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https://issues.apache.org/jira/browse/NUTCH-1941?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14378821#comment-14378821
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Sebastian Nagel commented on NUTCH-1941:
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Great, that's a step forward. Before going into details (and testing), let's
discuss whether we should solve the problem by
# for a list of agent names <a,b,c> take r₁ times a, r₂ times b, r₃ times c (r
being a random number)
# or, alternatively, just choose a random element from <a,b,c> every time an
agent name is needed
The task is to change the agent name (ev. in a manner which is hard to detect).
Both solutions are applicable but solution 2 seems to have a couple of
advantages:
- it's much easier to implement, e.g. (untested draft given that userAgentNames
is already filled):
{code}
public String getUserAgent() {
if (userAgentNames != null) {
// choose one of alternative agents
int i = ThreadLocalRandom.current().nextInt(0, userAgentNames.size());
return userAgentNames.get(i);
}
return userAgent;
}
{code}
- no synchronization required. Solution 1 would need synchronization: it may be
sensitive to race conditions, but also the visibility of variables shared
between Fetcher threads matters.
- to make agent names unevenly distributed: just add some names multiple times
to the list. Because names are randomly chosen the ordering in the file does
not matter.
> Optional rolling http.agent.name's
> ----------------------------------
>
> Key: NUTCH-1941
> URL: https://issues.apache.org/jira/browse/NUTCH-1941
> Project: Nutch
> Issue Type: New Feature
> Components: fetcher, protocol
> Reporter: Lewis John McGibbney
> Priority: Trivial
> Attachments: NUTCH-1941-ITR2.patch, NUTCH-1941-itr3.patch,
> NUTCH-1941-ver1.patch, agent.names.txt, nutch.patch
>
>
> In some scenarios, even whilst adhering to fetcher.crawl.delay, web admins
> can block your fetcher based merely on your crawler name.
> I propose the ability to implement rolling http.agent.name's which could be
> substituted every 5 seconds for example. This would mean that successive
> requests to the same domain would be sent with different http.agent.name.
> This behavior should be off by default.
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