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"""
maxminddb.decoder
~~~~~~~~~~~~~~~~~
This package contains code for decoding the MaxMind DB data section.
"""
from __future__ import unicode_literals
import struct
from maxminddb.compat import byte_from_int, int_from_bytes
from maxminddb.errors import InvalidDatabaseError
class Decoder(object): # pylint: disable=too-few-public-methods
"""Decoder for the data section of the MaxMind DB"""
def __init__(self, database_buffer, pointer_base=0, pointer_test=False):
"""Created a Decoder for a MaxMind DB
Arguments:
database_buffer -- an mmap'd MaxMind DB file.
pointer_base -- the base number to use when decoding a pointer
pointer_test -- used for internal unit testing of pointer code
"""
self._pointer_test = pointer_test
self._buffer = database_buffer
self._pointer_base = pointer_base
def _decode_array(self, size, offset):
array = []
for _ in range(size):
(value, offset) = self.decode(offset)
array.append(value)
return array, offset
def _decode_boolean(self, size, offset):
return size != 0, offset
def _decode_bytes(self, size, offset):
new_offset = offset + size
return self._buffer[offset:new_offset], new_offset
# pylint: disable=no-self-argument
# |-> I am open to better ways of doing this as long as it doesn't involve
# lots of code duplication.
def _decode_packed_type(type_code, type_size, pad=False):
# pylint: disable=protected-access, missing-docstring
def unpack_type(self, size, offset):
if not pad:
self._verify_size(size, type_size)
new_offset = offset + type_size
packed_bytes = self._buffer[offset:new_offset]
if pad:
packed_bytes = packed_bytes.rjust(type_size, b'\x00')
(value, ) = struct.unpack(type_code, packed_bytes)
return value, new_offset
return unpack_type
def _decode_map(self, size, offset):
container = {}
for _ in range(size):
(key, offset) = self.decode(offset)
(value, offset) = self.decode(offset)
container[key] = value
return container, offset
_pointer_value_offset = {
1: 0,
2: 2048,
3: 526336,
4: 0,
}
def _decode_pointer(self, size, offset):
pointer_size = ((size >> 3) & 0x3) + 1
new_offset = offset + pointer_size
pointer_bytes = self._buffer[offset:new_offset]
packed = pointer_bytes if pointer_size == 4 else struct.pack(
b'!c', byte_from_int(size & 0x7)) + pointer_bytes
unpacked = int_from_bytes(packed)
pointer = unpacked + self._pointer_base + \
self._pointer_value_offset[pointer_size]
if self._pointer_test:
return pointer, new_offset
(value, _) = self.decode(pointer)
return value, new_offset
def _decode_uint(self, size, offset):
new_offset = offset + size
uint_bytes = self._buffer[offset:new_offset]
return int_from_bytes(uint_bytes), new_offset
def _decode_utf8_string(self, size, offset):
new_offset = offset + size
return self._buffer[offset:new_offset].decode('utf-8'), new_offset
_type_decoder = {
1: _decode_pointer,
2: _decode_utf8_string,
3: _decode_packed_type(b'!d', 8), # double,
4: _decode_bytes,
5: _decode_uint, # uint16
6: _decode_uint, # uint32
7: _decode_map,
8: _decode_packed_type(
b'!i', 4, pad=True), # int32
9: _decode_uint, # uint64
10: _decode_uint, # uint128
11: _decode_array,
14: _decode_boolean,
15: _decode_packed_type(b'!f', 4), # float,
}
def decode(self, offset):
"""Decode a section of the data section starting at offset
Arguments:
offset -- the location of the data structure to decode
"""
new_offset = offset + 1
(ctrl_byte, ) = struct.unpack(b'!B', self._buffer[offset:new_offset])
type_num = ctrl_byte >> 5
# Extended type
if not type_num:
(type_num, new_offset) = self._read_extended(new_offset)
if type_num not in self._type_decoder:
raise InvalidDatabaseError('Unexpected type number ({type}) '
'encountered'.format(type=type_num))
(size, new_offset) = self._size_from_ctrl_byte(ctrl_byte, new_offset,
type_num)
return self._type_decoder[type_num](self, size, new_offset)
def _read_extended(self, offset):
(next_byte, ) = struct.unpack(b'!B', self._buffer[offset:offset + 1])
type_num = next_byte + 7
if type_num < 7:
raise InvalidDatabaseError(
'Something went horribly wrong in the decoder. An '
'extended type resolved to a type number < 8 '
'({type})'.format(type=type_num))
return type_num, offset + 1
def _verify_size(self, expected, actual):
if expected != actual:
raise InvalidDatabaseError(
'The MaxMind DB file\'s data section contains bad data '
'(unknown data type or corrupt data)')
def _size_from_ctrl_byte(self, ctrl_byte, offset, type_num):
size = ctrl_byte & 0x1f
if type_num == 1:
return size, offset
bytes_to_read = 0 if size < 29 else size - 28
new_offset = offset + bytes_to_read
size_bytes = self._buffer[offset:new_offset]
# Using unpack rather than int_from_bytes as it is about 200 lookups
# per second faster here.
if size == 29:
size = 29 + struct.unpack(b'!B', size_bytes)[0]
elif size == 30:
size = 285 + struct.unpack(b'!H', size_bytes)[0]
elif size > 30:
size = struct.unpack(b'!I', size_bytes.rjust(4,
b'\x00'))[0] + 65821
return size, new_offset
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