Message encoding and length (or terminator or checksum or error correction
or...) should be part of the transport protocol, in my humble opinion.
--
Gavin Andresen
> On Jan 26, 2014, at 6:01 PM, Mike Hearn <m...@plan99.net> wrote:
>
> 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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