Python code coverage for Lib/chunk.py

#	count	content
1	n/a	"""Simple class to read IFF chunks.
2	n/a
3	n/a	An IFF chunk (used in formats such as AIFF, TIFF, RMFF (RealMedia File
4	n/a	Format)) has the following structure:
5	n/a
6	n/a	+----------------+
7	n/a	\| ID (4 bytes) \|
8	n/a	+----------------+
9	n/a	\| size (4 bytes) \|
10	n/a	+----------------+
11	n/a	\| data \|
12	n/a	\| ... \|
13	n/a	+----------------+
14	n/a
15	n/a	The ID is a 4-byte string which identifies the type of chunk.
16	n/a
17	n/a	The size field (a 32-bit value, encoded using big-endian byte order)
18	n/a	gives the size of the whole chunk, including the 8-byte header.
19	n/a
20	n/a	Usually an IFF-type file consists of one or more chunks. The proposed
21	n/a	usage of the Chunk class defined here is to instantiate an instance at
22	n/a	the start of each chunk and read from the instance until it reaches
23	n/a	the end, after which a new instance can be instantiated. At the end
24	n/a	of the file, creating a new instance will fail with an EOFError
25	n/a	exception.
26	n/a
27	n/a	Usage:
28	n/a	while True:
29	n/a	try:
30	n/a	chunk = Chunk(file)
31	n/a	except EOFError:
32	n/a	break
33	n/a	chunktype = chunk.getname()
34	n/a	while True:
35	n/a	data = chunk.read(nbytes)
36	n/a	if not data:
37	n/a	pass
38	n/a	# do something with data
39	n/a
40	n/a	The interface is file-like. The implemented methods are:
41	n/a	read, close, seek, tell, isatty.
42	n/a	Extra methods are: skip() (called by close, skips to the end of the chunk),
43	n/a	getname() (returns the name (ID) of the chunk)
44	n/a
45	n/a	The __init__ method has one required argument, a file-like object
46	n/a	(including a chunk instance), and one optional argument, a flag which
47	n/a	specifies whether or not chunks are aligned on 2-byte boundaries. The
48	n/a	default is 1, i.e. aligned.
49	n/a	"""
50	n/a
51	n/a	class Chunk:
52	n/a	def __init__(self, file, align=True, bigendian=True, inclheader=False):
53	n/a	import struct
54	n/a	self.closed = False
55	n/a	self.align = align # whether to align to word (2-byte) boundaries
56	n/a	if bigendian:
57	n/a	strflag = '>'
58	n/a	else:
59	n/a	strflag = '<'
60	n/a	self.file = file
61	n/a	self.chunkname = file.read(4)
62	n/a	if len(self.chunkname) < 4:
63	n/a	raise EOFError
64	n/a	try:
65	n/a	self.chunksize = struct.unpack_from(strflag+'L', file.read(4))[0]
66	n/a	except struct.error:
67	n/a	raise EOFError
68	n/a	if inclheader:
69	n/a	self.chunksize = self.chunksize - 8 # subtract header
70	n/a	self.size_read = 0
71	n/a	try:
72	n/a	self.offset = self.file.tell()
73	n/a	except (AttributeError, OSError):
74	n/a	self.seekable = False
75	n/a	else:
76	n/a	self.seekable = True
77	n/a
78	n/a	def getname(self):
79	n/a	"""Return the name (ID) of the current chunk."""
80	n/a	return self.chunkname
81	n/a
82	n/a	def getsize(self):
83	n/a	"""Return the size of the current chunk."""
84	n/a	return self.chunksize
85	n/a
86	n/a	def close(self):
87	n/a	if not self.closed:
88	n/a	try:
89	n/a	self.skip()
90	n/a	finally:
91	n/a	self.closed = True
92	n/a
93	n/a	def isatty(self):
94	n/a	if self.closed:
95	n/a	raise ValueError("I/O operation on closed file")
96	n/a	return False
97	n/a
98	n/a	def seek(self, pos, whence=0):
99	n/a	"""Seek to specified position into the chunk.
100	n/a	Default position is 0 (start of chunk).
101	n/a	If the file is not seekable, this will result in an error.
102	n/a	"""
103	n/a
104	n/a	if self.closed:
105	n/a	raise ValueError("I/O operation on closed file")
106	n/a	if not self.seekable:
107	n/a	raise OSError("cannot seek")
108	n/a	if whence == 1:
109	n/a	pos = pos + self.size_read
110	n/a	elif whence == 2:
111	n/a	pos = pos + self.chunksize
112	n/a	if pos < 0 or pos > self.chunksize:
113	n/a	raise RuntimeError
114	n/a	self.file.seek(self.offset + pos, 0)
115	n/a	self.size_read = pos
116	n/a
117	n/a	def tell(self):
118	n/a	if self.closed:
119	n/a	raise ValueError("I/O operation on closed file")
120	n/a	return self.size_read
121	n/a
122	n/a	def read(self, size=-1):
123	n/a	"""Read at most size bytes from the chunk.
124	n/a	If size is omitted or negative, read until the end
125	n/a	of the chunk.
126	n/a	"""
127	n/a
128	n/a	if self.closed:
129	n/a	raise ValueError("I/O operation on closed file")
130	n/a	if self.size_read >= self.chunksize:
131	n/a	return b''
132	n/a	if size < 0:
133	n/a	size = self.chunksize - self.size_read
134	n/a	if size > self.chunksize - self.size_read:
135	n/a	size = self.chunksize - self.size_read
136	n/a	data = self.file.read(size)
137	n/a	self.size_read = self.size_read + len(data)
138	n/a	if self.size_read == self.chunksize and \
139	n/a	self.align and \
140	n/a	(self.chunksize & 1):
141	n/a	dummy = self.file.read(1)
142	n/a	self.size_read = self.size_read + len(dummy)
143	n/a	return data
144	n/a
145	n/a	def skip(self):
146	n/a	"""Skip the rest of the chunk.
147	n/a	If you are not interested in the contents of the chunk,
148	n/a	this method should be called so that the file points to
149	n/a	the start of the next chunk.
150	n/a	"""
151	n/a
152	n/a	if self.closed:
153	n/a	raise ValueError("I/O operation on closed file")
154	n/a	if self.seekable:
155	n/a	try:
156	n/a	n = self.chunksize - self.size_read
157	n/a	# maybe fix alignment
158	n/a	if self.align and (self.chunksize & 1):
159	n/a	n = n + 1
160	n/a	self.file.seek(n, 1)
161	n/a	self.size_read = self.size_read + n
162	n/a	return
163	n/a	except OSError:
164	n/a	pass
165	n/a	while self.size_read < self.chunksize:
166	n/a	n = min(8192, self.chunksize - self.size_read)
167	n/a	dummy = self.read(n)
168	n/a	if not dummy:
169	n/a	raise EOFError