how to calculate protocol buffer message size without parsing the full message?

[Sean Nguyen]

Hi,

I want to calculate the protocol buffer message size without reading the stream to the end? I don't see the size of the outer most message is stored. For example:

message Person {
   optional string name = 1;
   optional uint32 age = 2;
}

There is no size store for the Person message if it is the outer most message. Is that correct? If it is not where I can find it?

Thanks,

Son Nguyen

[Marc Gravell]

The outermost message is not stored with a length; this allows multiple messages to be merged by concatenation. The default behaviour for a protobuf parser at the root-object is "read until you run out of data". If you have written multiple messages without some kind of "framing" (usually adding length-prefixes manually) then it will be very hard to unscramble the data. If you need to append individual messages and want to parse them back individually, one option is to encapsulate each in a parent object with a "repeated" element, with a single element per object. Alternatively, add your own frames.

Marc

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[Oliver Jowett]

On Sun, Apr 21, 2013 at 9:48 PM, Oliver Wang <pyth...@gmail.com> wrote:

Can't you use ByteSize() method to get the size?

Not when you're parsing - you don't have a message instance yet!

Oliver