I had the same idea (writing the size of the message first and then
the message). Here is a simple reader and writer for Python with this
idea. Note that I assume the message size is an (unsigned) integer of
4 bytes. For very long messages, this won't work. However, I am
relying on the assumption that messages aren't that large. If they
are, then you probably need a different format for storing the data
anyway (break up into many protocol buffers.)
Comments welcome.
Mark
class ProtocolBufferFileReader:
def __init__(self, input_filename, message_constructor):
self.file = open(input_filename, 'rb')
self.message_constructor = message_constructor
def next(self):
read_byte = self.file.read(4)
if len(read_byte) == 0:
raise StopIteration
size = struct.unpack('I', read_byte)[0]
message = self.message_constructor()
bytes_read = message.MergeFromString(self.file.read(size))
return message
def __iter__(self):
return self
def close(self):
self.file.close()
class ProtocolBufferFileWriter:
def __init__(self, output_filename):
self.file = open(output_filename, 'wb')
def write(self, message):
string_to_write = message.SerializeToString()
size = struct.pack('I', message.ByteSize())
self.file.write(size)
self.file.write(message.SerializeToString())
def flush(self):
self.file.flush()
def close(self):
self.file.close()
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