Why does Web.PB keep calling function that return blobs until the return is null?

Does anybody know a good reason why Web.PB keeps calling a blob
returning function until the function returns (null)? I can see how this
might be a convienence in some situations but if I designed Web.PB, I
wouldn't have thought to do this. 

The f_retrieve_picture in u_web_examples has a comment that reads:
/*
        Web.pb functions with a blob datatype will be called 
        repeatedly until a Null blob is returned.  This is to allow you
        the ability to stream the amount of data sent back with each 
        request.  Once your function has completed its output, returning 
        a null blob will complete the transaction.
*/

Why do you want to stream the amount of data?
-- 
-----
Tom Cervenka
ezad1@insnet.com
0
Tom
10/17/1997 1:11:02 AM
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Tom Cervenka <ezad1@insnet.com> wrote:

>Why do you want to stream the amount of data?

I believe there is an upper limit on how much data can be sent in a single
burst. Whether this is an HTML, PowerBuilder or HTTP limitation I cannot say.
---
Craig Wagner		| E-mail:  cwagner@metacorp.com
Certified PowerBuilder	| Web:     http://www.teleport.com/~wagnerc
 Developer Professional | Phone:   (503) 452-6343
 and Instructor         | Portland, OR USA
0
cwagner
10/17/1997 1:19:17 AM
Tom-

It is my understanding that "blob" returns were architected in this way to
allow you to return portions of your response at a time if your application
required it.  For example, if you had an exceptionally large binary file to
return, you could segment how much data is returned each call until the
entire file is returned.

-kevin
Kevin P. Micalizzi
kevinmic@sybase.com

Tom Cervenka wrote in message <3446BB26.6570@insnet.com>...
>Does anybody know a good reason why Web.PB keeps calling a blob
>returning function until the function returns (null)? I can see how this
>might be a convienence in some situations but if I designed Web.PB, I
>wouldn't have thought to do this.
>
>The f_retrieve_picture in u_web_examples has a comment that reads:
>/*
>        Web.pb functions with a blob datatype will be called
>        repeatedly until a Null blob is returned.  This is to allow you
>        the ability to stream the amount of data sent back with each
>        request.  Once your function has completed its output, returning
>        a null blob will complete the transaction.
>*/
>
>Why do you want to stream the amount of data?
>--
>-----
>Tom Cervenka
>ezad1@insnet.com


0
Kevin
10/19/1997 12:51:05 PM
Kevin P. Micalizzi [Sybase] wrote:

Kevin, thanks for the response. I have to ask, though, why do I want to
segment an exceptionally large binary file? I would rather just load the
whole thing into a blob and return it once. I'd don't know how big blobs
can be but BlobEdit lets me edit up to 4,294,967,295 bytes. I guess if
I  wanted to return a file bigger than this, I'd need to have a
mechanism for multiple returns but I don't think I'll be building an
application with this requirement in the near future.

I first thought that Web.PB had this behavior to allow me to return
status messages to the browser. Or if I had a large interlaced GIF to
return, I could send 32K chunks and the browser would start displaying
before it received the entire picture. But it doesn't seem to work this
way. Web.PB seems to buffer each return from the blob returning
function  and only sends data back to the server when the function
returns a (null). It would be nice if it worked this way. Maybe it does
with NSAPI or ISAPI but it isn't working that way with CGI. 

> 
> Tom-
> 
> It is my understanding that "blob" returns were architected in this way to
> allow you to return portions of your response at a time if your application
> required it.  For example, if you had an exceptionally large binary file to
> return, you could segment how much data is returned each call until the
> entire file is returned.
> 
> -kevin
> Kevin P. Micalizzi
> kevinmic@sybase.com
> 


-- 
-----
Tom Cervenka
ezad1@insnet.com
0
Tom
10/20/1997 3:28:10 PM
Tom,

The term is called blocking.  Each time Web.PB calls the blob function
it returns that content back to the web server which forwards it back to
the browser.  From what I can remember, the browsers used to have
problems with receiving large streams of data.

I was able to confirm that web.pb was NOT buffering the data.  I did
this by using a function that returned a http authentication in the http
response header.  Until the browser responses to the dialog, the web.pb
client thread is hung wait for the browser to respond.  I also returned
a cookie as a meta tag in the middle of the document in the second or
third blob call.  In between each call I popped up a messagebox and the
messagebox never appeared until I closed the appropriate dialog on the
browser.

HTH,

John Martin
Powersoft Product Support Eng.




0
John
11/11/1997 7:53:24 PM
Reply:

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