new InvalidOperationException("This resource filter cannot be reused.");
+            }
+        }
+        
+        public abstract bool InitFilter();
+        protected abstract string ProcessResponse(string text);
+        public abstract void Dispose();
+    }
+}

TweetDuck.csproj

@@ -72,6 +72,7 @@
     <Compile Include="Core\FormManager.cs" />
     <Compile Include="Core\Handling\ContextMenuGuide.cs" />
     <Compile Include="Core\Handling\DragHandlerBrowser.cs" />
+    <Compile Include="Core\Handling\Filters\ResponseFilterBase.cs" />
     <Compile Include="Core\Handling\General\BrowserProcessHandler.cs" />
     <Compile Include="Core\Handling\ContextMenuBase.cs" />
     <Compile Include="Core\Handling\ContextMenuBrowser.cs" />