Replace ipv4 v6 sc 37307

[LeiGlobus]

One of the steps in making sure ipv6 is supported is too remove the usage of the ipv4 loopback address 127.0.0.1, replacing it with ::1 to confirm that things work with ipv6. (127.0.0.1 has already been working since beginning of history, so doesn't need to be kept in most circumstances.

We also decided that we should not go the extra mile to ensure that ipv6 is compatible with HTEX, as that's being deprecated. All the 127.0.0.1 should be only in the htex module.

[sc-37307]

[khk-globus]

If localhost is allowed, then any name should be allowed. This has historically required a valid IP address, which is coming from either the default (signature argument) or the caller of this __init__ method, so I don't think this needs changing here.

Testing will confirm or rebuke the need.

[LeiGlobus]

I'm not informed enough regarding how this address is used, other than the general 'local' communication need. However, I did test (on Ubuntu) a few different parameters, after removing this check.

1. localhost works
2. an arbitrary address obviously doesn't work: zmq.error.ZMQError: Cannot assign requested address (addr='tcp://cnn.com:54419')

so, to be safe and modify the current behavior as little as possible, I only make an exception for 'localhost' but do ip address validation otherwise. If I remove the check altogether, that would need more testing of non-localhost DNS names, which I don't know how many lower layers can handle.

So, still leaning toward only making an exception for localhost to get rid of the dependence on 127.0.0.1. Note that '::1' does not work when directly passed to zmq, even if it's a valid ipv6 address.

[khk-globus]

cnn.com won't work because that's, well, not this host (which I think your 2nd point is saying?). But a friendly reminder that the technical specification of ZMQ's socket .bind() method says:

When assigning a local address to a socket using zmq_bind() with the tcp transport, the endpoint shall be interpreted as an interface followed by a colon and the TCP port number to use.

An interface may be specified by either of the following:

• The wild-card *, meaning all available interfaces.

• The primary IPv4 or IPv6 address assigned to the interface, in its numeric representation.

• The non-portable interface name as defined by the operating system.

Meaning, it would, absent our ministrations, be completely valid to specify an interface -- indeed, that's the more fundamental detail from ZMQ's perspective! We could handle localhost singularly, but I think we can be more general about this solve.

[khk-globus]

But ... I think I've changed from my initial comment. Meh. This is a smaller detail than the need to make sure ipv6 is well handled. Your call.

[LeiGlobus]

I changed the validation to allow both hostname and ipv4/ipv6 addresses. Added the utility method in class and in test, and if it's used elsewhere, we can move it to a more general location.