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/*
C#: The Complete Reference
by Herbert Schildt
Publisher: Osborne/McGraw-Hill (March 8, 2002)
ISBN: 0072134852
*/
// MiniCrawler: A skeletal Web crawler.
using System;
using System.Net;
using System.IO;
public class MiniCrawler {
// Find a link in a content string.
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.Compare(answer, "L", true) == 0) {
uristr = string.Copy(link);
break;
} else if(string.Compare(answer, "Q", true) == 0) {
break;
} else if(string.Compare(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.");
}
}
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