CODEWITHSUNDEEP
rubythread-safetyfilenamestemp
iltempo
iltempo

Reputation: 16012

Creating a thread-safe temporary file name

When using Tempfile Ruby is creating a file with a thread-safe and inter-process-safe name. I only need a file name in that way.

I was wondering if there is a more straight forward approach way than:

t = Tempfile.new(['fleischwurst', '.png'])
temp_path = t.path
t.close
t.unlink

Upvotes: 37

Views: 13274

Answers (4)

Jan
Jan

Reputation: 11726

Dir::Tmpname.create

You could use Dir::Tmpname.create. It figures out what temporary directory to use (unless you pass it a directory). It's a little ugly to use given that it expects a block:

require 'tmpdir'
# => true
Dir::Tmpname.create(['prefix-', '.ext']) {}
# => "/tmp/prefix-20190827-1-87n9iu.ext"
Dir::Tmpname.create(['prefix-', '.ext'], '/my/custom/directory') {}
# => "/my/custom/directory/prefix-20190827-1-11x2u0h.ext"

The block is there for code to test if the file exists and raise an Errno::EEXIST so that a new name can be generated with incrementing value appended on the end.

The Rails Solution

The solution implemented by Ruby on Rails is short and similar to the solution originally implemented in Ruby:

require 'tmpdir'
# => true
File.join(Dir.tmpdir, "YOUR_PREFIX-#{Time.now.strftime("%Y%m%d")}-#{$$}-#{rand(0x100000000).to_s(36)}-YOUR_SUFFIX")
=> "/tmp/YOUR_PREFIX-20190827-1-wyouwg-YOUR_SUFFIX"
File.join(Dir.tmpdir, "YOUR_PREFIX-#{Time.now.strftime("%Y%m%d")}-#{$$}-#{rand(0x100000000).to_s(36)}-YOUR_SUFFIX")
=> "/tmp/YOUR_PREFIX-20190827-1-140far-YOUR_SUFFIX"

Dir::Tmpname.make_tmpname (Ruby 2.5.0 and earlier)

Dir::Tmpname.make_tmpname was removed in Ruby 2.5.0. Prior to Ruby 2.4.4 it could accept a directory path as a prefix, but as of Ruby 2.4.4, directory separators are removed.

Digging in tempfile.rb you'll notice that Tempfile includes Dir::Tmpname. Inside you'll find make_tmpname which does what you ask for.

require 'tmpdir'
# => true
File.join(Dir.tmpdir, Dir::Tmpname.make_tmpname("prefix-", nil))
# => "/tmp/prefix-20190827-1-dfhvld"
File.join(Dir.tmpdir, Dir::Tmpname.make_tmpname(["prefix-", ".ext"], nil))
# => "/tmp/prefix-20190827-1-19zjck1.ext"
File.join(Dir.tmpdir, Dir::Tmpname.make_tmpname(["prefix-", ".ext"], "suffix"))
# => "/tmp/prefix-20190827-1-f5ipo7-suffix.ext"

Upvotes: 62

Abe Voelker
Abe Voelker

Reputation: 31574

Since Dir::Tmpname.make_tmpname was removed in Ruby 2.5.0, this one falls back to using SecureRandom:

require "tmpdir"

def generate_temp_filename(ext=".png")
  filename = begin
    Dir::Tmpname.make_tmpname(["x", ext], nil)
  rescue NoMethodError
    require "securerandom"
    "#{SecureRandom.urlsafe_base64}#{ext}"
  end
  File.join(Dir.tmpdir, filename)
end

Upvotes: 3

Paulo Fidalgo
Paulo Fidalgo

Reputation: 22296

Since you only need the filename, what about using the SecureRandom for that:

require 'securerandom'

filename =  "#{SecureRandom.hex(6)}.png" #=> "0f04dd94addf.png"

You can also use SecureRandom.alphanumeric

Upvotes: 1

dinman2022
dinman2022

Reputation: 129

I found the Dir:Tmpname solution did not work for me. When evaluating this:

Dir::Tmpname.make_tmpname "/tmp/blob", nil

Under MRI Ruby 1.9.3p194 I get:

uninitialized constant Dir::Tmpname (NameError)

Under JRuby 1.7.5 (1.9.3p393) I get:

NameError: uninitialized constant Dir::Tmpname

You might try something like this:

def temp_name(file_name='', ext='', dir=nil)
    id   = Thread.current.hash * Time.now.to_i % 2**32
    name = "%s%d.%s" % [file_name, id, ext]
    dir ? File.join(dir, name) : name
end

Upvotes: -2

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