fragmentation.py
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00032 
00033 from rosbridge_library.capability import Capability
00034 import math
00035 
00036 
00037 class Fragmentation(Capability):
00038     """ The Fragmentation capability doesn't define any incoming operation
00039     handlers, but provides methods to fragment outgoing messages """
00040     
00041     fragmentation_seed = 0
00042 
00043     def __init__(self, protocol):
00044         # Call superclass constructor
00045         Capability.__init__(self, protocol)
00046 
00047     def fragment(self, message, fragment_size, mid=None):
00048         """ Serializes the provided message, then splits the serialized
00049         message according to fragment_size, then sends the fragments.
00050         
00051         If the size of the message is less than the fragment size, then
00052         the original message is returned rather than a single fragment
00053         
00054         Since fragmentation is typically only used for very large messages,
00055         this method returns a generator for fragments rather than a list
00056         
00057         Keyword Arguments
00058         message       -- the message dict object to be fragmented
00059         fragment_size -- the max size for the fragments
00060         mid           -- (optional) if provided, the fragment messages
00061         will be given this id.  Otherwise an id will be auto-generated.
00062 
00063         Returns a generator of message dict objects representing the fragments
00064         """
00065         # All fragmented messages need an ID so they can be reconstructed
00066         if mid is None:
00067             mid = self.fragmentation_seed
00068             self.fragmentation_seed = self.fragmentation_seed + 1
00069             
00070         serialized = self.protocol.serialize(message, mid)
00071         
00072         if serialized is None:
00073             return []
00074         
00075         message_length = len(serialized)
00076         if message_length <= fragment_size:
00077             return [message]
00078 
00079         msg_id = message.get("id", None)
00080 
00081         expected_duration = int(math.ceil(math.ceil(message_length / float(fragment_size))) * self.protocol.delay_between_messages)
00082 
00083         log_msg = "sending " + str(int(math.ceil(message_length / float(fragment_size)))) + " parts [fragment size: " + str(fragment_size) +"; expected duration: ~" + str(expected_duration) + "s]"
00084         self.protocol.log("info", log_msg)
00085 
00086         return self._fragment_generator(serialized, fragment_size, mid)
00087     
00088     def _fragment_generator(self, msg, size, mid):
00089         """ Returns a generator of fragment messages """
00090         total = ((len(msg)-1) / size) + 1
00091         n = 0
00092         for i in range(0, len(msg), size):
00093             fragment = msg[i:i+size]
00094             yield self._create_fragment(fragment, n, total, mid)
00095             n = n + 1
00096     
00097     def _create_fragment(self, fragment, num, total, mid):
00098         """ Given a string fragment of the original message, creates
00099         the appropriate fragment message """
00100         return {
00101             "op": "fragment",
00102             "id": mid,
00103             "data": fragment,
00104             "num": num,
00105             "total": total
00106         }


rosbridge_library
Author(s): Jonathan Mace
autogenerated on Mon Oct 6 2014 06:58:09