3 ms·

Ideally, a server binding to "localhost" should create a listening socket for each of its IP addresses (e.g. 127.0.0.1 and ::1), and a client connecting to "loc

by p1mrx 9y ago

Ideally, a server binding to "localhost" should create a listening socket for each of its IP addresses (e.g. 127.0.0.1 and ::1), and a client connecting to "localhost" should try each IP address in order, until one succeeds. But a lot of standard libraries (including parts of Java and Go) get this wrong, and pick exactly one IP address arbitrarily. When you combine a buggy client with a buggy server, and their preferences for IPv4/IPv6 disagree, then all hell breaks loose. These are the open bugs I'm aware of: https://bugs.openjdk.java.net/browse/JDK-8170568 https://bugs.openjdk.java.net/browse/JDK-8170568 https://github.com/golang/go/issues/9334 https://github.com/golang/go/issues/9334

fulafel 9y ago
Or use a single socket for both protocols (set the IPV6_V6ONLY socket option to false).
- p1mrx 9y ago
  That works when binding to :: (all interfaces), but it's irrelevant when binding to "localhost", because you can only bind one address per socket.
  - fulafel 9y ago
    Yes, I thought it worked for ::1 too but you're right.
user5994461 9y ago
An interface on linux has only one ip address. The "localhost" interface will either designate the ipv4 127.0.0.1 interface or the ipv6 ::1 interface. That's the realm of undefined behavior and system specifics. This whole IETF draft looks like a mess. They should reserve the names localhost4 and localhost6.
- pilif 9y ago
  > An interface on linux has only one ip address. absolutely not true. Neither for IPv4 nor IPv6, where it's even the default to have a multitude of addresses on an interface. > The "localhost" interface will either designate the ipv4 127.0.0.1 interface or the ipv6 ::1 interface. That's the realm of undefined behavior and system specifics. no it won't. My loopback (lo) interface has both 127.0.0.1 and ::1 as its addresses.
- justinclift 9y ago
  > An interface on linux has only one ip address. Just to point out, while the behaviour of any one OS is a useful data point for the discussion, it's not super useful to say "because OS 'foo' does things in a certain way, a well used programming language should limit it's design to that OS's way of doing things." :) Hmmm, I guess I'm trying to say that (at least) Go should be fairly OS agnostic about this.
- __david__ 9y ago
  > An interface on linux has only one ip address. Eh? $ ifconfig lo lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536 inet 127.0.0.1 netmask 255.0.0.0 inet6 ::1 prefixlen 128 scopeid 0x10<host> loop txqueuelen 1000 (Local Loopback)

by p1mrx 9y ago

fulafel 9y ago

Or use a single socket for both protocols (set the IPV6_V6ONLY socket option to false).

p1mrx 9y ago
That works when binding to :: (all interfaces), but it's irrelevant when binding to "localhost", because you can only bind one address per socket.
- fulafel 9y ago
  Yes, I thought it worked for ::1 too but you're right.

user5994461 9y ago

An interface on linux has only one ip address. The "localhost" interface will either designate the ipv4 127.0.0.1 interface or the ipv6 ::1 interface. That's the realm of undefined behavior and system specifics. This whole IETF draft looks like a mess. They should reserve the names localhost4 and localhost6.

pilif 9y ago
> An interface on linux has only one ip address. absolutely not true. Neither for IPv4 nor IPv6, where it's even the default to have a multitude of addresses on an interface. > The "localhost" interface will either designate the ipv4 127.0.0.1 interface or the ipv6 ::1 interface. That's the realm of undefined behavior and system specifics. no it won't. My loopback (lo) interface has both 127.0.0.1 and ::1 as its addresses.
justinclift 9y ago
> An interface on linux has only one ip address. Just to point out, while the behaviour of any one OS is a useful data point for the discussion, it's not super useful to say "because OS 'foo' does things in a certain way, a well used programming language should limit it's design to that OS's way of doing things." :) Hmmm, I guess I'm trying to say that (at least) Go should be fairly OS agnostic about this.
__david__ 9y ago
> An interface on linux has only one ip address. Eh? $ ifconfig lo lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536 inet 127.0.0.1 netmask 255.0.0.0 inet6 ::1 prefixlen 128 scopeid 0x10<host> loop txqueuelen 1000 (Local Loopback)