Sjoerd Mullender writes:

"""
Extended chunk so that it can also handle formats that are almost
according to EA IFF 85.  In particular, added options to handle
little-endian and to handle formats that include the header size in
the chunk size value.

Fixed a bug where the header size was included in the chunk size, which
it isn't according to EA IFF 85.

Added a new method getsize() to get the size of the chunk (excluding
header).

Fixed chunk documentation (TIFF doesn't look like it uses chunks).
Converted wave to use chunk.  Wave uses EA IFF 85 chunks except that
it uses little-endian encoding of integer data.

Removed __del__ methods from aifc and wave since I got an
AttributeError there upon exit.
"""

3 files changed, 50 insertions, 147 deletions

diff --git a/Lib/aifc.py b/Lib/aifc.py
index a4d9616..6c19dea 100644
--- a/Lib/aifc.py
+++ b/Lib/aifc.py
@@ -293,8 +293,6 @@ class Aifc_read:
 		self._comm_chunk_read = 0
 		while 1:
 			self._ssnd_seek_needed = 1
-			#DEBUG: SGI's soundfiler has a bug.  There should
-			# be no need to check for EOF here.
 			try:
 				chunk = Chunk(self._file)
 			except EOFError:
@@ -337,10 +335,6 @@ class Aifc_read:
 		# else, assume it is an open file object already
 		self.initfp(f)
 
-	def __del__(self):
-		if self._file:
-			self.close()
-
 	#
 	# User visible methods.
 	#
diff --git a/Lib/chunk.py b/Lib/chunk.py
index 231a59c..fbbb1c1 100644
--- a/Lib/chunk.py
+++ b/Lib/chunk.py
@@ -49,19 +49,24 @@ default is 1, i.e. aligned.
 """
 
 class Chunk:
-    def __init__(self, file, align = 1):
+    def __init__(self, file, align = 1, bigendian = 1, inclheader = 0):
         import struct
         self.closed = 0
         self.align = align	# whether to align to word (2-byte) boundaries
+        if bigendian:
+            strflag = '>'
+        else:
+            strflag = '<'
         self.file = file
         self.chunkname = file.read(4)
         if len(self.chunkname) < 4:
             raise EOFError
         try:
-            self.chunksize = struct.unpack('>l', file.read(4))[0]
+            self.chunksize = struct.unpack(strflag+'l', file.read(4))[0]
         except struct.error:
             raise EOFError
-        self.chunksize = self.chunksize - 8 # subtract header
+        if inclheader:
+            self.chunksize = self.chunksize - 8 # subtract header
         self.size_read = 0
         try:
             self.offset = self.file.tell()
@@ -74,6 +79,10 @@ class Chunk:
         """Return the name (ID) of the current chunk."""
         return self.chunkname
 
+    def getsize(self):
+        """Return the size of the current chunk."""
+        return self.chunksize
+
     def close(self):
         if not self.closed:
             self.skip()
diff --git a/Lib/wave.py b/Lib/wave.py
index 5344db2..aec9bdf 100644
--- a/Lib/wave.py
+++ b/Lib/wave.py
@@ -85,87 +85,7 @@ if struct.pack("h", 1) == "\000\001":
 else:
 	big_endian = 0
 
-def _read_long(file):
-	x = 0L
-	for i in range(4):
-		byte = file.read(1)
-		if byte == '':
-			raise EOFError
-		x = x + (ord(byte) << (8 * i))
-	if x >= 0x80000000L:
-		x = x - 0x100000000L
-	return int(x)
-
-def _read_ulong(file):
-	x = 0L
-	for i in range(4):
-		byte = file.read(1)
-		if byte == '':
-			raise EOFError
-		x = x + (ord(byte) << (8 * i))
-	return x
-
-def _read_short(file):
-	x = 0
-	for i in range(2):
-		byte = file.read(1)
-		if byte == '':
-			raise EOFError
-		x = x + (ord(byte) << (8 * i))
-	if x >= 0x8000:
-		x = x - 0x10000
-	return x
-
-def _write_short(f, x):
-	d, m = divmod(x, 256)
-	f.write(chr(m))
-	f.write(chr(d))
-
-def _write_long(f, x):
-	if x < 0:
-		x = x + 0x100000000L
-	for i in range(4):
-		d, m = divmod(x, 256)
-		f.write(chr(int(m)))
-		x = d
-
-class Chunk:
-	def __init__(self, file):
-		self.file = file
-		self.chunkname = self.file.read(4)
-		if len(self.chunkname) < 4:
-			raise EOFError
-		self.chunksize = _read_long(self.file)
-		self.size_read = 0
-		self.offset = self.file.tell()
-
-	def rewind(self):
-		self.file.seek(self.offset, 0)
-		self.size_read = 0
-
-	def setpos(self, pos):
-		if pos < 0 or pos > self.chunksize:
-			raise RuntimeError
-		self.file.seek(self.offset + pos, 0)
-		self.size_read = pos
-		
-	def read(self, length):
-		if self.size_read >= self.chunksize:
-			return ''
-		if length > self.chunksize - self.size_read:
- 			length = self.chunksize - self.size_read
-		data = self.file.read(length)
-		self.size_read = self.size_read + len(data)
-		return data
-
-	def skip(self):
-		try:
-			self.file.seek(self.chunksize - self.size_read, 1)
-		except RuntimeError:
-			while self.size_read < self.chunksize:
-				dummy = self.read(8192)
-				if not dummy:
-					raise EOFError
+from chunk import Chunk
 
 class Wave_read:
 	# Variables used in this class:
@@ -197,41 +117,34 @@ class Wave_read:
 	# _data_chunk -- instantiation of a chunk class for the DATA chunk
 	# _framesize -- size of one frame in the file
 
-## 	access _file, _nchannels, _nframes, _sampwidth, _framerate, \
-## 		  _comptype, _compname, _soundpos, \
-## 		  _fmt_chunk_read, _data_seek_needed, \
-## 		  _data_chunk, _framesize: private
-
 	def initfp(self, file):
-		self._file = file
 		self._convert = None
 		self._soundpos = 0
-		form = self._file.read(4)
-		if form != 'RIFF':
+		self._file = Chunk(file, bigendian = 0)
+		if self._file.getname() != 'RIFF':
 			raise Error, 'file does not start with RIFF id'
-		formlength = _read_long(self._file)
-		if formlength <= 0:
-			raise Error, 'invalid FORM chunk data size'
-		formdata = self._file.read(4)
-		formlength = formlength - 4
-		if formdata != 'WAVE':
+		if self._file.read(4) != 'WAVE':
 			raise Error, 'not a WAVE file'
 		self._fmt_chunk_read = 0
-		while formlength > 0:
+		self._data_chunk = None
+		while 1:
 			self._data_seek_needed = 1
-			chunk = Chunk(self._file)
-			if chunk.chunkname == 'fmt ':
+			try:
+				chunk = Chunk(self._file, bigendian = 0)
+			except EOFError:
+				break
+			chunkname = chunk.getname()
+			if chunkname == 'fmt ':
 				self._read_fmt_chunk(chunk)
 				self._fmt_chunk_read = 1
-			elif chunk.chunkname == 'data':
+			elif chunkname == 'data':
 				if not self._fmt_chunk_read:
 					raise Error, 'data chunk before fmt chunk'
 				self._data_chunk = chunk
 				self._nframes = chunk.chunksize / self._framesize
 				self._data_seek_needed = 0
-			formlength = formlength - 8 - chunk.chunksize
-			if formlength > 0:
-				chunk.skip()
+				break
+			chunk.skip()
 		if not self._fmt_chunk_read or not self._data_chunk:
 			raise Error, 'fmt chunk and/or data chunk missing'
 
@@ -241,10 +154,6 @@ class Wave_read:
 		# else, assume it is an open file object already
 		self.initfp(f)
 
-	def __del__(self):
-		if self._file:
-			self.close()
-
 	#
 	# User visible methods.
 	#
@@ -298,10 +207,10 @@ class Wave_read:
 
 	def readframes(self, nframes):
 		if self._data_seek_needed:
-			self._data_chunk.rewind()
+			self._data_chunk.seek(0, 0)
 			pos = self._soundpos * self._framesize
 			if pos:
-				self._data_chunk.setpos(pos)
+				self._data_chunk.seek(pos, 0)
 			self._data_seek_needed = 0
 		if nframes == 0:
 			return ''
@@ -310,12 +219,17 @@ class Wave_read:
 			# something that only looks like a file object, so
 			# we have to reach into the innards of the chunk object
 			import array
+			chunk = self._data_chunk
 			data = array.array(_array_fmts[self._sampwidth])
 			nitems = nframes * self._nchannels
-			if nitems * self._sampwidth > self._data_chunk.chunksize - self._data_chunk.size_read:
-				nitems = (self._data_chunk.chunksize - self._data_chunk.size_read) / self._sampwidth
-			data.fromfile(self._data_chunk.file, nitems)
-			self._data_chunk.size_read = self._data_chunk.size_read + nitems * self._sampwidth
+			if nitems * self._sampwidth > chunk.chunksize - chunk.size_read:
+				nitems = (chunk.chunksize - chunk.size_read) / self._sampwidth
+			data.fromfile(chunk.file.file, nitems)
+			# "tell" data chunk how much was read
+			chunk.size_read = chunk.size_read + nitems * self._sampwidth
+			# do the same for the outermost chunk
+			chunk = chunk.file
+			chunk.size_read = chunk.size_read + nitems * self._sampwidth
 			data.byteswap()
 			data = data.tostring()
 		else:
@@ -328,16 +242,12 @@ class Wave_read:
 	#
 	# Internal methods.
 	#
-## 	access *: private
 
 	def _read_fmt_chunk(self, chunk):
-		wFormatTag = _read_short(chunk)
-		self._nchannels = _read_short(chunk)
-		self._framerate = _read_long(chunk)
-		dwAvgBytesPerSec = _read_long(chunk)
-		wBlockAlign = _read_short(chunk)
+		wFormatTag, self._nchannels, self._framerate, dwAvgBytesPerSec, wBlockAlign = struct.unpack('<hhllh', chunk.read(14))
 		if wFormatTag == WAVE_FORMAT_PCM:
-			self._sampwidth = (_read_short(chunk) + 7) / 8
+			sampwidth = struct.unpack('<h', chunk.read(2))[0]
+			self._sampwidth = (sampwidth + 7) / 8
 		else:
 			raise Error, 'unknown format: ' + `wFormatTag`
 		self._framesize = self._nchannels * self._sampwidth
@@ -369,10 +279,6 @@ class Wave_write:
 	# _nframeswritten -- the number of frames actually written
 	# _datawritten -- the size of the audio samples actually written
 
-## 	access _file, _comptype, _compname, _nchannels, _sampwidth, \
-## 		  _framerate, _nframes, _nframeswritten, \
-## 		  _datalength, _datawritten: private
-
 	def __init__(self, f):
 		if type(f) == type(''):
 			f = __builtin__.open(f, 'wb')
@@ -512,7 +418,6 @@ class Wave_write:
 	#
 	# Internal methods.
 	#
-## 	access *: private
 
 	def _ensure_header_written(self, datasize):
 		if not self._datawritten:
@@ -530,28 +435,23 @@ class Wave_write:
 			self._nframes = initlength / (self._nchannels * self._sampwidth)
 		self._datalength = self._nframes * self._nchannels * self._sampwidth
 		self._form_length_pos = self._file.tell()
-		_write_long(self._file, 36 + self._datalength)
-		self._file.write('WAVE')
-		self._file.write('fmt ')
-		_write_long(self._file, 16)
-		_write_short(self._file, WAVE_FORMAT_PCM)
-		_write_short(self._file, self._nchannels)
-		_write_long(self._file, self._framerate)
-		_write_long(self._file, self._nchannels * self._framerate * self._sampwidth)
-		_write_short(self._file, self._nchannels * self._sampwidth)
-		_write_short(self._file, self._sampwidth * 8)
-		self._file.write('data')
+		self._file.write(struct.pack('<lsslhhllhhs',
+			36 + self._datalength, 'WAVE', 'fmt ', 16,
+			WAVE_FORMAT_PCM, self._nchannels, self._framerate,
+			self._nchannels * self._framerate * self._sampwidth,
+			self._nchannels * self._sampwidth,
+			self._sampwidth * 8, 'data'))
 		self._data_length_pos = self._file.tell()
-		_write_long(self._file, self._datalength)
+		self._file.write(struct.pack('<l', self._datalength))
 
 	def _patchheader(self):
 		if self._datawritten == self._datalength:
 			return
 		curpos = self._file.tell()
 		self._file.seek(self._form_length_pos, 0)
-		_write_long(self._file, 36 + self._datawritten)
+		self._file.write(struct.pack('<l', 36 + self._datawritten))
 		self._file.seek(self._data_length_pos, 0)
-		_write_long(self._file, self._datawritten)
+		self._file.write(struct.pack('<l', self._datawritten))
 		self._file.seek(curpos, 0)
 		self._datalength = self._datawritten