hydra-notify: enable IPv6 support

[fogti]

HTTP::Server::PSGI uses the ipv6 flag to decide between
IO::Socket::INET and IO::Socket::IP
(https://metacpan.org/dist/Plack/source/lib/HTTP/Server/PSGI.pm#L80-84)
and (from IO/Socket/IP.pm):

CIO::Socket::IP - Family-neutral IP socket supporting both IPv4 and IPv6

so setting the ipv6 flag makes it support both IPv4 and IPv6.

Fixes #1394

[benaryorg]

I just compiled a version of hydra with a patch setting the flag, but it seems like it doesn't quite work that way:

Starting the Prometheus exporter, listening on http://127.0.0.1:9199/metrics.
failed to listen to port 9199: Invalid argument at /nix/store/vs5db18kx919dgbnz1akfq4d5wf28m5f-hydra-perl-deps/lib/perl5/site_perl/5.38.2/HTTP/Server/PSGI.pm line 103.

[fogti]

I tested using:

use strict;
use warnings;
use HTTP::Server::PSGI;

my $server = HTTP::Server::PSGI->new(
    host => '::1', 
   # host => '127.0.0.1', # alternatively
    port => 8080,
    timeout => 1,
    ipv6 => 1,
);

my $app = sub {
  return [
    '200',
    [ 'Content-Type' => 'text/html' ],
    [ 42 ],
  ];
};

$server->run($app);

for me, both IPv4 and IPv6 appear to work, I'm using perl 5.38.2 and Plack 1.5.100.
so idk what's wrong here.

switching ipv6 => 1 on and off results in some differences, IO::Socket::IP parses /etc/protocols and /etc/nsswitch.conf and does appear to request some info via NetLink: sendto(3, [{nlmsg_len=20, nlmsg_type=0x16 /* NLMSG_??? */, nlmsg_flags=NLM_F_REQUEST|0x300, nlmsg_seq=1721465735, nlmsg_pid=0}, "\x00\x00\x00\x00"], 20, 0, {sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, 12) = 20

[fogti]

It might be useful to invoke the hydra-notify service in strace, to look where it goes wrong (I have no Hydra running here, and setting one up just to test this doesn't seem worth it)

[benaryorg]

This is what happens after reading /etc/protocols:

[pid 1465031] 14:58:57.292905 socket(AF_NETLINK, SOCK_RAW|SOCK_CLOEXEC, NETLINK_ROUTE) = 4
[pid 1465031] 14:58:57.292940 bind(4, {sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, 12) = 0
[pid 1465031] 14:58:57.292970 getsockname(4, {sa_family=AF_NETLINK, nl_pid=1465031, nl_groups=00000000}, [12]) = 0
[pid 1465031] 14:58:57.293005 sendto(4, [{nlmsg_len=20, nlmsg_type=RTM_GETADDR, nlmsg_flags=NLM_F_REQUEST|NLM_F_DUMP, nlmsg_seq=1721487537, nlmsg_pid=0}, {ifa_family=AF_UNSPEC, ...}], 20, 0, {sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, 12) = 20
[pid 1465031] 14:58:57.293118 recvmsg(4, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base=[{nlmsg_len=76, nlmsg_type=RTM_NEWADDR, nlmsg_flags=NLM_F_MULTI, nlmsg_seq=1721487537, nlmsg_pid=1465031}, {ifa_family=AF_INET, ifa_prefixlen=8, ifa_flags=IFA_F_PERMANENT, ifa_scope=RT_SCOPE_HOST, ifa_index=if_nametoindex("lo")}, [[{nla_len=8, nla_type=IFA_ADDRESS}, inet_addr("127.0.0.1")], [{nla_len=8, nla_type=IFA_LOCAL}, inet_addr("127.0.0.1")], [{nla_len=7, nla_type=IFA_LABEL}, "lo"], [{nla_len=8, nla_type=IFA_FLAGS}, IFA_F_PERMANENT], [{nla_len=20, nla_type=IFA_CACHEINFO}, {ifa_prefered=4294967295, ifa_valid=4294967295, cstamp=1553, tstamp=1553}]]], iov_len=4096}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 76
[pid 1465031] 14:58:57.293200 recvmsg(4, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base=[[{nlmsg_len=80, nlmsg_type=RTM_NEWADDR, nlmsg_flags=NLM_F_MULTI, nlmsg_seq=1721487537, nlmsg_pid=1465031}, {ifa_family=AF_INET6, ifa_prefixlen=128, ifa_flags=IFA_F_PERMANENT, ifa_scope=RT_SCOPE_HOST, ifa_index=if_nametoindex("lo")}, [[{nla_len=20, nla_type=IFA_ADDRESS}, inet_pton(AF_INET6, "::1")], [{nla_len=20, nla_type=IFA_CACHEINFO}, {ifa_prefered=4294967295, ifa_valid=4294967295, cstamp=1553, tstamp=1553}], [{nla_len=8, nla_type=IFA_FLAGS}, IFA_F_PERMANENT], [{nla_len=5, nla_type=IFA_PROTO}, "\x01"]]], [{nlmsg_len=72, nlmsg_type=RTM_NEWADDR, nlmsg_flags=NLM_F_MULTI, nlmsg_seq=1721487537, nlmsg_pid=1465031}, {ifa_family=AF_INET6, ifa_prefixlen=64, ifa_flags=0, ifa_scope=RT_SCOPE_UNIVERSE, ifa_index=if_nametoindex("eth0")}, [[{nla_len=20, nla_type=IFA_ADDRESS}, inet_pton(AF_INET6, "2001:41d0:303:192:216:3eff:fe29:dd82")], [{nla_len=20, nla_type=IFA_CACHEINFO}, {ifa_prefered=1766, ifa_valid=3566, cstamp=1984, tstamp=3233695}], [{nla_len=8, nla_type=IFA_FLAGS}, IFA_F_MANAGETEMPADDR|IFA_F_NOPREFIXROUTE]]], [{nlmsg_len=80, nlmsg_type=RTM_NEWADDR, nlmsg_flags=NLM_F_MULTI, nlmsg_seq=1721487537, nlmsg_pid=1465031}, {ifa_family=AF_INET6, ifa_prefixlen=64, ifa_flags=IFA_F_PERMANENT, ifa_scope=RT_SCOPE_LINK, ifa_index=if_nametoindex("eth0")}, [[{nla_len=20, nla_type=IFA_ADDRESS}, inet_pton(AF_INET6, "fe80::216:3eff:fe29:dd82")], [{nla_len=20, nla_type=IFA_CACHEINFO}, {ifa_prefered=4294967295, ifa_valid=4294967295, cstamp=1553, tstamp=1553}], [{nla_len=8, nla_type=IFA_FLAGS}, IFA_F_PERMANENT], [{nla_len=5, nla_type=IFA_PROTO}, "\x03"]]]], iov_len=4096}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 232
[pid 1465031] 14:58:57.293356 recvmsg(4, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base=[{nlmsg_len=20, nlmsg_type=NLMSG_DONE, nlmsg_flags=NLM_F_MULTI, nlmsg_seq=1721487537, nlmsg_pid=1465031}, 0], iov_len=4096}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 20
[pid 1465031] 14:58:57.293446 socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 5
[pid 1465031] 14:58:57.293514 connect(5, {sa_family=AF_UNIX, sun_path="/var/run/nscd/socket"}, 110) = 0
[pid 1465031] 14:58:57.293574 sendto(5, "\2\0\0\0\r\0\0\0\6\0\0\0hosts\0", 18, MSG_NOSIGNAL, NULL, 0) = 18
[pid 1465031] 14:58:57.293669 poll([{fd=5, events=POLLIN|POLLERR|POLLHUP}], 1, 5000) = 1 ([{fd=5, revents=POLLIN|POLLHUP}])
[pid 1465031] 14:58:57.293729 recvmsg(5, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="", iov_len=6}, {iov_base="", iov_len=8}], msg_iovlen=2, msg_controllen=0, msg_flags=MSG_CMSG_CLOEXEC}, MSG_CMSG_CLOEXEC) = 0
[pid 1465031] 14:58:57.293765 close(5)  = 0
[pid 1465031] 14:58:57.293795 close(4)  = 0
[pid 1465031] 14:58:57.293890 write(2, "failed to listen to port 9199: Invalid argument at /nix/store/vs5db18kx919dgbnz1akfq4d5wf28m5f-hydra-perl-deps/lib/perl5/site_perl/5.38.2/HTTP/Server/PSGI.pm line 103.\n", 168) = 168

Don't ask me what that nscd request is about, considering it mentions hosts I would assume that it's the equivalent of getent hosts but then again, shouldn't there be an address listed with that.…

So with the "Invalid argument" not actually being a syscall returning EINVAL I am confused.
I also wonder why my route table is read, which seems wildly inappropriate for binding to a socket (which should just be binding and then maybe responding no an error, but I see no bind here other than the AF_NETLINK one which.… what?).

Exactly the same thing happens when binding to 0.0.0.0.

[Mic92]

For ipv6, glibc needs to look at interfaces (netlink) to figure out things like interface identifier. That's why you see that.