Class: BinData::IO::Read

Inherits:
Object
  • Object
show all
Defined in:
lib/bindata/io.rb

Overview

Create a new IO Read wrapper around io. io must provide #read, #pos if reading the current stream position and #seek if setting the current stream position. If io is a string it will be automatically wrapped in an StringIO object.

The IO can handle bitstreams in either big or little endian format.

M  byte1   L      M  byte2   L
S 76543210 S      S fedcba98 S
B          B      B          B

In big endian format:

readbits(6), readbits(5) #=> [765432, 10fed]

In little endian format:

readbits(6), readbits(5) #=> [543210, a9876]

Defined Under Namespace

Modules: SeekableStream, UnSeekableStream

Instance Method Summary collapse

Constructor Details

#initialize(io) ⇒ Read

Returns a new instance of Read.

Raises:

  • (ArgumentError) 


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# File 'lib/bindata/io.rb', line 33

def initialize(io)
  raise ArgumentError, "io must not be a BinData::IO::Read" if BinData::IO::Read === io

  # wrap strings in a StringIO
  if io.respond_to?(:to_str)
    io = BinData::IO.create_string_io(io.to_str)
  end

  @raw_io = io

  # bits when reading
  @rnbits  = 0
  @rval    = 0
  @rendian = nil

  @buffer_end_pos = nil

  extend seekable? ? SeekableStream : UnSeekableStream
end

Instance Method Details

#read_all_bytes ⇒ Object

Reads all remaining bytes from the stream.



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# File 'lib/bindata/io.rb', line 91

def read_all_bytes
  reset_read_bits
  read
end

#readbits(nbits, endian) ⇒ Object

Reads exactly nbits bits from the stream. endian specifies whether the bits are stored in :big or :little endian format.



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# File 'lib/bindata/io.rb', line 98

def readbits(nbits, endian)
  if @rendian != endian
    # don't mix bits of differing endian
    reset_read_bits
    @rendian = endian
  end

  if endian == :big
    read_big_endian_bits(nbits)
  else
    read_little_endian_bits(nbits)
  end
end

#readbytes(n) ⇒ Object

Reads exactly n bytes from io.

If the data read is nil an EOFError is raised.

If the data read is too short an IOError is raised.

Raises:

  • (EOFError) 


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# File 'lib/bindata/io.rb', line 81

def readbytes(n)
  reset_read_bits

  str = read(n)
  raise EOFError, "End of file reached" if str.nil?
  raise IOError, "data truncated" if str.size < n
  str
end

#reset_read_bits ⇒ Object

Discards any read bits so the stream becomes aligned at the next byte boundary.



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# File 'lib/bindata/io.rb', line 114

def reset_read_bits
  @rnbits = 0
  @rval   = 0
end

#seekbytes(n) ⇒ Object

Seek n bytes from the current position in the io stream.



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# File 'lib/bindata/io.rb', line 71

def seekbytes(n)
  reset_read_bits
  seek(n)
end

#with_buffer(n, &block) ⇒ Object

Sets a buffer of n bytes on the io stream. Any reading or seeking calls inside the block will be contained within this buffer.



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# File 'lib/bindata/io.rb', line 55

def with_buffer(n, &block)
  prev = @buffer_end_pos
  if prev
    avail = prev - offset
    n = avail if n > avail
  end
  @buffer_end_pos = offset + n
  begin
    block.call
    read
  ensure
    @buffer_end_pos = prev
  end
end