Class: Tempfile

Inherits:
File
  • Object
show all
Defined in:
lib/tempfile.rb

Overview

A utility class for managing temporary files. When you create a Tempfile object, it will create a temporary file with a unique filename. A Tempfile objects behaves just like a File object, and you can perform all the usual file operations on it: reading data, writing data, changing its permissions, etc. So although this class does not explicitly document all instance methods supported by File, you can in fact call any File instance method on a Tempfile object.

Synopsis

require 'tempfile'

file = Tempfile.new('foo')
file.path      # => A unique filename in the OS's temp directory,
               #    e.g.: "/tmp/foo.24722.0"
               #    This filename contains 'foo' in its basename.
file.write("hello world")
file.rewind
file.read      # => "hello world"
file.close
file.unlink    # deletes the temp file

Good practices

Explicit close

When a Tempfile object is garbage collected, or when the Ruby interpreter exits, its associated temporary file is automatically deleted. This means that it's unnecessary to explicitly delete a Tempfile after use, though it's a good practice to do so: not explicitly deleting unused Tempfiles can potentially leave behind a large number of temp files on the filesystem until they're garbage collected. The existence of these temp files can make it harder to determine a new Tempfile filename.

Therefore, one should always call #unlink or close in an ensure block, like this:

file = Tempfile.new('foo')
begin
   # ...do something with file...
ensure
   file.close
   file.unlink   # deletes the temp file
end

Tempfile.create { … } exists for this purpose and is more convenient to use. Note that Tempfile.create returns a File instance instead of a Tempfile, which also avoids the overhead and complications of delegation.

Tempfile.open('foo') do |file|
   # ...do something with file...
end

Unlink after creation

On POSIX systems, it's possible to unlink a file right after creating it, and before closing it. This removes the filesystem entry without closing the file handle, so it ensures that only the processes that already had the file handle open can access the file's contents. It's strongly recommended that you do this if you do not want any other processes to be able to read from or write to the Tempfile, and you do not need to know the Tempfile's filename either.

For example, a practical use case for unlink-after-creation would be this: you need a large byte buffer that's too large to comfortably fit in RAM, e.g. when you're writing a web server and you want to buffer the client's file upload data.

Please refer to #unlink for more information and a code example.

Minor notes

Tempfile's filename picking method is both thread-safe and inter-process-safe: it guarantees that no other threads or processes will pick the same filename.

Tempfile itself however may not be entirely thread-safe. If you access the same Tempfile object from multiple threads then you should protect it with a mutex.

Defined Under Namespace

Classes: Remover

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(basename = "", tmpdir = nil, mode: 0, **options) ⇒ Tempfile

Creates a file in the underlying file system; returns a new Tempfile object based on that file.

If possible, consider instead using Tempfile.create, which:

  • Avoids the performance cost of delegation, incurred when Tempfile.new calls its superclass DelegateClass(File).

  • Does not rely on a finalizer to close and unlink the file, which can be unreliable.

Creates and returns file whose:

  • Class is Tempfile (not File, as in Tempfile.create).

  • Directory is the system temporary directory (system-dependent).

  • Generated filename is unique in that directory.

  • Permissions are 0600; see File Permissions.

  • Mode is 'w+' (read/write mode, positioned at the end).

The underlying file is removed when the Tempfile object dies and is reclaimed by the garbage collector.

Example:

f = Tempfile.new # => #<Tempfile:/tmp/20220505-17839-1s0kt30>
f.class               # => Tempfile
f.path                # => "/tmp/20220505-17839-1s0kt30"
f.stat.mode.to_s(8)   # => "100600"
File.exist?(f.path)   # => true
File.unlink(f.path)   #
File.exist?(f.path)   # => false

Argument basename, if given, may be one of:

  • A string: the generated filename begins with basename:

    Tempfile.new('foo') # => #<Tempfile:/tmp/foo20220505-17839-1whk2f>

  • An array of two strings [prefix, suffix]: the generated filename begins with prefix and ends with suffix:

    Tempfile.new(%w/foo .jpg/) # => #<Tempfile:/tmp/foo20220505-17839-58xtfi.jpg>

With arguments basename and tmpdir, the file is created in directory tmpdir:

Tempfile.new('foo', '.') # => #<Tempfile:./foo20220505-17839-xfstr8>

Keyword arguments mode and options are passed directly to method File.open:

  • The value given with mode must be an integer, and may be expressed as the logical OR of constants defined in File::Constants.

  • For options, see Open Options.

Related: Tempfile.create.


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# File 'lib/tempfile.rb', line 148

def initialize(basename="", tmpdir=nil, mode: 0, **options)
  warn "Tempfile.new doesn't call the given block.", uplevel: 1 if block_given?

  @unlinked = false
  @mode = mode|File::RDWR|File::CREAT|File::EXCL
  ::Dir::Tmpname.create(basename, tmpdir, **options) do |tmpname, n, opts|
    opts[:perm] = 0600
    @tmpfile = File.open(tmpname, @mode, **opts)
    @opts = opts.freeze
  end
  ObjectSpace.define_finalizer(self, Remover.new(@tmpfile))

  super(@tmpfile)
end

Class Method Details

.create(basename = "", tmpdir = nil, mode: 0, **options) ⇒ Object

Creates a file in the underlying file system; returns a new File object based on that file.

With no block given and no arguments, creates and returns file whose:

  • Class is File (not Tempfile).

  • Directory is the system temporary directory (system-dependent).

  • Generated filename is unique in that directory.

  • Permissions are 0600; see File Permissions.

  • Mode is 'w+' (read/write mode, positioned at the end).

With no block, the file is not removed automatically, and so should be explicitly removed.

Example:

f = Tempfile.create     # => #<File:/tmp/20220505-9795-17ky6f6>
f.class                 # => File
f.path                  # => "/tmp/20220505-9795-17ky6f6"
f.stat.mode.to_s(8)     # => "100600"
File.exist?(f.path)     # => true
File.unlink(f.path)
File.exist?(f.path)     # => false

Argument basename, if given, may be one of:

  • A string: the generated filename begins with basename:

    Tempfile.create('foo') # => #<File:/tmp/foo20220505-9795-1gok8l9>

  • An array of two strings [prefix, suffix]: the generated filename begins with prefix and ends with suffix:

    Tempfile.create(%w/foo .jpg/) # => #<File:/tmp/foo20220505-17839-tnjchh.jpg>

With arguments basename and tmpdir, the file is created in directory tmpdir:

Tempfile.create('foo', '.') # => #<File:./foo20220505-9795-1emu6g8>

Keyword arguments mode and options are passed directly to method File.open:

  • The value given with mode must be an integer, and may be expressed as the logical OR of constants defined in File::Constants.

  • For options, see Open Options.

With a block given, creates the file as above, passes it to the block, and returns the block's value; before the return, the file object is closed and the underlying file is removed:

Tempfile.create {|file| file.path } # => "/tmp/20220505-9795-rkists"

Related: Tempfile.new.


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# File 'lib/tempfile.rb', line 398

def Tempfile.create(basename="", tmpdir=nil, mode: 0, **options)
  tmpfile = nil
  Dir::Tmpname.create(basename, tmpdir, **options) do |tmpname, n, opts|
    mode |= File::RDWR|File::CREAT|File::EXCL
    opts[:perm] = 0600
    tmpfile = File.open(tmpname, mode, **opts)
  end
  if block_given?
    begin
      yield tmpfile
    ensure
      unless tmpfile.closed?
        if File.identical?(tmpfile, tmpfile.path)
          unlinked = File.unlink tmpfile.path rescue nil
        end
        tmpfile.close
      end
      unless unlinked
        begin
          File.unlink tmpfile.path
        rescue Errno::ENOENT
        end
      end
    end
  else
    tmpfile
  end
end

.open(*args, **kw) ⇒ Object

Creates a new Tempfile.

This method is not recommended and exists mostly for backward compatibility. Please use Tempfile.create instead, which avoids the cost of delegation, does not rely on a finalizer, and also unlinks the file when given a block.

Tempfile.open is still appropriate if you need the Tempfile to be unlinked by a finalizer and you cannot explicitly know where in the program the Tempfile can be unlinked safely.

If no block is given, this is a synonym for Tempfile.new.

If a block is given, then a Tempfile object will be constructed, and the block is run with the Tempfile object as argument. The Tempfile object will be automatically closed after the block terminates. However, the file will not be unlinked and needs to be manually unlinked with Tempfile#close! or Tempfile#unlink. The finalizer will try to unlink but should not be relied upon as it can keep the file on the disk much longer than intended. For instance, on CRuby, finalizers can be delayed due to conservative stack scanning and references left in unused memory.

The call returns the value of the block.

In any case, all arguments (*args) will be passed to Tempfile.new.

Tempfile.open('foo', '/home/temp') do |f|
   # ... do something with f ...
end

# Equivalent:
f = Tempfile.open('foo', '/home/temp')
begin
   # ... do something with f ...
ensure
   f.close
end


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# File 'lib/tempfile.rb', line 326

def open(*args, **kw)
  tempfile = new(*args, **kw)

  if block_given?
    begin
      yield(tempfile)
    ensure
      tempfile.close
    end
  else
    tempfile
  end
end

Instance Method Details

#close(unlink_now = false) ⇒ Object

Closes the file. If unlink_now is true, then the file will be unlinked (deleted) after closing. Of course, you can choose to later call #unlink if you do not unlink it now.

If you don't explicitly unlink the temporary file, the removal will be delayed until the object is finalized.


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# File 'lib/tempfile.rb', line 182

def close(unlink_now=false)
  _close
  unlink if unlink_now
end

#close! ⇒ Object

Closes and unlinks (deletes) the file. Has the same effect as called close(true).


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# File 'lib/tempfile.rb', line 189

def close!
  close(true)
end

#inspect ⇒ Object

:stopdoc:


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# File 'lib/tempfile.rb', line 258

def inspect
  if @tmpfile.closed?
    "#<#{self.class}:#{path} (closed)>"
  else
    "#<#{self.class}:#{path}>"
  end
end

#open ⇒ Object

Opens or reopens the file with mode “r+”.


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# File 'lib/tempfile.rb', line 164

def open
  _close
  mode = @mode & ~(File::CREAT|File::EXCL)
  @tmpfile = File.open(@tmpfile.path, mode, **@opts)
  __setobj__(@tmpfile)
end

#path ⇒ Object

Returns the full path name of the temporary file. This will be nil if #unlink has been called.


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# File 'lib/tempfile.rb', line 242

def path
  @unlinked ? nil : @tmpfile.path
end

#size ⇒ Object Also known as: length

Returns the size of the temporary file. As a side effect, the IO buffer is flushed before determining the size.


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# File 'lib/tempfile.rb', line 248

def size
  if !@tmpfile.closed?
    @tmpfile.size # File#size calls rb_io_flush_raw()
  else
    File.size(@tmpfile.path)
  end
end

#unlink ⇒ Object Also known as: delete

Unlinks (deletes) the file from the filesystem. One should always unlink the file after using it, as is explained in the “Explicit close” good practice section in the Tempfile overview:

file = Tempfile.new('foo')
begin
   # ...do something with file...
ensure
   file.close
   file.unlink   # deletes the temp file
end

On POSIX systems it's possible to unlink a file before closing it. This practice is explained in detail in the Tempfile overview (section “Unlink after creation”); please refer there for more information.

However, unlink-before-close may not be supported on non-POSIX operating systems. Microsoft Windows is the most notable case: unlinking a non-closed file will result in an error, which this method will silently ignore. If you want to practice unlink-before-close whenever possible, then you should write code like this:

file = Tempfile.new('foo')
file.unlink   # On Windows this silently fails.
begin
   # ... do something with file ...
ensure
   file.close!   # Closes the file handle. If the file wasn't unlinked
                 # because #unlink failed, then this method will attempt
                 # to do so again.
end


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# File 'lib/tempfile.rb', line 226

def unlink
  return if @unlinked
  begin
    File.unlink(@tmpfile.path)
  rescue Errno::ENOENT
  rescue Errno::EACCES
    # may not be able to unlink on Windows; just ignore
    return
  end
  ObjectSpace.undefine_finalizer(self)
  @unlinked = true
end