extended_bin: Support 'inet_dist_use_interface' in vm.args

[weiss]

Support specifying the kernel option inet_dist_use_interface in the vm.args file. If ERL_DIST_PORT is set while using Erlang/OTP 23 or newer, make sure to hand over the inet_dist_use_interface address to erl_call's -address option.

My own use case is binding the VM to 127.0.0.1 (if not actually running a cluster) and still being able to use ERL_DIST_PORT.

[tsloughter]

Thanks. But weird that the command line kernel option is a tuple and not just an ip string. I don't like having to parse that in shell script :( but I guess no way around it.

[weiss]

I don't like having to parse that in shell script :(

Yes, ugliness :unamused:

I guess no way around it.

I see no way, except maybe giving up on the idea of specifying the address to use by the main node and by erl_call in a single place. I.e., just add some RPC_ADDRESS (or whetever) variable for erl_call to use, and let the user specify both inet_dist_user_interface and that new variable. (Would be good enough for me personally, and would allow for keeping the inet_dist_user_interface setting in sys.config, where it looks less ugly to me. But would be ugly in a different way.)

[weiss]

I see no way

Well I guess another way would be using Erlang instead, e.g. something along the following lines. But it's probably preferable not to spin up the VM for that job.

# Convert {127,0,0,1} to 127.0.0.1
addr_tuple_to_str() {
    addr="$1"
    code="catch io:format(\"~s\", [inet:ntoa($addr)]), halt()."
    result="$("$BINDIR/erl" -noinput -boot no_dot_erlang -eval "$code")"

    if [ -n "$result" ]; then
        printf '%s' "$result"
    else
        echo "Cannot parse IP address tuple: '$addr'" >&2
    fi
}

[tsloughter]

Oh, duh, its using a tuple because its using -kernel ... so it is not an exposed erl arg like my original thinking.

[weiss]

Oh, duh, its using a tuple because its using -kernel ... so it is not an exposed erl arg like my original thinking.

Yes. That's the (only) way of telling the VM to dist-listen on localhost, I think? Which doesn't seem like an obscure use case to me? (I just want to use the extended start script for controlling my daemon, rather than running an actual cluster.)

[tsloughter]

Not obscure at all. Something we should have supported for using the shell, rpc, etc stuff a long long time ago :).

I think this is good, just being cautious since tiny changes in this particular code has broken certain users before. It is a mess.

[weiss]

just being cautious since tiny changes in this particular code has broken certain users before. It is a mess.

Totally makes sense, I'm very happy with such detailed review! :+1: