Class: BinData::IO::Read

Inherits:
Object
  • Object
show all
Includes:
Common
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]

Instance Method Summary collapse

Constructor Details

#initialize(io) ⇒ Read

Returns a new instance of Read.



239
240
241
242
243
244
245
246
 
# File 'lib/bindata/io.rb', line 239

def initialize(io)
  super(io)

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

Instance Method Details

#offset ⇒ Object

Returns the current offset of the io stream. Offset will be rounded up when reading bitfields.



259
260
261
 
# File 'lib/bindata/io.rb', line 259

def offset
  offset_raw
end

#read_all_bytes ⇒ Object

Reads all remaining bytes from the stream.



284
285
286
287
 
# File 'lib/bindata/io.rb', line 284

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.



291
292
293
294
295
296
297
298
299
300
301
302
303
 
# File 'lib/bindata/io.rb', line 291

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) 


274
275
276
277
278
279
280
281
 
# File 'lib/bindata/io.rb', line 274

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.



307
308
309
310
 
# File 'lib/bindata/io.rb', line 307

def reset_read_bits
  @rnbits = 0
  @rval   = 0
end

#seekbytes(n) ⇒ Object

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



264
265
266
267
 
# File 'lib/bindata/io.rb', line 264

def seekbytes(n)
  reset_read_bits
  seek(n)
end

#with_buffer(n) ⇒ 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.



250
251
252
253
254
255
 
# File 'lib/bindata/io.rb', line 250

def with_buffer(n)
  with_buffer_common(n) do
    yield
    read
  end
end