Adding starter code and solution for p4runtime exercise (#81)

Summary of changes:
- Adding the p4runtime starter code and solution.
- Adding NO_P4, BMV2_SWITCH_EXE and P4C_ARGS to utils/Makefile
- Updated p4runtime/Makefile to use variables
- Adding conversion functions for match and action param values
- Separating P4Info and P4Runtime libraries
- Updating global README and adding p4runtime/README.md
- Disabling screen saver on VM GUI
- Adding desktop icons for Terminal, Wireshare and Sublime Text
- Updating topo.pdf -> png for Markdown viewing in basic_tunnel and
  p4runtime READMEs

P4D2_2017_Fall/exercises/p4runtime/p4runtime_lib/convert.py

@@ -0,0 +1,119 @@
+# Copyright 2017-present Open Networking Foundation
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+import re
+import socket
+
+import math
+
+'''
+This package contains several helper functions for encoding to and decoding from byte strings:
+- integers
+- IPv4 address strings
+- Ethernet address strings
+'''
+
+mac_pattern = re.compile('^([\da-fA-F]{2}:){5}([\da-fA-F]{2})$')
+def matchesMac(mac_addr_string):
+    return mac_pattern.match(mac_addr_string) is not None
+
+def encodeMac(mac_addr_string):
+    return mac_addr_string.replace(':', '').decode('hex')
+
+def decodeMac(encoded_mac_addr):
+    return ':'.join(s.encode('hex') for s in encoded_mac_addr)
+
+ip_pattern = re.compile('^(\d{1,3}\.){3}(\d{1,3})$')
+def matchesIPv4(ip_addr_string):
+    return ip_pattern.match(ip_addr_string) is not None
+
+def encodeIPv4(ip_addr_string):
+    return socket.inet_aton(ip_addr_string)
+
+def decodeIPv4(encoded_ip_addr):
+    return socket.inet_ntoa(encoded_ip_addr)
+
+def bitwidthToBytes(bitwidth):
+    return int(math.ceil(bitwidth / 8.0))
+
+def encodeNum(number, bitwidth):
+    byte_len = bitwidthToBytes(bitwidth)
+    num_str = '%x' % number
+    if number >= 2 ** bitwidth:
+        raise Exception("Number, %d, does not fit in %d bits" % (number, bitwidth))
+    return ('0' * (byte_len * 2 - len(num_str)) + num_str).decode('hex')
+
+def decodeNum(encoded_number):
+    return int(encoded_number.encode('hex'), 16)
+
+def encode(x, bitwidth):
+    'Tries to infer the type of `x` and encode it'
+    byte_len = bitwidthToBytes(bitwidth)
+    if (type(x) == list or type(x) == tuple) and len(x) == 1:
+        x = x[0]
+    encoded_bytes = None
+    if type(x) == str:
+        if matchesMac(x):
+            encoded_bytes = encodeMac(x)
+        elif matchesIPv4(x):
+            encoded_bytes = encodeIPv4(x)
+        else:
+            # Assume that the string is already encoded
+            encoded_bytes = x
+    elif type(x) == int:
+        encoded_bytes = encodeNum(x, bitwidth)
+    else:
+        raise Exception("Encoding objects of %r is not supported" % type(x))
+    assert(len(encoded_bytes) == byte_len)
+    return encoded_bytes
+
+if __name__ == '__main__':
+    # TODO These tests should be moved out of main eventually
+    mac = "aa:bb:cc:dd:ee:ff"
+    enc_mac = encodeMac(mac)
+    assert(enc_mac == '\xaa\xbb\xcc\xdd\xee\xff')
+    dec_mac = decodeMac(enc_mac)
+    assert(mac == dec_mac)
+
+    ip = "10.0.0.1"
+    enc_ip = encodeIPv4(ip)
+    assert(enc_ip == '\x0a\x00\x00\x01')
+    dec_ip = decodeIPv4(enc_ip)
+    assert(ip == dec_ip)
+
+    num = 1337
+    byte_len = 5
+    enc_num = encodeNum(num, byte_len * 8)
+    assert(enc_num == '\x00\x00\x00\x05\x39')
+    dec_num = decodeNum(enc_num)
+    assert(num == dec_num)
+
+    assert(matchesIPv4('10.0.0.1'))
+    assert(not matchesIPv4('10.0.0.1.5'))
+    assert(not matchesIPv4('1000.0.0.1'))
+    assert(not matchesIPv4('10001'))
+
+    assert(encode(mac, 6 * 8) == enc_mac)
+    assert(encode(ip, 4 * 8) == enc_ip)
+    assert(encode(num, 5 * 8) == enc_num)
+    assert(encode((num,), 5 * 8) == enc_num)
+    assert(encode([num], 5 * 8) == enc_num)
+
+    num = 256
+    byte_len = 2
+    try:
+        enc_num = encodeNum(num, 8)
+        raise Exception("expected exception")
+    except Exception as e:
+        print e