Message encoding and length (or termin= ator or checksum or error correction or...) should be part of the transport p= rotocol, in my humble opinion.

--

Gavin Andresen

On Jan 26, 2014, at 6:01 PM, Mike Hearn <mike@plan99.net> wrote:

To be more accurate, the embedded mess= ages already have length prefixes :-)

On Sun, Jan 26, 2014 at 11:14 PM, Andreas Schil= dbach <andreas@schildbach.de> wrote:

Just keep in mind that if it turns out we need= to retrofit messages with
length prefixes I fear we will have to restart with new mime-types. The
nature of prefixes being always at the start means this rules out simply
= incrementing a protocol version number.

Correcting myself:

> it might be a good idea to apply this to all messages if any.

Of course I only mean the "root" messages, namely PaymentRequest,
Payment, and PaymentACK. The embedded messages don't need length prefixes.

On 01/26/2014 11:00 PM, Mike Hearn wrote:
> I think for "binding" the payment protocol to those transports we shoul= d
> indeed use protobuf varint length prefixes. But it's unnecessary for al= l
> cases. Unless Gavin feels it'd be better to be consistent everywhere an= d
> is willing to change the spec and code - as far as I know though we're<= br> > trying to ship 0.9rc1 soonish .....
>
>
> On Sun, Jan 26, 2014 at 10:32 PM, Andreas Schildbach

> <an= dreas@schildbach.de <mailto:= andreas@schildbach.de>> wrote:
>
> Bluetooth, Wifi Direct, HTTP request/responses via broken= proxies, smoke
> signals... basically anything that is a stream rather tha= n a file.
>
> Right, NFC NDEF and QR codes are not affected, so we can s= kip 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 f= iles and HTTP
> > responses it's not a problem in practice. i'd guess n= or for NFC
> tags nor
> > QR codes.
> >
> >
> > On Sun, Jan 26, 2014 at 10:11 PM, Andreas Schildbach=
> > <andreas= @schildbach.de <mailto:andre= as@schildbach.de>

> <mailto:andreas@schildbach.de <mailto:andreas@schildbach.de>>> wrote:
> >
> > I'm experimenting with BIP70/71 (payme= nt protocol) usage in
> face to face
> > payments (more on that soon).
> >
> > I've excountered an issue with the pro= tobuf format. Protobufs
> are not
> > self-delimiting. That means if you're r= eading from an undelimited
> > stream, you will read endlessly becaus= e you don't know how
> much to read.
> >
> > The current BIP70 implementations prob= ably work because
> they're reading
> > either from a file or from an HTTP res= ource which sets the
> > Content-Length header. Trouble is the C= ontent-Length header is
> optional,
> > and also there are many kinds of strea= ms that don't have this
> built-in
> > delimiting mechanism.
> >
> > The Java protobuf API solves this by o= ffering 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 implementa= tions for other
> languages but I'd
> > expect them to offer something compati= ble.
> >
> > However, this leading varint is an inc= ompatible change and
> would need to
> > be added to the spec.
> >
> > I specifically encountered this with P= aymentMessage and
> PaymentACK, but
> > it might be a good idea to apply this t= o all messages if any.
> Open for
> > discussion.
> >
> >
> >
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