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To: bitcoin-development@lists.sourceforge.net
From: Andreas Schildbach <andreas@schildbach.de>
Date: Sun, 26 Jan 2014 22:32:52 +0100
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	<CANEZrP2F-1aqzBfUB82riWOwTABf1arbx70FdQ-XndQ91m_QqA@mail.gmail.com>
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In-Reply-To: <CANEZrP2F-1aqzBfUB82riWOwTABf1arbx70FdQ-XndQ91m_QqA@mail.gmail.com>
Subject: Re: [Bitcoin-development] BIP70/71 issue, RFD
Precedence: list

Bluetooth, Wifi Direct, HTTP request/responses via broken proxies, smoke
signals... basically anything that is a stream rather than a file.

Right, NFC NDEF and QR codes are not affected, so we can skip the
delimiter for these mediums.


On 01/26/2014 10:24 PM, Mike Hearn wrote:
> Which medium is this an issue for? As you note, for files and HTTP
> responses it's not a problem in practice. i'd guess nor for NFC tags nor
> QR codes.
> 
> 
> On Sun, Jan 26, 2014 at 10:11 PM, Andreas Schildbach
> <andreas@schildbach.de <mailto:andreas@schildbach.de>> wrote:
> 
>     I'm experimenting with BIP70/71 (payment protocol) usage in face to face
>     payments (more on that soon).
> 
>     I've excountered an issue with the protobuf format. Protobufs are not
>     self-delimiting. That means if you're reading from an undelimited
>     stream, you will read endlessly because you don't know how much to read.
> 
>     The current BIP70 implementations probably work because they're reading
>     either from a file or from an HTTP resource which sets the
>     Content-Length header. Trouble is the Content-Length header is optional,
>     and also there are many kinds of streams that don't have this built-in
>     delimiting mechanism.
> 
>     The Java protobuf API solves this by offering delimited I/O, like
> 
>     payment.writeDelimitedTo(os);
> 
>     This writes the size of the message as a varint before writing the data.
>     I don't know about protobuf implementations for other languages but I'd
>     expect them to offer something compatible.
> 
>     However, this leading varint is an incompatible change and would need to
>     be added to the spec.
> 
>     I specifically encountered this with PaymentMessage and PaymentACK, but
>     it might be a good idea to apply this to all messages if any. Open for
>     discussion.
> 
> 
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