Reduce use of tempfile (fix #25)

safer/__init__.py

@@ -1,5 +1,4 @@
-"""
-# 🧿 `safer`: A safer writer 🧿
+"""# 🧿 `safer`: A safer writer 🧿
 
 Avoid partial writes or corruption!
 
@@ -42,6 +41,10 @@
 It also has a useful `dry_run` setting to let you test your code without
 actually overwriting the target file.
 
+NOTE: Just like plain old `open`, if a file that is already opened for writing
+is opened again before the first write has completed, the results are
+unpredictable: so don't do it!
+
 * `safer.writer()` wraps an existing writer, socket or stream and writes a
   whole response or nothing
 
@@ -67,7 +70,6 @@
 does not work on Windows.  (In fact, it's unclear if any of this works on
 Windows, but that certainly won't.  Windows developer solicted!)
 
-
 ### Example: `safer.writer()`
 
 `safer.writer()` wraps an existing stream - a writer, socket, or callback -
@@ -143,6 +145,7 @@
         for item in items:
             print(item)
         # Either the whole file is written, or nothing
+
 """
 import contextlib
 import functools
@@ -657,14 +660,16 @@ def __init__(
         self.target_file = target_file
         self.dry_run = dry_run
         self.is_binary = is_binary
+        if temp_file is True:
+            parent, file = os.path.split(target_file)
+            temp_file = os.path.join(parent, f'.{file}.tmp-safer')
+
         super().__init__(temp_file, delete_failures, parent)
 
     def _success(self):
         if not self.dry_run:
             if os.path.exists(self.target_file):
                 shutil.copymode(self.target_file, self.temp_file)
-            else:
-                os.chmod(self.temp_file, 0o100644)
             os.replace(self.temp_file, self.target_file)
 
         elif callable(self.dry_run):

test/test_open.py

@@ -102,15 +102,15 @@ def test_two_errors(self, safer_open):
             fp.write('OK!')
             if uses_files:
                 after = set(os.listdir('.'))
-                assert len(before) + 2 == len(after)
-                assert len(after.difference(before)) == 2
+                assert len(before) + 1 == len(after)
+                assert len(after.difference(before)) == 1
 
         assert FILENAME.read_text() == 'OK!'
 
         if uses_files:
             after = set(os.listdir('.'))
-            assert len(before) + 1 == len(after)
-            assert len(after.difference(before)) == 1
+            assert len(before) == len(after)
+            assert len(after.difference(before)) == 0
 
     def test_error_with_copy(self, safer_open):
         FILENAME.write_text('hello')
@@ -214,3 +214,17 @@ def test_file_exists_error(self, safer_open):
         with safer_open(FILENAME, 'wt') as fp:
             fp.write('goodbye')
         assert FILENAME.read_text() == 'goodbye'
+
+    def test_tempfile_perms(self, safer_open):
+        temp_files = False, True, 'three'
+        perms = []
+        for temp_file in temp_files:
+            filename = str(temp_file)
+            if isinstance(temp_file, str):
+                temp_file += '.tmpfile'
+            with safer_open(filename, 'w', temp_file=temp_file):
+                pass
+            perms.append(os.stat(filename).st_mode)
+
+        assert perms == [perms[0]] * len(perms)
+        assert perms[0] in (0o100644, 0o100664)