From: Tom <tomz@freedommail.ch>
To: bitcoin-dev@lists.linuxfoundation.org,
	Andreas Schildbach <andreas@schildbach.de>
Date: Wed, 21 Sep 2016 14:58:02 +0200
Message-ID: <58983644.DvMMf90VdX@garp>
In-Reply-To: <nrtsok$lp5$1@blaine.gmane.org>
References: <7844645.RLYLWYmWtM@garp> <nrtsok$lp5$1@blaine.gmane.org>
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Subject: Re: [bitcoin-dev] Requesting BIP assignment; Flexible Transactions.
Precedence: list

On Wednesday 21 Sep 2016 14:00:23 Andreas Schildbach via bitcoin-dev wrote:
> Just glancing over your BIP, I wonder if we should use Protobuf. It uses
> this "flexible" format already and is quite compact/binary. We use
> Protobuf already for the payment protocol, and there is very good tool
> support.

There is a lot of overlap between different binary formats. Looking through 
the on-the-wire protocol you'll see that my spec is very similar. Practically 
all the advantages of protobuf are present in CMF. I can write you a java 
parser if you want, it should be easy to port from Qt/C++ code :)
https://github.com/bitcoinclassic/transactions

CMF: 
https://github.com/bitcoinclassic/documentation/blob/master/spec/compactmessageformat.md

There is no tool support needed, just one or two classes. Which personally I 
think is an advantage.


Some advantages of CMF over protobuf from the top of my head;

* It reuses the var-int parsing that Bitcoin uses (which is itself slightly 
different from others).

* zero-copy support (not relevant for this bip, though).

* Additional values addition (i.e. adding new data) is .. tricky in protobuf.
https://developers.google.com/protocol-buffers/docs/proto#updating

* In my experience parsing a message manually (like a SOX parser) is much 
better in reporting errors and detecting wrong usages than auto-generated code 
(but personally I'm not much a fan of auto-generated APIs) at all...

* Generated parsing/writing code will not be as fast as we can make it.

* CMF is more compact (uses less bytes) for its messages.


Protobuf is something I've used before and I think we can do better. I think 
that CMF together with some support classes can do this better.