Add Size2 option handling according to RFC7959

Signed-off-by: Hubert Miś <hubert.mis@gmail.com>

coapthon/defines.py

@@ -124,6 +124,7 @@ class OptionRegistry(object):
     LOCATION_QUERY = OptionItem(20,"Location-Query",STRING,  True, None)
     BLOCK2 =        OptionItem(23, "Block2",        INTEGER, False, None)
     BLOCK1 =        OptionItem(27, "Block1",        INTEGER, False, None)
+    SIZE2 =         OptionItem(28, "Size2",         INTEGER, False, 0)
     PROXY_URI =     OptionItem(35, "Proxy-Uri",     STRING,  False, None)
     PROXY_SCHEME =  OptionItem(39, "Proxy-Schema",  STRING,  False, None)
     SIZE1 =         OptionItem(60, "Size1",         INTEGER, False, None)
@@ -147,6 +148,7 @@ class OptionRegistry(object):
         20: LOCATION_QUERY,
         23: BLOCK2,
         27: BLOCK1,
+        28: SIZE2,
         35: PROXY_URI,
         39: PROXY_SCHEME,
         60: SIZE1,

coapthon/layers/blocklayer.py

@@ -225,6 +225,9 @@ class BlockLayer(object):
 
                 self._block2_receive[key_token] = BlockItem(byte, num, m, size)
 
+            if transaction.request.size2 is not None:
+                transaction.response.size2 = len(transaction.response.payload)
+
             if len(transaction.response.payload) > (byte + size):
                 m = 1
             else:

coapthon/messages/message.py

@@ -641,6 +641,38 @@ class Message(object):
         """
         self.del_option_by_number(defines.OptionRegistry.BLOCK2.number)
 
+    @property
+    def size2(self):
+        """
+        Get the Size2 option.
+
+        :return: the Size2 value
+        """
+        value = None
+        for option in self.options:
+            if option.number == defines.OptionRegistry.SIZE2.number:
+                value = option.value
+        return value
+
+    @size2.setter
+    def size2(self, value):
+        """
+        Set the Size2 option.
+
+        :param value: the Block2 value
+        """
+        option = Option()
+        option.number = defines.OptionRegistry.SIZE2.number
+        option.value = value
+        self.add_option(option)
+
+    @size2.deleter
+    def size2(self):
+        """
+        Delete the Size2 option.
+        """
+        self.del_option_by_number(defines.OptionRegistry.SIZE2.number)
+
     @property
     def line_print(self):
         """