message_conversion.py

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#!/usr/bin/env python
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import roslib
import rospy

from rosbridge_library.internal import ros_loader

import re
import string
from base64 import standard_b64encode, standard_b64decode


type_map = {
   "bool":    ["bool"],
   "int":     ["int8", "byte", "uint8", "char",
               "int16", "uint16", "int32", "uint32",
               "int64", "uint64", "float32", "float64"],
   "float":   ["float32", "float64"],
   "str":     ["string"],
   "unicode": ["string"],
   "long":    ["uint64"]
}
primitive_types = [bool, int, long, float]
string_types = [str, unicode]
list_types = [list, tuple]
ros_time_types = ["time", "duration"]
ros_primitive_types = ["bool", "byte", "char", "int8", "uint8", "int16",
                       "uint16", "int32", "uint32", "int64", "uint64",
                       "float32", "float64", "string"]
ros_header_types = ["Header", "std_msgs/Header", "roslib/Header"]
ros_binary_types = ["uint8[]", "char[]"]
list_braces = re.compile(r'\[[^\]]*\]')


class InvalidMessageException(Exception):
    def __init__(self, inst):
        Exception.__init__(self, "Unable to extract message values from %s instance" % type(inst).__name__)


class NonexistentFieldException(Exception):
    def __init__(self, basetype, fields):
        Exception.__init__(self, "Message type %s does not have a field %s" % (basetype, '.'.join(fields)))


class FieldTypeMismatchException(Exception):
    def __init__(self, roottype, fields, expected_type, found_type):
        if roottype == expected_type:
            Exception.__init__(self, "Expected a JSON object for type %s but received a %s" % (roottype, found_type))
        else:
            Exception.__init__(self, "%s message requires a %s for field %s, but got a %s" % (roottype, expected_type, '.'.join(fields), found_type))


def extract_values(inst):
    rostype = getattr(inst, "_type", None)
    if rostype is None:
        raise InvalidMessageException()
    return _from_inst(inst, rostype)


def populate_instance(msg, inst):
    """ Returns an instance of the provided class, with its fields populated
    according to the values in msg """
    return _to_inst(msg, inst._type, inst._type, inst)


def _from_inst(inst, rostype):
    # Special case for uint8[], we base64 encode the string
    if rostype in ros_binary_types:
        return standard_b64encode(inst)

    # Check for time or duration
    if rostype in ros_time_types:
        return {"secs": inst.secs, "nsecs": inst.nsecs}

    # Check for primitive types
    if rostype in ros_primitive_types:
        return inst

    # Check if it's a list or tuple
    if type(inst) in list_types:
        return _from_list_inst(inst, rostype)

    # Assume it's otherwise a full ros msg object
    return _from_object_inst(inst, rostype)


def _from_list_inst(inst, rostype):
    # Can duck out early if the list is empty
    if len(inst) == 0:
        return []

    # Remove the list indicators from the rostype
    rostype = list_braces.sub("", rostype)
    
    # Shortcut for primitives
    if rostype in ros_primitive_types:
        return list(inst)

    # Call to _to_inst for every element of the list
    return [_from_inst(x, rostype) for x in inst]


def _from_object_inst(inst, rostype):
    # Create an empty dict then populate with values from the inst
    msg = {}
    for field_name, field_rostype in zip(inst.__slots__, inst._slot_types):
        field_inst = getattr(inst, field_name)
        msg[field_name] = _from_inst(field_inst, field_rostype)
    return msg


def _to_inst(msg, rostype, roottype, inst=None, stack=[]):
    # Check if it's uint8[], and if it's a string, try to b64decode
    if rostype in ros_binary_types:
        return _to_binary_inst(msg)

    # Check the type for time or rostime
    if rostype in ros_time_types:
        return _to_time_inst(msg, rostype, inst)

    # Check to see whether this is a primitive type
    if rostype in ros_primitive_types:
        return _to_primitive_inst(msg, rostype, roottype, stack)

    # Check whether we're dealing with a list type
    if inst is not None and type(inst) in list_types:
        return _to_list_inst(msg, rostype, roottype, inst, stack)

    # Otherwise, the type has to be a full ros msg type, so msg must be a dict
    if inst is None:
        inst = ros_loader.get_message_instance(rostype)

    return _to_object_inst(msg, rostype, roottype, inst, stack)


def _to_binary_inst(msg):
    if type(msg) in string_types:
        try:
            return standard_b64decode(msg)
        except:
            return msg
    else:
        try:
            return str(bytearray(msg))
        except:
            return msg


def _to_time_inst(msg, rostype, inst=None):
    # Create an instance if we haven't been provided with one
    if rostype == "time" and msg == "now":
        return rospy.get_rostime()

    if inst is None:
        if rostype == "time":
            inst = rospy.rostime.Time()
        elif rostype == "duration":
            inst = rospy.rostime.Duration()
        else:
            return None

    # Copy across the fields
    for field in ["secs", "nsecs"]:
        try:
            if field in msg:
                setattr(inst, field, msg[field])
        except TypeError:
            continue

    return inst


def _to_primitive_inst(msg, rostype, roottype, stack):
    # Typecheck the msg
    msgtype = type(msg)
    if msgtype in primitive_types and rostype in type_map[msgtype.__name__]:
        return msg
    elif msgtype in string_types and rostype in type_map[msgtype.__name__]:
        return msg.encode("ascii", "ignore")
    raise FieldTypeMismatchException(roottype, stack, rostype, msgtype)


def _to_list_inst(msg, rostype, roottype, inst, stack):
    # Typecheck the msg
    if type(msg) not in list_types:
        raise FieldTypeMismatchException(roottype, stack, rostype, type(msg))

    # Can duck out early if the list is empty
    if len(msg) == 0:
        return []

    # Remove the list indicators from the rostype
    rostype = list_braces.sub("", rostype)

    # Call to _to_inst for every element of the list
    return [_to_inst(x, rostype, roottype, None, stack) for x in msg]


def _to_object_inst(msg, rostype, roottype, inst, stack):
    # Typecheck the msg
    if type(msg) is not dict:
        raise FieldTypeMismatchException(roottype, stack, rostype, type(msg))

    # Substitute the correct time if we're an std_msgs/Header
    if rostype in ros_header_types:
        inst.stamp = rospy.get_rostime()

    inst_fields = dict(zip(inst.__slots__, inst._slot_types))

    for field_name in msg:
        # Add this field to the field stack
        field_stack = stack + [field_name]

        # Raise an exception if the msg contains a bad field
        if not field_name in inst_fields:
            raise NonexistentFieldException(roottype, field_stack)

        field_rostype = inst_fields[field_name]
        field_inst = getattr(inst, field_name)

        field_value = _to_inst(msg[field_name], field_rostype,
                    roottype, field_inst, field_stack)

        setattr(inst, field_name, field_value)

    return inst