'RE: suggest improvement for java doc for getting address of local host'

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List:       openjdk-net-dev
Subject:    RE: suggest improvement for java doc for getting address of local host
From:       <mark.yagnatinsky () barclays ! com>
Date:       2022-08-05 15:51:20
Message-ID: MN2PR12MB36166C378168949B3CF39107F99E9 () MN2PR12MB3616 ! namprd12 ! prod ! outlook ! com
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Thanks for the re-direct.  Following up on what Alan Bateman said, it seems that Java \
prefers to return an IPv4 address if it can. However, if there are multiple IPv4 \
addresses, then there are no guarantees about which one is returned, either in theory \
or in practice, right? Java is at the whims of whatever order the OS returned things \
in, which could change essentially at random, correct?  Or not quite?

-----Original Message-----
From: David Holmes <david.holmes@oracle.com> 
Sent: Friday, August 5, 2022 12:20 AM
To: Yagnatinsky, Mark : Markets Pre Trade <mark.yagnatinsky@barclays.com>; \
                net-dev@openjdk.org
Subject: Re: suggest improvement for java doc for getting address of local host

On 5/08/2022 8:24 am, mark.yagnatinsky@barclays.com wrote:
> I suspect that this is the wrong list; please redirect me if so.

Redirected to net-dev

Cheers,
David

> The docs for this method:
> 
> https://clicktime.symantec.com/15siKxwAAWWL3eZqGu9Fo?h=L5Cz6B7AzyisGrH
> 4l0L4X529kjHrv3YxbQf5lwngdkA=&u=https://docs.oracle.com/en/java/javase
> /18/docs/api/java.base/java/net/InetAddress.html%23getLocalHost%28%29
> <https://clicktime.symantec.com/15siKxwAAWWL3eZqGu9Fo?h=L5Cz6B7AzyisGr
> H4l0L4X529kjHrv3YxbQf5lwngdkA=&u=https://docs.oracle.com/en/java/javas
> e/18/docs/api/java.base/java/net/InetAddress.html%23getLocalHost%28%29
> > 
> 
> say that it “Returns the address of the local host. This is achieved 
> by retrieving the name of the host from the system, then resolving 
> that name into an InetAddress.”
> 
> This is true enough in simple cases, but horribly misleading in 
> non-trivial cases.
> 
> As far as I can tell it can’t return “the address” because the local 
> host may have multiple addresses.
> 
> Instead it returns “an address” of the local host.  My laptop right 
> now has 3 addresses: IPv6 loopback, IPv4 from home WiFi, and IPv4 from 
> company network via VPN.
> 
> As far as I can tell (please correct me if I’m wrong!!) if there are 
> multiple addresses, the current implementation makes no effort to pick 
> a more “useful” one.
> 
> Instead, it takes whatever addresses it gets from the OS and returns 
> the first one.
> 
> Thus, in theory, and even in practice, it’s perfectly possible to get 
> into a situation where all of the following hold:
> 
> “It worked fine yesterday!”
> 
> “I didn’t change anything, honest!”
> 
> And yet, “nothing works today” (because, unbeknownst to mere mortals 
> like me, the OS happened to return things in a different order today.)
> 
> Again, please correct me if I’m wrong and there actually are some 
> guarantees, either by virtue of the spec, or by virtue of “it just so 
> happens that in practice you will tend to get XYZ”.
> 
> But if I’m right, then I suggest the following tweak to the documentation:
> 
> Returns the address of the local host.  If the local host has multiple 
> addresses, an arbitrary one will be chosen and returned.
> 
> This is achieved by retrieving the name of the host from the system, 
> then resolving that name into a list of one or more `InetAddress`es 
> and then choosing an arbitrary address from that list.
> 
> (irrelevant but: really wish Javadoc had a lightweight notation for 
> code like markdown’s `code(blocks)`)
> 
> Just my two cents.  Again, please redirect me if this is the wrong 
> list, and correct me if I’m wrong re: no guarantees about which 
> address is returned.
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This message is for information purposes only. It is not a recommendation, advice, \
offer or solicitation to buy or sell a product or service, nor an official \
confirmation of any transaction. It is directed at persons who are professionals and \
is intended for the recipient(s) only. It is not directed at retail customers. This \
message is subject to the terms at: \
https://www.cib.barclays/disclosures/web-and-email-disclaimer.html. 

For important disclosures, please see: \
https://www.cib.barclays/disclosures/sales-and-trading-disclaimer.html regarding \
marketing commentary from Barclays Sales and/or Trading desks, who are active market \
participants; https://www.cib.barclays/disclosures/barclays-global-markets-disclosures.html \
regarding our standard terms for Barclays Corporate and Investment Bank where we \
trade with you in principal-to-principal wholesale markets transactions; and in \
respect to Barclays Research, including disclosures relating to specific issuers, \
see: http://publicresearch.barclays.com. \
__________________________________________________________________________________  \
If you are incorporated or operating in Australia, read these important disclosures: \
https://www.cib.barclays/disclosures/important-disclosures-asia-pacific.html. \
__________________________________________________________________________________ \
For more details about how we use personal information, see our privacy notice: \
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