services.py

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from threading import Thread
from rospy import ServiceProxy, resolve_name
from rosservice import get_service_type
from rosbridge_library.internal.ros_loader import get_service_class
from rosbridge_library.internal.ros_loader import get_service_request_instance
from rosbridge_library.internal.message_conversion import populate_instance
from rosbridge_library.internal.message_conversion import extract_values
 
 
class InvalidServiceException(Exception):
    def __init__(self, servicename):
        Exception.__init__(self, "Service %s does not exist" % servicename)
 
 
class ServiceCaller(Thread):
 
    def __init__(self, service, args, success_callback, error_callback):
        """ Create a service caller for the specified service.  Use start()
        to start in a separate thread or run() to run in this thread.
 
        Keyword arguments:
        service          -- the name of the service to call
        args             -- arguments to pass to the service.  Can be an
        ordered list, or a dict of name-value pairs.  Anything else will be
        treated as though no arguments were provided (which is still valid for
        some kinds of service)
        success_callback -- a callback to call with the JSON result of the
        service call
        error_callback   -- a callback to call if an error occurs.  The
        callback will be passed the exception that caused the failure
 
         """
        Thread.__init__(self)
        self.daemon = True
        self.service = service
        self.args = args
        self.success = success_callback
        self.error = error_callback
 
    def run(self):
        try:
            # Call the service and pass the result to the success handler
            self.success(call_service(self.service, self.args))
        except Exception as e:
            # On error, just pass the exception to the error handler
            self.error(e)
 
 
def args_to_service_request_instance(service, inst, args):
    """ Populate a service request instance with the provided args
 
    args can be a dictionary of values, or a list, or None
 
    Propagates any exceptions that may be raised. """
    msg = {}
    if isinstance(args, list):
        msg = dict(zip(inst.__slots__, args))
    elif isinstance(args, dict):
        msg = args
 
    # Populate the provided instance, propagating any exceptions
    populate_instance(msg, inst)
 
 
def call_service(service, args=None):
    # Given the service name, fetch the type and class of the service,
    # and a request instance
 
    service = resolve_name(service)
 
    service_type = get_service_type(str(service))
    if service_type is None:
        raise InvalidServiceException(service)
    service_class = get_service_class(service_type)
    inst = get_service_request_instance(service_type)
 
    # Populate the instance with the provided args
    args_to_service_request_instance(service, inst, args)
 
    # Call the service
    proxy = ServiceProxy(service, service_class)
    response = proxy.call(inst)
 
    # Turn the response into JSON and pass to the callback
    json_response = extract_values(response)
 
    return json_response