82 lines
2.4 KiB
Ruby
82 lines
2.4 KiB
Ruby
# typed: strict
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# frozen_string_literal: true
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require "fileutils"
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class File
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# Write to a file atomically. Useful for situations where you don't
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# want other processes or threads to see half-written files.
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#
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# File.atomic_write('important.file') do |file|
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# file.write('hello')
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# end
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#
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# This method needs to create a temporary file. By default it will create it
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# in the same directory as the destination file. If you don't like this
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# behavior you can provide a different directory but it must be on the
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# same physical filesystem as the file you're trying to write.
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#
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# File.atomic_write('/data/something.important', '/data/tmp') do |file|
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# file.write('hello')
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# end
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sig {
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type_parameters(:out).params(
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file_name: T.any(Pathname, String),
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temp_dir: String,
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_block: T.proc.params(arg0: Tempfile).returns(T.type_parameter(:out)),
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).returns(T.type_parameter(:out))
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}
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def self.atomic_write(file_name, temp_dir = dirname(file_name), &_block)
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require "tempfile" unless defined?(Tempfile)
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Tempfile.open(".#{basename(file_name)}", temp_dir) do |temp_file|
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temp_file.binmode
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return_val = yield temp_file
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temp_file.close
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old_stat = if exist?(file_name)
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# Get original file permissions
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stat(file_name)
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else
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# If not possible, probe which are the default permissions in the
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# destination directory.
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probe_stat_in(dirname(file_name))
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end
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if old_stat
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# Set correct permissions on new file
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begin
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chown(old_stat.uid, old_stat.gid, T.must(temp_file.path))
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# This operation will affect filesystem ACL's
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chmod(old_stat.mode, T.must(temp_file.path))
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rescue Errno::EPERM, Errno::EACCES
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# Changing file ownership failed, moving on.
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end
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end
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# Overwrite original file with temp file
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rename(T.must(temp_file.path), file_name)
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return_val
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end
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end
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# Private utility method.
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sig { params(dir: String).returns(T.nilable(File::Stat)) }
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private_class_method def self.probe_stat_in(dir) # :nodoc:
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basename = [
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".permissions_check",
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Thread.current.object_id,
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Process.pid,
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rand(1_000_000),
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].join(".")
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file_name = join(dir, basename)
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FileUtils.touch(file_name)
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stat(file_name)
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rescue Errno::ENOENT
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file_name = nil
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ensure
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FileUtils.rm_f(file_name) if file_name
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end
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end
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