"""Simple class to read IFF chunks.

[0] Fix | Delete

[1] Fix | Delete

An IFF chunk (used in formats such as AIFF, TIFF, RMFF (RealMedia File

[2] Fix | Delete

Format)) has the following structure:

[3] Fix | Delete

[4] Fix | Delete

+----------------+

[5] Fix | Delete

| ID (4 bytes) |

[6] Fix | Delete

+----------------+

[7] Fix | Delete

| size (4 bytes) |

[8] Fix | Delete

+----------------+

[9] Fix | Delete

| data |

[10] Fix | Delete

| ... |

[11] Fix | Delete

+----------------+

[12] Fix | Delete

[13] Fix | Delete

The ID is a 4-byte string which identifies the type of chunk.

[14] Fix | Delete

[15] Fix | Delete

The size field (a 32-bit value, encoded using big-endian byte order)

[16] Fix | Delete

gives the size of the whole chunk, including the 8-byte header.

[17] Fix | Delete

[18] Fix | Delete

Usually an IFF-type file consists of one or more chunks. The proposed

[19] Fix | Delete

usage of the Chunk class defined here is to instantiate an instance at

[20] Fix | Delete

the start of each chunk and read from the instance until it reaches

[21] Fix | Delete

the end, after which a new instance can be instantiated. At the end

[22] Fix | Delete

of the file, creating a new instance will fail with an EOFError

[23] Fix | Delete

exception.

[24] Fix | Delete

[25] Fix | Delete

Usage:

[26] Fix | Delete

while True:

[27] Fix | Delete

try:

[28] Fix | Delete

chunk = Chunk(file)

[29] Fix | Delete

except EOFError:

[30] Fix | Delete

break

[31] Fix | Delete

chunktype = chunk.getname()

[32] Fix | Delete

while True:

[33] Fix | Delete

data = chunk.read(nbytes)

[34] Fix | Delete

if not data:

[35] Fix | Delete

pass

[36] Fix | Delete

# do something with data

[37] Fix | Delete

[38] Fix | Delete

The interface is file-like. The implemented methods are:

[39] Fix | Delete

read, close, seek, tell, isatty.

[40] Fix | Delete

Extra methods are: skip() (called by close, skips to the end of the chunk),

[41] Fix | Delete

getname() (returns the name (ID) of the chunk)

[42] Fix | Delete

[43] Fix | Delete

The __init__ method has one required argument, a file-like object

[44] Fix | Delete

(including a chunk instance), and one optional argument, a flag which

[45] Fix | Delete

specifies whether or not chunks are aligned on 2-byte boundaries. The

[46] Fix | Delete

default is 1, i.e. aligned.

[47] Fix | Delete

"""

[48] Fix | Delete

[49] Fix | Delete

class Chunk:

[50] Fix | Delete

def __init__(self, file, align=True, bigendian=True, inclheader=False):

[51] Fix | Delete

import struct

[52] Fix | Delete

self.closed = False

[53] Fix | Delete

self.align = align # whether to align to word (2-byte) boundaries

[54] Fix | Delete

if bigendian:

[55] Fix | Delete

strflag = '>'

[56] Fix | Delete

else:

[57] Fix | Delete

strflag = '<'

[58] Fix | Delete

self.file = file

[59] Fix | Delete

self.chunkname = file.read(4)

[60] Fix | Delete

if len(self.chunkname) < 4:

[61] Fix | Delete

raise EOFError

[62] Fix | Delete

try:

[63] Fix | Delete

self.chunksize = struct.unpack_from(strflag+'L', file.read(4))[0]

[64] Fix | Delete

except struct.error:

[65] Fix | Delete

raise EOFError from None

[66] Fix | Delete

if inclheader:

[67] Fix | Delete

self.chunksize = self.chunksize - 8 # subtract header

[68] Fix | Delete

self.size_read = 0

[69] Fix | Delete

try:

[70] Fix | Delete

self.offset = self.file.tell()

[71] Fix | Delete

except (AttributeError, OSError):

[72] Fix | Delete

self.seekable = False

[73] Fix | Delete

else:

[74] Fix | Delete

self.seekable = True

[75] Fix | Delete

[76] Fix | Delete

def getname(self):

[77] Fix | Delete

"""Return the name (ID) of the current chunk."""

[78] Fix | Delete

return self.chunkname

[79] Fix | Delete

[80] Fix | Delete

def getsize(self):

[81] Fix | Delete

"""Return the size of the current chunk."""

[82] Fix | Delete

return self.chunksize

[83] Fix | Delete

[84] Fix | Delete

def close(self):

[85] Fix | Delete

if not self.closed:

[86] Fix | Delete

try:

[87] Fix | Delete

self.skip()

[88] Fix | Delete

finally:

[89] Fix | Delete

self.closed = True

[90] Fix | Delete

[91] Fix | Delete

def isatty(self):

[92] Fix | Delete

if self.closed:

[93] Fix | Delete

raise ValueError("I/O operation on closed file")

[94] Fix | Delete

return False

[95] Fix | Delete

[96] Fix | Delete

def seek(self, pos, whence=0):

[97] Fix | Delete

"""Seek to specified position into the chunk.

[98] Fix | Delete

Default position is 0 (start of chunk).

[99] Fix | Delete

If the file is not seekable, this will result in an error.

[100] Fix | Delete

"""

[101] Fix | Delete

[102] Fix | Delete

if self.closed:

[103] Fix | Delete

raise ValueError("I/O operation on closed file")

[104] Fix | Delete

if not self.seekable:

[105] Fix | Delete

raise OSError("cannot seek")

[106] Fix | Delete

if whence == 1:

[107] Fix | Delete

pos = pos + self.size_read

[108] Fix | Delete

elif whence == 2:

[109] Fix | Delete

pos = pos + self.chunksize

[110] Fix | Delete

if pos < 0 or pos > self.chunksize:

[111] Fix | Delete

raise RuntimeError

[112] Fix | Delete

self.file.seek(self.offset + pos, 0)

[113] Fix | Delete

self.size_read = pos

[114] Fix | Delete

[115] Fix | Delete

def tell(self):

[116] Fix | Delete

if self.closed:

[117] Fix | Delete

raise ValueError("I/O operation on closed file")

[118] Fix | Delete

return self.size_read

[119] Fix | Delete

[120] Fix | Delete

def read(self, size=-1):

[121] Fix | Delete

"""Read at most size bytes from the chunk.

[122] Fix | Delete

If size is omitted or negative, read until the end

[123] Fix | Delete

of the chunk.

[124] Fix | Delete

"""

[125] Fix | Delete

[126] Fix | Delete

if self.closed:

[127] Fix | Delete

raise ValueError("I/O operation on closed file")

[128] Fix | Delete

if self.size_read >= self.chunksize:

[129] Fix | Delete

return b''

[130] Fix | Delete

if size < 0:

[131] Fix | Delete

size = self.chunksize - self.size_read

[132] Fix | Delete

if size > self.chunksize - self.size_read:

[133] Fix | Delete

size = self.chunksize - self.size_read

[134] Fix | Delete

data = self.file.read(size)

[135] Fix | Delete

self.size_read = self.size_read + len(data)

[136] Fix | Delete

if self.size_read == self.chunksize and \

[137] Fix | Delete

self.align and \

[138] Fix | Delete

(self.chunksize & 1):

[139] Fix | Delete

dummy = self.file.read(1)

[140] Fix | Delete

self.size_read = self.size_read + len(dummy)

[141] Fix | Delete

return data

[142] Fix | Delete

[143] Fix | Delete

def skip(self):

[144] Fix | Delete

"""Skip the rest of the chunk.

[145] Fix | Delete

If you are not interested in the contents of the chunk,

[146] Fix | Delete

this method should be called so that the file points to

[147] Fix | Delete

the start of the next chunk.

[148] Fix | Delete

"""

[149] Fix | Delete

[150] Fix | Delete

if self.closed:

[151] Fix | Delete

raise ValueError("I/O operation on closed file")

[152] Fix | Delete

if self.seekable:

[153] Fix | Delete

try:

[154] Fix | Delete

n = self.chunksize - self.size_read

[155] Fix | Delete

# maybe fix alignment

[156] Fix | Delete

if self.align and (self.chunksize & 1):

[157] Fix | Delete

n = n + 1

[158] Fix | Delete

self.file.seek(n, 1)

[159] Fix | Delete

self.size_read = self.size_read + n

[160] Fix | Delete

return

[161] Fix | Delete

except OSError:

[162] Fix | Delete

pass

[163] Fix | Delete

while self.size_read < self.chunksize:

[164] Fix | Delete

n = min(8192, self.chunksize - self.size_read)

[165] Fix | Delete

dummy = self.read(n)

[166] Fix | Delete

if not dummy:

[167] Fix | Delete

raise EOFError

[168] Fix | Delete

[169] Fix | Delete