atomic_write.rb in autoproj-2.17.0

- old
+ new
@@ -1,37 +1,74 @@
+# frozen_string_literal: true
+
+require "tempfile"
+require "fileutils"
+
 module Autoproj
     module Ops
+        # Write to a file atomically. Useful for situations where you don't
+        # want other processes or threads to see half-written files.
+        #
+        #   File.atomic_write('important.file') do |file|
+        #     file.write('hello')
+        #   end
+        #
+        # This method needs to create a temporary file. By default it will create it
+        # in the same directory as the destination file. If you don't like this
+        # behavior you can provide a different directory but it must be on the
+        # same physical filesystem as the file you're trying to write.
+        #
+        #   File.atomic_write('/data/something.important', '/data/tmp') do |file|
+        #     file.write('hello')
+        #   end
+        #
         # Shamelessly stolen from ActiveSupport
-        def self.atomic_write(file_name, temp_dir = Dir.tmpdir)
-            require "tempfile" unless defined?(Tempfile)
-            require "fileutils" unless defined?(FileUtils)
+        def self.atomic_write(file_name, temp_dir = File.dirname(file_name))
+            Tempfile.open(".#{File.basename(file_name)}", temp_dir) do |temp_file|
+                temp_file.binmode
+                yield temp_file
+                temp_file.close
 
-            temp_file = Tempfile.new(File.basename(file_name), temp_dir)
-            yield temp_file
-            temp_file.flush
-            begin temp_file.fsync
-            rescue NotImplementedError
-            end
-            temp_file.close
+                old_stat = begin
+                    # Get original file permissions
+                    File.stat(file_name)
+                rescue Errno::ENOENT
+                    # If not possible, probe which are the default permissions in the
+                    # destination directory.
+                    probe_stat_in(File.dirname(file_name))
+                end
 
-            begin
-                # Get original file permissions
-                old_stat = File.stat(file_name)
-            rescue Errno::ENOENT
-                # No old permissions, write a temp file to determine the defaults
-                check_name = File.join(
-                    File.dirname(file_name), ".permissions_check.#{Thread.current.object_id}.#{Process.pid}.#{rand(1000000)}"
-                )
-                File.open(check_name, "w") {}
-                old_stat = File.stat(check_name)
-                File.unlink(check_name)
+                if old_stat
+                    # Set correct permissions on new file
+                    begin
+                        File.chown(old_stat.uid, old_stat.gid, temp_file.path)
+                        # This operation will affect filesystem ACL's
+                        File.chmod(old_stat.mode, temp_file.path)
+                    rescue Errno::EPERM, Errno::EACCES
+                        # Changing file ownership failed, moving on.
+                    end
+                end
+
+                # Overwrite original file with temp file
+                File.rename(temp_file.path, file_name)
             end
+        end
 
-            # Overwrite original file with temp file
-            FileUtils.mv(temp_file.path, file_name)
+        # Private utility method.
+        def self.probe_stat_in(dir) # :nodoc:
+            basename = [
+                ".permissions_check",
+                Thread.current.object_id,
+                Process.pid,
+                rand(1000000)
+            ].join(".")
 
-            # Set correct permissions on new file
-            File.chown(old_stat.uid, old_stat.gid, file_name)
-            File.chmod(old_stat.mode, file_name)
+            file_name = File.join(dir, basename)
+            FileUtils.touch(file_name)
+            File.stat(file_name)
+        rescue Errno::ENOENT
+            file_name = nil
+        ensure
+            FileUtils.rm_f(file_name) if file_name
         end
     end
 end