Feature Request: Force IPv4 or IPv6 flag

[andersmarkendahl]

What is missing?

For testing purposes when using the kahttp client it would be helpful with a flag that can force the client to connect over specific IPfamily only. This so that a host that should be reachable over both IPfamilies can be tested properly.

Suggestion

Similar flags exist in curl and wget

man wget
[...]
       -4
       --inet4-only
       -6
       --inet6-only
           Force connecting to IPv4 or IPv6 addresses.  With --inet4-only or
           -4, Wget will only connect to IPv4 hosts, ignoring AAAA records in
           DNS, and refusing to connect to IPv6 addresses specified in URLs.
           Conversely, with --inet6-only or -6, Wget will only connect to IPv6
           hosts and ignore A records and IPv4 addresses....

[uablrek]

Work-around

Set the -srccidr parameter to the address for the outgoing interface using the desired family;

$ ifconfig eth1
eth1      Link encap:Ethernet  HWaddr 00:00:00:01:01:03  
          inet addr:192.168.1.3  Bcast:0.0.0.0  Mask:255.255.255.0
          inet6 addr: fe80::200:ff:fe01:103/64 Scope:Link
          inet6 addr: 1000::1:c0a8:103/120 Scope:Global
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2257 errors:0 dropped:0 overruns:0 frame:0
          TX packets:2268 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:181094 (176.8 KiB)  TX bytes:202952 (198.1 KiB)
$ kahttp kahttp -address http://vm-001/cgi-bin/info -monitor -timeout 5s -srccidr 192.168.1.3/32
... (ipv4 used)
$ kahttp kahttp -address http://vm-001/cgi-bin/info -monitor -timeout 5s -srccidr 1000::1:c0a8:103/128
... (ipv6 used)

Note that masks must be /32 and /128.

[uablrek]

It is not so easy (anymore) to enforce ipv6/ipv4 in go. They are using "Happy Eyeballs" which means; try ipv6 first, Fast Fallback to ipv4 if it doesn't work. See; https://godoc.org/net#Dialer

I am sure it can be done in some way but if the work-around above is enough I will let this issue rest for some time.

[andersmarkendahl]

An update on this issue. We are actively using the proposed WA (srccidr flag) since a few weeks back and it seems to work fine for our purposes.
Example:

is_v6() {
  test "${1#*":"}" != "$1" && return 0
  return 1
}
get_src() {
  ip=$1
  if $(is_v6 $ip);then
    src=$(ip -6 route get $ip | grep -Eo 'src \S+' | cut -d' ' -f2)
    src="$src/128"
  else
    src=$(ip route get $ip | grep -Eo 'src \S+' | cut -d' ' -f2)
    src="$src/32"
  fi
  echo $src
}
kahttp ... -srccidr $(get_src 1000::1)
kahttp ... -srccidr $(get_src 10.0.0.1)

If this is too tricky to improve, then you can close this issue.
If you plan to improve later you can keep open.

[uablrek]

I document the -srccidr and close this issue.