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:
Of course I only mean the "root" messages, namely PaymentRequest,
> it might be a good idea to apply this to all messages if any.
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
> <andreas@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 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>
> > <mailto:Bitcoin-development@lists.sourceforge.net> <mailto: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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