Class: Amp::Support::MultiIO

Inherits:
Object
  • Object
show all
Defined in:
lib/amp/support/multi_io.rb

Overview

MultiIO

A MultiIO is a class which joins multiple IO classes together. It responds to #read, and its constituent IOs must respond to #read. Since, currently, it only needs to be able to read (and perhaps rewind), that’s all it does. It allows one to feed, say, 3 separate input IO objects into a GZipWriter, and have it seamlessly traverse all 3 IOs.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(*ios) ⇒ MultiIO

Initializes the MultiIO to contain the given IO objects, in the order in which they are specified as arguments.

Parameters:

  • ios (Array<IO>) —

    The IO objects we are concatenating



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# File 'lib/amp/support/multi_io.rb', line 24

def initialize(*ios)
  @ios = ios
  rewind
end

Instance Attribute Details

#current_io_idx ⇒ Object

Points to the current IO object in the @ios array.



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# File 'lib/amp/support/multi_io.rb', line 14

def current_io_idx
  @current_io_idx
end

#current_pos ⇒ Object

Tracks our current index into the “joined” stream. In other words, if they were all lumped into 1 stream, how many bytes in would we be?



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# File 'lib/amp/support/multi_io.rb', line 17

def current_pos
  @current_pos
end

#ios ⇒ Object

These are all the base IO objects we are joining together.



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# File 'lib/amp/support/multi_io.rb', line 12

def ios
  @ios
end

Instance Method Details

#read(amt = nil) ⇒ String

Reads from the concatenated IO stream, crossing streams if necessary. (DON’T CROSS THE STREAMS!!!!)

Parameters:

  • amt (Integer) (defaults to: nil) —

    (nil) The number of bytes to read from the overall stream. If nil, reads until the end of the stream.

Returns:

  • (String) —

    the data read in from the stream



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# File 'lib/amp/support/multi_io.rb', line 50

def read(amt=nil)
  if amt==nil # if nil, read it all
    return @ios[@current_io_idx..-1].map {|io| io.read}.join
  end
  results = [] # result strings
  amount_read = 0 # how much have we read? We need this to match the +amt+ param
  cur_spot = current_io.tell # our current position
  while amount_read < amt # until we've read enough to meet the request
    results << current_io.read(amt - amount_read) # read enough to finish
    amount_read += current_io.tell - cur_spot # but we might not have actually read that much
    @current_pos += current_io.tell - cur_spot # update ivar
    # Do we need to go to the next IO stream?
    if amount_read < amt && @current_io_idx < @ios.size - 1
      # go to the next stream
      @current_io_idx += 1 
      # reset it just in case
      current_io.seek(0)
    # are we at the last stream?
    elsif @current_io_idx >= @ios.size - 1
      break
    end
    # if we need to read from another stream, then remember we're at the start of it
    cur_spot = 0
  end
  # join 'em up
  results.join
end

#rewind ⇒ Object

Rewinds all the IO objects to position 0.



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# File 'lib/amp/support/multi_io.rb', line 31

def rewind
  @ios.each {|io| io.seek(0) } 
  @current_pos = 0
  @current_io_idx = 0
end

#tell ⇒ Integer

Gets the current position in the concatenated IO stream.

Returns:

  • (Integer) —

    position in the IO stream (if all were 1 big stream, that is)



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# File 'lib/amp/support/multi_io.rb', line 41

def tell; @current_pos; end