net.http ListenAndServe. netstat only list ipv6 port

[che...@garena.com]

Ubuntu 10.04

Go 1.1.1

In the code:

    Log.Fatal(http.ListenAndServe(":3000", nil)

Then 'netstat -a | grep LISTEN', we can only see

    tcp6 0 0 [::]:3000     [::]:* LISTEN

There's no 'tcp 0 0 *:3000 *:* LISTEN', but actually the server is able to be visited with IPv4 addresses. 

Even when I changed the code to

   Log.Fatal(http.ListenAndServe("0.0.0.0:3000", nil)

The issue still keeps the same.

Anyone know the reason and solution? Thanks a lot.

[Svip]

If the server is visitable via IPv4, why is this a problem? Or are
you looking for an answer?

If so, I think it has something to do with IPv6 support in Linux
systems, which prefers IPv6 and then later reverts to IPv4 if IPv6 is
not available. I could be wrong, but I assume that's what's
happening.

[minux]

on linux, by default, net.ipv6.bindv6only is 0, so ipv4 packets could also be received from

ipv6 sockets with ipv4-mapped ipv6 address. thus you only need to listen on tcp6 socket

and we can support both ipv4 and ipv6.

if you want explicitly only listen on ipv4 port, you will have to use net.Listen("tcp4", "0.0.0.0:3000")

and then pass the listener to http.Serve.

[che...@garena.com]

Thanks for both of your answers.

Yes, there's no problem regards to usage. The only problem is that it confuses some administration tools and persons. Since normally no one are using IPv6 addresses, so they only check the ipv4 ports and cannot find the proper result.

The question is that other programs (such as sshd) listen both at IPv4 and IPv6 ports and I thought that was a normal behaviour compared with net/http. The net/http's behavior is not correct in my opinion, especially when I explicitly wrote "ListenAndServ("0.0.0.0:80", nil)" .   

[Dave Cheney]

ListenAndServer is a convenience, if you need more control then use
net.ListenTCP("tcp4", ...) then pass that listener to net.Serve.

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