Parse HTML with Html Agility Pack in C#

Here's a short, simple tutorial on how to parse or scrape an html page. I'll be using Html Agility Pack to help me parse the document. One could use Regular Expressions as well, but let's not get into that at the moment.

Alright so, what is Html Agility Pack?

"This is an agile HTML parser that builds a read/write DOM and supports plain XPATH or XSLT (you actually don't HAVE to understand XPATH nor XSLT to use it, don't worry...). It is a .NET code library that allows you to parse "out of the web" HTML files. The parser is very tolerant with "real world" malformed HTML. The object model is very similar to what proposes System.Xml, but for HTML documents (or streams)."

In simple words, it allows you to parse HTML documents with ease, even in some malformed HTML document. Wow, that's impressive!

Let's start

Just for the sake of testing this awesome library, we're going to target its main page (http://htmlagilitypack.codeplex.com/) and extract the reviews from "Most Helpful Reviews" section.

Create a new project and add a reference to the Html Agility Pack library. By the way, the one I used targets the .NET Framework 2.0.

Here's how my scraping function looks like (without any error handling):

Most helpful reviews function - C#

Yup, it's small and does the job pretty well. Don't worry yet, let me explain the code. I'm using XPath to navigate to my desired element (the review element in this case) here.

Let me break the XPath query I used:

• // means select all the specified elements no matter where they are present in the document. 
• //div means I want to select all div elements and I do not simply care where they are present in the root document.
• [@id='recent_reviews'] means I want to select those div elements whose id equals 'recent_reviews'.
• //p means I want to select all p elements inside the div elements (which we have already selected just above) without caring where they are located.

The SelectNodes method will return our desired elements list. We then simply iterate over each element and extract the inner text of the element (the p element in this case).

In case you're wondering how I got the location of the element inside the document, Right click -> Inspect element (Google Chrome) works wonders ;)

Let me show you just that

Review elements location in the document.

As you can see all p elements are located inside a div element with id equals 'recent_reviews'.

I hope this now makes it a bit easier to understand the code. Feel free to leave any questions, comments, or suggestions you might have. Enjoy scraping!

Dynamic Win32 API Call + Anti User-mode hooking [C#]

When I was working with various user-mode hooking techniques, I developed this very simple way to bypass any trivial user-mode hooks applied to Win32 APIs.

Key features:

• 32-bit and 64-bit support.
• Bypasses trivial user-mode hooks at runtime (IAT,  Hotpatching, etc.)
• Dynamically calls Win32 API by loading the library or module (if not already loaded) and getting the target function address at runtime.

To-do list / What doesn't work at the moment since I'm so lazy to implement it:

• No support for Nt/Zw version APIs i.e. system calls. Don't use this to call them - unless you want your application to crash.
• No support for functions not implementing the standard function prologue. (GetCurrentProcess, GetCurrentProcessId, etc.)

Here's the source code of the native DLL: Anti.cpp

Here's a simple wrapper class for using the DLL: DynamicApi.cs

Here's how you'd use it: SampleUsage.cs

Alright so, that's it for now. If you've any questions or suggestions, just leave them below in the comments section. Have fun! ;)

QBitmap - MUCH faster image processing [C#]

As the GetPixel and SetPixel functions provided by the .NET framework are (so) slow, I had to write my own implementation of it. This Bitmap class allows you to access image pixels directly from the memory (via unsafe code.) Trust me, this is way faster!

Features:

• Way faster than the core framework's implementation. (~ 10 times faster!)
• Supports Format32bppArgb, Format24bppRgb.

To-do list:

• Support for more image formats.
• Suggestions?

Here it is, QBitmap.cs:

// http://codecav.blogspot.in/
public unsafe class QBitmap : IDisposable
    {
        private Bitmap _bitmap;
        private BitmapData _bitmapData;
 
        public int Width { get; private set; }
 
        public int Height { get; private set; }
 
        public PixelFormat PixelFormat { get; private set; }
 
        public QBitmap(Bitmap bitmap)
        {
            _bitmap = bitmap;
 
            Initialize();
        }
 
        private void Initialize()
        {
            if (_bitmap == null)
                throw new ArgumentNullException();
 
            Width = _bitmap.Width;
            Height = _bitmap.Height;
            PixelFormat = _bitmap.PixelFormat;
        }
 
        public void LockBits()
        {
            try
            {
                _bitmapData = _bitmap.LockBits(new Rectangle(0, 0, Width, Height), ImageLockMode.ReadWrite, PixelFormat);
            }
            catch (Exception e)
            {
                throw new Exception(e.Message);
            }
        }
 
        public void UnlockBits()
        {
            try
            {
                _bitmap.UnlockBits(_bitmapData);
            }
            catch (Exception e)
            {
                throw new Exception(e.Message);
            }
        }
 
        public Color GetPixel(int x, int y)
        {
            byte a = 0, r, g, b;
            var pData = (byte*) _bitmapData.Scan0.ToPointer();
 
            switch (PixelFormat)
            {
                case PixelFormat.Format32bppArgb:
                    b = *(pData + (y * _bitmapData.Stride) + (x * 4));
                    g = *(pData + (y * _bitmapData.Stride) + (x * 4) + 1);
                    r = *(pData + (y * _bitmapData.Stride) + (x * 4) + 2);
                    a = *(pData + (y * _bitmapData.Stride) + (x * 4) + 3);
                    break;
 
                case PixelFormat.Format24bppRgb:
                    b = *(pData + (y * _bitmapData.Stride) + (x * 3));
                    g = *(pData + (y * _bitmapData.Stride) + (x * 3) + 1);
                    r = *(pData + (y * _bitmapData.Stride) + (x * 3) + 2);
                    break;
 
                // Support for more formats.
                case PixelFormat.Format8bppIndexed:
                case PixelFormat.Format4bppIndexed:
                case PixelFormat.Format1bppIndexed:
                default:
                    throw new NotSupportedException("The specified pixel format is not supported.");
            }
 
            return Color.FromArgb(a, r, g, b);
        }
 
        public void SetPixel(int x, int y, Color color)
        {
            var pData = (byte*) _bitmapData.Scan0.ToPointer();
 
            switch (PixelFormat)
            {
                case PixelFormat.Format32bppArgb:
                    *(pData + (y*_bitmapData.Stride) + (x*4)) = color.B;
                    *(pData + (y*_bitmapData.Stride) + (x*4) + 1) = color.G;
                    *(pData + (y*_bitmapData.Stride) + (x*4) + 2) = color.R;
                    *(pData + (y*_bitmapData.Stride) + (x*4) + 3) = color.A;
                    break;
 
                case PixelFormat.Format24bppRgb:
                    *(pData + (y*_bitmapData.Stride) + (x*3)) = color.B;
                    *(pData + (y*_bitmapData.Stride) + (x*3) + 1) = color.G;
                    *(pData + (y*_bitmapData.Stride) + (x*3) + 2) = color.R;
                    break;
 
                // Support for more formats.
                case PixelFormat.Format8bppIndexed:
                case PixelFormat.Format4bppIndexed:
                case PixelFormat.Format1bppIndexed:
                default:
                    throw new NotSupportedException("The specified pixel format is not supported.");
            }
        }
 
        private bool _disposed;
        public void Dispose()
        {
            if (_disposed)
                return;
 
            _bitmap.Dispose();
            _bitmap = null;
 
            _disposed = true;
        }
    }

Usage:

// QBitmap usage (http://codecav.blogspot.in/)
 
var image = (Bitmap) Image.FromFile("Path\To\Image.png");
 
using (var qBitmap = new QBitmap(image))
{
        qBitmap.LockBits();
 
        // Perform operations on the image.
 
        qBitmap.UnlockBits();
}

Feel free to ask/suggest anything. Have fun with it!

Sudoku Solver - Backtracking Algorithm

I coded this a few weeks ago, so here it is. A simple, neat and highly customizable Sudoku solver (with a simple board) in C# based on the Backtracking algorithm.

In action:

Sudoku solver in C#

And here's the source code

• SudukoBoard.cs:

  // SudukoBoard.cs public class SudokuBoard : GroupBox { public sealed class SudokuCell : TextBox { public int X { get; private set; } public int Y { get; private set; } /// 
   /// Thread-safe Get/Set Text. /// 
   public string Value { get { string text = string.Empty; Invoke(new MethodInvoker(delegate { text = Text; })); return text; } set { Invoke(new MethodInvoker(delegate { Text = value; })); } } // Ctor. public SudokuCell(int x, int y, int width, int height) { X = x; Y = y; Width = width; Height = height; TextAlign = HorizontalAlignment.Center; Font = new Font("Verdana", 8, FontStyle.Regular); } // Only digits (except 0) are allowed. protected override void OnKeyPress(KeyPressEventArgs e) { if (char.IsWhiteSpace(e.KeyChar) || (!char.IsDigit(e.KeyChar) && e.KeyChar != (char) 8) || e.KeyChar == (char) 48) e.Handled = true; base.OnKeyPress(e); } } // An array representing the board. private readonly SudokuCell[,] _cell; private readonly int _cellWidth, _cellHeight; // Current board values. All operations/verifications are performed on this array. public readonly string[,] CurrBoardValues; public SudokuCell this[int x, int y] { get { return _cell[x, y]; } } // Ctor. public SudokuBoard(int cellWidth, int cellHeight) { _cellWidth = cellHeight; _cellHeight = cellHeight; Width = cellWidth * 9 + 20; Height = cellHeight * 9 + 28; _cell = new SudokuCell[9, 9]; CurrBoardValues = new string[9, 9]; CreateBoardControl(); } // Creates the actual sudoku board control (an array of SudokuCell in a GroupBox.) private void CreateBoardControl() { int extraSpaceX, extraSpaceY = 0; for (int y = 0; y < 9; y++) { extraSpaceX = 0; if (y != 0 && y % 3 == 0) extraSpaceY += 3; for (int x = 0; x < 9; x++) { if (x != 0 && x % 3 == 0) extraSpaceX += 3; _cell[x, y] = new SudokuCell(x, y, _cellHeight, _cellHeight) { MaxLength = 1, Location = new Point(Location.X + 7 + x * _cellWidth + extraSpaceX, Location.Y + 15 + y * _cellHeight + extraSpaceY) }; _cell[x, y].TextChanged += OnSudokuCellTextChanged; Controls.Add(_cell[x, y]); } } } private void OnSudokuCellTextChanged(object sender, EventArgs eventArgs) { var cell = (SudokuCell) sender; TryMove(cell); } #region Public methods public void ClearBoard() { for (int y = 0; y < 9; y++) { for (int x = 0; x < 9; x++) { _cell[x, y].Value = CurrBoardValues[x, y] = string.Empty; } } } public void UpdateBoard() { for (int y = 0; y < 9; y++) { for (int x = 0; x < 9; x++) { _cell[x, y].Value = CurrBoardValues[x, y]; } } } public bool TryMove(SudokuCell cell) { return TryMove(cell.X, cell.Y, cell.Value); } public bool TryMove(int x, int y, string value) { CurrBoardValues[x, y] = value; /* !IsMoveAllowedInRow(x, y, value) || !IsMoveAllowedInColumn(x, y, value) || !IsMoveAllowedInCurrentBox(x, y, value) */ if (!IsMoveAllowed(x, y, value)) { _cell[x, y].Value = string.Empty; CurrBoardValues[x, y] = string.Empty; return false; } return true; } #endregion #region Rules public bool IsMoveAllowed(int x, int y, string value) { return IsMoveAllowedInRow(x, y, value) && IsMoveAllowedInColumn(x, y, value) && IsMoveAllowedInCurrentBox(x, y, value); } private bool IsMoveAllowedInRow(int x, int y, string value) { for (int i = 0; i < 9; i++) { if (i == x) continue; if (CurrBoardValues[i, y] == value) return false; } return true; } private bool IsMoveAllowedInColumn(int x, int y, string value) { for (int i = 0; i < 9; i++) { if (i == y) continue; if (CurrBoardValues[x, i] == value) return false; } return true; } private bool IsMoveAllowedInCurrentBox(int x, int y, string value) { int boxX = 0, boxY = 0; if (x > 5) boxX = 6; else if (x > 2) boxX = 3; if (y > 5) boxY = 6; else if (y > 2) boxY = 3; for (int j = 0; j < 3; j++) { for (int i = 0; i < 3; i++) { if (boxX + i == x && boxY + j == y) continue; if (CurrBoardValues[boxX + i, boxY + j] == value) return false; } } return true; } #endregion } 

• SudokuSolver.cs:

  // SudokuSolver.cs public class SudokuSolver { private int _numOfTrials; private readonly SudokuBoard _board; private readonly AutoResetEvent _solvedEvent; public SudokuSolver(SudokuBoard board) { _board = board; _numOfTrials = 0; _solvedEvent = new AutoResetEvent(false); } #region Solve public void Solve() { var thread = new Thread(StartBacktrackSolver) { IsBackground = true }; thread.Start(); // Waiting for the solver thread to solve. _solvedEvent.WaitOne(); _board.UpdateBoard(); OnGameCompleted(_numOfTrials); _numOfTrials = 0; } private void StartBacktrackSolver() { BacktrackSolver(0, 0); _solvedEvent.Set(); } // Backtrack solving algorithm. private bool BacktrackSolver(int x, int y) { if (x == 9) { if (y == 8) return true; // game solved! x = 0; y++; } // pre-solved value. if (!string.IsNullOrEmpty(_board.CurrBoardValues[x, y])) { return BacktrackSolver(x + 1, y); } // Trying every possible (1 - 9) value on each cell. for (int i = 1; i < 10; i++) { if (_board.IsMoveAllowed(x, y, i.ToString())) { _numOfTrials++; _board.CurrBoardValues[x, y] = i.ToString(); // Moving on to the next cell. if (BacktrackSolver(x + 1, y)) return true; // game solved. // DEAD END reached. } } // DEAD END (no move was possible!) _board.CurrBoardValues[x, y] = string.Empty; return false; } #endregion public delegate void GameCompletedHandler(int numOfTrials); public event GameCompletedHandler GameCompleted; private void OnGameCompleted(int numOfTrials) { if (GameCompleted != null) GameCompleted(numOfTrials); } }

• Usage: http://pastebin.com/AK213QTN

Wanna try it? Here's just the executable:
http://www.mediafire.com/?umzad2b7jsgyjcg

Found a bug or something? Let me know.
Enjoy! ;)