Implement total Show functions for SockAddr

[karknu]

The previous implementation of show SockAddr used unsafePerformIO and getNameInfo. getNameInfo depends on show SockAddr in case of a failure which causes exceptions within exceptions within exceptions...

This is not just a theoretical problem. It is possible to get getnameinfo to fail on OSX using a multicast address with a reserved scope. This is because OSX attempts to map the second 16 bit word of an IPv6 address to a device name.
Example from C's getnameinfo:

0xff01:0x000a:: -> ff01::%bridge0
0xff01:0x0010:: -> ff01::%utun0
0xff01:0x0011:: -> getnameinfo: Device not configured

The showHostAddress and showHostAddress6 are based on showIPv4 and
showIPv6 in the iproute package.

[kazu-yamamoto]

I agree to throw away getNameInfo for this purpose.

1. Would you start with a test case of multicast address which fails on macOS?
2. Then, add your fix code. Unfortunately, @vdukhovni improved the code of iproute recently. So, please check it out on github.

You can use push -f for this PR as you like.

[karknu]

1. Would you start with a test case of multicast address which fails on macOS?

@kazu-yamamoto I've added test cases for getNameInfo and show SockAddr. The test case works for multicast IPv6 address with reserved scope will fail on OSX with

    works for multicast IPv6 address with reserved scope FAILED [1]

Failures:

  tests/Network/SocketSpec.hs:267:9: 
  1) Network.Socket, show SocketAddr, works for multicast IPv6 address with reserved scope
       uncaught exception: IOException of type NoSuchThing
spec: encountered an exception while trying to report an exception.
One possible reason for this is that we failed while trying to encode an error message. Check that your locale is configured properly.
Test suite spec: FAIL

without my patch.

2. Then, add your fix code. Unfortunately, @vdukhovni improved the code of `iproute` recently. So, please check it out on github.

From what I can see @vdukhovni's changes did not affect the show functions for IPv4 and IPv6 addresses.

[vdukhovni]

From what I can see @vdukhovni's changes did not affect the show functions for IPv4 and IPv6 addresses.

That's correct, I only changed the various getters and setters for the binary forms.
My next pull request implements an optimized ByteString Builder for IPv4 and IPv6, but that too does not affect the String Show instances. The bestgap function from that code can speed up the String conversion for IPv6 by about a factor of 1.5, but it is not clear this is worth making a change for.

https://github.com/kazu-yamamoto/iproute/pull/46/files#diff-f237be36f8b3d58098397869af5e00cdR229-R271

[kazu-yamamoto]

@karknu @vdukhovni Thank you for clarification. This PR now looks great.

Rebased and merged. Thank you for your contribution!

It would be nice if we implemented getAddrInfo and getNameInfo purely in Haskell someday!