To be more accurate, the embedded messages already have length prefixes :-)
On Sun, Jan 26, 2014 at 11:14 PM, Andreas Schildbach
<andr...@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 should
> > indeed use protobuf varint length prefixes. But it's unnecessary for all
> > cases. Unless Gavin feels it'd be better to be consistent everywhere and
> > is willing to change the spec and code - as far as I know though we're
> > trying to ship 0.9rc1 soonish .....
> >
> >
> > On Sun, Jan 26, 2014 at 10:32 PM, Andreas Schildbach
> > <andr...@schildbach.de <mailto:andr...@schildbach.de>> wrote:
> >
> > 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
> > > <andr...@schildbach.de <mailto:andr...@schildbach.de>
> > <mailto:andr...@schildbach.de <mailto:andr...@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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