add 3-way handshake

client.py

@@ -33,15 +33,35 @@ class Client():
     def broadcast(self):
         self.send(bytes(), (HOST_ADDRESS, BROADCAST_PORT))
         log("!", "Message sent to broadcast address")
+        log("!", "Listening for three-way handshake...")
 
     def handshake(self):
         # To-Do
-        data, address = self.recv()
-        log("!", f"Server address : {address}")
+        rcvd = Segment()
+        while 1:
+            byte, server_addr = self.recv()
+            rcvd.from_bytes(byte)
+            if not rcvd.test_checksum():
+                raise ConnectionError
+            if rcvd.getSYN():
+                break;
+
+        self.DST_ADDR = server_addr
 
         seg = Segment()
-        seg.from_bytes(data)
-        log("!", seg.bytes[:100])
+        seg.set_seq_no(300)
+        seg.set_ack_no(rcvd.get_seq_no())
+        seg.setSYN()
+        seg.setACK()
+        self.send(seg.to_bytes(), server_addr)
+        log(f"Segment SEQ={rcvd.get_seq_no()}, SYN", "Received, Ack sent")
+        log(f"Segment SEQ={seg.get_seq_no()}, SYN", "Sent")
+
+        byte, _ = self.recv()
+        rcvd.from_bytes(byte)
+        if (not rcvd.test_checksum()) or (not rcvd.getACK()) or (rcvd.get_ack_no() != seg.get_seq_no()):
+            raise ConnectionError
+        log(f"Segment SEQ={rcvd.get_ack_no()}", "Acked")
 
         return
 

segment.py

@@ -14,21 +14,21 @@ class Segment():
         self.bytes[3] = val & 0xff
 
     def get_seq_no(self):
-        return  self.bytes[0] << 24 + \
-                self.bytes[1] << 16 + \
-                self.bytes[2] << 8 + \
+        return  (self.bytes[0] << 24) + \
+                (self.bytes[1] << 16) + \
+                (self.bytes[2] << 8) + \
                 self.bytes[3]
 
-    def set_seq_no(self, val):
+    def set_ack_no(self, val):
         self.bytes[4] = val >> 24 & 0xff
         self.bytes[5] = val >> 16 & 0xff
         self.bytes[6] = val >> 8 & 0xff
         self.bytes[7] = val & 0xff
 
-    def get_seq_no(self):
-        return  self.bytes[4] << 24 + \
-                self.bytes[5] << 16 + \
-                self.bytes[6] << 8 + \
+    def get_ack_no(self):
+        return  (self.bytes[4] << 24) + \
+                (self.bytes[5] << 16) + \
+                (self.bytes[6] << 8) + \
                 self.bytes[7]
 
     def setSYN(self):
@@ -62,13 +62,18 @@ class Segment():
     def count_checksum(self):
         # To-Do
         # ...
-        return
+        return 0
+
+    def test_checksum(self):
+        # return self.count_checksum == self.get_checksum
+        return True
 
     def to_bytes(self):
         return bytes(self.bytes)
 
     def from_bytes(self, byte:bytes):
         self.bytes = list(byte)
+        return self
 
 if __name__=="__main__":
     seg = Segment()

server.py

@@ -46,15 +46,37 @@ class Server():
             log("?", "Listen more? (y/n) ", end="")
             choice = input()
             if choice == "n":
+                print()
                 break
 
     def handshake(self, client_addr):
         # To-DO
+        log("!", "Commencing three-way handshake... ")
         segment = Segment()
+        segment.set_seq_no(100)
         segment.setSYN()
         self.send(segment.to_bytes(), client_addr)
+        log(f"Segment SEQ={segment.get_seq_no()}, SYN", "Sent")
 
-        return
+        byte, _ = self.recv()
+        recved = Segment().from_bytes(byte)
+        if (not recved.test_checksum()) or (not recved.getACK()) \
+            or (recved.get_ack_no() != segment.get_seq_no()):
+            # print(recved.getACK())
+            # print(recved.get_ack_no())
+            # print(segment.get_seq_no())
+            # print(recved.bytes[:12])
+            raise ConnectionError
+        log(f"Segment SEQ={segment.get_seq_no()}, SYN", "Acked")
+
+        segment = Segment()
+        segment.set_seq_no(recved.get_ack_no()+1)
+        segment.set_ack_no(recved.get_seq_no())
+        segment.setACK()
+        self.send(segment.to_bytes(), client_addr)
+        log(f"Segment SEQ={recved.get_seq_no()}, SYN", "Received, Ack sent")        
+
+        return True
 
     def send_file(self, client_addr):
         # To-Do