tests/multi_net/udp_data.py: Make UDP test more reliable.

The current test depends on a specific number and order of packets to pass,
which can't be reproduced every run due to the unreliable UDP protocol.
This patch adds simple packets sequencing, retransmits with timeouts, and a
packet loss threshold, to make the test more tolerant to UDP protocol
packet drops and reordering.

tests/multi_net/udp_data.py

@@ -3,34 +3,68 @@
 import socket
 
 NUM_NEW_SOCKETS = 4
-NUM_TRANSFERS = 4
+NUM_TRANSFERS = 10
+TOTAL_PACKETS = NUM_NEW_SOCKETS * NUM_TRANSFERS
+# If more than 75% of packets are lost, the test fails.
+PACKET_LOSS_THRESH = 0.75 * TOTAL_PACKETS
 PORT = 8000
 
+
+def print_stats(seq):
+    if (TOTAL_PACKETS - seq) > PACKET_LOSS_THRESH:
+        print(
+            "packet loss %.1f%% %d/%d"
+            % (((TOTAL_PACKETS - seq) / TOTAL_PACKETS * 100), seq, TOTAL_PACKETS)
+        )
+    else:
+        print("pass")
+
+
 # Server
 def instance0():
+    seq = 0
     multitest.globals(IP=multitest.get_network_ip())
     multitest.next()
     for i in range(NUM_NEW_SOCKETS):
         s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
         s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
-        s.bind(socket.getaddrinfo("0.0.0.0", PORT)[0][-1])
+        s.bind(socket.getaddrinfo("0.0.0.0", PORT + i)[0][-1])
+        s.settimeout(0.250)
         multitest.broadcast("server ready")
         for j in range(NUM_TRANSFERS):
-            data, addr = s.recvfrom(1000)
-            print(data)
-            s.sendto(b"server to client %d %d" % (i, j), addr)
+            try:
+                data, addr = s.recvfrom(1000)
+            except:
+                continue
+            if int(data) == seq:
+                if seq < (TOTAL_PACKETS - PACKET_LOSS_THRESH):
+                    print(seq)
+                seq += 1
+                s.sendto(b"%d" % (seq), addr)
         s.close()
 
+    print_stats(seq)
+
 
 # Client
 def instance1():
+    seq = 0
     multitest.next()
-    ai = socket.getaddrinfo(IP, PORT)[0][-1]
     for i in range(NUM_NEW_SOCKETS):
+        ai = socket.getaddrinfo(IP, PORT + i)[0][-1]
         s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+        s.settimeout(0.250)
         multitest.wait("server ready")
         for j in range(NUM_TRANSFERS):
-            s.sendto(b"client to server %d %d" % (i, j), ai)
-            data, addr = s.recvfrom(1000)
-            print(data)
+            s.sendto(b"%d" % (seq), ai)
+            try:
+                data, addr = s.recvfrom(1000)
+            except:
+                continue
+            if int(data) == seq + 1:
+                if seq < (TOTAL_PACKETS - PACKET_LOSS_THRESH):
+                    print(seq)
+                seq += 1
         s.close()
+
+    print_stats(seq)