Storing multiple messages in one protocol buffer binary file

Question

I have repeating messages which I want to store in a single file. Currently I have to wrap this repeating message in another message. Is there a way around this?

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Answer 1

Protobuf doesn't support this functionality. It can be used to just serialize one message, but this serialized message doesn't contain information about its type (Box or Boxes) and length. So if you want to store multiple message you have to include type and length of message as well. Writing algorithm (in pseudo language) could look like this:

for every message {
    write(type_of_message) // 1 byte long
    write(length_of_serialized_message) // 4 bytes long
    write(serialized_message)
}

Load algorithm:

while(end_of_file) {

    type = read(1) // 1 byte
    length = read(4) // 4 bytes
    buffer = read(length)
    switch (type) {
      case 1:
         deserialise_message_1(buffer)
      case 2:
         deserialise_message_2(buffer)
    }
}