Channel.py

##########################################################
# This RNS example demonstrates how to set up a link to  #
# a destination, and pass structured messages over it    #
# using a channel.                                       #
##########################################################

import os
import sys
import time
import argparse
from datetime import datetime

import RNS
from RNS.vendor import umsgpack

# Let's define an app name. We'll use this for all
# destinations we create. Since this echo example
# is part of a range of example utilities, we'll put
# them all within the app namespace "example_utilities"
APP_NAME = "example_utilities"

##########################################################
#### Shared Objects ######################################
##########################################################

# Channel data must be structured in a subclass of
# MessageBase. This ensures that the channel will be able
# to serialize and deserialize the object and multiplex it
# with other objects. Both ends of a link will need the
# same object definitions to be able to communicate over
# a channel.
#
# Note: The objects we wish to use over the channel must
# be registered with the channel, and each link has a
# different channel instance. See the client_connected
# and link_established functions in this example to see
# how message types are registered.

# Let's make a simple message class called StringMessage
# that will convey a string with a timestamp.

class StringMessage(RNS.MessageBase):
    # The MSGTYPE class variable needs to be assigned a
    # 2 byte integer value. This identifier allows the
    # channel to look up your message's constructor when a
    # message arrives over the channel.
    #
    # MSGTYPE must be unique across all message types we
    # register with the channel. MSGTYPEs >= 0xf000 are
    # reserved for the system.
    MSGTYPE = 0x0101

    # The constructor of our object must be callable with
    # no arguments. We can have parameters, but they must
    # have a default assignment.
    #
    # This is needed so the channel can create an empty
    # version of our message into which the incoming
    # message can be unpacked.
    def __init__(self, data=None):
        self.data = data
        self.timestamp = datetime.now()

    # Finally, our message needs to implement functions
    # the channel can call to pack and unpack our message
    # to/from the raw packet payload. We'll use the
    # umsgpack package bundled with RNS. We could also use
    # the struct package bundled with Python if we wanted
    # more control over the structure of the packed bytes.
    #
    # Also note that packed message objects must fit
    # entirely in one packet. The number of bytes
    # available for message payloads can be queried from
    # the channel using the Channel.MDU property. The
    # channel MDU is slightly less than the link MDU due
    # to encoding the message header.

    # The pack function encodes the message contents into
    # a byte stream.
    def pack(self) -> bytes:
        return umsgpack.packb((self.data, self.timestamp))

    # And the unpack function decodes a byte stream into
    # the message contents.
    def unpack(self, raw):
        self.data, self.timestamp = umsgpack.unpackb(raw)


##########################################################
#### Server Part #########################################
##########################################################

# A reference to the latest client link that connected
latest_client_link = None

# This initialisation is executed when the users chooses
# to run as a server
def server(configpath):
    # We must first initialise Reticulum
    reticulum = RNS.Reticulum(configpath)
    
    # Randomly create a new identity for our link example
    server_identity = RNS.Identity()

    # We create a destination that clients can connect to. We
    # want clients to create links to this destination, so we
    # need to create a "single" destination type.
    server_destination = RNS.Destination(
        server_identity,
        RNS.Destination.IN,
        RNS.Destination.SINGLE,
        APP_NAME,
        "channelexample"
    )

    # We configure a function that will get called every time
    # a new client creates a link to this destination.
    server_destination.set_link_established_callback(client_connected)

    # Everything's ready!
    # Let's Wait for client requests or user input
    server_loop(server_destination)

def server_loop(destination):
    # Let the user know that everything is ready
    RNS.log(
        "Link example "+
        RNS.prettyhexrep(destination.hash)+
        " running, waiting for a connection."
    )

    RNS.log("Hit enter to manually send an announce (Ctrl-C to quit)")

    # We enter a loop that runs until the users exits.
    # If the user hits enter, we will announce our server
    # destination on the network, which will let clients
    # know how to create messages directed towards it.
    while True:
        entered = input()
        destination.announce()
        RNS.log("Sent announce from "+RNS.prettyhexrep(destination.hash))

# When a client establishes a link to our server
# destination, this function will be called with
# a reference to the link.
def client_connected(link):
    global latest_client_link
    latest_client_link = link

    RNS.log("Client connected")
    link.set_link_closed_callback(client_disconnected)

    # Register message types and add callback to channel
    channel = link.get_channel()
    channel.register_message_type(StringMessage)
    channel.add_message_handler(server_message_received)

def client_disconnected(link):
    RNS.log("Client disconnected")

def server_message_received(message):
    """
    A message handler
    @param message: An instance of a subclass of MessageBase
    @return: True if message was handled
    """
    global latest_client_link
    # When a message is received over any active link,
    # the replies will all be directed to the last client
    # that connected.

    # In a message handler, any deserializable message
    # that arrives over the link's channel will be passed
    # to all message handlers, unless a preceding handler indicates it
    # has handled the message.
    #
    #
    if isinstance(message, StringMessage):
        RNS.log("Received data on the link: " + message.data + " (message created at " + str(message.timestamp) + ")")

        reply_message = StringMessage("I received \""+message.data+"\" over the link")
        latest_client_link.get_channel().send(reply_message)

        # Incoming messages are sent to each message
        # handler added to the channel, in the order they
        # were added.
        # If any message handler returns True, the message
        # is considered handled and any subsequent
        # handlers are skipped.
        return True


##########################################################
#### Client Part #########################################
##########################################################

# A reference to the server link
server_link = None

# This initialisation is executed when the users chooses
# to run as a client
def client(destination_hexhash, configpath):
    # We need a binary representation of the destination
    # hash that was entered on the command line
    try:
        dest_len = (RNS.Reticulum.TRUNCATED_HASHLENGTH//8)*2
        if len(destination_hexhash) != dest_len:
            raise ValueError(
                "Destination length is invalid, must be {hex} hexadecimal characters ({byte} bytes).".format(hex=dest_len, byte=dest_len//2)
            )
            
        destination_hash = bytes.fromhex(destination_hexhash)
    except:
        RNS.log("Invalid destination entered. Check your input!\n")
        exit()

    # We must first initialise Reticulum
    reticulum = RNS.Reticulum(configpath)

    # Check if we know a path to the destination
    if not RNS.Transport.has_path(destination_hash):
        RNS.log("Destination is not yet known. Requesting path and waiting for announce to arrive...")
        RNS.Transport.request_path(destination_hash)
        while not RNS.Transport.has_path(destination_hash):
            time.sleep(0.1)

    # Recall the server identity
    server_identity = RNS.Identity.recall(destination_hash)

    # Inform the user that we'll begin connecting
    RNS.log("Establishing link with server...")

    # When the server identity is known, we set
    # up a destination
    server_destination = RNS.Destination(
        server_identity,
        RNS.Destination.OUT,
        RNS.Destination.SINGLE,
        APP_NAME,
        "channelexample"
    )

    # And create a link
    link = RNS.Link(server_destination)

    # We'll also set up functions to inform the
    # user when the link is established or closed
    link.set_link_established_callback(link_established)
    link.set_link_closed_callback(link_closed)

    # Everything is set up, so let's enter a loop
    # for the user to interact with the example
    client_loop()

def client_loop():
    global server_link

    # Wait for the link to become active
    while not server_link:
        time.sleep(0.1)

    should_quit = False
    while not should_quit:
        try:
            print("> ", end=" ")
            text = input()

            # Check if we should quit the example
            if text == "quit" or text == "q" or text == "exit":
                should_quit = True
                server_link.teardown()

            # If not, send the entered text over the link
            if text != "":
                message = StringMessage(text)
                packed_size = len(message.pack())
                channel = server_link.get_channel()
                if channel.is_ready_to_send():
                    if packed_size <= channel.MDU:
                        channel.send(message)
                    else:
                        RNS.log(
                            "Cannot send this packet, the data size of "+
                            str(packed_size)+" bytes exceeds the link packet MDU of "+
                            str(channel.MDU)+" bytes",
                            RNS.LOG_ERROR
                        )
                else:
                    RNS.log("Channel is not ready to send, please wait for " +
                            "pending messages to complete.", RNS.LOG_ERROR)

        except Exception as e:
            RNS.log("Error while sending data over the link: "+str(e))
            should_quit = True
            server_link.teardown()

# This function is called when a link
# has been established with the server
def link_established(link):
    # We store a reference to the link
    # instance for later use
    global server_link
    server_link = link

    # Register messages and add handler to channel
    channel = link.get_channel()
    channel.register_message_type(StringMessage)
    channel.add_message_handler(client_message_received)

    # Inform the user that the server is
    # connected
    RNS.log("Link established with server, enter some text to send, or \"quit\" to quit")

# When a link is closed, we'll inform the
# user, and exit the program
def link_closed(link):
    if link.teardown_reason == RNS.Link.TIMEOUT:
        RNS.log("The link timed out, exiting now")
    elif link.teardown_reason == RNS.Link.DESTINATION_CLOSED:
        RNS.log("The link was closed by the server, exiting now")
    else:
        RNS.log("Link closed, exiting now")
    
    RNS.Reticulum.exit_handler()
    time.sleep(1.5)
    os._exit(0)

# When a packet is received over the channel, we
# simply print out the data.
def client_message_received(message):
    if isinstance(message, StringMessage):
        RNS.log("Received data on the link: " + message.data + " (message created at " + str(message.timestamp) + ")")
        print("> ", end=" ")
        sys.stdout.flush()


##########################################################
#### Program Startup #####################################
##########################################################

# This part of the program runs at startup,
# and parses input of from the user, and then
# starts up the desired program mode.
if __name__ == "__main__":
    try:
        parser = argparse.ArgumentParser(description="Simple channel example")

        parser.add_argument(
            "-s",
            "--server",
            action="store_true",
            help="wait for incoming link requests from clients"
        )

        parser.add_argument(
            "--config",
            action="store",
            default=None,
            help="path to alternative Reticulum config directory",
            type=str
        )

        parser.add_argument(
            "destination",
            nargs="?",
            default=None,
            help="hexadecimal hash of the server destination",
            type=str
        )

        args = parser.parse_args()

        if args.config:
            configarg = args.config
        else:
            configarg = None

        if args.server:
            server(configarg)
        else:
            if (args.destination == None):
                print("")
                parser.print_help()
                print("")
            else:
                client(args.destination, configarg)

    except KeyboardInterrupt:
        print("")
        exit()