Re: HTML Device Driver

[Pete Jemian <prjemian@gmail.com>]

I suggest something such as "tidy" (http://tidy.sourceforge.net/) is 
used to clean up the HTML or XML input to make it valid XML.  Then use 
XPATH to pick the desired items from the cleaned up XML.

On 7/28/10 11:14 AM, J. Lewis Muir wrote:
> On 7/28/10 10:33 AM, David Dudley wrote:
>    
> > Here’s a new one for you (Got Ralph and Michael going about how to do
> > it, anyway ;-)
> >
> > Almost all of the PLC equipment we’re going to be using on NSLS/2 is
> > connected on Ethernet.
> >
> > It is common practice in the communications modules now, to integrate an
> > embedded WEB server into the device.  Both the Siemens and Rockwell
> > hardware we’re going to use have that capability, as well as most of the
> > new generation of instrumentation.
> >
> > Does anyone have knowledge of an EPICS device driver that is capable of
> > reading and interpreting a WEB page or XML page?  Seems that this would
> > be the most universal way to read data from all this differing
> > equipment, if such a driver was available.
> >
> > David Dudley
> >      
> Hi, David.
>
> Are you asking about a generic EPICS device driver for communicating
> with devices via HTTP and capable of interpreting HTML or XML, or are
> you asking about existing drivers that do this for a particular device?
>
> I've written two drivers that communicate w/ the device via HTTP and
> then extract the needed information from an HTML response:
>
>    http://www.imca.aps.anl.gov/~jlmuir/sw/dli-epcr.html
>    http://www.imca.aps.anl.gov/~jlmuir/sw/websensor-em01b.html
>
> These drivers use asyn but have hacks to deal w/ the connection getting
> closed after each request which asyn did not handle well before asyn
> 4-13.  According to the asyn 4-13 release notes, new behavior has been
> added to handle this by specifying "http" as the protocol in
> drvAsynIPPortConfigure.  I haven't tried it yet.
>
> Certainly something generic could be written to make it easy to
> construct the HTTP request, handle any authentication, and handle the
> response.  This might provide something like the httplib module in Python.
>
> I think it would get more difficult if you wanted to go beyond that.  A
> simple method for interpreting the response is to use regular expression
> matching to extract the desired information.  One would then typically
> want to convert that text into some more appropriate value (e.g. a
> double) in the driver.
>
> A more powerful approach would be to actually provide an HTML or XML
> parser allowing access to the response via SAX or a DOM.  I'm not sure
> how this would work for devices that return invalid HTML or XML
> responses.  I would bet that many devices do not actually respond with
> valid HTML or XML.
>
> Lewis
>
>    

--


----------------------------------------------------------
 Pete R. Jemian, Ph.D.<jemian@anl.gov>
 Beam line Controls and Data Acquisition, Group Leader
 Advanced Photon Source,   Argonne National Laboratory
 Argonne, IL  60439                   630 - 252 - 3189
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