From e60c643b5f46d9365dc67e6022c904f10c261b45 Mon Sep 17 00:00:00 2001
From: Jean-Paul Calderone <exarkun@twistedmatrix.com>
Date: Wed, 18 Nov 2020 10:57:38 -0500
Subject: [PATCH] Make configutil.write_config atomic and also make it take a
 FilePath

---
 src/allmydata/test/test_configutil.py |  7 +++++--
 src/allmydata/util/configutil.py      | 17 +++++++++++++++--
 2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/src/allmydata/test/test_configutil.py b/src/allmydata/test/test_configutil.py
index 9e792dc87..19e5b303d 100644
--- a/src/allmydata/test/test_configutil.py
+++ b/src/allmydata/test/test_configutil.py
@@ -15,6 +15,9 @@ if PY2:
 
 import os.path
 
+from twisted.python.filepath import (
+    FilePath,
+)
 from twisted.trial import unittest
 
 from allmydata.util import configutil
@@ -55,7 +58,7 @@ enabled = false
 
         # test that set_config can mutate an existing option
         configutil.set_config(config, "node", "nickname", "Alice!")
-        configutil.write_config(tahoe_cfg, config)
+        configutil.write_config(FilePath(tahoe_cfg), config)
 
         config = configutil.get_config(tahoe_cfg)
         self.failUnlessEqual(config.get("node", "nickname"), "Alice!")
@@ -63,7 +66,7 @@ enabled = false
         # test that set_config can set a new option
         descriptor = "Twas brillig, and the slithy toves Did gyre and gimble in the wabe"
         configutil.set_config(config, "node", "descriptor", descriptor)
-        configutil.write_config(tahoe_cfg, config)
+        configutil.write_config(FilePath(tahoe_cfg), config)
 
         config = configutil.get_config(tahoe_cfg)
         self.failUnlessEqual(config.get("node", "descriptor"), descriptor)
diff --git a/src/allmydata/util/configutil.py b/src/allmydata/util/configutil.py
index 4bee7d043..d905a8e00 100644
--- a/src/allmydata/util/configutil.py
+++ b/src/allmydata/util/configutil.py
@@ -59,8 +59,21 @@ def set_config(config, section, option, value):
     assert config.get(section, option) == value
 
 def write_config(tahoe_cfg, config):
-    with open(tahoe_cfg, "w") as f:
-        config.write(f)
+    """
+    Write a configuration to a file.
+
+    :param FilePath tahoe_cfg: The path to which to write the config.
+
+    :param ConfigParser config: The configuration to write.
+
+    :return: ``None``
+    """
+    tmp = tahoe_cfg.temporarySibling()
+    # FilePath.open can only open files in binary mode which does not work
+    # with ConfigParser.write.
+    with open(tmp.path, "wt") as fp:
+        config.write(fp)
+    tmp.moveTo(tahoe_cfg)
 
 def validate_config(fname, cfg, valid_config):
     """