this seems to be a resurrection of a protobuf-net specific discussion, so
let me jump in...
The SerializeWithLengthPrefix method, by default, aims to represent data in
a way that is a valid protobuf stream - in particular, as though it were
simply a member of a parent object or list. As such, it encodes a [
field-number and "string" marker ], then the length - as two separate
varints.
So assuming the data was stored in this way (the default), consuming 2
defaults should consume the header information - the second of the 2 values
being the length of the subsequent payload. If the data was stored with
different header-formats, then you may need to adjust - for example the
fixed32 obviously requires 4 bytes to be consumed.
Does that make sense? or have I missed the point of the question?
Marc
On 20 February 2013 13:32, Paul Shafer <prabo...@gmail.com> wrote:
> First time poster and new to protobuf/protobuf-net so forgive me if this
> has already been addressed. But I've searched quite a bit and cant find
> an"official" answer.
>
> If you want to use the fieldNumber argument in
> your SerializeWithLengthPrefix/TryDeserializeWithLengthPrefix for message
> type identification (or for whatever reason), all works great between two
> C#/.NET apps. However if you have a c++ app using protobuf talking to a
> C#/.NET app using protobuf-net, the fieldNumber argument will cause grief.
> It took wireshark, plus diving into protobuf-net code and protobuf code to
> find that the fieldNumber is encoded like (I assume) any other field within
> a message. Whereas the c++ protobuf has no such notion (that I could find)
> unless you want to use a CodedOutputSTream - which then has both a WriteTag
> and WriteVarint32 (which WriteTag calls). However WriteTag/WriteVarint32
> does NOT encode the same as the fieldNumber with SerializeWithLengthPrefix.
> So... what do to?
>
> Again, perhaps this has been addressed already but here's my solution (on
> the c++ side):
>
> #define PROTO_NET_TAG(x) (((x) << 3) | (2 & 7))
>
> ...
> google::protobuf::io::ZeroCopyOutputStream* raw_output = new
> google::protobuf::io::StringOutputStream(str);
> google::protobuf::io::CodedOutputStream * coded = new
> google::protobuf::io::CodedOutputStream(raw_output);
> coded->WriteTag(PROTO_NET_TAG(msgTag));
> coded->WriteVarint32(msg->ByteSize());
> msg->SerializeToCodedStream(coded);
>
> ...
>
>
>
> On Monday, August 24, 2009 5:33:26 PM UTC-6, Peter Keen wrote:
>>
>> I looked at the protobuf-net source a little bit and it looks like if
>> you write the length with WriteLittleEndian32 instead of WriteVarint32
>> you should be good to go, as long as you use PrefixStyle.Fixed32
>> within the C# call to DeserialzeWithLengthPrefix().
>>
>> --Pete
>>
>> On Mon, Aug 24, 2009 at 4:17 PM, Jay Thomas<jaydian...@gmail.**com>
>> wrote:
>> >
>> > This code ideally has to operate with C# code on the other side of the
>> > socket that uses the DeserializeWithLengthPrefix() method call. The
>> > message originates in C++ environment on a linux box and terminates in
>> > C# environment on a windows PC. Why doesn't C++ support the same
>> > methods as C#? The only document that I've seen that has list of
>> > methods available is the message.h header file, installed into my
>> > Linux usr directory.
>> >
>> >
>> > On Aug 24, 4:05 pm, Peter Keen <peter.k...@gmail.com> wrote:
>> >> You sort of have to roll your own. In my project I'm doing something
>> like this:
>> >>
>> >> coded_output->WriteVarint32(**message->ByteSize());
>> >> message->**SerializeToCodedStream(coded_**output);
>> >>
>> >> And then on the reading side:
>> >>
>> >> uint32_t size;
>> >> if (! coded_input->ReadVarint32(&**size)) {
>> >> return NULL; // just an example. probably don't want to do this;
>> >>
>> >> }
>> >>
>> >> Message * m = new Message;
>> >> CodedInputStream::Limit limit = coded_input->PushLimit(size);
>> >> message->ParseFromCodedStream(**coded_input);
>> >> coded_input->PopLimit(limit);
>> >>
>> >> The biggest thing that helped me along was finding the Limit docs. I
>> >> couldn't figure out how to parse from a ZeroCopyInputStream without
>> >> consuming the entire stream, and then I ran across that and everything
>> >> became much more clear.
>> >>
>> >> --Pete
>> >>
>> >> On Mon, Aug 24, 2009 at 3:54 PM, Jay Thomas<jaydianetho...@gmail.**com>
>> wrote:
>> >>
>> >> > Hello
>> >>
>> >> > I am looking for a way to serialize/deserialize with length prefix
>> >> > under c++. The serialized bytes will sent to a TCP socket. I am
>> >> > aware that C# has a method SerializeWithLengthPrefix() and
>> >> > DeserializeWithLengthPrefix(). Are there any such analogous methods
>> >> > for C++? Please point out any documentation that I may have missed
>> >> > here.
>> >>
>> >> > Thanks for any assistance.
>> >>
>> >> > Jay
>> > >
>> >
>>
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Regards,
Marc
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