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From Ted Ross <tr...@redhat.com>
Subject Re: Proof of Concept JavaScript Proton implementation.
Date Tue, 19 Nov 2013 20:18:27 GMT

This looks really interesting.  Can you provide any details about the 
WebSockets encapsulation (i.e. how WS messages and frames are used)?



On 11/19/2013 02:56 PM, Fraser Adams wrote:
> Hey all,
> For the last couple of weekends I've been working on a Proof of 
> Concept JavaScript implementation of Proton.
> The approach that I've taken is (I think) quite interesting/unusual 
> but it's an approach that offers a high level of synergy with 
> implementations for other languages that are essentially bindings to 
> proton-c.
> The "magic elixir" in this is the downright amazing emscripten 
> https://github.com/kripken/emscripten/wiki which (believe it or not) 
> is essentially a cross-compiler that can compile C/C++ to JavaScript. 
> Moreover the JavaScript that it compiles to is a particular subset 
> called asm.js http://asmjs.org/ which can be extremely aggressively 
> optimised and is subject to a lot of research by Mozilla in particular 
> (the main emscripten maintainer is actually a Mozilla researcher, 
> though I believe emscripten is something of a side project).
> It's well worth visiting the emscripten page with a modern browser, 
> the Epic Citadel demo is awesome :-)
> So in a nutshell what I've done is to compile proton-c into JavaScript
> So I'm underselling it a bit :-) I had to do a fair bit of work to 
> make it that simple, in particular I had to add/fix a number of 
> emscripten's library functions (Proton used a few things that weren't 
> implemented) but the cool thing is that those are now in emscripten 
> for everyone's benefit.
> A really nice thing is that I've not actually had to modify any of the 
> engine/messenger code at all - one I started to figure out what I was 
> doing wrong that is :-) all I've really needed to to was to modify 
> send.c/recv.c so that they behave in a non-blocking manner (you may 
> have seen my mail at the weekend before I finally figured it out :-))
> I've got CMake able to cross-compile in a repeatable fashion so the 
> only change to any existing Proton stuff that is required is an 
> addition to the top-level CMakeLists.txt that detects the presence of 
> emscripten and its dependencies and if present fires off 
> "add_subdirectory(bindings/javascript)" e.g.
> # Build the JavaScript language binding.
> # This is somewhat different to the other language bindings in that it 
> does not use swig. It uses a C/C++ to
> # JavaScript cross-compiler called emscripten 
> (https://github.com/kripken/emscripten). Emscripten takes C/C++
> # and "compiles" it into a highly optimisable subset of JavaScript 
> called asm.js (http://asmjs.org/) that can
> # be aggressively optimised and run at near-native speed (usually 
> between 1.5 to 10 times slower than native C/C++).
> option("BUILD_JAVASCRIPT" "Build JavaScript language binding" ON)
>   # First check that Node.js is installed as that is needed by 
> emscripten.
>   find_program(NODE node)
>   if (NOT NODE)
>     message(STATUS "Node.js (http://nodejs.org) is not installed: 
> can't build JavaScript binding")
>   else (NOT NODE)
>     # Check that the emscripten C/C++ to JavaScript cross-compiler is 
> installed.
>     find_program(EMCC emcc)
>     if (NOT EMCC)
>       message(STATUS "Emscripten 
> (https://github.com/kripken/emscripten) is not installed: can't build 
> JavaScript binding")
>     else (NOT EMCC)
>       add_subdirectory(bindings/javascript)
>     endif (NOT EMCC)
>   endif (NOT NODE)
> So the main purpose of this mail is to give a heads up of it and to 
> ask if it'd be OK to start commiting it and give others some 
> visibility of it.
> At this stage it's something of a Proof of Concept, in particular:
> * I haven't exported any actual JavaScript bindings so although it's 
> JavaScript actual JavaScript clients would find it awkward to call the 
> API as yet.
> * As alluded above and at the weekend the demo code I've got calling 
> messenger isn't especially elegant, I think I know how to get things 
> behaving more asynchronously, but haven't tried it yet (and my hunch 
> may be wrong).
> * Transport is entirely over WebSockets :-) so I've actually got send 
> and recv running on Node.js (and also send on a browser) but it'd be 
> useful to have them communicate via TCP sockets too - though that'd 
> need a proxy.
> * I still (perhaps amusingly given this) don't know that much about 
> Proton, so I've only really got send and recv to play with I'm not 
> really sure where there may be other messenger examples to exercise it 
> a bit better (in particular message type interoperability would be 
> good to test). I'd be grateful for pointers - is the object.c test the 
> best place to look for this? And I couldn't see any tests for the 
> "tracker" capabilities??
> * In case it wasn't clear from the WebSockets it'll only work in a 
> relatively modern browser at the moment both for the WebSocket stuff 
> and for the fact that it relies on ArrayBuffers (though there's an 
> emscripten compile option to allow the use of native JavaScript Arrays 
> instead)
> Finally it's probably worth pointing out some pros and cons for this 
> approach to creating a JavaScript Proton
> Pro:
> * It's using the existing proton-c code base with the posix driver.c 
> completely unchanged (with the simple test I've done to date) so from 
> a broad maintenance/"Total cost of Ownership" perspective it means 
> essentially very little extra maintenance costs.
> * It follows the same "pattern" as Python/Perl/PHP/Ruby/Java JNI 
> albeit it's cross-compiled rather than a pure binding.
> * It should be somewhat faster than "handwritten" JavaScript. This 
> might seem counter-intuitive but it's worth looking at the 
> emscripten/asm.js documentation. From my own experience I've ported 
> zlib to JavaScript for another project I'm working on and inflate was 
> *significantly* faster than the literal port of tinflate that I had 
> previously used - and that was on a relatively old Firefox without 
> asm.js optimisations.
> Con:
> * The compiled code is likely to be somewhat larger than hand written 
> JavaScript. I haven't done an optimised & minified build yet so I 
> can't say for sure how big it will actually be. The unoptimised 
> send.js/recv.js are 1.5MB each so at a guess they'll probably come out 
> at arounf the ~500K mark (though they should also gzip quite well).
> * The compiled code isn't necessarily hugely readable. It's "OK" when 
> not optimised but.... (to be fair I used it to figure out how to get 
> the missing library calls working so it's not *totally* impenetrable :-))
> I hope that this is something that'll be useful/interesting please do 
> let me know if you're all happy for me to get it kicked off into the 
> Proton code base.
> Best regards,
> Frase
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