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

From: Takeshi Yoshino <tyoshino@google.com>
Date: Wed, 2 Nov 2016 14:34:26 +0900
Message-ID: <CAH9hSJZB0SyFiqLqLjd9R-T11yTa12Ekb-H8hYwfc6FeOjD2xQ@mail.gmail.com>
To: Wenbo Zhu <wenboz@google.com>
Cc: Costin Manolache <costin@gmail.com>, Loïc Hoguin <essen@ninenines.eu>, "ietf-http-wg@w3.org Group" <ietf-http-wg@w3.org>
On Mon, Oct 31, 2016 at 5:57 AM, Wenbo Zhu <wenboz@google.com> wrote:

>
>
> 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.
>>
>
>>
Yeah, at least the Content-Type in the HTTP request gets eliminated.


> 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)
>

Agreed. Let's discuss the metadata needs separately. I agree it's important.


>
>
>>
>> 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
>>>
>>>
>>>
>>>
>
Received on Wednesday, 2 November 2016 05:35:20 UTC

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