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<== Date ==> <== Thread ==>
Subject: Re: stream/asyn devices
From: Dirk Zimoch <[email protected]>
To: Emmanuel Mayssat <[email protected]>
Cc: epics <[email protected]>
Date: Fri, 27 Jul 2007 10:01:44 +0200
Hi Emmanuel,

Emmanuel Mayssat wrote:
Update on stream device records

Stream records are actually quite simple to implement.
I found what appears to be bugs in the implementation, but some could
describe those as features. Mainly the entire part of the afternoon was
spend on trying to find out how the terminator is matched.

Although terminator appears to be of unlimited length in stream, it
seems that asyn impose its 2 chars limits for eos. As a result the
stream terminator consist of the last 2 char of its value.

StreamDevice works around this limitation of asyn. But that requires that asyn allows to read the input in multiple parts. Actually, stream gives the last one or two characters of the terminator (as much as the underlying asyn port driver accepts) to asynOctett. When asynOctett thinks it has found a terminator, StreamDevice checks if the full terminator matches. If not, it restores whatever terminator part asyn had cut off and tries to read more.


Stream device can actually handle http connection (not permanent
connection) with the "disconnect" protocol option. That was a good
surprise.

I never tried to read http with StreamDevice so far. I am not sure if the http server closes the connection automatically. But you're right, you can include manual connect/disconnect into the protocol. I found that asyn's auto-connect does not always work as expected. I had situations where access to a disconencted port failed even though asyn did auto-connect only the second access succeeded. Thus, it is probably better to do an explicite conenct first.


The matching works well (once the terminator issue was handled), but I
would have loved traditional regex matching. Matching a complex/long
reply like a web page seems tedious.

Yes. That's still missing. Regexp matching is a rather complex issue. I just did not find the time to implement it. But the good news is that you can add new % formats by writing a C++ class for it. Look how it is done in the *Converter.cc files. I think I will use a format like %/regexp/ once I find the time to do it.


But overall, I have been impressed by this record and would encourage
all of you to have a closer look at stream. BTW, I use stream from the
synApps-5.2 package.

The latest version is always available at http://epics.web.psi.ch/software/streamdevice/. I don't know and have no control over the version in synApps.

StreamDevice is not the new devGpib. It just uses the same lower level driver, asyn. Thus, it is an alternative to devGpib. The real new devGpib which has the same API as the old one is included in asyn. Actually, I have written StreamDevice to have a more flexible API which is easier to use (e.g. no compilation)

Best regards,
Dirk


--
Emmanuel Mayssat


On Thu, 2007-07-26 at 14:59 -0700, Emmanuel Mayssat wrote:
Hello again,

I have a device which has a web server and a simple web page.
My record should fetch the web page and extract the value between the
<epics> and </epics> tags. Can asyn do that? ( it probably can ;)

Better yet, I looked at the streamDriver which is also said to work on
TCP/IP. Can stream records do that?
One could argue that the TCP/IP connection is not permanent (i.e the
server kicks you out if the client is idle, but asyn should
auto-reconnect right?)

http://epics.web.psi.ch/software/streamdevice/doc/

Also is stream the new devGpib ?

--
Emmanuel







References:
stream/asyn devices Emmanuel Mayssat
Re: stream/asyn devices Emmanuel Mayssat
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