tests/multi_net: Add test for DTLS server and client.

This adds a multi-test for DTLS server and client behaviour.  It works on
all ports that enable this feature (eg unix, esp32, rp2, stm32), but
bare-metal ports that use lwIP are not reliable as the DTLS server because
the lwIP bindings only support queuing one UDP packet at a time (that needs
to be fixed).

Also, to properly implement a DTLS server sockets need to support
`socket.recvfrom(n, MSG_PEEK)`.  That can be implemented in the future.

Signed-off-by: Damien George <[email protected]>

tests/multi_net/tls_dtls_server_client.py

@@ -0,0 +1,89 @@
+# Test DTLS server and client, sending a small amount of data between them.
+
+try:
+    import socket
+    import tls
+except ImportError:
+    print("SKIP")
+    raise SystemExit
+
+PORT = 8000
+
+# These are test certificates. See tests/README.md for details.
+certfile = "ec_cert.der"
+keyfile = "ec_key.der"
+
+try:
+    with open(certfile, "rb") as cf:
+        cert = cadata = cf.read()
+    with open(keyfile, "rb") as kf:
+        key = kf.read()
+except OSError:
+    print("SKIP")
+    raise SystemExit
+
+
+# DTLS server.
+def instance0():
+    multitest.globals(IP=multitest.get_network_ip())
+
+    # Create a UDP socket and bind it to accept incoming connections.
+    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()
+
+    # Wait for the client to connect.
+    data, client_addr = s.recvfrom(1)
+    print("incoming connection", data)
+
+    # Connect back to the client, so the UDP socket can be used like a stream.
+    s.connect(client_addr)
+
+    # Create the DTLS context and load the certificate.
+    ctx = tls.SSLContext(tls.PROTOCOL_DTLS_SERVER)
+    ctx.load_cert_chain(cert, key)
+
+    # Wrap the UDP socket in server mode.
+    print("wrap socket")
+    s = ctx.wrap_socket(s, server_side=1)
+
+    # Transfer some data.
+    for _ in range(4):
+        print(s.recv(16))
+        s.send(b"server to client")
+
+    # Close the DTLS and UDP connection.
+    s.close()
+
+
+# DTLS client.
+def instance1():
+    multitest.next()
+
+    # Create a UDP socket and connect to the server.
+    addr = socket.getaddrinfo(IP, PORT)[0][-1]
+    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+    print("connect")
+    s.connect(addr)
+
+    # Send one byte to indicate a connection, and so the server can obtain our address.
+    s.write("X")
+
+    # Create a DTLS context and load the certificate.
+    ctx = tls.SSLContext(tls.PROTOCOL_DTLS_CLIENT)
+    ctx.verify_mode = tls.CERT_REQUIRED
+    ctx.load_verify_locations(cadata)
+
+    # Wrap the UDP socket.
+    print("wrap socket")
+    s = ctx.wrap_socket(s, server_hostname="micropython.local")
+
+    # Transfer some data.
+    for _ in range(4):
+        s.send(b"client to server")
+        print(s.recv(16))
+
+    # Close the DTLS and UDP connection.
+    s.close()

tests/multi_net/tls_dtls_server_client.py.exp

@@ -0,0 +1,14 @@
+--- instance0 ---
+incoming connection b'X'
+wrap socket
+b'client to server'
+b'client to server'
+b'client to server'
+b'client to server'
+--- instance1 ---
+connect
+wrap socket
+b'server to client'
+b'server to client'
+b'server to client'
+b'server to client'