public static async Task <IEnumerable <string> > GetDisallowedUrls(IWebAgent webAgent, string domain)
{
var uri = new Uri($"http://{domain}/robots.txt");
var list = new List <string>();
var text = "";
using (var response = await webAgent.ExecuteRequest(uri))
{
if ((int)response.StatusCode >= 400 || (int)response.StatusCode <= 599)
{
return(list);
}
using (var stream = webAgent.GetCompressedStream(response))
using (var reader = new StreamReader(stream, Encoding.Default))
{
text = reader.ReadToEnd();
}
}
var lines = text.ToLower().Split(Environment.NewLine.ToCharArray(), StringSplitOptions.RemoveEmptyEntries);
var name = webAgent.AgentName.ToLower();
var applicable = false;
foreach (var line in lines)
{
if (line.Contains("user-agent"))
{
applicable = line.Contains("*") || line.Contains(name);
}
if (line.Contains("disallow") && applicable)
{
var split = line.Split(':');
if (split.Length < 2)
{
continue;
}
var rule = split[1].Trim();
list.Add(rule);
}
}
return(list);
}
private async Task ThreadAction(IWorker worker, CrawlJob job)
{
// sort out multi threading holding pattern
if (worker.Id != 0)
{
while (_queue.Count < (worker.Id + 1) && !_cancelSource.Token.IsCancellationRequested && !_aThreadIsComplete)
{
Thread.Sleep(100);
}
}
while (job.CompletionConditions.All(cc => !cc.ConditionMet(GetCrawlProgress())) &&
!_cancelSource.Token.IsCancellationRequested &&
!_aThreadIsComplete)
{
if (worker.Id == 0 && NeedsUpdate())
{
_updateAction(GetCrawlProgress());
}
// set up fallback and retry policies
var fallback = Policy <Uri> .Handle <CrawlQueueEmptyException>()
.Fallback((cToken) =>
{
_aThreadIsComplete = true;
return(null);
});
var retry = Policy <Uri> .Handle <CrawlQueueEmptyException>()
.WaitAndRetry(10, tryNum => TimeSpan.FromMilliseconds(tryNum * 200));
// will attempt to get a new item from the queue, retrying as per above policies
var next = Policy.Wrap(fallback, retry).Execute(() =>
{
var n = GetNext();
if (n == null)
{
throw new CrawlQueueEmptyException();
}
return(n);
});
// fallback will set this if we failed to get a new link (this will end the crawl)
if (_aThreadIsComplete)
{
continue;
}
try
{
// access it
var responseTask = _webAgent.ExecuteRequest(next);
// log that we've crawled it
_crawled.Add(next);
var response = await responseTask;
if (response != null)
{
var html = HTMLRetriever.GetHTML(_webAgent.GetCompressedStream(response));
// parse the contents for new links and data user wants
var data = DataExtractor.Extract(html, job.Domain, job.Regex);
// add each of the links extracted if:
// the queue is not too large
// the link is not disallowed by the domain's robots.txt file
// the link is not already in the queue
// the link has not already been crawled
// each of the user defined enqueue conditions returns true
foreach (var link in data.Links)
{
if (_queue.Count < QUEUE_MAX &&
RobotParser.UriIsAllowed(_disallowedUrls, link) &&
!_queue.Contains(link) &&
!_crawled.Contains(link) &&
job.EnqueueConditions.All(ec => ec.ConditionMet(link)))
{
_queue.Enqueue(link);
}
}
// add data matching the regex to the return list
foreach (var foundData in data.Data)
{
_results.Add(foundData);
}
}
}
catch (WebException e)
{
_errors.Add(e);
}
}
if (!_aThreadIsComplete)
{
_aThreadIsComplete = true;
}
worker.DoneEvent.Set();
}
