Is<property>() methods disagree with net.IP for 4in6 addresses #183

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1. moreati commented on Jun 2, 2021

   

   moreati

   on Jun 2, 2021

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   Python 3.9.5 ipaddress (for the properties it has in common) agrees with netaddr

   Code

   import ipaddress
   import platform
   
   print(f"Python {platform.python_version()}")
   
   addresses = [
       "::ffff:e000:0",
       "::ffff:e00f:0",
       "::ffff:7f00:1",
   ]
   
   attributes = [
       "is_multicast",
       "is_loopback",
   ]
   
   for s in addresses:
       ip = ipaddress.ip_address(s)
       print(f"\t\t{ip}")
       for attr in attributes:
           result = getattr(ip, attr)
           print(f"{attr}\t{result}")

   ± python3.9 issue183.py 
   Python 3.9.5
   		::ffff:e000:0
   is_multicast	False
   is_loopback	False
   		::ffff:e00f:0
   is_multicast	False
   is_loopback	False
   		::ffff:7f00:1
   is_multicast	False
   is_loopback	False
   
2. moreati commented on Jun 10, 2021

   

   moreati

   on Jun 10, 2021

   ContributorAuthor

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   More background research

   Platform	Callable/property	Result	Discussions, bugs/PRs
   Python 3.9	ipaddress.ip_address.is_loopback	false
   Rust 1.52.1	std::net::IpAddr: is_loopback()	false	rust-lang/rust#69772, rust-lang/rust#85655
   .NET 4,7,2	System.Net.IPAddress.IsLoopback()	false
   .NET Rosalyn 3.8	System.Net..IPAddress.IsLoopback()	false
   .NET 5.0	System.Net..IPAddress.IsLoopback()	true	dotnet/runtime#28740

   Last updated: 2021-06-10

   TODO

   • Java (possible difference between OpenJDK and Oracle JDK)
   • Try cross comparison with https://github.com/KodrAus/ipcheck

   👍React with 👍1Reacted by John Behm

   ❤️React with ❤️1Reacted by Brad Fitzpatrick
3. bradfitz commented on Jun 10, 2021

   

   bradfitz

   on Jun 10, 2021

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   @moreati, thanks for the info!

   I think we want to keep all the IsFoo methods not unwrapping. The 4-in-6 handling being too aggressive in Go std's net package was one of the problems we wanted to fix with netaddr. (see the third bullet under Motivation at https://pkg.go.dev/inet.af/netaddr)

   But, yeah, we can document it.

   @danderson, @mdlayher, @josharian, sound good?

   👍React with 👍1Reacted by Josh Bleecher Snyder
4. mdlayher commented on Jun 11, 2021

   

   mdlayher

   on Jun 11, 2021

   Member

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   Agreed. +1 to documenting but I still think 4-in-6 mapping is too niche for the prominence it has in the current stdlib.
5. jxsl13 commented on Jun 13, 2021

   

   jxsl13

   on Jun 13, 2021

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   Might be useful for this issue: IsPrivate from the latest Go changelog: https://tip.golang.org/doc/go1.17
   scroll down to the net package changelog.