test_non-ros_service_client_fragmented.py

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#!/usr/bin/python
from __future__ import print_function
import socket
from rosbridge_library.util import json





client_socket_timeout = 6                       # seconds
max_msg_length = 2000000                        # bytes

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

service_name = "send_bytes"                     # service name
request_byte_count = 500000                   
receiving_fragment_size = 1000
receive_message_intervall = 0.0






def request_service():
    service_request_object = { "op" : "call_service",                           # op-code for rosbridge
                               "service": "/"+service_name,                     # select service
                               "fragment_size": receiving_fragment_size,        # optional: tells rosbridge to send fragments if message size is bigger than requested
                               "message_intervall": receive_message_intervall,
                               "args": { "count" : request_byte_count           # count is the parameter for send_bytes as defined in srv-file (always put into args field!)
                                        }
                              }
    service_request = json.dumps(service_request_object)
    print("sending JSON-message to rosbridge:", service_request)
    sock.send(service_request)





try:
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)                    #connect to rosbridge
    sock.settimeout(client_socket_timeout)
    sock.connect((rosbridge_ip, rosbridge_port))

    request_service()                                                           # send service_request

    incoming = None
    buffer = ""
    done = False
    result = None
    reconstructed = None
    while not done:     # should not need a loop (maximum wait can be set by client_socket_timeout), but since its for test/demonstration only .. leave it as it is for now
        try:
            incoming = sock.recv(max_msg_length)                                # receive service_response from rosbridge
            if buffer == "":
                buffer = incoming
                if incoming == "":
                    print("closing socket")
                    sock.close()
                    break
            else:
                buffer = buffer + incoming
            #print "buffer-length:", len(buffer)
            try:                                                                # try to access service_request directly (not fragmented)
                data_object = json.loads(buffer)
                if data_object["op"] == "service_response":
                    reconstructed = buffer
                    done = True
            except Exception as e:
                #print "direct access to JSON failed.."
                #print e
                pass
            try:                                        
                #print "defragmenting incoming messages"
                result_string = buffer.split("}{")                              # split buffer into fragments and re-fill curly brackets
                result = []
                for fragment in result_string:
                    if fragment[0] != "{":
                        fragment = "{"+fragment
                    if fragment[len(fragment)-1] != "}":
                        fragment = fragment + "}"
                    try:
                        result.append(json.loads(fragment))                     # try to parse json from string, and append if successful
                    except Exception as e:
                        #print e
                        #print result_string
                        raise                                                   # re-raise the last exception, allows to see and continue with processing of exception

                fragment_count = len(result)
                print("fragment_count:", fragment_count)
                announced = int(result[0]["total"])
                if fragment_count == announced:                                 # if all fragments received --> sort and defragment
                    # sort fragments
                    sorted_result = [None] * fragment_count
                    unsorted_result = []
                    for fragment in result:
                        unsorted_result.append(fragment)
                        sorted_result[int(fragment["num"])] = fragment
                    reconstructed = ''
                    for fragment in sorted_result:
                        reconstructed = reconstructed + fragment["data"]
                    done = True
            except Exception as e:
                #print e
                pass
        except Exception as e:
#            print e
            pass


    returned_data = json.loads(reconstructed)                                   # when service response is received --> access it (as defined in srv-file)
    if returned_data["values"] == None:
        print("response was None -> service was not available")
    else:
        print("received:")
        print(returned_data["values"]["data"].decode('base64','strict'))         # decode values-field
    
except Exception as e:
    print("ERROR - could not receive service_response")
    print(e)

sock.close()                                                                    # close socket