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#! /usr/bin/python from gzip import GzipFile from StringIO import StringIO class GZipPipe(StringIO) : """This class implements a compression pipe suitable for asynchronous process. Only one buffer of data is read/compressed at a time. The process doesn't read the whole file at once : This improves performance and prevent hight memory consumption for big files.""" # Size of the internal buffer CHUNCK_SIZE = 1024 def __init__(self, source = None, name = "data") : """Constructor @param source Source data to compress (as a stream/File/Buffer - anything with a read() method) @param name Name of the data within the zip file""" # Source file self.source = source # OEF reached for source ? self.source_eof = False # Buffer self.buffer = "" StringIO.__init__(self) # Inherited constructor # Init ZipFile that writes to us (the StringIO buffer) self.zipfile = GzipFile(name, 'wb', 9, self) def write(self, data) : """The write mzthod shouldn't be called from outside. A GZipFile was created with this current object as a output buffer anbd it fills it whenever we write to it (calling the read method of this object will do it for you) """ self.buffer += data def read(self, size = -1) : """Calling read() on a zip pipe will suck data from the source stream. @param size Maximum size to read - Read whole compressed file if not specified. @return Compressed data""" # Feed the zipped buffer by writing source data to the zip stream while ((len(self.buffer) < size) or (size == -1)) and not self.source_eof : # No source given in input if self.source == None: break # Get a chunk of source data chunk = self.source.read(GZipPipe.CHUNCK_SIZE) # Feed the source zip file (that fills the compressed buffer) self.zipfile.write(chunk) # End of source file ? if (len(chunk) < GZipPipe.CHUNCK_SIZE) : self.source_eof = True self.zipfile.flush() self.zipfile.close() break # We have enough data in the buffer (or source file is EOF): Give it to the output if size == 0: result = "" if size >= 1 : result = self.buffer[0:size] self.buffer = self.buffer[size:] else : # size < 0 : All requested result = self.buffer self.buffer = "" return result
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