From 7ddc90edf2d74e92256f219a76bfcc073d9b4d5c Mon Sep 17 00:00:00 2001
From: Oliver Sanders <oliver.sanders@metoffice.gov.uk>
Date: Fri, 31 Jul 2020 13:28:40 +0100
Subject: [PATCH] scan: use non-blocking io to read the contact file

---
 cylc/flow/network/scan_nt.py          |  4 +--
 cylc/flow/suite_files.py              | 43 +++++++++++++++++++------
 setup.py                              |  1 +
 tests/integration/test_suite_files.py | 46 +++++++++++++++++++++++++++
 4 files changed, 82 insertions(+), 12 deletions(-)
 create mode 100644 tests/integration/test_suite_files.py

diff --git a/cylc/flow/network/scan_nt.py b/cylc/flow/network/scan_nt.py
index a47440a83a0..6d89a99aaa3 100644
--- a/cylc/flow/network/scan_nt.py
+++ b/cylc/flow/network/scan_nt.py
@@ -37,7 +37,7 @@
     ContactFileFields,
     SuiteFiles,
     get_suite_title,
-    load_contact_file
+    load_contact_file_async
 )
 
 
@@ -169,7 +169,7 @@ async def contact_info(flow):
 
     """
     flow.update(
-        load_contact_file(flow['name'], path=flow['path'])
+        await load_contact_file_async(flow['name'], run_dir=flow['path'])
     )
     return flow
 
diff --git a/cylc/flow/suite_files.py b/cylc/flow/suite_files.py
index 4b0007b387d..1588d3fc56b 100644
--- a/cylc/flow/suite_files.py
+++ b/cylc/flow/suite_files.py
@@ -17,20 +17,23 @@
 
 # Note: Some modules are NOT imported in the header. Expensive modules are only
 # imported on demand.
-from functools import lru_cache
+from pathlib import Path
 import os
 import re
 import shutil
-import stat
 import zmq.auth
 
+import aiofiles
+
 from cylc.flow import LOG
 from cylc.flow.cfgspec.glbl_cfg import glbl_cfg
 from cylc.flow.exceptions import SuiteServiceFileError
-from cylc.flow.pathutil import get_remote_suite_run_dir, get_suite_run_dir
-import cylc.flow.flags
+from cylc.flow.pathutil import get_suite_run_dir
 from cylc.flow.hostuserutil import (
-    get_host, get_user, is_remote, is_remote_host, is_remote_user)
+    get_user,
+    is_remote_host,
+    is_remote_user
+)
 from cylc.flow.unicode_rules import SuiteNameValidator
 
 from enum import Enum
@@ -375,13 +378,10 @@ def get_suite_srv_dir(reg, suite_owner=None):
     return os.path.join(run_d, SuiteFiles.Service.DIRNAME)
 
 
-def load_contact_file(reg, path=None, owner=None, host=None):
+def load_contact_file(reg, owner=None, host=None):
     """Load contact file. Return data as key=value dict."""
     file_base = SuiteFiles.Service.CONTACT
-    if path:
-        path = path / SuiteFiles.Service.DIRNAME
-    else:
-        path = get_suite_srv_dir(reg)
+    path = get_suite_srv_dir(reg)
     file_content = _load_local_item(file_base, path)
     if file_content:
         data = {}
@@ -393,6 +393,29 @@ def load_contact_file(reg, path=None, owner=None, host=None):
         raise SuiteServiceFileError("Couldn't load contact file")
 
 
+async def load_contact_file_async(reg, run_dir=None):
+    if not run_dir:
+        path = Path(
+            get_suite_srv_dir(reg),
+            SuiteFiles.Service.CONTACT
+        )
+    else:
+        path = Path(
+            run_dir,
+            SuiteFiles.Service.DIRNAME,
+            SuiteFiles.Service.CONTACT
+        )
+    try:
+        async with aiofiles.open(path, mode='r') as cont:
+            data = {}
+            async for line in cont:
+                key, value = [item.strip() for item in line.split("=", 1)]
+                data[key] = value
+            return data
+    except IOError:
+        raise SuiteServiceFileError("Couldn't load contact file")
+
+
 def parse_suite_arg(options, arg):
     """From CLI arg "SUITE", return suite name and suite.rc path.
 
diff --git a/setup.py b/setup.py
index a4453e26491..a34549bfeef 100644
--- a/setup.py
+++ b/setup.py
@@ -42,6 +42,7 @@ def find_version(*file_paths):
 
 
 install_requires = [
+    'aiofiles==0.5.*',
     'ansimarkup>=1.0.0',
     'colorama>=0.4,<=1',
     'click>=7.0',
diff --git a/tests/integration/test_suite_files.py b/tests/integration/test_suite_files.py
new file mode 100644
index 00000000000..5f1ec2cd9f3
--- /dev/null
+++ b/tests/integration/test_suite_files.py
@@ -0,0 +1,46 @@
+# THIS FILE IS PART OF THE CYLC SUITE ENGINE.
+# Copyright (C) NIWA & British Crown (Met Office) & Contributors.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import pytest
+
+from cylc.flow.suite_files import (
+    ContactFileFields as CFF,
+    load_contact_file,
+    load_contact_file_async
+)
+
+
+@pytest.fixture(scope='module')
+async def myflow(mod_flow, mod_scheduler, mod_run, mod_one_conf):
+    reg = mod_flow(mod_one_conf)
+    schd = mod_scheduler(reg)
+    async with mod_run(schd):
+        yield schd
+
+
+def test_load_contact_file(myflow):
+    cont = load_contact_file(myflow.suite)
+    assert cont[CFF.HOST] == myflow.host
+
+
+@pytest.mark.asyncio
+async def test_load_contact_file_async(myflow):
+    cont = await load_contact_file_async(myflow.suite)
+    assert cont[CFF.HOST] == myflow.host
+
+    # compare the async interface to the sync interface
+    cont2 = load_contact_file(myflow.suite)
+    assert cont == cont2