Hello Paul,
I contributed the emscripten based proton JavaScript binding a while back.
1. Re: "The only think I can find are JavaScript bindings that are
cross-compiled from the C version using Emscripten:
https://github.com/apache/qpid-proton/tree/master/proton-c/bindings/javascript
That doesn't look like the 'pure-JavaScript implementation' mentioned on
http://qpid.apache.org/proton/"";
I think that's a little unfair, if you take a look at what emscripten is
it is an LLVM back-end that allows things supported by LLVM front-ends
such as C/C++ etc. to be compiled to that back-end language, so in
practice it compiles the proton C code into asm.js
http://asmjs.org/faq.html which *is* pure JavaScript and certainly
closer to pure JavaScript than most of the node bindings I've seen which
compile the C code and use native code bindings so won't run in a
browser. The original intent of the JavaScript binding was to have
something that would run in a browser and as it happens also ran happily
in node.
2. It was built to use the proton messenger API. I suspect that's
probably the main issue now, as many people seem to have moved away from
messenger due to issues with error handling when the remote end
terminated. Funnily enough though, the JavaScript binding was actually
more tolerant than the basic C one because I actually monkey patched
this stuff so when I received websocket error events the JavaScript
binding reconnected fairly well. I tried to make the JavaScript binding
to messenger follow the same patterns as the python binding, so it had a
fairly idiomatic feel JavaScript feel.
3. "I had a brief look at the JavaScript bindings history and while it
does seem to get an occassional update, I wonder if it is up to date
with the ongoing developments of Qpid Proton ". That's a fair
observation. It actually took quite a bit of energy to put the binding
together in the first place, but it was entirely my spare time effort
and I'm afraid I've been busy on other things recently. TBH there didn't
seem to be a great deal of interest in it, so I'm afraid I somewhat lost
motivation.
I think that when Gordon did rhea https://github.com/grs/rhea I got
fairly confused about what the direction was going to be, especially
when the dispatch router UI started using that instead of the emscripten
based binding (as I say there didn't seem to be a great deal of interest
which had a bit of an effect on my motivation). I realise that the
emscripten approach can result in somewhat larger javascript files, but
OTOH because it is based on a virtual heap built on ArrayBuffers it had
pretty good support for being able to transport arbitrary binary
objects, which is something that many JavaScript implementations of
things often fall down on, I'm not sure if rhea supports this (it may,
I've not checked) but I explicitly did that for the emscripten based
binding, which works fairly well as it's built on ArrayBuffers.
I keep meaning to get back to it, I think a lot of the thinking in
proton has been around reactive APIs which are a better fit for
JavaScript and it'd make sense to move away from messenger API to those,
but as I say in general there hasn't been that much interest and I've
had commitments elsewhere.
4. Re "In fact, from a recent mail thread I think it may not even
compile at present, and its probably overdue for the community to have a
discussion about its future as a result. ". That's a shame, TBH one of
the problems I had was chasing my tail keeping up to date with changes
given juggling this with family and other tech commitments, I had sort
of hoped that the community would keep an eye on it and at least keep it
compiling.
It's a difficult call, in actual fact one of the motivations for going
down the emscripten based approach was because it is essentially a case
of compiling from the "canonical" proton C code. It really *should* be
possible to be slap bang up to date with whatever is in the underlying C
trunk (provided of course a little TLC is given). Part of the reason I
went with that approach was that I'd seen proton-C and proton-J diverge
and I figured that if I'd done a ground up JavaScript implementation it
would stand less chance of keeping up with changes and improvements to
the underlying protocol engine and the code base would diverge. I still
think that is actually a fair premise and conceptually follows the
approach of the various swigged bindings, but as I say is still needs a
little TLC to make that situation hold.
Another reason why emscripten can be a good choice is because of
performance (a key use case for emscriptem is porting games to the web -
take a look at the website there are some really cool things). To be
fair I haven't compared the proton JS binding performance with rhea, but
in the general sense compiling well written C/C++ applications to
JavaScript can give much better performance than pure idiomatic
JavaScript partly because of things like type coercion, partly because
of the virtual heap and avoiding garbage collection lags and partly
because some engines (notably in FireFox and Edge) have really good
asm.js optimisations and do ahead-of-time compilation of asm.js blocks.
When I emscriptened gzip in FireFox a while back I was seeing > 80%
native performance and it's improving all the time. There is also a
roadmap towards WebAssembly which should increase the performance even
more. The down side is of course the larger JS file and some awkwardness
binding idiomatic JavaScript to a C-like API. Most of the actual JS code
in the proton JavaScript binding is the "binding" stuff to make it look
like idiomatic JavaScript. If you take a look at that stuff and compare
it with the python binding that wraps the swigged C you should see that
they are actually pretty similar (I actually used the python binding for
inspiration TBH).
I think that the arguments for and against doing an emscriptened binding
and a ground up implementation are largely the same as those for using a
swig binding versus a ground up implementation for other languages.
Sorry it's not a really "tidy" answer, but at least it's an honest one :-)
I'm hoping to find time to get back into doing qpid things, and
JavaScript is one of the things I care most about, but I'd definitely
like to see somewhat more cohesion. By my observation Proton has got a
bit "fragmented" with a range of APIs and not seen a lot of clarity on
approach/roadmap and it has seemed that different languages seem to have
taken different approaches so I've never really pinned down what might
be described as a common API. On the one hand so what, but on the other
I'm a big fan of polyglot software development and it'd be quite nice to
be able to switch between languages and follow a somewhat similar
approach, which doesn't seem to be the case at the moment.
Another thing that seems to be missing (though I may just be out of the
loop) is a clean way to use the AMQP link attachment protocol, for
example if you look at the qpid messaging API (that's the one in the
main qpid repo) and also JMS they make use of a JSON-like "address
string" which contains a "link: " stanza that allows one to configure
how link attachment works, that's really useful for AMQP consumers
subscribing to messages off a broker as you can use that to specify
message selectors and do useful things like have non-exclusive queues
where multiple instances of a consumer can read messages off the same
queue, which is great if you want to scale out consumers. Now you can do
that with the proton API (and indeed messenger uses the low-level proton
engine), but it's quite fiddly and it would be nice to see APIs to make
that much more convenient.
It'd also be nice to have a node binding that accepted both WebSockets
and TCP, of course browsers can only do the former and that was the main
target of the emscripten based binding so you could certainly create a
node app that you could connect to via a WebSocket from a browser, but I
never got round to supporting TCP connections too which would be useful.
The Java broker supports both which is really helpful but the C++ broker
(which is the one I mainly use) does not (which would be a nice
addition). I *think* that there is work ongoing in dispatch router to
support WebSockets and that may be a good way to bridge to the C++
broker but it'd still be nice if it had native support.
HTH,
Regards,
Frase
On 03/03/17 07:51, Paul wrote:
Tnx for the claification.
Too bad the things claimed on the website aren't true, as I was
particular interested in being able to use the exact same library/API
in both Java and JavaScript (as we use both in our stack), as to not
have to deal with two separate libraries/api's that do the same thing,
albeit in a different language.
Paul
On 3/2/2017 11:46 AM, Robbie Gemmell wrote:
On 2 March 2017 at 07:56, Paul <[email protected]> wrote:
Hi,
Based on http://qpid.apache.org/proton/overview.html (and
http://qpid.apache.org/proton/), I'm looking for the JavaScript
implementation.
The only think I can find are JavaScript bindings that are
cross-compiled
from the C version using Emscripten:
https://github.com/apache/qpid-proton/tree/master/proton-c/bindings/javascript
That doesn't look like the 'pure-JavaScript implementation'
mentioned on
http://qpid.apache.org/proton/ and the 'At its core Proton provides
three
parallel implementations.....' mentioned on
http://qpid.apache.org/proton/overview.html
Am I completely overlooking something somewhere or?
No, you aren't missing anything, the site is in error.
I think these references are the result of folks getting a little
ahead of reality in times past and it not subsequently being spotted
and reigned back in to reflect what actually happened, which was the
binding using emscripten that you referenced. I have updated the site
to remove those mentions, thanks for pointing them out.
I had a brief look at the JavaScript bindings history and while it
does seem
to get an occassional update, I wonder if it is up to date with the
ongoing
developments of Qpid Proton
I think it would be fair to say the JavaScript binding is not up to
date with ongoing development. In fact, from a recent mail thread I
think it may not even compile at present, and its probably overdue for
the community to have a discussion about its future as a result.
For now, if you are looking for a Javascript AMQP 1.0 implementation
you might consider one written by Gordon Sim,
https://github.com/grs/rhea, which loosely follows the style of the
Proton Container api in the Python binding which Gordon also did much
of the work on.
TIA,
Paul
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