test_non-ros_service_server_fragmented.py

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#!/usr/bin/python
import sys
import socket
import time
from random import randint
from rosbridge_library.util import json


####################### variables begin ########################################
# these parameters should be changed to match the actual environment           #
################################################################################

tcp_socket_timeout = 10                          # seconds
max_msg_length = 20000                           # bytes

rosbridge_ip = "localhost"                       # hostname or ip
rosbridge_port = 9090                            # port as integer

service_type = "rosbridge_library/SendBytes"                       # make sure this matches an existing service type on rosbridge-server (in specified srv_module)
service_name = "send_bytes"                      # service name

send_fragment_size = 1000
# delay between sends to rosbridge is not needed anymore, if using my version of protocol (uses buffer to collect data from stream)
send_fragment_delay = 0.000#1
receive_fragment_size = 10
receive_message_intervall = 0.0

####################### variables end ##########################################


####################### service_calculation begin ##############################
# change this function to match whatever service should be provided            #
################################################################################

def calculate_service_response(request):
    request_object = json.loads(request)                                        # parse string for service request
    args = request_object["args"]                                               # get parameter field (args)
    count = int(args["count"] )                                                 # get parameter(s) as described in corresponding ROS srv-file
    
    message = ""
    # calculate service response
    for i in range(0,count):
        #message += str(chr(randint(32,126)))
        message+= str(chr(randint(32,126)))
        if i% 100000 == 0:
            print count - i, "bytes left to generate"

    """
    IMPORTANT!
    use base64 encoding to avoid JSON-parsing problems!
    --> use .decode("base64","strict") at client side
    """
    message = message.encode('base64','strict')
    service_response_data = { "data": message}                                  # service response (as defined in srv-file)

    response_object = { "op": "service_response",
                        "id": request_object["id"],
                        "data": service_response_data                           # put service response in "data"-field of response object (in this case it's twice "data", because response value is also named data (in srv-file)
                      }
    response_message = json.dumps(response_object)
    return response_message

####################### service_calculation end ################################



####################### helper functions / and variables begin #################
# should not need to be changed (but could be improved )                       #
################################################################################

buffer = ""

def connect_tcp_socket():
    tcp_sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)                # connect to rosbridge
    tcp_sock.settimeout(tcp_socket_timeout)
    tcp_sock.connect((rosbridge_ip, rosbridge_port))
    return tcp_sock

def advertise_service():                                                        # advertise service
    advertise_message_object = {"op":"advertise_service",
                                "type": service_type,
                                "service": service_name,
                                "fragment_size": receive_fragment_size,
                                "message_intervall": receive_message_intervall
                                }
    advertise_message = json.dumps(advertise_message_object)                    
    tcp_socket.send(str(advertise_message))

def unadvertise_service():                                                      # unadvertise service
    unadvertise_message_object = {"op":"unadvertise_service",
                                  "service": service_name
                                 }
    unadvertise_message = json.dumps(unadvertise_message_object)                   
    tcp_socket.send(str(unadvertise_message))

def wait_for_service_request():                                                 # receive data from rosbridge
    data = None
    global buffer

    try:
        done = False
        global buffer
        while not done:
            incoming = tcp_socket.recv(max_msg_length)                          # get data from socket
            if incoming == '':
                print "connection closed by peer"
                sys.exit(1)
            buffer = buffer + incoming                                          # append data to buffer
            try:                                                                # try to parse JSON from buffer
                data_object = json.loads(buffer)
                if data_object["op"] == "call_service":
                    data = buffer
                    done = True
                    return data                                                 # if parsing was successful --> return data string
            except Exception, e:
                #print "direct_access error:"
                #print e
                pass
               
            #print "trying to defragment"
            try:                                                                # opcode was not "call_service" -> try to defragment
                result_string = buffer.split("}{")                              # split buffer into fragments and re-fill with curly brackets
                result = []
                for fragment in result_string:
                    if fragment[0] != "{":
                        fragment = "{"+fragment
                    if fragment[len(fragment)-1] != "}":
                        fragment = fragment + "}"
                    result.append(json.loads(fragment))

                try:                                                            # try to defragment when received all fragments
                    fragment_count = len(result)
                    announced = int(result[0]["total"])

                    if fragment_count == announced:
                        reconstructed = ""
                        sorted_result = [None] * fragment_count                 # sort fragments..
                        unsorted_result = []
                        for fragment in result:
                            unsorted_result.append(fragment)
                            sorted_result[int(fragment["num"])] = fragment

                        for fragment in sorted_result:                          # reconstruct from fragments
                            reconstructed = reconstructed + fragment["data"]

                        #print "reconstructed", reconstructed
                        buffer = ""                                             # empty buffer
                        done = True
                        print "reconstructed message from", len(result), "fragments"
                        #print reconstructed
                        return reconstructed
                except Exception, e:
                    print "not possible to defragment:", buffer
                    print e
            except Exception, e:
                print "defrag_error:", buffer
                print e
                pass
    except Exception, e:
        #print "network-error(?):", e
        pass
    return data

def send_service_response(response):                                            # send response to rosbridge
    tcp_socket.send(response)

def list_of_fragments(full_message, fragment_size):                             # create fragment messages for a huge message
    message_id = randint(0,64000)                                               # generate random message id
    fragments = []                                                              # generate list of data fragments
    cursor = 0
    while cursor < len(full_message):
        fragment_begin = cursor
        if len(full_message) < cursor + fragment_size:
            fragment_end = len(full_message)
            cursor = len(full_message)
        else:
            fragment_end = cursor + fragment_size
            cursor += fragment_size
        fragment = full_message[fragment_begin:fragment_end]
        fragments.append(fragment)

    fragmented_messages_list = []                                               # generate list of fragmented messages (including headers)
    if len(fragments) > 1:
        for count, fragment in enumerate(fragments):                            # iterate through list and have index counter
            fragmented_message_object = {"op":"fragment",                       #   create python-object for each fragment message
                                         "id": str(message_id),
                                         "data": str(fragment),
                                         "num": count,
                                         "total": len(fragments)
                                         }
            fragmented_message = json.dumps(fragmented_message_object)          # create JSON-object from python-object for each fragment message
            fragmented_messages_list.append(fragmented_message)                 # append JSON-object to list of fragmented messages
    else:                                                                       # if only 1 fragment --> do not send as fragment, but as service_response
        fragmented_messages_list.append(str(fragment))
    return fragmented_messages_list                                             # return list of 'ready-to-send' fragmented messages

####################### helper functions end ###################################


####################### script begin ###########################################
# should not need to be changed (but could be improved )                       #
################################################################################

tcp_socket = connect_tcp_socket()                                               # open tcp_socket
advertise_service()                                                             # advertise service in ROS (via rosbridge)
print "service provider started and waiting for requests"

try:                                                                            # allows to catch KeyboardInterrupt
    while True:                                                                 # loop forever (or until ctrl-c is pressed)
        data = None
        try:                                                                    # allows to catch any Exception (network, json, ..)
          data = wait_for_service_request()                                     # receive request from rosbridge
          if data == '':                                                        # exit on empty string
              break                                                             
          elif data != None and len(data) > 0:                                  # received service_request (or at least some data..)
            response = calculate_service_response(data)                         # generate service_response

            print "response calculated, now splitting into fragments.."
            fragment_list = list_of_fragments(response, send_fragment_size)     # generate fragments to send to rosbridge

            print "sending", len(fragment_list), "messages as response"
            for fragment in fragment_list:
                #print "sending:" ,fragment
                send_service_response(fragment)                                 # send service_response to rosbridge (or fragments; just send any list entry)
                time.sleep(send_fragment_delay)                                 # (not needed if using patched rosbridge protocol.py)
        except Exception, e:
          print e
          pass
except KeyboardInterrupt:
    try:
        unadvertise_service()                                                   # unadvertise service
        tcp_socket.close()                                                      # close tcp_socket
    except Exception, e:
        print e
    print "non-ros_service_server stopped because user pressed \"Ctrl-C\""