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Buffer: send and receive binary data over Channel

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(also some minor fixes in channel)
This commit is contained in:
Aaron Heise 2023-03-02 17:13:55 -06:00
parent 58004d7c05
commit aac2b9f987
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8 changed files with 835 additions and 13 deletions
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323
Examples/Buffer.py Normal file
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@ -0,0 +1,323 @@
##########################################################
# This RNS example demonstrates how to set up a link to #
# a destination, and pass binary data over it using a #
# using a channel buffer. #
##########################################################
from __future__ import annotations
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"
##########################################################
#### Server Part #########################################
##########################################################
# A reference to the latest client link that connected
latest_client_link = None
# A reference to the latest buffer object
latest_buffer = 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,
"bufferexample"
)
# 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_buffer
latest_client_link = link
RNS.log("Client connected")
link.set_link_closed_callback(client_disconnected)
# If a new connection is received, the old reader
# needs to be disconnected.
if latest_buffer:
latest_buffer.close()
# Create buffer objects.
# The stream_id parameter to these functions is
# a bit like a file descriptor, except that it
# is unique to the *receiver*.
#
# In this example, both the reader and the writer
# use stream_id = 0, but there are actually two
# separate unidirectional streams flowing in
# opposite directions.
#
channel = link.get_channel()
latest_buffer = RNS.Buffer.create_bidirectional_buffer(0, 0, channel, server_buffer_ready)
def client_disconnected(link):
RNS.log("Client disconnected")
def server_buffer_ready(ready_bytes: int):
"""
Callback from buffer when buffer has data available
:param ready_bytes: The number of bytes ready to read
"""
global latest_buffer
data = latest_buffer.read(ready_bytes)
data = data.decode("utf-8")
RNS.log("Received data on the link: " + data)
reply_message = "I received \""+data+"\" over the buffer"
reply_message = reply_message.encode("utf-8")
latest_buffer.write(reply_message)
latest_buffer.flush()
##########################################################
#### Client Part #########################################
##########################################################
# A reference to the server link
server_link = None
# A reference to the buffer object, needed to share the
# object from the link connected callback to the client
# loop.
buffer = 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,
"bufferexample"
)
# 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()
else:
# Otherwise, encode the text and write it to the buffer.
text = text.encode("utf-8")
buffer.write(text)
# Flush the buffer to force the data to be sent.
buffer.flush()
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, buffer
server_link = link
# Create buffer, see server_client_connected() for
# more detail about setting up the buffer.
channel = link.get_channel()
buffer = RNS.Buffer.create_bidirectional_buffer(0, 0, channel, client_buffer_ready)
# 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 the buffer has new data, read it and write it to the terminal.
def client_buffer_ready(ready_bytes: int):
global buffer
data = buffer.read(ready_bytes)
RNS.log("Received data on the link: " + data.decode("utf-8"))
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 buffer 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()

9
Examples/Channel.py
View File

@ -243,11 +243,6 @@ def client(destination_hexhash, configpath):
# And create a link
link = RNS.Link(server_destination)
# We set a callback that will get executed
# every time a packet is received over the
# link
link.set_packet_callback(client_message_received)
# We'll also set up functions to inform the
# user when the link is established or closed
link.set_link_established_callback(link_established)
@ -330,7 +325,7 @@ def link_closed(link):
time.sleep(1.5)
os._exit(0)
# When a packet is received over the link, we
# When a packet is received over the channel, we
# simply print out the data.
def client_message_received(message):
if isinstance(message, StringMessage):
@ -348,7 +343,7 @@ def client_message_received(message):
# starts up the desired program mode.
if __name__ == "__main__":
try:
parser = argparse.ArgumentParser(description="Simple link example")
parser = argparse.ArgumentParser(description="Simple channel example")
parser.add_argument(
"-s",

305
RNS/Buffer.py Normal file
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@ -0,0 +1,305 @@
from __future__ import annotations
import sys
from threading import RLock
from RNS.vendor import umsgpack
from RNS.Channel import Channel, MessageBase, SystemMessageTypes
import RNS
from io import RawIOBase, BufferedRWPair, BufferedReader, BufferedWriter
from typing import Callable
from contextlib import AbstractContextManager
class StreamDataMessage(MessageBase):
MSGTYPE = SystemMessageTypes.SMT_STREAM_DATA
"""
Message type for ``Channel``. ``StreamDataMessage``
uses a system-reserved message type.
"""
STREAM_ID_MAX = 65535
"""
While not essential for the current message packing
method (umsgpack), the stream id is clamped to the
size of a UInt16 for future struct packing.
"""
OVERHEAD = 0
"""
The number of bytes used by this messa
When the Buffer package is imported, this value is
calculated based on the value of RNS.Link.MDU.
"""
MAX_DATA_LEN = 0
"""
When the Buffer package is imported, this value is
calculcated based on the value of OVERHEAD
"""
def __init__(self, stream_id: int = None, data: bytes = None, eof: bool = False):
"""
This class is used to encapsulate binary stream
data to be sent over a ``Channel``.
:param stream_id: id of stream relative to receiver
:param data: binary data
:param eof: set to True if signalling End of File
"""
super().__init__()
if stream_id is not None and stream_id > self.STREAM_ID_MAX:
raise ValueError("stream_id must be 0-65535")
self.stream_id = stream_id
self.data = data or bytes()
self.eof = eof
def pack(self) -> bytes:
if self.stream_id is None:
raise ValueError("stream_id")
return umsgpack.packb((self.stream_id, self.eof, bytes(self.data)))
def unpack(self, raw):
self.stream_id, self.eof, self.data = umsgpack.unpackb(raw)
_link_sized_bytes = ("\0"*RNS.Link.MDU).encode("utf-8")
StreamDataMessage.OVERHEAD = len(StreamDataMessage(stream_id=StreamDataMessage.STREAM_ID_MAX,
data=_link_sized_bytes,
eof=True).pack()) - len(_link_sized_bytes) - 6 # 6 is envelope overhead
StreamDataMessage.MAX_DATA_LEN = RNS.Link.MDU - StreamDataMessage.OVERHEAD
_link_sized_bytes = None
class RawChannelReader(RawIOBase, AbstractContextManager):
"""
An implementation of RawIOBase that receives
binary stream data sent over a ``Channel``.
This class generally need not be instantiated directly.
Use :func:`RNS.Buffer.create_reader`,
:func:`RNS.Buffer.create_writer`, and
:func:`RNS.Buffer.create_bidirectional_buffer` functions
to create buffered streams with optional callbacks.
For additional information on the API of this
object, see the Python documentation for
``RawIOBase``.
"""
def __init__(self, stream_id: int, channel: Channel):
"""
Create a raw channel reader.
:param stream_id: local stream id to receive at
:param channel: ``Channel`` object to receive from
"""
self._stream_id = stream_id
self._channel = channel
self._lock = RLock()
self._buffer = bytearray()
self._eof = False
self._channel._register_message_type(StreamDataMessage, is_system_type=True)
self._channel.add_message_handler(self._handle_message)
self._listeners: [Callable[[int], None]] = []
def add_ready_callback(self, cb: Callable[[int], None]):
"""
Add a function to be called when new data is available.
The function should have the signature ``(ready_bytes: int) -> None``
:param cb: function to call
"""
with self._lock:
self._listeners.append(cb)
def remove_ready_callback(self, cb: Callable[[int], None]):
"""
Remove a function added with :func:`RNS.RawChannelReader.add_ready_callback()`
:param cb: function to remove
"""
with self._lock:
self._listeners.remove(cb)
def _handle_message(self, message: MessageBase):
if isinstance(message, StreamDataMessage):
if message.stream_id == self._stream_id:
with self._lock:
if message.data is not None:
self._buffer.extend(message.data)
if message.eof:
self._eof = True
for listener in self._listeners:
try:
listener(len(self._buffer))
except Exception as ex:
RNS.log("Error calling RawChannelReader(" + str(self._stream_id) + ") callback: " + str(ex))
return True
return False
def _read(self, __size: int) -> bytes | None:
with self._lock:
result = self._buffer[:__size]
self._buffer = self._buffer[__size:]
return result if len(result) > 0 or self._eof else None
def readinto(self, __buffer: bytearray) -> int | None:
ready = self._read(len(__buffer))
if ready:
__buffer[:len(ready)] = ready
return len(ready) if ready else None
def writable(self) -> bool:
return False
def seekable(self) -> bool:
return False
def readable(self) -> bool:
return True
def close(self):
with self._lock:
self._channel.remove_message_handler(self._handle_message)
self._listeners.clear()
def __enter__(self):
return self
def __exit__(self, exc_type, exc_val, exc_tb):
self.close()
return False
class RawChannelWriter(RawIOBase, AbstractContextManager):
"""
An implementation of RawIOBase that receives
binary stream data sent over a channel.
This class generally need not be instantiated directly.
Use :func:`RNS.Buffer.create_reader`,
:func:`RNS.Buffer.create_writer`, and
:func:`RNS.Buffer.create_bidirectional_buffer` functions
to create buffered streams with optional callbacks.
For additional information on the API of this
object, see the Python documentation for
``RawIOBase``.
"""
def __init__(self, stream_id: int, channel: Channel):
"""
Create a raw channel writer.
:param stream_id: remote stream id to sent do
:param channel: ``Channel`` object to send on
"""
self._stream_id = stream_id
self._channel = channel
self._eof = False
def write(self, __b: bytes) -> int | None:
try:
if self._channel.is_ready_to_send():
chunk = __b[:StreamDataMessage.MAX_DATA_LEN]
message = StreamDataMessage(self._stream_id, chunk, self._eof)
self._channel.send(message)
return len(chunk)
except RNS.Channel.ChannelException as cex:
if cex.type != RNS.Channel.CEType.ME_LINK_NOT_READY:
raise
return 0
def close(self):
self._eof = True
self.write(bytes())
def __enter__(self):
return self
def __exit__(self, exc_type, exc_val, exc_tb):
self.close()
return False
def seekable(self) -> bool:
return False
def readable(self) -> bool:
return False
def writable(self) -> bool:
return True
class Buffer:
"""
Static functions for creating buffered streams that send
and receive over a ``Channel``.
These functions use ``BufferedReader``, ``BufferedWriter``,
and ``BufferedRWPair`` to add buffering to
``RawChannelReader`` and ``RawChannelWriter``.
"""
@staticmethod
def create_reader(stream_id: int, channel: Channel,
ready_callback: Callable[[int], None] | None = None) -> BufferedReader:
"""
Create a buffered reader that reads binary data sent
over a ``Channel``, with an optional callback when
new data is available.
Callback signature: ``(ready_bytes: int) -> None``
For more information on the reader-specific functions
of this object, see the Python documentation for
``BufferedReader``
:param stream_id: the local stream id to receive from
:param channel: the channel to receive on
:param ready_callback: function to call when new data is available
:return: a BufferedReader object
"""
reader = RawChannelReader(stream_id, channel)
if ready_callback:
reader.add_ready_callback(ready_callback)
return BufferedReader(reader)
@staticmethod
def create_writer(stream_id: int, channel: Channel) -> BufferedWriter:
"""
Create a buffered writer that writes binary data over
a ``Channel``.
For more information on the writer-specific functions
of this object, see the Python documentation for
``BufferedWriter``
:param stream_id: the remote stream id to send to
:param channel: the channel to send on
:return: a BufferedWriter object
"""
writer = RawChannelWriter(stream_id, channel)
return BufferedWriter(writer)
@staticmethod
def create_bidirectional_buffer(receive_stream_id: int, send_stream_id: int, channel: Channel,
ready_callback: Callable[[int], None] | None = None) -> BufferedRWPair:
"""
Create a buffered reader/writer pair that reads and
writes binary data over a ``Channel``, with an
optional callback when new data is available.
Callback signature: ``(ready_bytes: int) -> None``
For more information on the reader-specific functions
of this object, see the Python documentation for
``BufferedRWPair``
:param receive_stream_id: the local stream id to receive at
:param send_stream_id: the remote stream id to send to
:param channel: the channel to send and receive on
:param ready_callback: function to call when new data is available
:return: a BufferedRWPair object
"""
reader = RawChannelReader(receive_stream_id, channel)
if ready_callback:
reader.add_ready_callback(ready_callback)
writer = RawChannelWriter(send_stream_id, channel)
return BufferedRWPair(reader, writer)

2
RNS/Channel.py
View File

@ -34,6 +34,8 @@ import RNS
from abc import ABC, abstractmethod
TPacket = TypeVar("TPacket")
class SystemMessageTypes(enum.IntEnum):
SMT_STREAM_DATA = 0xff00
class ChannelOutletBase(ABC, Generic[TPacket]):
"""

1
RNS/__init__.py
View File

@ -33,6 +33,7 @@ from .Reticulum import Reticulum
from .Identity import Identity
from .Link import Link, RequestReceipt
from .Channel import MessageBase
from .Buffer import Buffer, RawChannelReader, RawChannelWriter
from .Transport import Transport
from .Destination import Destination
from .Packet import Packet

42
docs/source/reference.rst
View File

@ -149,6 +149,48 @@ This chapter lists and explains all classes exposed by the Reticulum Network Sta
.. autoclass:: RNS.MessageBase()
:members:
.. _api-buffer:
.. only:: html
|start-h3| Buffer |end-h3|
.. only:: latex
Buffer
------
.. autoclass:: RNS.Buffer
:members:
.. _api-rawchannelreader:
.. only:: html
|start-h3| RawChannelReader |end-h3|
.. only:: latex
RawChannelReader
----------------
.. autoclass:: RNS.RawChannelReader
:members: __init__, add_ready_callback, remove_ready_callback
.. _api-rawchannelwriter:
.. only:: html
|start-h3| RawChannelWriter |end-h3|
.. only:: latex
RawChannelWriter
----------------
.. autoclass:: RNS.RawChannelWriter
:members: __init__
.. _api-transport:
.. only:: html

103
tests/channel.py
View File

@ -2,6 +2,7 @@ from __future__ import annotations
import threading
import RNS
from RNS.Channel import MessageState, ChannelOutletBase, Channel, MessageBase
import RNS.Buffer
from RNS.vendor import umsgpack
from typing import Callable
import contextlib
@ -91,15 +92,18 @@ class ChannelOutletTest(ChannelOutletBase):
self._rtt = rtt
self._usable = True
self.packets = []
self.lock = threading.RLock()
self.packet_callback: Callable[[ChannelOutletBase, bytes], None] | None = None
def send(self, raw: bytes) -> Packet:
with self.lock:
packet = Packet(raw)
packet.send()
self.packets.append(packet)
return packet
def resend(self, packet: Packet) -> Packet:
with self.lock:
packet.send()
return packet
@ -370,6 +374,105 @@ class TestChannel(unittest.TestCase):
self.eat_own_dog_food(message, check)
def test_buffer_small_bidirectional(self):
data = "Hello\n"
with RNS.Buffer.create_bidirectional_buffer(0, 0, self.h.channel) as buffer:
count = buffer.write(data.encode("utf-8"))
buffer.flush()
self.assertEqual(len(data), count)
self.assertEqual(1, len(self.h.outlet.packets))
packet = self.h.outlet.packets[0]
self.h.channel._receive(packet.raw)
result = buffer.readline()
self.assertIsNotNone(result)
self.assertEqual(len(result), len(data))
decoded = result.decode("utf-8")
self.assertEqual(data, decoded)
def test_buffer_big(self):
writer = RNS.Buffer.create_writer(15, self.h.channel)
reader = RNS.Buffer.create_reader(15, self.h.channel)
data = "01234556789"*1024 # 10 KB
count = 0
write_finished = False
def write_thread():
nonlocal count, write_finished
count = writer.write(data.encode("utf-8"))
writer.flush()
writer.close()
write_finished = True
threading.Thread(target=write_thread, name="Write Thread", daemon=True).start()
while not write_finished or next(filter(lambda x: x.state != MessageState.MSGSTATE_DELIVERED,
self.h.outlet.packets), None) is not None:
with self.h.outlet.lock:
for packet in self.h.outlet.packets:
if packet.state != MessageState.MSGSTATE_DELIVERED:
self.h.channel._receive(packet.raw)
packet.delivered()
time.sleep(0.0001)
self.assertEqual(len(data), count)
read_finished = False
result = bytes()
def read_thread():
nonlocal read_finished, result
result = reader.read()
read_finished = True
threading.Thread(target=read_thread, name="Read Thread", daemon=True).start()
timeout_at = time.time() + 7
while not read_finished and time.time() < timeout_at:
time.sleep(0.001)
self.assertTrue(read_finished)
self.assertEqual(len(data), len(result))
decoded = result.decode("utf-8")
self.assertSequenceEqual(data, decoded)
def test_buffer_small_with_callback(self):
callbacks = 0
last_cb_value = None
def callback(ready: int):
nonlocal callbacks, last_cb_value
callbacks += 1
last_cb_value = ready
data = "Hello\n"
with RNS.RawChannelWriter(0, self.h.channel) as writer, RNS.RawChannelReader(0, self.h.channel) as reader:
reader.add_ready_callback(callback)
count = writer.write(data.encode("utf-8"))
writer.flush()
self.assertEqual(len(data), count)
self.assertEqual(1, len(self.h.outlet.packets))
packet = self.h.outlet.packets[0]
self.h.channel._receive(packet.raw)
self.assertEqual(1, callbacks)
self.assertEqual(len(data), last_cb_value)
result = reader.readline()
self.assertIsNotNone(result)
self.assertEqual(len(result), len(data))
decoded = result.decode("utf-8")
self.assertEqual(data, decoded)
if __name__ == '__main__':
unittest.main(verbosity=2)

51
tests/link.py
View File

@ -396,6 +396,48 @@ class TestLink(unittest.TestCase):
self.assertEqual(l1.status, RNS.Link.CLOSED)
self.assertEqual(0, len(l1._channel._rx_ring))
def test_11_buffer_round_trip(self):
global c_rns
init_rns(self)
print("")
print("Buffer round trip test")
# TODO: Load this from public bytes only
id1 = RNS.Identity.from_bytes(bytes.fromhex(fixed_keys[0][0]))
self.assertEqual(id1.hash, bytes.fromhex(fixed_keys[0][1]))
dest = RNS.Destination(id1, RNS.Destination.OUT, RNS.Destination.SINGLE, APP_NAME, "link", "establish")
self.assertEqual(dest.hash, bytes.fromhex("fb48da0e82e6e01ba0c014513f74540d"))
l1 = RNS.Link(dest)
time.sleep(1)
self.assertEqual(l1.status, RNS.Link.ACTIVE)
buffer = None
received = []
def handle_data(ready_bytes: int):
data = buffer.read(ready_bytes)
received.append(data)
channel = l1.get_channel()
buffer = RNS.Buffer.create_bidirectional_buffer(0, 0, channel, handle_data)
buffer.write("Hi there".encode("utf-8"))
buffer.flush()
time.sleep(0.5)
self.assertEqual(1 , len(received))
rx_message = received[0].decode("utf-8")
self.assertEqual("Hi there back at you", rx_message)
l1.teardown()
time.sleep(0.5)
self.assertEqual(l1.status, RNS.Link.CLOSED)
def size_str(self, num, suffix='B'):
units = ['','K','M','G','T','P','E','Z']
@ -462,6 +504,15 @@ def targets(yp=False):
channel.register_message_type(MessageTest)
channel.add_message_handler(handle_message)
buffer = None
def handle_buffer(ready_bytes: int):
data = buffer.read(ready_bytes)
buffer.write((data.decode("utf-8") + " back at you").encode("utf-8"))
buffer.flush()
buffer = RNS.Buffer.create_bidirectional_buffer(0, 0, channel, handle_buffer)
m_rns = RNS.Reticulum("./tests/rnsconfig")
id1 = RNS.Identity.from_bytes(bytes.fromhex(fixed_keys[0][0]))
d1 = RNS.Destination(id1, RNS.Destination.IN, RNS.Destination.SINGLE, APP_NAME, "link", "establish")