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's it's unnecessary to explicitly delete a Tempfile after use, though it's good practice to do so: not explicitly deleting unused Tempfiles can potentially leave behind large amounts of tempfiles 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

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 temporary file with permissions 0600 (= only readable and writable by the owner) and opens it with mode “w+”.

The basename parameter is used to determine the name of the temporary file. You can either pass a String or an Array with 2 String elements. In the former form, the temporary file's base name will begin with the given string. In the latter form, the temporary file's base name will begin with the array's first element, and end with the second element. For example:

file = Tempfile.new('hello')
file.path  # => something like: "/tmp/hello2843-8392-92849382--0"

# Use the Array form to enforce an extension in the filename:
file = Tempfile.new(['hello', '.jpg'])
file.path  # => something like: "/tmp/hello2843-8392-92849382--0.jpg"

The temporary file will be placed in the directory as specified by the tmpdir parameter. By default, this is Dir.tmpdir.

file = Tempfile.new('hello', '/home/aisaka')
file.path  # => something like: "/home/aisaka/hello2843-8392-92849382--0"

You can also pass an options hash. Under the hood, Tempfile creates the temporary file using File.open. These options will be passed to File.open. This is mostly useful for specifying encoding options, e.g.:

Tempfile.new('hello', '/home/aisaka', encoding: 'ascii-8bit')

# You can also omit the 'tmpdir' parameter:
Tempfile.new('hello', encoding: 'ascii-8bit')

Note: mode keyword argument, as accepted by Tempfile, can only be numeric, combination of the modes defined in File::Constants.

Exceptions

If Tempfile.new cannot find a unique filename within a limited number of tries, then it will raise an exception.


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# File 'lib/tempfile.rb', line 122

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 temporary file as usual File object (not Tempfile). It doesn't use finalizer and delegation.

If no block is given, this is similar to Tempfile.new except creating File instead of Tempfile. The created file is not removed automatically. You should use File.unlink to remove it.

If a block is given, then a File object will be constructed, and the block is invoked with the object as the argument. The File object will be automatically closed and the temporary file is removed after the block terminates. The call returns the value of the block.

In any case, all arguments (basename, tmpdir, mode, and **options) will be treated as Tempfile.new.

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

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# File 'lib/tempfile.rb', line 323

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.

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 said object as argument. The Tempfile object will be automatically closed after the block terminates. 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 286

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 156

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 163

def close!
  close(true)
end

#inspectObject

:stopdoc:


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# File 'lib/tempfile.rb', line 232

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

#openObject

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


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# File 'lib/tempfile.rb', line 138

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

#pathObject

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 216

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

#sizeObject 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 222

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

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 200

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