Added support for fragmenting packets

Packets larger the HW_MTU will be fragmented on transmit and reassembled
on receive.

RNS/Interfaces/MeshtasticInterface.py

@@ -1,8 +1,8 @@
 
 from .Interface import Interface
 from pubsub import pub
-import time
-import sys
+import os
+import struct
 import RNS
 
 try:
@@ -11,6 +11,9 @@ try:
 
     class MeshtasticInterface(Interface):
 
+        FLAG_SPLIT = 0x01
+        SEQ_UNSET = 0xFF
+
         @staticmethod
         def onReceive(packet, interface):
             if packet['decoded']['portnum'] == "PRIVATE_APP":
@@ -38,6 +41,10 @@ try:
             self.bitrate = 5469
             self.bitrate_kbps = 5.47
 
+            self.buffer = None
+            self.sequence = 0xFF
+            self.ready = False
+
             self.interface = None
 
             try:
@@ -62,20 +69,106 @@ try:
             RNS.log("Initialized Meshtastic interface!", RNS.LOG_DEBUG)
 
         def processIncoming(self, data):
-            RNS.log("Received Meshtastic packet "+RNS.prettyhexrep(data), RNS.LOG_DEBUG)
+            RNS.log("Received Meshtastic packet of "+str(len(data))+" bytes: "+RNS.prettyhexrep(data), RNS.LOG_DEBUG)
+
             self.rxb += len(data)
-            self.owner.inbound(data, self)
+
+            # check for fragmented packet
+            header = data[0]
+            split = (header & self.FLAG_SPLIT) == self.FLAG_SPLIT
+            sequence = header >> 1
+            RNS.log("incoming sequence: "+str(sequence), RNS.LOG_DEBUG)
+
+            if split and self.sequence == self.SEQ_UNSET:
+                # This is the first part of a split
+                #  packet, so we set the self.sequence variable
+                #  and add the data to the buffer.
+                self.buffer = data[1:]
+                self.sequence = sequence
+
+                #last_rssi = LoRa.packetRssi();
+                #last_snr_raw = LoRa.packetSnrRaw();
+
+            elif split and self.sequence == sequence:
+                # This is subsequent part of a split
+                #  packet, so we add it to the buffer.
+                self.buffer += data[1:]
+
+                #last_rssi = (last_rssi+LoRa.packetRssi())/2;
+                #last_snr_raw = (last_snr_raw+LoRa.packetSnrRaw())/2;
+
+            elif not split and self.sequence == sequence:
+                # This is not a split packet but it carries
+                #  the last sequence id, so it must be the
+                #  last part of a split packet.
+                self.buffer += data[1:]
+                self.sequence = self.SEQ_UNSET
+
+                #last_rssi = LoRa.packetRssi();
+                #last_snr_raw = LoRa.packetSnrRaw();
+
+                # pass the buffer on to RNS
+                RNS.log("Received Reticulum packet of "+str(len(self.buffer))+" bytes over Meshtastic interface", RNS.LOG_DEBUG)
+                self.owner.inbound(self.buffer, self)
+                self.buffer = None
+
+            elif split and self.sequence != sequence:
+                # This split packet does not carry the
+                #  same sequence id, so we must assume
+                #  that we are seeing the first part of
+                #  a new split packet.
+                # If we already had part of a split
+                #  packet in the buffer then we clear it.
+                if self.buffer != None:
+                    RNS.log("Discarding incomplete buffer from previous split packet!", RNS.LOG_ERROR)
+                self.buffer = data[1:]
+                self.sequence = sequence
+
+                #last_rssi = LoRa.packetRssi();
+                #last_snr_raw = LoRa.packetSnrRaw();
+
+            elif not split:
+                # This is not a split packet, so we
+                # just read it whole
+                self.buffer = data[1:]
+                self.sequence = self.SEQ_UNSET
+
+                #last_rssi = LoRa.packetRssi();
+                #last_snr_raw = LoRa.packetSnrRaw();
+
+                # pass the buffer on to RNS
+                RNS.log("Received Reticulum packet of "+str(len(self.buffer))+" bytes over Meshtastic interface", RNS.LOG_DEBUG)
+                self.owner.inbound(self.buffer, self)
+                self.buffer = None
 
         def processOutgoing(self, data):
             if self.interface == None:
                 return
-            RNS.log("Sending Meshtastic packet "+RNS.prettyhexrep(data), RNS.LOG_DEBUG)
-            try:
-                #self.interface.sendData(data)
-                self.interface.sendData(data, portNum=256, channelIndex=self.channel)
-                self.txb += len(data)
-            except Exception as e:
-                RNS.log("Could not transmit on "+str(self)+". The contained exception was: "+str(e), RNS.LOG_ERROR)
+            RNS.log("Sending Reticulum packet of "+str(len(data))+" bytes over Meshtastic interface", RNS.LOG_DEBUG)
+
+            header = int.from_bytes(os.urandom(1), "big") & 0xFE
+            RNS.log("outgoing sequence: "+str(header >> 1), RNS.LOG_DEBUG)
+            if len(data) > self.HW_MTU-1:
+                header |= self.FLAG_SPLIT
+
+            sent = 0
+            while sent < len(data):
+                size = len(data) - sent
+                if size > self.HW_MTU-1:
+                    size = self.HW_MTU-1
+                # clear split flag for last part
+                if sent+size >= len(data):
+                    header &= ~self.FLAG_SPLIT
+                buffer = struct.pack("!B", header) + data[sent:sent+size]
+                sent += size
+
+                RNS.log("Sending Meshtastic packet of "+str(len(buffer))+" bytes: "+RNS.prettyhexrep(buffer), RNS.LOG_DEBUG)
+                try:
+                    #self.interface.sendData(buffer)
+                    self.interface.sendData(buffer, portNum=256, channelIndex=self.channel)
+                    self.txb += len(buffer)
+                except Exception as e:
+                    RNS.log("Could not transmit on "+str(self)+". The contained exception was: "+str(e), RNS.LOG_ERROR)
 
         def __str__(self):
             if self.port == None: