Re: [Bitcoin-development] BIP70/71 issue, RFD

[Mike Hearn <mike@plan99.net>]

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To be more accurate, the embedded messages already have length prefixes :-)


On Sun, Jan 26, 2014 at 11:14 PM, Andreas Schildbach
<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 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: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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