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From "Thamme Gowda N (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (NUTCH-2144) Plugin to override db.ignore.external to exempt interesting external domain URLs
Date Mon, 19 Oct 2015 22:27:27 GMT

    [ https://issues.apache.org/jira/browse/NUTCH-2144?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14964175#comment-14964175
] 

Thamme Gowda N edited comment on NUTCH-2144 at 10/19/15 10:26 PM:
------------------------------------------------------------------

Thanks for your feedback. I agree that the content-type will be missing for newly discovered
URLs. I am double sure that HTTP HEAD requests add lots of overhead.

First I apply regex filter to limit urls. So HEAD call is made only on the URLs matched by
regex. However that was still not sufficient, so content type filter is made optional.

For example, 
{color:red}
  image/jpeg,image/png,image/gif=.*\.(jpg|JPG|png|PNG|gif|GIF)$
{color}

the above rule makes HTTP HEAD call to the urls matched by regex to determine content type.

However, 
{color:red}
    =.*\.(jpg|JPG|png|PNG|gif|GIF)$
{color}

rule doesn't make HTTP HEAD, because the content type filter is not applied.


was (Author: thammegowda):
Thanks for your feedback. I agree that the content-type will be missing for newly discovered
URLs. I am double sure that HTTP HEAD requests add lots of overhead.

First I apply regex filter to limit urls. So HEAD call is made only on the URLs matched by
regex. However that was still not sufficient, so content type filter is made optional.

For example, 
{color:red}
  image/jpeg,image/png,image/gif=.*\.(jpg|JPG|png$|PNG|gif|GIF)$
{color}

the above rule makes HTTP HEAD call to the urls matched by regex to determine content type.

However, 
{color:red}
    =.*\.(jpg|JPG|png$|PNG|gif|GIF)$
{color}

rule doesn't make HTTP HEAD, because the content type filter is not applied.

> Plugin to override db.ignore.external to exempt interesting external domain URLs
> --------------------------------------------------------------------------------
>
>                 Key: NUTCH-2144
>                 URL: https://issues.apache.org/jira/browse/NUTCH-2144
>             Project: Nutch
>          Issue Type: New Feature
>          Components: crawldb, fetcher
>            Reporter: Thamme Gowda N
>            Priority: Minor
>         Attachments: ignore-exempt.patch, ignore-exempt.patch
>
>
> Create a rule based urlfilter plugin that allows focused crawler (db.ignore.external.links=true)
to fetch static resources from external domains.
> The generalized version of this: This plugin should permit interesting URLs from external
domains (by overriding db.ignore.external). The interesting urls are decided from a combination
of regex and mime-type rules.
> Concrete use case:
>   When using Nutch to crawl images from a set of domains, the crawler needs to fetch
all images which may be linked from CDNs and other domains. In this scenario, allowing all
external links and then writing hundreds of regular expressions is not feasible for large
number of domains.



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