tests/multi_net: Add test coverage for socket recv flag MSG_DONTWAIT.

Adding multi_net case for UDP only, as TCP timing is hard to test reliably.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

tests/multi_net/udp_recv_dontwait.py

@@ -0,0 +1,59 @@
+# Test UDP recv and recvfrom with MSG_DONTWAIT
+import random
+import socket
+
+try:
+    import errno, time
+except ImportError:
+    print("SKIP")
+    raise SystemExit
+
+
+# Server
+def instance0():
+    PORT = random.randrange(10000, 50000)
+    multitest.globals(IP=multitest.get_network_ip(), PORT=PORT)
+    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])
+    multitest.next()
+    begin = time.ticks_ms()
+
+    # do some recvs before instance1 starts, when we know no packet is waiting
+    try:
+        print(s.recvfrom(8, socket.MSG_DONTWAIT))
+    except OSError as e:
+        print(e.errno == errno.EAGAIN)
+    try:
+        print(s.recv(8, socket.MSG_DONTWAIT))
+    except OSError as e:
+        print(e.errno == errno.EAGAIN)
+
+    # the above steps should not have taken any substantial time
+    elapsed = time.ticks_diff(time.ticks_ms(), begin)
+    print(True if elapsed < 50 else elapsed)
+
+    # Now instance1 will send us a UDP packet
+    multitest.broadcast("0-ready")
+    multitest.wait("1-sent")
+
+    for _ in range(10):  # retry if necessary, to allow for network delay
+        time.sleep_ms(100)
+        try:
+            print(s.recv(8, socket.MSG_DONTWAIT))
+            break
+        except OSError as er:
+            if er.errno != errno.EAGAIN:
+                raise er
+    s.close()
+
+
+# Client
+def instance1():
+    multitest.next()
+    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+    s.connect(socket.getaddrinfo(IP, PORT)[0][-1])
+    multitest.wait("0-ready")
+    print(s.send(b"abcdefgh"))
+    multitest.broadcast("1-sent")
+    s.close()

tests/multi_net/udp_recv_dontwait.py.exp

@@ -0,0 +1,7 @@
+--- instance0 ---
+True
+True
+True
+b'abcdefgh'
+--- instance1 ---
+8