Csharp/CSharp Tutorial/Network/Mini Crawler

MiniCrawler: A skeletal Web crawler.

//Code revised from
//C# 2.0 The Complete Reference
// 
using System; 
using System.Net; 
using System.IO; 
 
class MiniCrawler {  
 
  static string FindLink(string htmlstr, ref int startloc) { 
    int i; 
    int start, end; 
    string uri = null; 
    string lowcasestr = htmlstr.ToLower(); 
 
    i = lowcasestr.IndexOf("href=\"http", startloc); 
    if(i != -1) { 
      start = htmlstr.IndexOf(""", i) + 1; 
      end = htmlstr.IndexOf(""", start); 
      uri = htmlstr.Substring(start, end-start); 
      startloc = end; 
    } 
             
    return uri; 
  } 
 
  public static void Main(string[] args) { 
    string link = null; 
    string str; 
    string answer; 
 
    int curloc; // holds current location in response 
 
    if(args.Length != 1) { 
      Console.WriteLine("Usage: MiniCrawler <uri>"); 
      return ; 
    } 
 
    string uristr = args[0]; // holds current URI 
 
    try { 
 
      do { 
        Console.WriteLine("Linking to " + uristr); 
 
        // Create a WebRequest to the specified URI. 
        HttpWebRequest req = (HttpWebRequest) WebRequest.Create(uristr); 
 
        uristr = null; // disallow further use of this URI 
 
        // Send that request and return the response. 
        HttpWebResponse resp = (HttpWebResponse) req.GetResponse(); 
 
        // From the response, obtain an input stream. 
        Stream istrm = resp.GetResponseStream(); 
 
        // Wrap the input stream in a StreamReader. 
        StreamReader rdr = new StreamReader(istrm); 
 
        // Read in the entire page. 
        str = rdr.ReadToEnd(); 
 
        curloc = 0; 
        
        do { 
          // Find the next URI to link to. 
          link = FindLink(str, ref curloc); 
 
          if(link != null) { 
            Console.WriteLine("Link found: " + link); 
 
            Console.Write("Link, More, Quit?"); 
            answer = Console.ReadLine(); 
 
            if(string.rupare(answer, "L", true) == 0) { 
              uristr = string.Copy(link); 
              break; 
            } else if(string.rupare(answer, "Q", true) == 0) { 
              break; 
            } else if(string.rupare(answer, "M", true) == 0) { 
              Console.WriteLine("Searching for another link."); 
            } 
          } else { 
            Console.WriteLine("No link found."); 
            break; 
          } 
 
        } while(link.Length > 0); 
 
        // Close the Response. 
        resp.Close(); 
      } while(uristr != null); 
 
    } catch(WebException exc) { 
      Console.WriteLine("Network Error: " + exc.Message +  
                        "\nStatus code: " + exc.Status); 
    } catch(ProtocolViolationException exc) { 
      Console.WriteLine("Protocol Error: " + exc.Message); 
    } catch(UriFormatException exc) { 
      Console.WriteLine("URI Format Error: " + exc.Message); 
    } catch(NotSupportedException exc) { 
      Console.WriteLine("Unknown Protocol: " + exc.Message); 
    } catch(IOException exc) { 
      Console.WriteLine("I/O Error: " + exc.Message); 
    } 
 
    Console.WriteLine("Terminating MiniCrawler."); 
  } 
}