boost serialization vs google protocol buffers?

I've played around a little with both systems, nothing serious, just some simple hackish stuff, but I felt that there's a real difference in how you're supposed to use the libraries.

With boost::serialization, you write your own structs/classes first, and then add the archiving methods, but you're still left with some pretty "slim" classes, that can be used as data members, inherited, whatever.

With protocol buffers, the amount of code generated for even a simple structure is pretty substantial, and the structs and code that's generated is more meant for operating on, and that you use protocol buffers' functionality to transport data to and from your own internal structures.

I have no experience with boost serialization, but I have used protocol buffers. I like protocol buffers a lot. Keep the following in mind (I say this with no knowledge of boost).

• Protocol buffers are very efficient so I don't imagine that being a serious issue vs. boost.
• Protocol buffers provide an intermediate representation that works with other languages (Python and Java... and more in the works). If you know you're only using C++, maybe boost is better, but the option to use other languages is nice.
• Protocol buffers are more like data containers... there is no object oriented nature, such as inheritance. Think about the structure of what you want to serialize.
• Protocol buffers are flexible because you can add "optional" fields. This basically means you can change the structure of protocol buffer without breaking compatibility.

Hope this helps.

boost.serialization just needs the C++ compiler and gives you some syntax sugar like

serialize_obj >> archive;
// ...
unserialize_obj << archive;

for saving and loading. If C++ is the only language you use you should give boost.serialization a serious shot.

I took a fast look at google protocol buffers. From what I see I'd say its not directly comparable to boost.serialization. You have to add a compiler for the .proto files to your toolchain and maintain the .proto files itself. The API doesn't integrate into C++ as boost.serialization does.

boost.serialization does the job its designed for very well: to serialize C++ objects :) OTOH an query-API like google protocol buffers has gives you more flexibility.

Since I only used boost.serialization so far I cannot comment on performance comparison.

I never implemented anything using boost's library, but I found Google protobuff's to be more thought-out, and the code is much cleaner and easier to read. I would suggest having a look at the various languages you want to use it with and have a read through the code and the documentation and make up your mind.

The one difficulty I had with protobufs was they named a very commonly used function in their generated code GetMessage(), which of course conflicts with the Win32 GetMessage macro.

I would still highly recommend protobufs. They're very useful.

I know that this is an older question now, but I thought I'd throw my 2 pence in!

With boost you get the opportunity to I'm write some data validation in your classes; this is good because the data definition and the checks for validity are all in one place.

With GPB the best you can do is to put comments in the .proto file and hope against all hope that whoever is using it reads it, pays attention to it, and implements the validity checks themselves.

Needless to say this is unlikely and unreliable if your relying on someone else at the other end of a network stream to do this with the same vigour as oneself. Plus if the constraints on validity change, multiple code changes need to be planned, coordinated and done.

Thus I consider GPB to be inappropriate for developments where there is little opportunity to regularly meet and talk with all team members.

==EDIT==

The kind of thing I mean is this:

message Foo
{
    int32 bearing = 1;
}

Now who's to say what the valid range of bearing is? We can have

message Foo
{
    int32 bearing = 1;  // Valid between 0 and 359
}

But that depends on someone else reading this and writing code for it. For example, if you edit it and the constraint becomes:

message Foo
{
    int32 bearing = 1;  // Valid between -180 and +180
}

you are completely dependent on everyone who has used this .proto updating their code. That is unreliable and expensive.

At least with Boost serialisation you're distributing a single C++ class, and that can have data validity checks built right into it. If those constraints change, then no one else need do any work other than making sure they're using the same version of the source code as you.

Alternative

There is an alternative: ASN.1. This is ancient, but has some really, really, handy things:

Foo ::= SEQUENCE
{
   bearing INTEGER (0..359)
}

Note the constraint. So whenever anyone consumes this .asn file, generates code, they end up with code that will automatically check that bearing is somewhere between 0 and 359. If you update the .asn file,

Foo ::= SEQUENCE
{
   bearing INTEGER (-180..180)
}

all they need to do is recompile. No other code changes are required.

You can also do:

bearingMin INTEGER ::= 0
bearingMax INTEGER ::= 360

Foo ::= SEQUENCE
{
   bearing INTEGER (bearingMin..<bearingMax)
}

Note the <. And also in most tools the bearingMin and bearingMax can appear as constants in the generated code. That's extremely useful.

Constraints can be quite elaborate:

Garr ::= INTEGER (0..10 | 25..32)

Look at Chapter 13 in this PDF; it's amazing what you can do;

Arrays can be constrained too:

Bar ::= SEQUENCE (SIZE(1..5)) OF Foo
Sna ::= SEQUENCE (SIZE(5)) OF Foo
Fee ::= SEQUENCE 
{
    boo SEQUENCE (SIZE(1..<6)) OF INTEGER (-180<..<180)
}

ASN.1 is old fashioned, but still actively developed, widely used (your mobile phone uses it a lot), and far more flexible than most other serialisation technologies. About the only deficiency that I can see is that there is no decent code generator for Python. If you're using C/C++, C#, Java, ADA then you are well served by a mixture of free (C/C++, ADA) and commercial (C/C++, C#, JAVA) tools.

I especially like the wide choice of binary and text based wireformats. This makes it extremely convenient in some projects. The wireformat list currently includes:

• BER (binary)
• PER (binary, aligned and unaligned. This is ultra bit efficient. For example, and INTEGER constrained between 0 and 15 will take up only 4 bits on the wire)
• OER
• DER (another binary)
• XML (also XER)
• JSON (brand new, tool support is still developing)

plus others.

Note the last two? Yes, you can define data structures in ASN.1, generate code, and emit / consume messages in XML and JSON. Not bad for a technology that started off back in the 1980s.

Versioning is done differently to GPB. You can allow for extensions:

Foo ::= SEQUENCE
{
   bearing INTEGER (-180..180),
   ...
}

This means that at a later date I can add to Foo, and older systems that have this version can still work (but can only access the bearing field).

I rate ASN.1 very highly. It can be a pain to deal with (tools might cost money, the generated code isn't necessarily beautiful, etc). But the constraints are a truly fantastic feature that has saved me a whole ton of heart ache time and time again. Makes developers whinge a lot when the encoders / decoders report that they've generated duff data.

Other links:

• Good intro
• Open source C/C++ compiler
• Open source compiler, does ADA too AFAIK
• Commercial, good
• Commercial, good
• Try it yourself online

Observations

To share data:

• Code first approaches (e.g. Boost serialisation) restrict you to the original language (e.g. C++), or force you to do a lot of extra work in another language
• Schema first is better, but
  • A lot of these leave big gaps in the sharing contract (i.e. no constraints). GPB is annoying in this regard, because it is otherwise very good.
  • Some have constraints (e.g. XSD, JSON), but suffer patchy tool support.
  • For example, Microsoft's xsd.exe actively ignores constraints in xsd files (MS's excuse is truly feeble). XSD is good (from the constraints point of view), but if you cannot trust the other guy to use a good XSD tool that enforces them for him/her then the worth of XSD is diminished
  • JSON validators are ok, but they do nothing to help you form the JSON in the first place, and aren't automatically called. There's no guarantee that someone sending you JSON message have run it through a validator. You have to remember to validate it yourself.
  • ASN.1 tools all seem to implement the constraints checking.

So for me, ASN.1 does it. It's the one that is least likely to result in someone else making a mistake, because it's the one with the right features and where the tools all seemingly endeavour to fully implement those features, and it is language neutral enough for most purposes.

To be honest, if GPB added a constraints mechanism that'd be the winner. XSD is close but the tools are almost universally rubbish. If there were decent code generators of other languages, JSON schema would be pretty good.

If GPB had constraints added (note: this would not change any of the wire formats), that'd be the one I'd recommend to everyone for almost every purpose. Though ASN.1's uPER is very useful for radio links.