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From "Owens, Steve" <Steve.Ow...@disney.com>
Subject Re: API Question
Date Fri, 15 Mar 2013 16:25:39 GMT
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 <shaun.mcginnity@gmail.com<mailto:shaun.mcginnity@gmail.com>>
Reply-To: "users@trafficserver.apache.org<mailto:users@trafficserver.apache.org>" <users@trafficserver.apache.org<mailto:users@trafficserver.apache.org>>
Date: Fri, 15 Mar 2013 07:09:12 -0700
To: "users@trafficserver.apache.org<mailto:users@trafficserver.apache.org>" <users@trafficserver.apache.org<mailto:users@trafficserver.apache.org>>
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:jpeach@apache.org]

Sent: Friday, March 15, 2013 3:12 AM

To: users@trafficserver.apache.org<mailto:users@trafficserver.apache.org>

Subject: Re: API Question



On 14/03/2013, at 5:13 PM, "Owens, Steve" <Steve.Owens@disney.com<mailto:Steve.Owens@disney.com>>
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

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