pyrtma 1.2.1

A Python client for RTMA/Dragonfly

pyrtma

RTMA/Dragonfly client written in python with no external dependencies. Based on and compatible with Dragonfly Messaging

Installation

pyrtma is available on PyPI

$ pip install pyrtma

Usage

Launch Manager

$ python -m pyrtma.manager -a "127.0.0.1"

Create a message in message.h

The recommended way of creating messages is to define them in a C header file (.h file).

// message.h

// Module IDs
#define MID_PERSON_PUBLISHER 112
#define MID_PERSON_SUBSCRIBER 113

// Message IDs
#define MT_PERSON_MESSAGE 1234
#define MT_ANOTHER_EXAMPLE 5678

// We can define other constants as well
#define STR_SIZE 32 


// Message definitions
typedef struct {
	char name[STR_SIZE];
	int age;
} MDF_PERSON_MESSAGE;

typedef struct {
	char value_str[STR_SIZE];
	int value_int;
    float value_float;
    double value_double
} MDF_ANOTHER_EXAMPLE;

Run the following command to compile the header file into Python types and files. This will output a message.py file.

$ python -m pyrtma.compile -i message.h -o message.py

# message.py
import ctypes
import pyrtma
from pyrtma.constants import *

# User Constants: message.h
STR_SIZE = 32

# User Message IDs: message.h
MT_PERSON_MESSAGE = 1234
MT_ANOTHER_EXAMPLE = 5678

# User Module IDs: message.h
MID_PERSON_PUBLISHER = 112
MID_PERSON_SUBSCRIBER = 113

# User Type Definitions: message.h
# User Message Definitions: message.h


@pyrtma.msg_def
class MDF_PERSON_MESSAGE(pyrtma.MessageData):
    _pack_ = True
    _fields_ = [
        ("name", ctypes.c_char * STR_SIZE),
        ("age", ctypes.c_long)
    ]
    type_id = MT_PERSON_MESSAGE
    type_name = "PERSON_MESSAGE"



@pyrtma.msg_def
class MDF_ANOTHER_EXAMPLE(pyrtma.MessageData):
    _pack_ = True
    _fields_ = [
        ("value_str", ctypes.c_char * STR_SIZE),
        ("value_int", ctypes.c_long),
        ("value_float", ctypes.c_float),
        ("value_double", ctypes.c_double)
    ]
    type_id = MT_ANOTHER_EXAMPLE
    type_name = "ANOTHER_EXAMPLE"

Note: Messages can also be defined in a Python file without the compile step

Create a publisher module in publisher.py

# publisher.py
import message
import pyrtma
import time

mod = pyrtma.Client(module_id=message.MID_PERSON_PUBLISHER)

# Connect to the manager
mod.connect(server_name="127.0.0.1:7111")

# Create an instance of the person message and populate with data
msg = message.MDF_PERSON_MESSAGE()
msg.name = "Alice"  # str gets converted to c_char
msg.age = 42

# Send the person message every second
while True:
    print("Sending message")
    mod.send_message(msg)
    time.sleep(1)

Create a subscriber module in subscriber.py

# subscriber.py
import message
import pyrtma

# Keeping module_id blank makes Manager dynamically create a module id.
# This is default behavior.
mod = pyrtma.Client()

# Connect to the manager
mod.connect(server_name="127.0.0.1:7111")

# Subscribe to the person message and pyrtma's exit message (when manager is closed)
mod.subscribe([message.MT_PERSON_MESSAGE, pyrtma.MT_EXIT])

while True:
    try:
        # Read a message. We can specify a time. -1 means it will block until
        # a message is received
        msg = mod.read_message(timeout=-1)
        if msg is not None:

            # Find out what kind of message we received
            # We can check the message id
            if msg.type_id == message.MDF_PERSON_MESSAGE.type_id:
                name = msg.data.name  # c_char get converted to str
                age = msg.data.age
                print(f"Hello my name is {name} and I am {age} years old")

            # Or we can check the message name
            elif msg.name == "EXIT":
                print("Goodbye.")
                break

    except KeyboardInterrupt:
        break

Launch the publisher

$ python publisher.py

Launch the subscriber

You should see the message 'Hello my name is Alice and I am 42 years old' print in your shell

$ python subscriber.py