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From Vinod Kone <vinodk...@apache.org>
Subject Re: [VOTE] Release Apache Mesos 0.24.0 (rc1)
Date Mon, 31 Aug 2015 21:47:36 GMT
I think you might be confused with the HTTP chunked encoding and RecordIO
encoding. Most HTTP client libraries dechunk the stream before presenting
it to the application. So the application needs to know the encoding of the
dechunked data to be able to process it.

In Mesos's case, the server (master here) can encode it in JSON or
Protobuf. We wanted to have a consistent way to encode both these formats
and Record-IO format was the one we settled on. Note that this format is
also used by the Twitter streaming API
<https://dev.twitter.com/streaming/overview/processing> (see delimited
messages section).

HTH,

On Mon, Aug 31, 2015 at 2:09 PM, Dario Rexin <dario.rexin@me.com> wrote:

> Hi Vino,
>
> On Aug 31, 2015, at 9:36 PM, Vinod Kone <vinodkone@apache.org> wrote:
>
> Hi Dario,
>
> Can you test with "curl --no-buffer" option? Looks like your stdout might
> be line-buffered.
>
>
> that did the trick, thanks!
>
>
> The reason we used record-io formatting is to be consistent in how we
> stream protobuf and json encoded data.
>
>
> How does simple chunked encoding prevent you from doing this?
>
> Thanks,
> Dario
>
> On Fri, Aug 28, 2015 at 2:04 PM, <dario.rexin@me.com> wrote:
>
>> Anand,
>>
>> thanks for the explanation. I didn't think about the case when you have
>> to split a message, now it makes sense.
>>
>> But the case I observed with curl is still weird. Even when splitting a
>> message, it should still receive both parts almost at the same time. Do you
>> have any idea why it could behave like this?
>>
>> On 28.08.2015, at 21:31, Anand Mazumdar <anand@mesosphere.io> wrote:
>>
>> Dario,
>>
>> Most HTTP libraries/parsers ( including one that Mesos uses internally )
>> provide a way to specify a default size of each chunk. If a Mesos Event is
>> too big , it would get split into smaller chunks and vice-versa.
>>
>> -anand
>>
>> On Aug 28, 2015, at 11:51 AM, dario.rexin@me.com wrote:
>>
>> Anand,
>>
>> in the example from my first mail you can see that curl prints the size
>> of a message and then waits for the next message and only when it receives
>> that message it will print the prior message plus the size of the next
>> message, but not the actual message.
>>
>> What's the benefit of encoding multiple messages in a single chunk? You
>> could simply create a single chunk per event.
>>
>> Cheers,
>> Dario
>>
>> On 28.08.2015, at 19:43, Anand Mazumdar <anand@mesosphere.io> wrote:
>>
>> Dario,
>>
>> Can you shed a bit more light on what you still find puzzling about the
>> CURL behavior after my explanation ?
>>
>> PS: A single HTTP chunk can have 0 or more Mesos (Scheduler API) Events.
>> So in your example, the first chunk had complete information about the
>> first “event”, followed by partial information about the subsequent event
>> from another chunk.
>>
>> As for the benefit of using RecordIO format here, how else do you think
>> we could have de-marcated two events in the response ?
>>
>> -anand
>>
>>
>> On Aug 28, 2015, at 10:01 AM, dario.rexin@me.com wrote:
>>
>> Anand,
>>
>> thanks for the explanation. I'm still a little puzzled why curl behaves
>> so strange. I will check how other client behave as soon as I have a chance.
>>
>> Vinod,
>>
>> what exactly is the benefit of using recordio here? Doesn't it make the
>> content-type somewhat wrong? If I send 'Accept: application/json' and
>> receive 'Content-Type: application/json', I actually expect to receive only
>> json in the message.
>>
>> Thanks,
>> Dario
>>
>> On 28.08.2015, at 18:13, Vinod Kone <vinodkone@apache.org> wrote:
>>
>> I'm happy to add the "\n" after the event (note it's different from
>> chunk) if that makes CURL play nicer. I'm not sure about the "\r" part
>> though? Is that a nice to have or does it have some other benefit?
>>
>> The design doc is not set in the stone since this has not been released
>> yet. So definitely want to do the right/easy thing.
>>
>> On Fri, Aug 28, 2015 at 7:53 AM, Anand Mazumdar <anand@mesosphere.io>
>> wrote:
>>
>>> Dario,
>>>
>>> Thanks for the detailed explanation and for trying out the new API.
>>> However, this is not a bug. The output from CURL is the encoding used by
>>> Mesos for the events stream. From the user doc
>>> <https://github.com/apache/mesos/blob/master/docs/scheduler_http_api.md>
>>> :
>>>
>>> *"Master encodes each Event in RecordIO format, i.e., string
>>> representation of length of the event in bytes followed by JSON or binary
>>> Protobuf  (possibly compressed) encoded event. Note that the value of
>>> length will never be ‘0’ and the size of the length will be the size of
>>> unsigned integer (i.e., 64 bits). Also, note that the RecordIO encoding
>>> should be decoded by the scheduler whereas the underlying HTTP chunked
>>> encoding is typically invisible at the application (scheduler) layer.“*
>>>
>>> If you run CURL with tracing enabled i.e. —trace, the output would be
>>> something similar to this:
>>>
>>> <= Recv header, 2 bytes (0x2)
>>> 0000: 0d 0a                                           ..
>>> <= Recv data, 115 bytes (0x73)
>>> 0000: 36 64 0d 0a 31 30 35 0a 7b 22 73 75 62 73 63 72 6d..105.{"subscr
>>> 0010: 69 62 65 64 22 3a 7b 22 66 72 61 6d 65 77 6f 72 ibed":{"framewor
>>> 0020: 6b 5f 69 64 22 3a 7b 22 76 61 6c 75 65 22 3a 22 k_id":{"value":"
>>> 0030: 32 30 31 35 30 38 32 35 2d 31 30 33 30 31 38 2d 20150825-103018-
>>> 0040: 33 38 36 33 38 37 31 34 39 38 2d 35 30 35 30 2d 3863871498-5050-
>>> 0050: 31 31 38 35 2d 30 30 31 30 22 7d 7d 2c 22 74 79 1185-0010"}},"ty
>>> 0060: 70 65 22 3a 22 53 55 42 53 43 52 49 42 45 44 22 pe":"SUBSCRIBED"
>>> 0070: 7d 0d 0a                                        }..
>>> <others
>>>
>>> In the output above, the chunks are correctly delimited by ‘CRLF' (0d
>>> 0a) as per the HTTP RFC. As mentioned earlier, the output that you observe
>>> on stdout with CURL is of the Record-IO encoding used for the events stream
>>> ( and is not related to the RFC ):
>>>
>>> event = event-size LF
>>>              event-data
>>>
>>> Looking forward to more bug reports as you try out the new API !
>>>
>>> -anand
>>>
>>> On Aug 28, 2015, at 12:56 AM, Dario Rexin <dario.rexin@me.com> wrote:
>>>
>>> -1 (non-binding)
>>>
>>> I found a breaking bug in the new HTTP API. The messages do not conform
>>> to the HTTP standard for chunked transfer encoding. in RFC 2616 Sec. 3 (
>>> http://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html) a chunk is
>>> defined as:
>>>
>>> chunk = chunk-size [ chunk-extension ] CRLF
>>>         chunk-data CRLF
>>>
>>>
>>> The HTTP API currently sends a chunk as:
>>>
>>> chunk = chunk-size LF
>>>         chunk-data
>>>
>>>
>>> A standard conform HTTP client like curl can’t correctly interpret the
>>> data as a complete chunk. In curl it currently looks like this:
>>>
>>> 104
>>>
>>> {"subscribed":{"framework_id":{"value":"20150820-114552-16777343-5050-43704-0000"}},"type":"SUBSCRIBED"}20
>>> {"type":"HEARTBEAT”}666
>>> …. waiting …
>>>
>>> {"offers":{"offers":[{"agent_id":{"value":"20150820-114552-16777343-5050-43704-S0"},"framework_id":{"value":"20150820-114552-16777343-5050-43704-0000"},"hostname":"localhost","id":{"value":"20150820-114552-16777343-5050-43704-O0"},"resources":[{"name":"cpus","role":"*","scalar":{"value":8},"type":"SCALAR"},{"name":"mem","role":"*","scalar":{"value":15360},"type":"SCALAR"},{"name":"disk","role":"*","scalar":{"value":2965448},"type":"SCALAR"},{"name":"ports","ranges":{"range":[{"begin":31000,"end":32000}]},"role":"*","type":"RANGES"}],"url":{"address":{"hostname":"localhost","ip":"127.0.0.1","port":5051},"path":"\/slave(1)","scheme":"http"}}]},"type":"OFFERS”}20
>>> … waiting …
>>> {"type":"HEARTBEAT”}20
>>> … waiting …
>>>
>>> It will receive a couple of messages after successful registration with
>>> the master and the last thing printed is a number (in this case 666). Then
>>> after some time it will print the first offers message followed by the
>>> number 20. The explanation for this behavior is, that curl can’t interpret
>>> the data it gets from Mesos as a complete chunk and waits for the missing
>>> data. So it prints what it thinks is a chunk (a message followed by the
>>> size of the next messsage) and keeps the rest of the message until another
>>> message arrives and so on. The fix for this is to terminate both lines, the
>>> message size and the message data, with CRLF.
>>>
>>> Cheers,
>>> Dario
>>>
>>>
>>>
>>
>>
>>
>
>

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