Experimental Physics and
Industrial Control System

Rod Nussbaumer <[email protected]> · Wed, 04 Mar 2009 11:45:18 -0800

Greetings, EPICS users.

I am trying to use streamDevice with regular expression support to parse

input from an instrument containing an embedded web server. So far, I've

successfully built and run the streamApp sample IOC that gets built with

the streamDevice distribution. I am able to parse a single HTML element

(TITLE, with minor mods to the example protocol file) from a static web

page served by an Apache web server. So, I think I've built everything

properly (streamDevice 2.4, asyn 4-9, EPICS 3.14.10, Linux=Scientific

Linux 4.x).

My difficulty is that the instrument produces a page containing three

strings that I wish to extract into three EPICS records. I'm testing

with string-in records for now, but eventually I would prefer to scan to

analog-in records. I am able to extract the first element from the HTML,

although I do get error messages from streamDevice:

"Input "HTTP/1.0 200 OK<0d><0a>Con..." does not match format

%.1/^MeasurePM*([0-9.]+)/"

However, I am unsure about how to get multiple fields scanned from the

HTML using a single HTTP GET. I would really like to avoid doing one

whole HTTP fetch per record, since the instrument is fairly primitive,

and can probably become overwhelmed by excessive traffic, and it may be

the case that readings on a single fetch are synchronized in time.

From my interpretation of the documentation, the scanner should stop,

leaving unread text in the pipeline once it has made a successful match.

However, I don't understand how to continue scanning the remainder of

the HTML page to extract the remaining data.

I attach below, the streamDevice protocol file I'm presently using (the

latest flavor that gets me closest to working), the relevant database,

and the entire HTML that the instrument returns. Much of this is based

on the examples from streamDevice.

#=========================<protocol file>=============================
# regular expression example
# extract the title of from a web page

outterminator = NL;
interminator = "</HTML>";  # terminators can have arbitrary length

# Web servers close the connection after sending a page.
# Thus, we can't use autoconnect (see drvAsynIPPortConfigure)
# Handle connection manually in protocol.

readTitle {
    extraInput=ignore;
    interminator = "</HTML>";  # terminators can have arbitrary length
    connect 1000;	        # connect to server, 1 second timeout
    out "GET http://isacwserv.triumf.ca";;    # HTTP request
    in "%.1/<TITLE>(.+)<\/TITLE>/";  # get string in <TITLE></TITLE>
    disconnect;
}

readPPM {
    extraInput=ignore;
    interminator = "</HTML>";  # terminators can have arbitrary length
    connect 1000;              # connect to server, 1 second timeout
    out "GET http://142.90.132.71/lcd.cgi";;    # HTTP request

 in "%.1/^Measure\(PPM\):\s*([0-9.]+)/"; # get string in Measure

field

}

readFLOW {
    extraInput=ignore;
    in "%.1/^Sample flow\(CC\):\\s*([0-9.]+)/"; # get string in Flow field
}

readSCALE {
    extraInput=ignore;
    in "%.1/Scale:\s*(.+)\n/";       # get string in Scale field
    disconnect;                      # servers closes, so do we.
}

#==================< EPICS db file >===========================
record (stringin, "ISAC:WSERV:TITLE")
{
    field (DTYP, "stream")
    field (INP,  "@regexp.proto readTITLE isacwserv")
}

record (stringin, "ISAC2:N2ANAL1:PPM")
{
    field (DTYP, "stream")
    field (FLNK, "ISAC2:N2ANAL1:FLOW")
    field (INP,  "@regexp.proto readPPM n2anal1")
}

record (stringin, "ISAC2:N2ANAL1:FLOW")
{
    field (DTYP, "stream")
    field (FLNK, "ISAC2:N2ANAL1:SCALE")
    field (INP,  "@regexp.proto readFLOW n2anal1")
}

record (stringin, "ISAC2:N2ANAL1:SCALE")
{
    field (DTYP, "stream")
    field (INP,  "@regexp.proto readSCALE n2anal1")
}

#==================< Instrument web page >=======================
# (additional line breaks inserted by e-mail; hopefully this gets
#  displayed as HTML text, and not as a web page)
#

<HTML><HEAD><meta http-equiv="refresh" content="1"></HEAD><BODY

bgcolor="#BEF06E"><!-- Affiche le contenu de l'écran -->

<FONT color="black" size="6"><B><PRE>
              &lt;&lt;RUN MODE>>        F4:RET
Measure(PPM): 2.3
Sample flow(CC): 50.0   Scale:0-10   PPM
System status:OK                        </PRE></FONT></B></BODY></HTML>

===============================================================

I am trying to extract the values for 'Measure (PPM)', 'flow(CC)', &

'Scale:'. When the 'FLOW' and 'SCALE' records process, streamDevice reports:

2009/03/04 10:49:59.678 n2anal1 ISAC2:N2ANAL1:PPM: Input "HTTP/1.0 200

OK<0d><0a>Con..." does not match format %.1/^MeasurePM*([0-9.]+)/

2009/03/04 10:49:59.680 n2anal1 ISAC2:N2ANAL1:FLOW: asynError in read:

142.90.132.71:80 connection closed

2009/03/04 10:49:59.680 n2anal1 ISAC2:N2ANAL1:FLOW: I/O error after

reading 0 bytes: ""

2009/03/04 10:49:59.680 n2anal1 ISAC2:N2ANAL1:FLOW: Protocol aborted

2009/03/04 10:50:00.677 timerQueue ISAC2:N2ANAL1:SCALE: I/O error after

reading 0 bytes: ""

2009/03/04 10:50:00.677 timerQueue ISAC2:N2ANAL1:SCALE: Protocol aborted

If I add some more backslashes to the regex in front of the parentheses

that are embedded in the HTML text, the error messages more closely

match the actual HTML text. I can't seem to find a 'right' combination

of back-slashes that makes streamDevice and PCRE happy.

Thanks for any insight.

Rod Nussbaumer
ISAC Controls, TRIUMF
Vancouver, Canada.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System