DNS.resolve() should not be sorted in HostEntry::removeDuplicates()

[lingyphone]

It is caused by commit 8030564#diff-b38b1a4ab2c3fa8c175cff4b6f7c55e7ce4cd720f423e0a2b91d88b8f472f3cc

And it ruins the DNS round-robin or DNS load-balance

[github-actions]

This issue is stale because it has been open for 365 days with no activity.

[github-actions]

This issue was closed because it has been inactive for 60 days since being marked as stale.

[matejk]

@lingyphone: is this issue still relevant?

[aleks-f]

@matejk yes, because of this. we should find another way to get rid of duplicates (and hope nobody found a reason to rely on it being ordered by now)

[rtoelhoej]

@aleks-f, @matejk
The sorting in removeDuplicates breaks DNS round-robin and DNS load-balance for our project as well.

We did tests and on Linux multiple IP's are returned with same value on Windows it doesn't return any duplicates, so it looks like removeDuplicates is a Unix/Linux fix.

A fix would be to change the removeDuplicates to remove without sorting, I think sorting was used because it's the easiest way to remove duplicates. (std::unique only checks next item in list, it doesn't check the whole list, so it requires the vector to be sorted.

Fix in Net\include\Poco\Net\HostEntry.h by updating removeDuplicates to use std::set/std::remove_if:

template <typename C>
void removeDuplicates(C& list)
{
	std::set<T> values;
	list.erase(std::remove_if(list.begin(), list.end(), [&](const T& value) { return !values.insert(value).second; }), list.end());
}