From 70d0931fcadd5f89b3c82440e6dc4bbdaf71d9e1 Mon Sep 17 00:00:00 2001
From: Oliver Sanders <oliver.sanders@metoffice.gov.uk>
Date: Fri, 9 Jul 2021 10:03:50 +0100
Subject: [PATCH] portability: path mac os dns issues

---
 .github/workflows/test_fast.yml       |  3 ---
 .github/workflows/test_functional.yml |  3 ---
 cylc/flow/hostuserutil.py             | 19 ++++++++++++++++++-
 etc/conf/macos-patch                  | 13 -------------
 4 files changed, 18 insertions(+), 20 deletions(-)
 delete mode 100644 etc/conf/macos-patch

diff --git a/.github/workflows/test_fast.yml b/.github/workflows/test_fast.yml
index bc3f40c9076..6545c8f05fb 100644
--- a/.github/workflows/test_fast.yml
+++ b/.github/workflows/test_fast.yml
@@ -44,9 +44,6 @@ jobs:
       - name: Brew Install
         if: startsWith(matrix.os, 'macos')
         run: |
-          # apply DNS patch
-          patch cylc/flow/hostuserutil.py < etc/conf/macos-patch
-
           brew update
           brew install shellcheck sqlite3 bash coreutils
 
diff --git a/.github/workflows/test_functional.yml b/.github/workflows/test_functional.yml
index f10f93b7b45..47d15a6b1d6 100644
--- a/.github/workflows/test_functional.yml
+++ b/.github/workflows/test_functional.yml
@@ -92,9 +92,6 @@ jobs:
       - name: Brew Install
         if: startsWith(matrix.os, 'macos')
         run: |
-          # apply DNS patch
-          patch cylc/flow/hostuserutil.py < etc/conf/macos-patch
-
           # install system deps
           brew update
           brew install bash coreutils gnu-sed
diff --git a/cylc/flow/hostuserutil.py b/cylc/flow/hostuserutil.py
index 3a6099ae82d..9ae71a8fd8a 100644
--- a/cylc/flow/hostuserutil.py
+++ b/cylc/flow/hostuserutil.py
@@ -44,15 +44,19 @@
 
 """
 
+from contextlib import suppress
 import os
 import pwd
 import socket
-from contextlib import suppress
+import sys
 from time import time
 
 from cylc.flow.cfgspec.glbl_cfg import glbl_cfg
 
 
+IS_MAC_OS = 'darwin' in sys.platform.lower()
+
+
 class HostUtil:
     """host and user ID utility."""
 
@@ -114,6 +118,19 @@ def _get_host_info(self, target=None):
         if target not in self._host_exs:
             if target is None:
                 target = socket.getfqdn()
+            if (
+                IS_MAC_OS
+                and target == (
+                    '1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.'
+                    '0.0.0.0.0.0.ip6.arpa'
+                )
+            ):
+                # Python's socket bindings don't play nicely with mac os
+                # so by default we get the above ip6.arpa adresss from
+                # socket.getfqdn, note this does *not* match `hostname -f`.
+                # https://github.com/cylc/cylc-flow/issues/2689
+                # https://github.com/cylc/cylc-flow/issues/3595
+                target = socket.gethostname()
             try:
                 self._host_exs[target] = socket.gethostbyname_ex(target)
             except IOError as exc:
diff --git a/etc/conf/macos-patch b/etc/conf/macos-patch
deleted file mode 100644
index 51ef158d55e..00000000000
--- a/etc/conf/macos-patch
+++ /dev/null
@@ -1,13 +0,0 @@
-diff --git a/cylc/flow/hostuserutil.py b/cylc/flow/hostuserutil.py
-index 21e51735e..17917b8fc 100644
---- a/cylc/flow/hostuserutil.py
-+++ b/cylc/flow/hostuserutil.py
-@@ -113,7 +113,7 @@ class HostUtil:
-         """Return the extended info of the current host."""
-         if target not in self._host_exs:
-             if target is None:
--                target = socket.getfqdn()
-+                target = socket.gethostname()
-             try:
-                 self._host_exs[target] = socket.gethostbyname_ex(target)
-             except IOError as exc: