Added support for dynamic link MTU to Channel and Buffer

RNS/Buffer.py

@@ -45,7 +45,8 @@ class StreamDataMessage(MessageBase):
     The stream id is limited to 2 bytes - 2 bit
     """
 
-    MAX_DATA_LEN = RNS.Link.MDU - 2 - 6  # 2 for stream data message header, 6 for channel envelope
+    OVERHEAD     = 2 + 6  # 2 for stream data message header, 6 for channel envelope
+    MAX_DATA_LEN = RNS.Link.MDU - OVERHEAD
     """
     When the Buffer package is imported, this value is
     calculcated based on the value of OVERHEAD
@@ -215,6 +216,7 @@ def __init__(self, stream_id: int, channel: Channel):
         self._stream_id = stream_id
         self._channel = channel
         self._eof = False
+        self._mdu = channel.mdu - StreamDataMessage.OVERHEAD
 
     def write(self, __b: bytes) -> int | None:
         try:

RNS/Channel.py

@@ -602,7 +602,7 @@ def send(self, message: MessageBase) -> Envelope:
         return envelope
 
     @property
-    def MDU(self):
+    def mdu(self):
         """
         Maximum Data Unit: the number of bytes available
         for a message to consume in a single send. This
@@ -611,7 +611,10 @@ def MDU(self):
 
         :return: number of bytes available
         """
-        return self._outlet.mdu - 6  # sizeof(msgtype) + sizeof(length) + sizeof(sequence)
+        mdu = self._outlet.mdu - 6  # sizeof(msgtype) + sizeof(length) + sizeof(sequence)
+        if mdu > 0xFFFF:
+            mdu = 0xFFFF
+        return mdu
 
 
 class LinkChannelOutlet(ChannelOutletBase):
@@ -639,7 +642,7 @@ def resend(self, packet: RNS.Packet) -> RNS.Packet:
 
     @property
     def mdu(self):
-        return self.link.MDU
+        return self.link.mdu
 
     @property
     def rtt(self):

RNS/Link.py

@@ -423,7 +423,7 @@ def request(self, path, data = None, response_callback = None, failed_callback =
         if timeout == None:
             timeout = self.rtt * self.traffic_timeout_factor + RNS.Resource.RESPONSE_MAX_GRACE_TIME*1.125
 
-        if len(packed_request) <= Link.MDU:
+        if len(packed_request) <= self.mdu:
             request_packet   = RNS.Packet(self, packed_request, RNS.Packet.DATA, context = RNS.Packet.REQUEST)
             packet_receipt   = request_packet.send()
 
@@ -775,7 +775,7 @@ def handle_request(self, request_id, unpacked_request):
                     if response != None:
                         packed_response = umsgpack.packb([request_id, response])
 
-                        if len(packed_response) <= Link.MDU:
+                        if len(packed_response) <= self.mdu:
                             RNS.Packet(self, packed_response, RNS.Packet.DATA, context = RNS.Packet.RESPONSE).send()
                         else:
                             response_resource = RNS.Resource(packed_response, self, request_id = request_id, is_response = True)