Shaun,
Thanks to your input I was able to identify the source of the problem.
In my main handle transformation method I was declaring a local variable
int64_t nBytesWritten = 0;
Then depending on what state I was in I was calling the appropriate handler sub
method. Each of the sub methods returns the number of bytes written to the
output by that method and I was aggregating those values via
nBytesWritten += subMethodCall(…);
At the end of my handle transformation method I was calling:
if (nBytesWritten > 0) {
/* Modify the output
* VIO to reflect how much data the output connection should
* expect. This allows the output connection to know when it
* is done reading. We then reenable the output connection so
* that it can consume the data we just gave it.
*/
TSVIONBytesSet(data->output_vio, nBytesWritten);
TSVIOReenable(data->output_vio);
}
At any rate this was working for small payloads but when the method was
re-entered nBytesWritten was being re-initialized to 0 and then incremented.
So the key is knowing that the value of nBytesWritten must be accumulated
across invocations of the transformation handler.
by making this value part of the transaction data, I am able to preserve it
across the invocations and the modified code:
if (data->nBytesWritten > 0) {
/* Modify the output
* VIO to reflect how much data the output connection should
* expect. This allows the output connection to know when it
* is done reading. We then reenable the output connection so
* that it can consume the data we just gave it.
*/
TSVIONBytesSet(data->output_vio, data->nBytesWritten);
TSVIOReenable(data->output_vio);
}
I am worried though about what you said regarding it getting confused and
sending a WRITE_COMPLETE event pre-maturely. Right now with my current test
cases seem to be working as expected but then again, it all seems like voodoo
and black magic under the ATS hood and I don't know that there isn't a test
case which would break this. I wish I could be more confident that the code I
am writing is going to work as intended under all cases.
For the moment however everything seems to work. I am logging the values of
the output nbytes and ndone. And it would seem that ndone is not getting
incremented at all during the multiple invocations of my transform handler.
Ideally what I would like to do is to have the down stream output handler
consume data as soon as it gets it from my transform, but not to stop or
terminate until I have finished sending ALL of my data downstream but I am
afraid to breathe on the code at this point until I find a breaking case which
will mandate a change.
Thank you for your help, you have truly made my day.
Steve Owens
From: Shaun mcginnity
<[email protected]<mailto:[email protected]>>
Reply-To:
"[email protected]<mailto:[email protected]>"
<[email protected]<mailto:[email protected]>>
Date: Fri, 15 Mar 2013 10:35:01 -0700
To: "[email protected]<mailto:[email protected]>"
<[email protected]<mailto:[email protected]>>
Subject: Re: API Question
Yes, it allows the VIO to know when it is done. We only set it when we have
read all the data from the input. I suspect if you continually set it the VIO
might think it is done and send a WRITE_COMPLETE but you actually still have
more to write.
Shaun
On Fri, Mar 15, 2013 at 5:20 PM, Owens, Steve
<[email protected]<mailto:[email protected]>> wrote:
Shaun,
Looking at the code for TSVIONBytesSet we have
void281<http://code.metager.de/source/xref/apache/trafficserver/trafficserver/proxy/InkIOCoreAPI.cc#281>TSVIONBytesSet<http://code.metager.de/source/s?refs=TSVIONBytesSet&project=apache>(TSVIO<http://code.metager.de/source/s?defs=TSVIO&project=apache>
viop<http://code.metager.de/source/s?refs=viop&project=apache>,
int64_t<http://code.metager.de/source/s?defs=int64_t&project=apache>
nbytes<http://code.metager.de/source/s?refs=nbytes&project=apache>)
282<http://code.metager.de/source/xref/apache/trafficserver/trafficserver/proxy/InkIOCoreAPI.cc#282>{
283<http://code.metager.de/source/xref/apache/trafficserver/trafficserver/proxy/InkIOCoreAPI.cc#283>
sdk_assert<http://code.metager.de/source/s?defs=sdk_assert&project=apache>(sdk_sanity_check_iocore_structure<http://code.metager.de/source/xref/apache/trafficserver/trafficserver/proxy/InkIOCoreAPI.cc#sdk_sanity_check_iocore_structure>(viop<http://code.metager.de/source/s?defs=viop&project=apache>)
== TS_SUCCESS<http://code.metager.de/source/s?defs=TS_SUCCESS&project=apache>);
284<http://code.metager.de/source/xref/apache/trafficserver/trafficserver/proxy/InkIOCoreAPI.cc#284>
sdk_assert<http://code.metager.de/source/s?defs=sdk_assert&project=apache>(nbytes<http://code.metager.de/source/s?defs=nbytes&project=apache>
>= 0);
285<http://code.metager.de/source/xref/apache/trafficserver/trafficserver/proxy/InkIOCoreAPI.cc#285>286<http://code.metager.de/source/xref/apache/trafficserver/trafficserver/proxy/InkIOCoreAPI.cc#286>
VIO<http://code.metager.de/source/s?defs=VIO&project=apache>
*vio<http://code.metager.de/source/s?refs=vio&project=apache> =
(VIO<http://code.metager.de/source/s?defs=VIO&project=apache>
*)viop<http://code.metager.de/source/s?defs=viop&project=apache>;
287<http://code.metager.de/source/xref/apache/trafficserver/trafficserver/proxy/InkIOCoreAPI.cc#287>
vio<http://code.metager.de/source/s?defs=vio&project=apache>->nbytes<http://code.metager.de/source/s?defs=nbytes&project=apache>
= nbytes<http://code.metager.de/source/s?defs=nbytes&project=apache>;
288<http://code.metager.de/source/xref/apache/trafficserver/trafficserver/proxy/InkIOCoreAPI.cc#288>}
It looks like this method updates the nbytes of the VIO. But it doesn't
explain what the implications of changing this value are. I am presuming that
when I called TSVConnWrite(output_conn, contp, data->output_reader, INT64_MAX);
That the value of vio->nbytes got set to INT64_MAX. Since my transform may or
may not know how much upstream data it needs to process I don't see any way for
it to update this value to anything meaningful and it makes me wonder why I
would want to.
In my STATE_EXIT processing I am calling: TSContCall(TSVIOContGet(input_vio),
TS_EVENT_VCONN_WRITE_COMPLETE, input_vio); But I don't call:
TSVConnShutdown(TSTransformOutputVConnGet(contp), 0, 1); until I receive the
TS_EVENT_VCONN_WRITE_COMPLETE event in my callbackHandler.
What would happen if I continuously update TSVIONBytesSet(output_vio,
total_written) to indicate how much I have written thus far?
Steve Owens
From: Shaun mcginnity
<[email protected]<mailto:[email protected]>>
Reply-To:
"[email protected]<mailto:[email protected]>"
<[email protected]<mailto:[email protected]>>
Date: Fri, 15 Mar 2013 09:48:05 -0700
To: "[email protected]<mailto:[email protected]>"
<[email protected]<mailto:[email protected]>>
Subject: Re: API Question
Hi Steve,
I believe that in a transform you should only call TSVConnWrite once.
You say you are shutting down the VIOs. Are you doing this when you receive a
WRITE_COMPLETE event? If not you may be closing the VIO early. You can tell the
output VIO that all the data has been written to it using
TSVIONBytesSet(output_vio, total_written);
Regards,
Shaun
On Fri, Mar 15, 2013 at 4:25 PM, Owens, Steve
<[email protected]<mailto:[email protected]>> wrote:
Shaun,
This is extremely helpful. In fact it would make a great addition to the
traffic server on line documentation. Personally I prefer to understand what
the methods I am calling do rather than not.
The one question that remains unanswered is whether or not this method needs to
be called more than once.
The reason for my question is this:
I have a transform which essentially prepends and postpends content to the
upstream content being served. It works in states
STATE_START = write the prefix content downstream and shift to STATE_MIDDLE.
STATE_MIDDLE = copy upstream content to downstream until there is no
more content and then shift to STATE_END.
STATE_END = write the suffix content downstream and shift to STATE_EXIT.
STATE_EXIT = clean up the transaction and shut down the VIO's because
were done.
This plugin works with smaller upstream content as expected. However when the
upstream content gets larger than about 30K, what I am seeing is that from the
transform plugin's perspective it is working as expected. The expected amount
of data is being copied downstream and the suffix is being written. I can tell
this because I am logging the values of upstream_avail, upstream_todo,
bytesWritten etc. And everything adds up to all content being delivered.
However the client is receiving truncated content and I am baffled as to why
this my be happening. I thought that maybe I was not properly using the
TSVConnWrite method but from your explanation of the method below, it would
seem that this is possibly not the case.
At any rate,
Thank you for the explanation.
Best Regards,
Steve Owens
From: Shaun mcginnity
<[email protected]<mailto:[email protected]>>
Reply-To:
"[email protected]<mailto:[email protected]>"
<[email protected]<mailto:[email protected]>>
Date: Fri, 15 Mar 2013 07:09:12 -0700
To: "[email protected]<mailto:[email protected]>"
<[email protected]<mailto:[email protected]>>
Subject: Re: API Question
Hi Steve,
TSVConnWrite initiates a write operation on the transform's downstream
VConnection. The last parameter is the total amount of data you are going to
write. INT64_MAX is effectively unlimited.
When you have data to write you get the VIO's buffer
(TSVIOBufferGet(output_vio)), and copy the data into it. Then the VIO is
reenabled. Reenabling the VIO causes an IMMEDIATE event to be sent to the VIO's
VConnection. When the VConnection's event handler has finished with the data it
will call your continuation back. If it expects you to send more data it will
pass a WRITE_READY event. If you have given the VIO the total amount of data as
set in TSVConnWrite it will call you back with a WRITE_COMPLETE event.
Thisbehaviour is the same as what the transform should do to its input VIO.
Since the downstream VConnection is the client and / or cache, if you do a
finite write, i.e. not INT64_MAX, then the HTTP transaction will close when the
limit is reached. Issuing another write in this case will probably not work.
You can do multiple writes on a NetVConnection though, e.g. as provided by
TSNetConnect.
Hope that helps.
Shaun
-----Original Message-----
From: James Peach [mailto:[email protected]]
Sent: Friday, March 15, 2013 3:12 AM
To: [email protected]<mailto:[email protected]>
Subject: Re: API Question
On 14/03/2013, at 5:13 PM, "Owens, Steve"
<[email protected]<mailto:[email protected]>> wrote:
> In looking at the following documentation:
> http://trafficserver.apache.org/docs/trunk/sdk/io-guide/transformations.en.html
>
> It would seem that the only mention of TSVConnWrite is to a single parameter
> method.
>
> Yet in my plugin I am using
>
> data->output_vio = TSVConnWrite(output_conn, contp, data->output_reader,
> INT64_MAX);
>
> What has changed about this method?
>
> What does it actually do?
It schedules data to be written to the VConnection.
>
> Do I need to call it every time the plugin is re-enabled? Or can I just call
> it once?
I don't know that I really understand the question, but if the length is
INT64_MAX you would only call it once. If you want you cancall it a multiple
times with shorter lengths.
J
