Github user zolvarga commented on the pull request:
https://github.com/apache/qpid-proton/pull/71#issuecomment-198544346
Hi Rob,
Thanks for the quick response. See answers/questions inlineâ¦
Cheers,
Zoltan
From: Robbie Gemmell [mailto:[email protected]]
Sent: Friday, March 18, 2016 10:15 AM
To: apache/qpid-proton <[email protected]>
Cc: Zoltan Varga <[email protected]>
Subject: Re: [qpid-proton] Adding WebSocket functionality to Proton-J (#71)
Hi Zoltan,
Sorry for the delay, I have finally given this a look, albeit a relatively
quick one. I havenât spent as long looking at it as I might like to (so I
might have completely misunderstood some things), and I havenât tried it out,
but Iâm off on vacation for the next week-and-a-bit and wanted to comment
before I disappear.
My initial reaction was that Iâm not sure I like the idea of the core
engine Transport having more things to do that arenât really about AMQP
directly, but more IO. On the other hand I guess this way lets it works across
different IO / API models, such as that imposed by the existing Reactor code,
and it would be optional so folks wouldnât need to use it if they have a
separate IO layer to do this. Probably something we should discuss in the
community.
[Zoltan] I agree, the design would be cleaner to separate the WebSocket IO
from the AMQP IO. I have tried to design it that way, but I could not find a
clean entry point in the reactor architecture where an âexternalâ WebSocket
implementation would handle the IO buffer. The reactor currently doesnât
provide IO independent events for modify the IO buffer before send and after
receive. We would need an interface here which communicates through
input/output buffers only, completely separated from the underlying channel. If
that kind of communication with reactor would be possible it would allow us to
use external WebSocket library. In that case the external library would do all
the IO (Socket, SSL engine etc.) and Proton-J would just handle a buffer
regarding the AMQP bits. I donât think Proton-J reactor is prepared to do
that but correct me if I am wrong. Please let me know if I missed something
here.
Setting that aside that for now, I had some more code-specific comments
from my initial look though:
* Silently skipping doing anything WebSockets if the
âconfigure/initâ step is missed out doesnât seem very nice. If folks call
the websocket() method then I think that is what they should actually get (or
some form of error upon use, if any further necessary config isnât then
provided). Doing away with the âisEnabledâ stuff would seem to simplify
things elsewhere too.
[Zoltan] I see your point. The current WebSocket initialization
implementation is following the implementation of the other layers (like SASL).
This is basically the consequence of the design choice to integrate WebSocket
IO into the reactor. We can discuss alternative approach if we decided on the
integration question you asked.
* Related to above, the reactor io handler always calling
transport.websocket() seems an odd choice. It wonât do much if not further
configured, so it seems whoever is ultimately configuring it (example would
help here) could request the websocket use originally too, in fact presumably
they would have to in order to get the object to configure it. Also WebSocket
webSocket = transport.webSocket(); creates an unused variable in the reactor.
[Zoltan] See the answer above. I know about the unused variable, I will
remove it.
* The configure method isnât actually exposed on the interface to let
it be called anyway?
[Zoltan] Good catch. I am going to change it.
* The tracking of the _webSocketHeaderSize and its use in pop seemed
frail, if someone calls head()/pending() more than once or pops less than the
total pending at each use it seemed like it could end up popping the wrong
amount from the underlying buffer.
* WebSocketHandlerImpl.unwrapBuffer(ByteBuffer) has some unused
variables. It also seems to make some questionable returns. E.g if there
arenât enough bytes (yet..they may still be coming) to determine a size, it
returns âinvalid lengthâ, and since the
WebSocketImpl.WebSocketTransportWrapper.processInput() method seems to treat
most return values as simply âpour the websocket input buffer into the
underlying inputâ, it would then seem it could do the wrong thing in such
cases. unwrapBuffer also doesnât seem to do anything with the actual lengths
it calculates.
[Zoltan] I am going to revisit the implementations point above.
* The above makes it seem like like it can only process 1 frame each
time process is called, and assuming only a single websocket frames content
will be present in the buffer and the start of the buffer is always the header.
Is that the case, or did I miss something important? Those seem like
assumptions that donât necessarily hold, and could give unexpected behaviour.
[Zoltan] Yes, that is the case but I think assumption here is correct. Even
if WebSocket frames contain partial AMQP messages the WebSocket frame will be
always complete.
* The Websocket impl âmax frame sizeâ isnât configurable and
seems a little arbitrary, but overlooking that it doesnt seem like the handler
will cope with an underlying buffer having more output than it can fit, either
due to a single larger frame, or the combination of multiple frames awaiting
transmission. The OOME thrown in that case is perhaps misleading (given there
is still memory, just not enough output buffer space, i.e another exception
type might be better), though I think it really just shouldnât throw an
exception and rather send what it can.
[Zoltan] I am going to revisit this too.
* The âclient-onlyâ impl detail mentioned here is not clear in the
code. Could use some doc, or maybe config? This is also a little unfortunate
since everything else in the Transport works at both ends of a connection.
[Zoltan] Yes, the server implementation is missing and it is unfortunate
but this is what we have currently. This would serve our scenarios and we were
focusing only client side implementation.
* It isnât clear why there a âWebsocketSnifferâ if the impl is
client-only, a sniffer would be used at a server end normally. Also, the only
non-test usage of it (in WebSocketImpl#wrap) seems strange in that it overrides
any choice anyway.
[Zoltan] I agree, if we support client implementation only.
P.S. please rebase Pull Requests against the current master to remove merge
commits and related noise from them.
[Zoltan] Sure.
â
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