I need a Powerful Web Scraper library [closed]
Scraping is easy really, you just have to parse the content you are downloading and get all the associated links.
The most important piece though is the part that processes the HTML. Because most browsers don't require the cleanest (or standards-compliant) HTML in order to be rendered, you need an HTML parser that is going to be able to make sense of HTML that is not always well-formed.
I recommend you use the HTML Agility Pack for this purpose. It does very well at handling non-well-formed HTML, and provides an easy interface for you to use XPath queries to get nodes in the resulting document.
Beyond that, you just need to pick a data store to hold your processed data (you can use any database technology for that) and a way to download content from the web, which .NET provides two high-level mechanisms for, the WebClient and HttpWebRequest/HttpWebResponse classes.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace SoftCircuits.Parsing
{
public class HtmlTag
{
/// <summary>
/// Name of this tag
/// </summary>
public string Name { get; set; }
/// <summary>
/// Collection of attribute names and values for this tag
/// </summary>
public Dictionary<string, string> Attributes { get; set; }
/// <summary>
/// True if this tag contained a trailing forward slash
/// </summary>
public bool TrailingSlash { get; set; }
/// <summary>
/// Indicates if this tag contains the specified attribute. Note that
/// true is returned when this tag contains the attribute even when the
/// attribute has no value
/// </summary>
/// <param name="name">Name of attribute to check</param>
/// <returns>True if tag contains attribute or false otherwise</returns>
public bool HasAttribute(string name)
{
return Attributes.ContainsKey(name);
}
};
public class HtmlParser : TextParser
{
public HtmlParser()
{
}
public HtmlParser(string html) : base(html)
{
}
/// <summary>
/// Parses the next tag that matches the specified tag name
/// </summary>
/// <param name="name">Name of the tags to parse ("*" = parse all tags)</param>
/// <param name="tag">Returns information on the next occurrence of the specified tag or null if none found</param>
/// <returns>True if a tag was parsed or false if the end of the document was reached</returns>
public bool ParseNext(string name, out HtmlTag tag)
{
// Must always set out parameter
tag = null;
// Nothing to do if no tag specified
if (String.IsNullOrEmpty(name))
return false;
// Loop until match is found or no more tags
MoveTo('<');
while (!EndOfText)
{
// Skip over opening '<'
MoveAhead();
// Examine first tag character
char c = Peek();
if (c == '!' && Peek(1) == '-' && Peek(2) == '-')
{
// Skip over comments
const string endComment = "-->";
MoveTo(endComment);
MoveAhead(endComment.Length);
}
else if (c == '/')
{
// Skip over closing tags
MoveTo('>');
MoveAhead();
}
else
{
bool result, inScript;
// Parse tag
result = ParseTag(name, ref tag, out inScript);
// Because scripts may contain tag characters, we have special
// handling to skip over script contents
if (inScript)
MovePastScript();
// Return true if requested tag was found
if (result)
return true;
}
// Find next tag
MoveTo('<');
}
// No more matching tags found
return false;
}
/// <summary>
/// Parses the contents of an HTML tag. The current position should be at the first
/// character following the tag's opening less-than character.
///
/// Note: We parse to the end of the tag even if this tag was not requested by the
/// caller. This ensures subsequent parsing takes place after this tag
/// </summary>
/// <param name="reqName">Name of the tag the caller is requesting, or "*" if caller
/// is requesting all tags</param>
/// <param name="tag">Returns information on this tag if it's one the caller is
/// requesting</param>
/// <param name="inScript">Returns true if tag began, and did not end, and script
/// block</param>
/// <returns>True if data is being returned for a tag requested by the caller
/// or false otherwise</returns>
protected bool ParseTag(string reqName, ref HtmlTag tag, out bool inScript)
{
bool doctype, requested;
doctype = inScript = requested = false;
// Get name of this tag
string name = ParseTagName();
// Special handling
if (String.Compare(name, "!DOCTYPE", true) == 0)
doctype = true;
else if (String.Compare(name, "script", true) == 0)
inScript = true;
// Is this a tag requested by caller?
if (reqName == "*" || String.Compare(name, reqName, true) == 0)
{
// Yes
requested = true;
// Create new tag object
tag = new HtmlTag();
tag.Name = name;
tag.Attributes = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
}
// Parse attributes
MovePastWhitespace();
while (Peek() != '>' && Peek() != NullChar)
{
if (Peek() == '/')
{
// Handle trailing forward slash
if (requested)
tag.TrailingSlash = true;
MoveAhead();
MovePastWhitespace();
// If this is a script tag, it was closed
inScript = false;
}
else
{
// Parse attribute name
name = (!doctype) ? ParseAttributeName() : ParseAttributeValue();
MovePastWhitespace();
// Parse attribute value
string value = String.Empty;
if (Peek() == '=')
{
MoveAhead();
MovePastWhitespace();
value = ParseAttributeValue();
MovePastWhitespace();
}
// Add attribute to collection if requested tag
if (requested)
{
// This tag replaces existing tags with same name
if (tag.Attributes.ContainsKey(name))
tag.Attributes.Remove(name);
tag.Attributes.Add(name, value);
}
}
}
// Skip over closing '>'
MoveAhead();
return requested;
}
/// <summary>
/// Parses a tag name. The current position should be the first character of the name
/// </summary>
/// <returns>Returns the parsed name string</returns>
protected string ParseTagName()
{
int start = Position;
while (!EndOfText && !Char.IsWhiteSpace(Peek()) && Peek() != '>')
MoveAhead();
return Substring(start, Position);
}
/// <summary>
/// Parses an attribute name. The current position should be the first character
/// of the name
/// </summary>
/// <returns>Returns the parsed name string</returns>
protected string ParseAttributeName()
{
int start = Position;
while (!EndOfText && !Char.IsWhiteSpace(Peek()) && Peek() != '>' && Peek() != '=')
MoveAhead();
return Substring(start, Position);
}
/// <summary>
/// Parses an attribute value. The current position should be the first non-whitespace
/// character following the equal sign.
///
/// Note: We terminate the name or value if we encounter a new line. This seems to
/// be the best way of handling errors such as values missing closing quotes, etc.
/// </summary>
/// <returns>Returns the parsed value string</returns>
protected string ParseAttributeValue()
{
int start, end;
char c = Peek();
if (c == '"' || c == '\'')
{
// Move past opening quote
MoveAhead();
// Parse quoted value
start = Position;
MoveTo(new char[] { c, '\r', '\n' });
end = Position;
// Move past closing quote
if (Peek() == c)
MoveAhead();
}
else
{
// Parse unquoted value
start = Position;
while (!EndOfText && !Char.IsWhiteSpace(c) && c != '>')
{
MoveAhead();
c = Peek();
}
end = Position;
}
return Substring(start, end);
}
/// <summary>
/// Locates the end of the current script and moves past the closing tag
/// </summary>
protected void MovePastScript()
{
const string endScript = "</script";
while (!EndOfText)
{
MoveTo(endScript, true);
MoveAhead(endScript.Length);
if (Peek() == '>' || Char.IsWhiteSpace(Peek()))
{
MoveTo('>');
MoveAhead();
break;
}
}
}
}
}
For simple websites ( = plain html only), Mechanize works really well and fast. For sites that use Javascript, AJAX or even Flash, you need a real browser solution such as iMacros.