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 <Steve.Owens@disney.com> wrote:
Shaun,

Looking at the code for TSVIONBytesSet we have
void
281TSVIONBytesSet(TSVIO viop, int64_t nbytes)
282{
283  sdk_assert(sdk_sanity_check_iocore_structure(viop) == TS_SUCCESS);
284  sdk_assert(nbytes >= 0);
285
286  VIO *vio = (VIO *)viop;
287  vio->nbytes = nbytes;
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


Date: Fri, 15 Mar 2013 09:48:05 -0700

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 <Steve.Owens@disney.com> 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 <shaun.mcginnity@gmail.com>
Reply-To: "users@trafficserver.apache.org" <users@trafficserver.apache.org>
Date: Fri, 15 Mar 2013 07:09:12 -0700
To: "users@trafficserver.apache.org" <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

Subject: Re: API Question

 

On 14/03/2013, at 5:13 PM, "Owens, Steve" <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