Current File : //usr/lib/calibre/calibre/ebooks/mobi/writer8/header.py
#!/usr/bin/env python3
__license__ = 'GPL v3'
__copyright__ = '2012, Kovid Goyal <kovid@kovidgoyal.net>'
__docformat__ = 'restructuredtext en'
import random, numbers
from io import BytesIO
from collections import OrderedDict
from struct import pack
from calibre.ebooks.mobi.utils import align_block
from polyglot.builtins import iteritems, as_bytes
NULL = 0xffffffff
zeroes = lambda x: b'\0'*x
nulls = lambda x: b'\xff'*x
short = lambda x: pack(b'>H', x)
class Header(OrderedDict):
HEADER_NAME = b''
DEFINITION = '''
'''
ALIGN_BLOCK = False
POSITIONS = {} # Mapping of position field to field whose position should
# be stored in the position field
SHORT_FIELDS = set()
def __init__(self):
OrderedDict.__init__(self)
for line in self.DEFINITION.splitlines():
line = line.strip()
if not line or line.startswith('#'):
continue
name, val = (x.strip() for x in line.partition('=')[0::2])
if val:
val = eval(val, {'zeroes':zeroes, 'NULL':NULL, 'DYN':None,
'nulls':nulls, 'short':short, 'random':random})
else:
val = 0
if name in self:
raise ValueError('Duplicate field in definition: %r'%name)
self[name] = val
@property
def dynamic_fields(self):
return tuple(k for k, v in iteritems(self) if v is None)
def __call__(self, **kwargs):
positions = {}
for name, val in iteritems(kwargs):
if name not in self:
raise KeyError('Not a valid header field: %r'%name)
self[name] = val
buf = BytesIO()
buf.write(as_bytes(self.HEADER_NAME))
for name, val in iteritems(self):
val = self.format_value(name, val)
positions[name] = buf.tell()
if val is None:
raise ValueError('Dynamic field %r not set'%name)
if isinstance(val, numbers.Integral):
fmt = b'H' if name in self.SHORT_FIELDS else b'I'
val = pack(b'>'+fmt, val)
buf.write(val)
for pos_field, field in iteritems(self.POSITIONS):
buf.seek(positions[pos_field])
buf.write(pack(b'>I', positions[field]))
ans = buf.getvalue()
if self.ALIGN_BLOCK:
ans = align_block(ans)
return ans
def format_value(self, name, val):
return val
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