Synnefo

# Copyright 2011-2012 GRNET S.A. All rights reserved.

#

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# without modification, are permitted provided that the following

# conditions are met:

#

#   1. Redistributions of source code must retain the above

#      copyright notice, this list of conditions and the following

#      disclaimer.

#

#   2. Redistributions in binary form must reproduce the above

#      copyright notice, this list of conditions and the following

#      disclaimer in the documentation and/or other materials

#      provided with the distribution.

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# THIS SOFTWARE IS PROVIDED BY GRNET S.A. ``AS IS'' AND ANY EXPRESS

# OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED

# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR

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from os import SEEK_CUR, SEEK_SET, fsync

from errno import ENOENT, EROFS

_zeros = ''

def zeros(nr):

    global _zeros

    size = len(_zeros)

    if nr == size:

        return _zeros

    if nr > size:

        _zeros += '\0' * (nr - size)

        return _zeros

    if nr < size:

        _zeros = _zeros[:nr]

        return _zeros

def file_sync_write_chunks(openfile, chunksize, offset, chunks, size=None):

    """Write given chunks to the given buffered file object.

       Writes never span across chunk boundaries.

       If size is given stop after or pad until size bytes have been written.

    """

    fwrite = openfile.write

    seek = openfile.seek

    padding = 0

    try:

        seek(offset * chunksize)

    except IOError, e:

        seek = None

        for x in xrange(offset):

            fwrite(zeros(chunksize))

    cursize = offset * chunksize

    for chunk in chunks:

        if padding:

            if seek:

                seek(padding - 1, SEEK_CUR)

                fwrite("\x00")

            else:

                fwrite(buffer(zeros(chunksize), 0, padding))

        if size is not None and cursize + chunksize >= size:

            chunk = chunk[:chunksize - (cursize - size)]

            fwrite(chunk)

            cursize += len(chunk)

            break

        fwrite(chunk)

        padding = chunksize - len(chunk)

    padding = size - cursize if size is not None else 0

    if padding <= 0:

        return

    q, r = divmod(padding, chunksize)

    for x in xrange(q):

        fwrite(zeros(chunksize))

    fwrite(buffer(zeros(chunksize), 0, r))

def file_sync_read_chunks(openfile, chunksize, nr, offset=0):

    """Read and yield groups of chunks from a buffered file object at offset.

       Reads never span accros chunksize boundaries.

    """

    fread = openfile.read

    remains = offset * chunksize

    seek = openfile.seek

    try:

        seek(remains)

    except IOError, e:

        seek = None

        while 1:

            s = fread(remains)

            remains -= len(s)

            if remains <= 0:

                break

    while nr:

        remains = chunksize

        chunk = ''

        while 1:

            s = fread(remains)

            if not s:

                if chunk:

                    yield chunk

                return

            chunk += s

            remains -= len(s)

            if remains <= 0:

                break

        yield chunk

        nr -= 1

class ContextFile(object):

    __slots__ = ("name", "fdesc", "create")

    def __init__(self, name, create=0):

        self.name = name

        self.fdesc = None

        self.create = create

        #self.dirty = 0

    def __enter__(self):

        name = self.name

        try:

            fdesc = open(name, 'rb+')

        except IOError, e:

            if self.create and e.errno == ENOENT:

                fdesc = open(name, 'w+')

            elif not self.create and e.errno == EROFS:

                fdesc = open(name, 'rb')

            else:

                raise

        self.fdesc = fdesc

        return self

    def __exit__(self, exc, arg, trace):

        fdesc = self.fdesc

        if fdesc is not None:

            #if self.dirty:

            #    fsync(fdesc.fileno())

            fdesc.close()

        return False  # propagate exceptions

    def seek(self, offset, whence=SEEK_SET):

        return self.fdesc.seek(offset, whence)

    def tell(self):

        return self.fdesc.tell()

    def truncate(self, size):

        self.fdesc.truncate(size)

    def sync_write(self, data):

        #self.dirty = 1

        self.fdesc.write(data)

    def sync_write_chunks(self, chunksize, offset, chunks, size=None):

        #self.dirty = 1

        return file_sync_write_chunks(self.fdesc, chunksize, offset, chunks, size)

    def sync_read(self, size):

        read = self.fdesc.read

        data = ''

        while 1:

            s = read(size)

            if not s:

                break

            data += s

        return data

    def sync_read_chunks(self, chunksize, nr, offset=0):

        return file_sync_read_chunks(self.fdesc, chunksize, nr, offset)