Re: WiSH: A General Purpose Message Framing over Byte-Stream Oriented Wire Protocols (HTTP)

Wenbo Zhu <wenboz@google.com> Sun, 30 October 2016 21:02 UTC

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From: Wenbo Zhu <wenboz@google.com>
Date: Sun, 30 Oct 2016 13:57:13 -0700
Message-ID: <CAD3-0rM35uXJnwfGay-1s9uw=-P71EubOkxFdKF=gjoXub8YXw@mail.gmail.com>
To: Costin Manolache <costin@gmail.com>
Cc: Takeshi Yoshino <tyoshino@google.com>, =?UTF-8?B?TG/Dr2MgSG9ndWlu?= <essen@ninenines.eu>, "ietf-http-wg@w3.org Group" <ietf-http-wg@w3.org>
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Subject: Re: WiSH: A General Purpose Message Framing over Byte-Stream Oriented Wire Protocols (HTTP)
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On Sun, Oct 30, 2016 at 10:25 AM, Costin Manolache <costin@gmail.com> wrote:

> Thanks for the answer and pointers. From earlier responses, it seems
> possible to use GET
> or a non-web-stream request to would avoid the extra cost of the
> pre-flight.
>

> One more question/issue: in some cases it would be good to send some
> metadata (headers) along with binary frames. For example in webpush the
> content is an encrypted
> blob, and needs headers for the key/salt. I would assume a lot of other
> 'binary' messages would
> benefit if simple metadata could be sent along. Would it be possible to
> use one of the reserved
> bits for 'has metadata' and add some encoded headers ? I know in websocket
> they are intended
> for 'extensions', but 'headers' seems a very common use case.
>
Q about webpush: is the metadata different for each binary message?

We discussed about metadata and how to use one of RSV bits etc. For the
current version, let's make sure the WS compatibility is fully addressed
(with minimum wire encoding like WiSH)


>
> Having the binary frame use some MIME encoding to pass both text headers
> and the binary blob
> is possible - but has complexity and overhead.
>
OTOH, if the binary blob relies on text headers (metata) to be useful, then
you probably need define a dedicated MIME encoding.



>
> Costin
>
> On Sun, Oct 30, 2016 at 5:27 AM Takeshi Yoshino <tyoshino@google.com>
> wrote:
>
>> Thanks, Van, Costin.
>>
>> On Sun, Oct 30, 2016 at 2:43 AM, Costin Manolache <costin@gmail.com>
>> wrote:
>>
>> Good point - websocket is widely deployed, including IoT - and the header
>> is pretty easy to handle anyways.
>> +1.
>>
>> One question: is this intended to be handled by browsers, and exposed
>> using the W3C websocket API ?
>> Will a regular app be able to make WiSH requests and parse the stream by
>> itself, without browser
>> interference ? And if yes, any advice on how it interact with CORS ?
>>
>>
>> The first step would be using Streams based upload/download via the Fetch
>> API + protocol processing in JS.
>>
>> The next step could be either introduction of an optimized native
>> implementation of WiSH parser/framer in the form of the TransformStream
>> which can be used as follows:
>>
>> const responsePromise = fetch(url, init);
>> responsePromise.then(response => {
>>   const wishStream = response.body().pipeThrough(wishTransformStream);
>>   function readAndProcessMessage() {
>>     const readPromise = wishStream.read();
>>     readPromise.then(result => {
>>       if (result.done) {
>>         // End of stream.
>>         return;
>>       }
>>
>>       const message = result.value;
>>       // Process the message
>>       // E.g. access message.opcode for opcode, message.body for the body
>> data
>>       readAndProcessMessage();
>>     });
>>   }
>>   readAndProcessMessage();
>> });
>>
>> and provide a polyfill that presents this as the WebSocket API, and (or
>> skip the step and) go further i.e. native implementation for everything if
>> it turns out optimization is critical.
>>
>> We need to discuss this also in W3C/WHATWG.
>>
>> Regarding CORS, if the request includes non CORS-safelisted headers,
>> fetch() based JS polyfills will be basically subject to the CORS preflight
>> requirement. We could try to exempt some of well defined headers if any for
>> CORS like WebSocket handshake's headers and server-sent event's
>> Last-Event-Id are exempted. Regarding the proposed subprotocol negotiation
>> in the form of combination of the Accept header and the Content-Type
>> header, the Accept header is one of the CORS-safelisted headers, so it's
>> not a problem. The Content-Type header is considered to be
>> non-CORS-safelisted if it's value is none of the CORS-safelisted media
>> types. So, WiSH media type would trigger the preflight unless we exclude it.
>>
>> Origin policy https://wicg.github.io/origin-policy/ might also help.
>>
>>
>>
>> Costin
>>
>> On Fri, Oct 28, 2016 at 12:06 PM Takeshi Yoshino <tyoshino@google.com>
>> wrote:
>>
>> Sorry for being ambivalent.
>>
>> We can of course revisit each design decision we made for RFC 6455
>> framing and search for the optimal again. But as:
>> - one of the main philosophies behind WiSH is compatibility with
>> WebSocket in terms of both spec and implementation
>> - the WebSocket is widely deployed and therefore we have a lot of
>> implementations in various languages/platform
>> - most browsers already have logic for the framing
>> - the framing is not considered to be so big pain
>> inheriting the WebSocket framing almost as-is is just good enough.
>> Basically, I'm leaning toward this plan.
>>
>> Takeshi
>>
>> On Sat, Oct 29, 2016 at 3:12 AM, Takeshi Yoshino <tyoshino@google.com>
>> wrote:
>>
>> On Sat, Oct 29, 2016 at 2:55 AM, Loïc Hoguin <essen@ninenines.eu> wrote:
>>
>> On 10/28/2016 08:41 PM, Costin Manolache wrote:
>>
>> Current overhead is 2 bytes if frame is up to 125 bytes long - which I
>> think it's not very common,
>> 4 bytes for up to 64k, and 10 bytes for anything larger.
>> IMHO adding one byte - i.e. making it fixed 5-byte, with first as is,
>> and next 4 fixed length would
>> be easiest to parse.
>>
>>
>> Is making it easy (or easier) to parse even a concern anymore?
>>
>> Considering the number of agents and servers already supporting
>> Websocket, the numerous libraries for nearly all languages and the great
>> autobahntestsuite project validating it all, reusing the existing code is a
>> very sensible solution.
>>
>>
>> Yeah, I've been having similar feeling regarding cost for parser/encoder
>> implementation though I might be biased.
>>
>>
>> There are obviously too many options to encode and each has benefits -
>> my only concern was
>> that the choice of 1, 2, 8 bytes for length may not match common sizes.
>>
>> ( in webpush frames will be <4k ).
>>
>>
>> --
>> Loïc Hoguin
>> https://ninenines.eu
>>
>>
>>
>>