Template protocol with xml data.

[thesamprice]

Im trying to interface to a gps signal simulator (spirent) and not sure of the best way to do this.

Commands are ascii, with the response being xml data.

It is a send / receive protocol so I was looking at the template protocol, but the xml responses was throwing me off.

In the basic example I would transmit ascii NULL, and receive back <msg>\n\t<status> 7 </status>\n</msg>\n\r
Another example
send STTIME
Response '<msg>\n\t<status> 7 </status>\n\t<data> 11-Sep-2010 22:00:24 </data>\n</msg>\n\r'

Response data is usually in the data attribute xml field.
Simulation status is always transmitted back with values 0-7.

A python example of the protocol
Client

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((self.TCP_IP, self.TCP_PORT))
s.send("NULL")

Server spirent

return_msg = b'<msg>\n\t<status> 7 </status>\n</msg>\n\r'
import socket

HOST = '127.0.0.1'  # Standard loopback interface address (localhost)
PORT = 65432        # Port to listen on (non-privileged ports are > 1023)

with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
    s.bind((HOST, PORT))
    s.listen()
    conn, addr = s.accept()
    with conn:
        print('Connected by', addr)
        while True:
            data = conn.recv(1024)
            if not data:
                continue
            print(data)
            conn.sendall(return_msg)
~

[thesamprice]

I tried chaining protocls

INTERFACE HW_SP tcpip_client_interface.rb <%= ENV["SPIRENT_IP"] %> <%= ENV["SPIRENT_PORT"] %> <%= ENV["SPIRENT_PORT"] %> 30 30
  PROTOCOL READ TemplateProtocol 0xa 0xa
  PROTOCOL READ StripXML
  TARGET SPIRENT

However it appears using TemplateProtocol vs the TEMPLATE command causes the template magic to not occur.

INTERFACE HW_SP tcpip_client_interface.rb <%= ENV["SPIRENT_IP"] %> <%= ENV["SPIRENT_PORT"] %> <%= ENV["SPIRENT_PORT"] %> 30 30 TEMPLATE 0xa 0xa
  TARGET SPIRENT

[thesamprice]

Ok i got something that worked.

I ended up creating a second protocol to strip off the XML flags.

  class StripXML < Protocol
    # def read_packet(packet)
    #   puts packet
    #   return packet
    # end
    def read_data(input)
      input = input.strip()
      status = ""
      data = ""
      error = ""

      if input.match(/\<status\>/)
        status = input[/\<status\>\s*(.*)\s*\<\/status\>/,1]
      else
        return input
      end

      if input.match(/\<data\>/)
        data = input[/\<data\>\s*(.*)\s*\<\/data\>/,1]
      end

      if input.match(/\<error\>/)
        error = input[/\<error\>\s*(.*)\s*\<\/error\>/,1]
      end

      res =  status + "," + data + "," + error + "\n"
      return res
    end
  end

Then I chained this together with the template protocol.

INTERFACE HW_SP tcpip_client_interface.rb <%= ENV["SPIRENT_IP"] %> <%= ENV["SPIRENT_PORT"] %> <%= ENV["SPIRENT_PORT"] %> 30 30
  TARGET SPIRENT
  PROTOCOL READ StripXML
  PROTOCOL READ_WRITE TemplateProtocol 0x0a 0xa 

Two things to note.

• TemplateProtocol **Must be ** READ_WRITE (Maybe raise an error if this is not the case????)
• read_data will sometimes be passed "", or 0. You should return the input if this is the case.

[ghost]

Cool! Glad you got it working. The ability to stack Protocol is exactly the right approach here.

[thesamprice]

I was also thinking of subclassing from TemplateProtocol.
And overriding the <> approach to use named regular expressions to identify destination fields.