def decode(cls, encoded, taxonomy=None):
"""Decode a field from a byte array.
Returns:
(field, num_read).
field: the field read from the byte array
num_read: number of bytes this field took up
Raises:
Error: if there is not enough bytes in the array for the field.
"""
assert len(encoded) >= 2
# prefix
pos = 0
fixedwidth, variablewidth, has_ordinal, has_name = \
prefix.decode_prefix(ord(encoded[pos]))
pos += 1
type_id = ord(encoded[pos])
# TODO(jamesc) - need to handle user supplied registries
field_type = DEFAULT_REGISTRY[type_id]
pos += 1
# ordinal
ordinal = None
if has_ordinal:
ordinal = codecs.dec_short(encoded[pos:])
pos += 2
# name
name = None
if has_name:
name_len = ord(encoded[pos])
pos += 1 # length encoded as 1 byte
name = codecs.dec_unicode(encoded[pos:pos + name_len])
pos += name_len
elif has_ordinal and taxonomy:
name = taxonomy.get_name(ordinal)
# value
if fixedwidth:
value = field_type.decoder(encoded[pos:pos +
field_type.fixed_size])
pos += field_type.fixed_size
else:
value_length = decode_value_length(encoded[pos:], variablewidth)
pos += variablewidth
if type_id == types.FUDGEMSG_TYPE_ID:
value = fudgemsg.message.Message.decode(
encoded[pos:pos + value_length], taxonomy)
else:
value = field_type.decoder(encoded[pos:pos + value_length])
pos += value_length
field = Field(field_type, ordinal, name, value)
return field, pos
def decode(cls, encoded, taxonomy=None):
"""Decode a field from a byte array.
Returns:
(field, num_read).
field: the field read from the byte array
num_read: number of bytes this field took up
Raises:
Error: if there is not enough bytes in the array for the field.
"""
assert len(encoded) >= 2
# prefix
pos = 0
fixedwidth, variablewidth, has_ordinal, has_name = \
prefix.decode_prefix(ord(encoded[pos]))
pos += 1
type_id = ord(encoded[pos])
# TODO(jamesc) - need to handle user supplied registries
field_type = DEFAULT_REGISTRY[type_id]
pos += 1
# ordinal
ordinal = None
if has_ordinal:
ordinal = codecs.dec_short(encoded[pos:])
pos += 2
# name
name = None
if has_name:
name_len = ord(encoded[pos])
pos += 1 # length encoded as 1 byte
name = codecs.dec_unicode(encoded[pos:pos+name_len])
pos += name_len
elif has_ordinal and taxonomy:
name = taxonomy.get_name(ordinal)
# value
if fixedwidth:
value = field_type.decoder(encoded[pos:pos+field_type.fixed_size])
pos += field_type.fixed_size
else:
value_length = decode_value_length(encoded[pos:], variablewidth)
pos += variablewidth
if type_id == types.FUDGEMSG_TYPE_ID:
value = fudgemsg.message.Message.decode(encoded[pos:pos+value_length], taxonomy)
else:
value = field_type.decoder(encoded[pos:pos+value_length])
pos += value_length
field = Field(field_type, ordinal, name, value)
return field, pos
def decode_value_length(encoded, width):
"""Decode the length of a value from a
var_width length.
Arguments:
encoded: The byte stream to read from
width: The number of bytes to read (1, 2, 4)
Return:
The decoded value length
"""
assert width in (0, 1, 2, 4)
if width == 0:
return 0
elif width == 1:
return codecs.dec_byte(encoded[0])
elif width == 2:
return codecs.dec_short(encoded[0:2])
else:
return codecs.dec_int(encoded[0:4])
def decode_value_length(encoded, width):
"""Decode the length of a value from a
var_width length.
Arguments:
encoded: The byte stream to read from
width: The number of bytes to read (1, 2, 4)
Return:
The decoded value length
"""
assert width in (0, 1, 2, 4)
if width == 0:
return 0
elif width == 1:
return codecs.dec_byte(encoded[0])
elif width == 2:
return codecs.dec_short(encoded[0:2])
else:
return codecs.dec_int(encoded[0:4])
