Source code for baseband.vlbi_base.header
# Licensed under the GPLv3 - see LICENSE
"""
Base definitions for VLBI Headers, used for VDIF and Mark 5B.
Defines a header class VLBIHeaderBase that can be used to hold the words
corresponding to a frame header, providing access to the values encoded in
via a dict-like interface. Definitions for headers are constructed using
the HeaderParser class.
"""
from __future__ import absolute_import, division, print_function
from copy import copy
import struct
import warnings
from collections import OrderedDict
import numpy as np
__all__ = ['four_word_struct', 'eight_word_struct',
'make_parser', 'make_setter',
'HeaderProperty', 'HeaderPropertyGetter',
'HeaderParser', 'VLBIHeaderBase']
four_word_struct = struct.Struct('<4I')
"""Struct instance that packs/unpacks 4 unsigned 32-bit integers."""
eight_word_struct = struct.Struct('<8I')
"""Struct instance that packs/unpacks 8 unsigned 32-bit integers."""
[docs]def make_parser(word_index, bit_index, bit_length, default=None):
"""Construct a function that converts specific bits from a header.
The function acts on a tuple/array of 32-bit words, extracting given bits
from a specific word and convert them to bool (for single bit) or integer.
The parameters are those that define header keywords, and all parsers do
``(words[word_index] >> bit_index) & ((1 << bit_length) - 1)``, except that
that they have been optimized for the specific cases of single bits,
full words, and items starting at bit 0. As a special case, bit_length=64
allows one to extract two words as a single (long) integer.
Parameters
----------
word_index : int
Index into the tuple of words passed to the function.
bit_index : int
Index to the starting bit of the part to be extracted.
bit_length : int
Number of bits to be extracted.
Returns
-------
parser : function
To be used as ``parser(words)``.
"""
if bit_length == 1:
def parser(words):
return (words[word_index] & (1 << bit_index)) != 0
elif bit_length == 32:
assert bit_index == 0
def parser(words):
return words[word_index]
elif bit_length == 64:
assert bit_index == 0
def parser(words):
return words[word_index] + words[word_index + 1] * (1 << 32)
else:
bit_mask = (1 << bit_length) - 1 # e.g., bit_length=8 -> 0xff
if bit_index == 0:
def parser(words):
return words[word_index] & bit_mask
else:
def parser(words):
return (words[word_index] >> bit_index) & bit_mask
return parser
[docs]def make_setter(word_index, bit_index, bit_length, default=None):
"""Construct a function that uses a value to set specific bits in a header.
The function will act on a tuple/array of words, setting given bits
from a given word using a value.
The parameters are just those that define header keywords.
Parameters
----------
word_index : int
Index into the tuple of words passed to the function.
bit_index : int
Index to the starting bit of the part to be extracted.
bit_length : int
Number of bits to be extracted.
default : int or bool or None
Possible default value to use in function if no default is passed on.
Returns
-------
setter : function
To be used as ``setter(words, value)``.
"""
def setter(words, value):
if value is None and default is not None:
value = default
bit_mask = (1 << bit_length) - 1
# Check that value will fit within the bit limits.
if np.any(value & bit_mask != value):
raise ValueError("{0} cannot be represented with {1} bits"
.format(value, bit_length))
if bit_length == 64:
word1 = value & (1 << 32) - 1
word2 = value >> 32
words[word_index] = word1
words[word_index + 1] = word2
return words
word = words[word_index]
# Zero the part to be set, and add the value.
bit_mask <<= bit_index
word = ((word | bit_mask) ^ bit_mask) | (value << bit_index)
words[word_index] = word
return words
return setter
def get_default(word_index, bit_index, bit_length, default=None):
return default
[docs]class HeaderProperty(object):
"""Mimic a dictionary, calculating entries from header words.
Used to calculate setter functions and extract default values.
Parameters
----------
header_parser : `HeaderParser`
A dict with header encoding information.
getter : function
Function that uses the encoding information to calculate a result.
"""
def __init__(self, header_parser, getter, doc=None):
self.header_parser = header_parser
self.getter = getter
if doc is not None:
self.__doc__ = doc
def __getitem__(self, item):
definition = self.header_parser[item]
return self.getter(*definition)
[docs]class HeaderPropertyGetter(object):
"""Special property for attaching HeaderProperty."""
def __init__(self, getter, doc=None):
self.getter = getter
self.__doc__ = doc or getter.__doc__
def __get__(self, instance, owner_cls=None):
if instance is None: # pragma: no cover
return self
return HeaderProperty(instance, getattr(instance, self.getter),
doc=self.__doc__)
[docs]class HeaderParser(OrderedDict):
"""Parser & setter for VLBI header keywords.
An ordered dict of header keywords, with values that describe how they are
encoded in a given VLBI header. Initialisation is as a normal OrderedDict,
with a key, value pairs. The value should be a tuple containing:
word_index : int
Index into the header words for this key.
bit_index : int
Index to the starting bit of the part used for this key.
bit_length : int
Number of bits.
default : int or bool or None
Possible default value to use in initialisation (e.g., a sync pattern).
The class provides dict-like properties ``parsers``, ``setters``, and
``defaults``, which return functions that get a given keyword from header
words, set the corresponding part of the header words to a value, or
return the default value (if defined).
Note that while in principle, parsers and setters could be calculated on
the fly, we precalculate the parsers to speed up header keyword access.
"""
def __init__(self, *args, **kwargs):
self._make_parser = kwargs.pop('make_parser', make_parser)
self._make_setter = kwargs.pop('make_setter', make_setter)
self._get_default = kwargs.pop('get_default', get_default)
# Use a dict rather than OrderedDict for the parsers for better speed.
# Note that this gets filled by calls to __setitem__.
self._parsers = {}
super(HeaderParser, self).__init__(*args, **kwargs)
[docs] def copy(self):
"""Make an independent copy."""
return self.__class__(self, make_parser=self._make_parser,
make_setter=self._make_setter,
get_default=self._get_default)
def __add__(self, other):
if not isinstance(other, HeaderParser):
return NotImplemented
result = self.copy()
result.update(other)
return result
def __setitem__(self, item, value):
self._parsers[item] = self._make_parser(*value)
super(HeaderParser, self).__setitem__(item, value)
@property
def parsers(self):
"""Dict with functions to get specific header values."""
return self._parsers
defaults = HeaderPropertyGetter(
'_get_default',
doc="Dict-like allowing access to default header values.")
setters = HeaderPropertyGetter(
'_make_setter',
doc="Dict-like returning function to set specific header value.")
[docs] def update(self, other):
"""Update the parser with the information from another one."""
if not isinstance(other, HeaderParser):
raise TypeError("can only update using a HeaderParser instance.")
super(HeaderParser, self).update(other)
# Update the parsers rather than recalculate all the functions.
self._parsers.update(other._parsers)
[docs]class VLBIHeaderBase(object):
"""Base class for all VLBI headers.
Defines a number of common routines.
Generally, the actual class should define:
_struct: `~struct.Struct` instance that can pack/unpack header words.
_header_parser: `HeaderParser` instance corresponding to this class.
_properties: tuple of properties accessible/usable in initialisation
It also should define properties (getters *and* setters):
payload_nbytes: number of bytes used by payload
frame_nbytes: total number of bytes for header + payload
get_time, set_time, and a corresponding time property:
time at start of payload
Parameters
----------
words : tuple or list of int, or None
header words (generally, 32 bit unsigned int). If `None`,
set to a list of zeros for later initialisation. If given as a tuple,
the header is immutable.
verify : bool
Whether to do basic verification of integrity. For the base class,
checks that the number of words is consistent with the struct size.
"""
_properties = ('payload_nbytes', 'frame_nbytes', 'time')
"""Properties accessible/usable in initialisation for all headers."""
def __init__(self, words, verify=True):
if words is None:
self.words = [0] * (self._struct.size // 4)
else:
self.words = words
if verify:
self.verify()
[docs] def verify(self):
"""Verify that the length of the words is consistent.
Subclasses should override this to do more thorough checks.
"""
assert len(self.words) == (self._struct.size // 4)
[docs] def copy(self, **kwargs):
"""Create a mutable and independent copy of the header.
Keyword arguments can be passed on as needed by possible subclasses.
"""
kwargs.setdefault('verify', False)
new = self.__class__(copy(self.words), **kwargs)
new.mutable = True
return new
def __copy__(self):
return self.copy()
@property
def nbytes(self):
"""Size of the header in bytes."""
return self._struct.size
@property
def mutable(self):
"""Whether the header can be modified."""
if isinstance(self.words, tuple):
return False
word0 = self.words[0]
try:
self.words[0] = 0
except Exception:
return False
else:
self.words[0] = word0
return True
@mutable.setter
def mutable(self, mutable):
if isinstance(self.words, np.ndarray):
self.words.flags['WRITEABLE'] = mutable
elif isinstance(self.words, tuple):
if mutable:
self.words = list(self.words)
elif isinstance(self.words, list):
if not mutable:
self.words = tuple(self.words)
else:
raise TypeError("do not know how to set mutability of '.words' "
"of class {0}".format(type(self.words)))
[docs] @classmethod
def fromfile(cls, fh, *args, **kwargs):
"""Read VLBI Header from file.
Arguments are the same as for class initialisation. The header
constructed will be immutable.
"""
s = fh.read(cls._struct.size)
if len(s) != cls._struct.size:
raise EOFError
return cls(cls._struct.unpack(s), *args, **kwargs)
[docs] def tofile(self, fh):
"""Write VLBI frame header to filehandle."""
return fh.write(self._struct.pack(*self.words))
[docs] @classmethod
def fromvalues(cls, *args, **kwargs):
"""Initialise a header from parsed values.
Here, the parsed values must be given as keyword arguments, i.e., for
any ``header = cls(<words>)``, ``cls.fromvalues(**header) == header``.
However, unlike for the `fromkeys` class method, data can also be set
using arguments named after header methods, such as ``time``.
Parameters
----------
*args
Possible arguments required to initialize an empty header.
**kwargs
Values used to initialize header keys or methods.
"""
# Initialize an empty header, and update it with the keyword arguments.
self = cls(None, *args, verify=False)
# Set defaults in keyword arguments.
for key in set(self.keys()).difference(kwargs.keys()):
default = self._header_parser.defaults[key]
if default is not None:
kwargs[key] = default
self.update(**kwargs)
return self
[docs] @classmethod
def fromkeys(cls, *args, **kwargs):
"""Initialise a header from parsed values.
Like fromvalues, but without any interpretation of keywords.
Raises
------
KeyError : if not all keys required are present in ``kwargs``
"""
self = cls(None, *args, verify=False)
not_in_both = (set(self.keys()).symmetric_difference(kwargs) -
{'verify'})
if not_in_both:
not_in_kwarg = set(self.keys()).difference(kwargs)
not_in_self = set(kwargs).difference(self.keys()) - {'verify'}
msg_parts = []
for item, msg in ((not_in_kwarg, "is missing keywords ({0})"),
(not_in_self, "contains extra keywords ({0})")):
if item:
msg_parts.append(msg.format(item))
raise KeyError("input list " + " and ".join(msg_parts))
self.update(**kwargs)
return self
[docs] def update(self, **kwargs):
"""Update the header by setting keywords or properties.
Here, any keywords matching header keys are applied first, and any
remaining ones are used to set header properties, in the order set
by the class (in ``_properties``).
Parameters
----------
verify : bool, optional
If `True` (default), verify integrity after updating.
**kwargs
Arguments used to set keywords and properties.
"""
verify = kwargs.pop('verify', True)
# First use keywords which are also keys into self.
for key in set(kwargs.keys()).intersection(self.keys()):
self[key] = kwargs.pop(key)
# Next, use remaining keyword arguments to set properties.
# Order is important, so we cannot use an intersection as above.
if kwargs:
for key in self._properties:
if key in kwargs:
setattr(self, key, kwargs.pop(key))
if kwargs:
warnings.warn("some keywords unused in header update: {0}"
.format(kwargs))
if verify:
self.verify()
def __getitem__(self, item):
"""Get the value a particular header item from the header words."""
try:
return self._header_parser._parsers[item](self.words)
except KeyError:
raise KeyError("{0} header does not contain {1}"
.format(self.__class__.__name__, item))
def __setitem__(self, item, value):
"""Set the value of a particular header item in the header words."""
try:
self._header_parser.setters[item](self.words, value)
except KeyError:
raise KeyError("{0} header does not contain {1}"
.format(self.__class__.__name__, item))
except(TypeError, ValueError):
if not self.mutable:
raise TypeError("header is immutable. Set '.mutable` attribute"
" or make a copy.")
else:
raise
def _ipython_key_completions_(self):
# Enables tab-completion of header keys in IPython.
return self.keys()
def __contains__(self, key):
return key in self.keys()
def __eq__(self, other):
return (type(self) is type(other) and
np.all(np.array(self.words, copy=False) ==
np.array(other.words, copy=False)))
@staticmethod
def _repr_as_hex(key):
return (key.startswith('bcd') or key.startswith('crc') or
key == 'sync_pattern')
def __repr__(self):
name = self.__class__.__name__
return ("<{0} {1}>".format(name, (",\n " + len(name) * " ").join(
["{0}: {1}".format(k, hex(self[k]) if self._repr_as_hex(k)
else self[k])
for k in self.keys()])))