class Down::ChunkedIO

Wraps an enumerator that yields chunks of content into an IO object. It implements some essential IO methods:

By default the Down::ChunkedIO caches all read content into a tempfile, allowing it to be rewindable. If rewindability won't be used, it can be disabled by setting `:rewindable` to false, which eliminates any disk I/O.

Any cleanup code (i.e. ensure block) that the given enumerator carries is guaranteed to get executed, either when all content has been retrieved or when Down::ChunkedIO is closed. One can also specify an `:on_close` callback that will also get executed in those situations.

Attributes

data[RW]
encoding[RW]
size[RW]

Public Class Methods

new(chunks:, size: nil, on_close: nil, data: {}, rewindable: true, encoding: nil) click to toggle source
# File lib/down/chunked_io.rb, line 29
def initialize(chunks:, size: nil, on_close: nil, data: {}, rewindable: true, encoding: nil)
  @chunks     = chunks
  @size       = size
  @on_close   = on_close
  @data       = data
  @encoding   = find_encoding(encoding || "binary")
  @rewindable = rewindable
  @buffer     = nil
  @position   = 0

  retrieve_chunk # fetch first chunk so that we know whether the file is empty
end

Public Instance Methods

close() click to toggle source

Implements IO#close semantics. Closes the Down::ChunkedIO by terminating chunk retrieval and deleting the cached content.

# File lib/down/chunked_io.rb, line 220
def close
  return if @closed

  chunks_fiber.resume(:terminate) if chunks_fiber.alive?
  cache.close! if cache
  @buffer = nil
  @closed = true
end
closed?() click to toggle source

Returns whether the Down::ChunkedIO has been closed.

# File lib/down/chunked_io.rb, line 230
def closed?
  !!@closed
end
each_chunk() { |retrieve_chunk until chunks_depleted?| ... } click to toggle source

Yields elements of the underlying enumerator.

# File lib/down/chunked_io.rb, line 43
def each_chunk
  fail IOError, "closed stream" if closed?

  return enum_for(__method__) unless block_given?

  yield retrieve_chunk until chunks_depleted?
end
eof?() click to toggle source

Implements IO#eof? semantics. Returns whether we've reached end of file. It returns true if cache is at the end and there is no more content to retrieve. Raises IOError if closed.

# File lib/down/chunked_io.rb, line 200
def eof?
  fail IOError, "closed stream" if closed?

  return false if cache && !cache.eof?
  @buffer.nil? && chunks_depleted?
end
gets(separator_or_limit = $/, limit = nil) click to toggle source

Implements IO#gets semantics. Without arguments it retrieves lines of content separated by newlines.

With `separator` argument it does the following:

  • if `separator` is a nonempty string returns chunks of content surrounded with that sequence of bytes

  • if `separator` is an empty string returns paragraphs of content (content delimited by two newlines)

  • if `separator` is nil returns all content

With `limit` argument returns maximum of that amount of bytes.

Returns nil if end of file is reached. Raises IOError if closed.

# File lib/down/chunked_io.rb, line 96
def gets(separator_or_limit = $/, limit = nil)
  fail IOError, "closed stream" if closed?

  if separator_or_limit.is_a?(Integer)
    separator = $/
    limit     = separator_or_limit
  else
    separator = separator_or_limit
  end

  return read if separator.nil?

  separator = "\n\n" if separator.empty?

  begin
    data = readpartial(limit)

    until data.include?(separator) || data.bytesize == limit || eof?
      remaining_length = limit - data.bytesize if limit
      data << readpartial(remaining_length, outbuf ||= String.new)
    end

    line, extra = data.split(separator, 2)
    line << separator if data.include?(separator)

    if cache
      cache.pos -= extra.to_s.bytesize
    else
      @buffer = @buffer.to_s.prepend(extra.to_s)
    end
  rescue EOFError
    line = nil
  end

  line
end
inspect() click to toggle source

Returns useful information about the Down::ChunkedIO object.

# File lib/down/chunked_io.rb, line 240
def inspect
  string  = String.new
  string << "#<#{self.class.name}"
  string << " chunks=#{@chunks.inspect}"
  string << " size=#{size.inspect}"
  string << " encoding=#{encoding.inspect}"
  string << " data=#{data.inspect}"
  string << " on_close=#{@on_close.inspect}"
  string << " rewindable=#{@rewindable.inspect}"
  string << " (closed)" if closed?
  string << ">"
end
pos() click to toggle source

Implements IO#pos semantics. Returns the current position of the Down::ChunkedIO.

# File lib/down/chunked_io.rb, line 193
def pos
  @position
end
read(length = nil, outbuf = nil) click to toggle source

Implements IO#read semantics. Without arguments it retrieves and returns all content.

With `length` argument returns exactly that number of bytes if they're available.

With `outbuf` argument each call will return that same string object, where the value is replaced with retrieved content.

If end of file is reached, returns empty string if called without arguments, or nil if called with arguments. Raises IOError if closed.

# File lib/down/chunked_io.rb, line 62
def read(length = nil, outbuf = nil)
  fail IOError, "closed stream" if closed?

  remaining_length = length

  begin
    data = readpartial(remaining_length, outbuf)
    data = data.dup unless outbuf
    remaining_length = length - data.bytesize if length
  rescue EOFError
  end

  until remaining_length == 0 || eof?
    data << readpartial(remaining_length)
    remaining_length = length - data.bytesize if length
  end

  data.to_s unless length && length > 0 && (data.nil? || data.empty?)
end
readpartial(length = nil, outbuf = nil) click to toggle source

Implements IO#readpartial semantics. If there is any content readily available reads from it, otherwise fetches and reads from the next chunk. It writes to and reads from the cache when needed.

Without arguments it either returns all content that's readily available, or the next chunk. This is useful when you don't care about the size of chunks and you want to minimize string allocations.

With `length` argument returns maximum of that amount of bytes.

With `outbuf` argument each call will return that same string object, where the value is replaced with retrieved content.

Raises EOFError if end of file is reached. Raises IOError if closed.

# File lib/down/chunked_io.rb, line 147
def readpartial(length = nil, outbuf = nil)
  fail IOError, "closed stream" if closed?

  data = outbuf.clear.force_encoding(@encoding) if outbuf

  return data.to_s if length == 0

  if cache && !cache.eof?
    data = cache.read(length, outbuf)
    data.force_encoding(@encoding)
  end

  if @buffer.nil? && (data.nil? || data.empty?)
    fail EOFError, "end of file reached" if chunks_depleted?
    @buffer = retrieve_chunk
  end

  remaining_length = data && length ? length - data.bytesize : length

  unless @buffer.nil? || remaining_length == 0
    if remaining_length && remaining_length < @buffer.bytesize
      buffered_data = @buffer.byteslice(0, remaining_length)
      @buffer       = @buffer.byteslice(remaining_length..-1)
    else
      buffered_data = @buffer
      @buffer       = nil
    end

    if data
      data << buffered_data
    else
      data = buffered_data
    end

    cache.write(buffered_data) if cache

    buffered_data.clear unless buffered_data.equal?(data)
  end

  @position += data.bytesize

  data
end
rewind() click to toggle source

Implements IO#rewind semantics. Rewinds the Down::ChunkedIO by rewinding the cache and setting the position to the beginning of the file. Raises IOError if closed or not rewindable.

# File lib/down/chunked_io.rb, line 210
def rewind
  fail IOError, "closed stream" if closed?
  fail IOError, "this Down::ChunkedIO is not rewindable" if cache.nil?

  cache.rewind
  @position = 0
end
rewindable?() click to toggle source

Returns whether the Down::ChunkedIO was specified as rewindable.

# File lib/down/chunked_io.rb, line 235
def rewindable?
  @rewindable
end

Private Instance Methods

cache() click to toggle source

If Down::ChunkedIO is specified as rewindable, returns a new Tempfile for writing read content to. This allows the Down::ChunkedIO to be rewinded.

# File lib/down/chunked_io.rb, line 257
def cache
  @cache ||= Tempfile.new("down-chunked_io", binmode: true) if @rewindable
end
chunks_depleted?() click to toggle source

Returns whether there is any content left to retrieve.

# File lib/down/chunked_io.rb, line 270
def chunks_depleted?
  !chunks_fiber.alive?
end
chunks_fiber() click to toggle source

Creates a Fiber wrapper around the underlying enumerator. The advantage of using a Fiber here is that we can terminate the chunk retrieval, in a way that executes any cleanup code that the enumerator potentially carries. At the end of iteration the :on_close callback is executed.

# File lib/down/chunked_io.rb, line 278
def chunks_fiber
  @chunks_fiber ||= Fiber.new do
    begin
      @chunks.each do |chunk|
        action = Fiber.yield chunk
        break if action == :terminate
      end
    ensure
      @on_close.call if @on_close
    end
  end
end
find_encoding(encoding) click to toggle source

Finds encoding by name. If the encoding couldn't be find, falls back to the generic binary encoding.

# File lib/down/chunked_io.rb, line 293
def find_encoding(encoding)
  Encoding.find(encoding)
rescue ArgumentError
  Encoding::BINARY
end
retrieve_chunk() click to toggle source

Returns current chunk and retrieves the next chunk. If next chunk is nil, we know we've reached EOF.

# File lib/down/chunked_io.rb, line 263
def retrieve_chunk
  chunk = @next_chunk
  @next_chunk = chunks_fiber.resume
  chunk.force_encoding(@encoding) if chunk
end