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try:
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from cStringIO import StringIO
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except ImportError:
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from StringIO import StringIO
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import struct
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# prefixed to all struct format strings
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STRUCT_PREFIX = '!'
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def hex (bytes) :
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return ' '.join(['%#04x' % ord(b) for b in bytes])
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class NotEnoughDataError (Exception) :
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pass
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class IStreamBase (object) :
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# prefixed to all struct format strings
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STRUCT_PREFIX = '!'
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class IReadStream (IStreamBase) :
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"""
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IReadStream simply provides various interfaces for reading bytes from a
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stream in various ways
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"""
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def read (self, size=None) :
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"""
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Read and return up to the given amount of bytes, or all bytes
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available if no size given.
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"""
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abstract
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def readStruct (self, fmt) :
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"""
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Reads the correct amount of data and then unpacks it according to
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the given format. Note that this always returns a tuple, for single
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items, use readItem
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"""
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fmt = self.STRUCT_PREFIX + fmt
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fmt_size = struct.calcsize(fmt)
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data = self.read(fmt_size)
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return struct.unpack(fmt, data)
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def readItem (self, fmt) :
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"""
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Reads the correct amount of data, unpacks it according to the
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given format, and then returns the first item.
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"""
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return self.readStruct(fmt)[0]
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def readVarLen (self, len_type) :
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"""
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Return the data part of a <length><data> structure.
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len_type indicates what type length has (struct format code).
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In the case of <length> being zero, returns an empty string.
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"""
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size = self.readItem(len_type)
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if size :
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return self.read(size)
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else :
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return ""
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def readEnum (self, enum) :
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"""
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Returns the item from the given list of enum values that corresponds
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to a single-byte value read from the stream
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"""
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return enum[self.readItem('B')]
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class ISeekableStream (IStreamBase) :
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"""
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Extends IStreamBase to provide the ability to seek backwards into the
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stream (which still does not know it's length, and thence cannot seek
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forwards).
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"""
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_position = None
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def tell (self) :
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"""
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Return the current offset into the seekable stream
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"""
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abstract
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def seek (self, pos) :
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"""
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Seek to the given position in the stream.
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"""
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abstract
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def mark (self) :
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"""
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Set a mark that can be later rolled back to with .reset()
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"""
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self._position = self.tell()
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def unmark (self) :
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"""
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Remove the mark without affecting the current position
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"""
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self._position = None
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def reset (self) :
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"""
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Rolls the buffer back to the position set earlier with mark()
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"""
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if self._position is not None :
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self.seek(self._position)
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self._position = None
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else :
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raise Exception("reset() without mark()")
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class ISeekableReadStream (ISeekableStream, IReadStream) :
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def peek (self, len=None) :
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"""
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Return a string representing what buf.read(len) would return, but do
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not affect future read operations
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"""
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pos = self.tell()
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data = self.read(len)
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self.seek(pos)
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return data
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class INonBlockingReadStream (IReadStream) :
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"""
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Otherwise identical to IReadStream, but read will either return size
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bytes, or raise a NotEnoughDataError
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"""
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pass
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class IWriteStream (IStreamBase) :
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"""
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IWriteStream provides various ways to write data to a byte stream
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"""
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def write (self, data) :
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"""
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Write the given bytes to the stream
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"""
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abstract
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def writeStruct (self, fmt, *args) :
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"""
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Pack the given arguments with the given struct format, and write it
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to the stream.
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"""
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self.write(struct.pack(self.STRUCT_PREFIX + fmt, *args))
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def writeVarLen (self, len_type, data) :
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"""
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Write a <length><data> field into the buffer. Len_type is the
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struct format code for the length field.
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"""
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self.writeStruct(len_type, len(data))
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self.write(data)
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def writeEnum (self, enum, name) :
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"""
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Write the single-byte value correspnding to the given name's
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position in the given enum
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"""
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self.writeStruct('B', enum.index(name))
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class IBufferBase (ISeekableStream) :
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"""
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A buffer simply provides a way to read and write data to/from a byte
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sequence stored in memory.
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"""
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def tell (self) :
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return self._buf.tell()
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def seek (self, offset) :
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return self._buf.seek(offset)
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def getvalue (self) :
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"""
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Returns the value of the buffer, i.e. a string with the contents of
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the buffer from position zero to the end.
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"""
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return self._buf.getvalue()
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class ReadBuffer (INonBlockingReadStream, ISeekableReadStream, IBufferBase) :
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"""
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A read-only buffer. Can be initialized with a given value and then later
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replaced in various ways, but cannot be modified.
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"""
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def __init__ (self, data="") :
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"""
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Initialize the buffer with the given data
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"""
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self._buf = StringIO(data)
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def read (self, size=None) :
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"""
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Return the given number of bytes, or raise a NotEnoughDataError
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"""
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if size == 0 :
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raise ValueError("can't read zero bytes")
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if size :
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ret = self._buf.read(size)
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else :
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ret = self._buf.read()
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if size and len(ret) < size :
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raise NotEnoughDataError()
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return ret
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def append (self, data) :
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"""
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Modify the buffer such that it contains the old data from this
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buffer, and the given data at the end. The read position in the buffer
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is kept the same.
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"""
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pos = self.tell()
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self._buf = StringIO(self._buf.getvalue() + data)
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self.seek(pos)
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def chop (self) :
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"""
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Discard the data in the buffer before the current read position.
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Also removes any marks.
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"""
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self._position = None
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self._buf = StringIO(self.read())
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def processWith (self, func) :
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"""
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Call the given function with this buffer as an argument after
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calling mark(). If the function
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a) returns None, the buffer is .chop()'d, and we repeat the
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process.
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b) raises a NotEnoughDataError, whereupon the buffer is rolled
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back to where it was before calling the function with
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chop().
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c) raises a StopIteration, whereupon we chop the buffer and
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return.
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d) returns something (i.e. ret is not None), whereupon we
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return that (and leave the current buffer position untouched).
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"""
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ret = None
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try :
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while ret is None :
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self.mark() # mark the position of the packet we are processing
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ret = func(self)
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if ret is None :
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# discard the processed packet and proceed to the next one
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self.chop()
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except NotEnoughDataError, e :
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self.reset() # reset position back to the start of the packet
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return e
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except StopIteration, e:
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self.chop()
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return e # processed ok, but we don't want to process any further packets
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else :
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return ret
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class WriteBuffer (IWriteStream, IBufferBase) :
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"""
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A write-only buffer. Data can be written to this buffer in various
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ways, but cannot be read from it except as a whole.
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"""
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def __init__ (self) :
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"""
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Initialize the buffer
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"""
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self._buf = StringIO()
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def write (self, data) :
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"""
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Write the given data to the current position in the stream,
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overwriting any previous data in that position, and extending
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the buffer if needed
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"""
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return self._buf.write(data)
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def readStringStream (stream, varlen_type) :
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"""
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Does readVarLen on an IReadStream until it returns something that evaluates to false ( == zero-length string)
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"""
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while True :
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item = stream.readVarLen(varlen_type)
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if item :
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yield item
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else :
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return
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def writeStringStream (stream, varlen_type, strings) :
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"""
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"""
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class StreamProtocol (object) :
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"""
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A mixin to let you use Buffer with twisted.internet.protocol.Protocol
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"""
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# a list of receivable command names
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RECV_COMMANDS = None
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# a list of sendable command names
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SEND_COMMANDS = None
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def __init__ (self) :
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"""
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Initialize the cross-dataReceived buffer
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"""
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self.in_buffer = ReadBuffer()
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def send (self, buf) :
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"""
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Write the contents of the given WriteBuffer to the transport
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"""
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self.transport.write(buf.getvalue())
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def dataReceived (self, data) :
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"""
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Buffer the incoming data and then try and process it
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"""
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self.in_buffer.append(data)
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ret = self.in_buffer.processWith(self.processPacket)
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def processPacket (self, buf) :
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"""
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Call processCommand with the buffer, handling the return value (either None or a deferred)
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"""
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ret = self.processCommand(buf)
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if ret :
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ret.addCallback(self.send)
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def processCommand (self, buf) :
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"""
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Process a command from the given buffer. May return a callback
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"""
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return self.readMethod(buf, self.RECV_COMMANDS, buf)
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# conveniance read/write
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def startCommand (self, cmd) :
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buf = WriteBuffer()
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buf.writeEnum(self.SEND_COMMANDS, cmd)
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return buf
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398 |
def readMethod (self, buf, methods, *args, **kwargs) :
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399 |
"""
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400 |
Reads a single-byte <methods>-enum value from the given buffer and
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use it to find the corresponding method (as <prefix>_<method-name>,
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prefix can be overriden with a keyword argument and defaults to
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'on'. If any extra arguments are given, they will be passed to the
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method.
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"""
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407 |
prefix = kwargs.pop("prefix", "on")
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return getattr(self, "%s_%s" % (prefix, buf.readEnum(methods)))(*args, **kwargs)
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410 |
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