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Web
Interfaces to MDSplus Data* |
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W. Davis, P. Roney, T. Carroll, T. Gibney, D. Mastrovito Princeton
Plasma Physics Laboratory, P.O. Box 451, Princeton, NJ 08543-0451 |
Abstract-- The MDSplus Data Acquisition System has been used
successfully on NSTX at PPPL since early 1999. While the X-window-based tools
supplied with MDSplus are powerful, and both the IDL programming language and
the supplied TDI language are effective for complex and specialized analyses,
some users prefer the convenience of applications that can be run in a Web
browser. Web users don't need to know about X-windows, or even have accounts or
privileges on server computers. The MDSplots page reads MDSplus
"Scope" setup files and plots MDSplus signals with overlays. It uses
a Perl script to open a pipe to an IDL subprocess. The TreeSearch page provides
several options for finding information in MDSplus trees. The MDSshots page
lists shots where the maximum for a specified signal is above or below a
specified value. A variety of information in an MS-SQL database is also
accessible from a Web browser. These utilities could be used at other sites
which keep data in MDSplus.
The
National Spherical Torus Experiment [1] (NSTX) experiments at the Princeton
Plasma Physics Laboratory (PPPL) has been using MDSplus for fusion since it
began operation in February of 1999 [2]. During an experimental cycle (called a
"shot") a plasma is produced and around 80 megabytes of data are acquired from
instruments in dozens of subsystems and transferred to a central computer
system during the subsequent 2-3 minutes [3].
MDSplus [4] is a data acquisition and storage system originally developed for C-MOD, RFX and ZTH, and is now used at 26 facilities world wide. By storing all the data in MDSplus, standard tools can access any type of data with a minimum of specialized knowledge. MDSplus is installed with several X-window/Motif tools, including Traverser for traversing the data hierarchy and setting hardware parameters, and Scope, for plotting x-y traces. The supplied Tree Data Interface Language (TDI) [5] and the Tree Command Language (TCL) also provide low-level capabilities. Remote computers may write to and read from MDSplus servers via TCP/IP connections from languages such as IDL [6], C++, Visual Basic, FORTRAN and LabView.
NSTX has a heterogeneous group of users. Some prefer the Unix operating system, some VMS, and some Windows. Some prefer Macintoshes as their workstation, some PC's, and others X-terminals. Some researchers can program effectively in a high-level computer language and others cannot. The majority of the scientists on NSTX are not full time on NSTX.
The X-window/Motif tools
supplied with MDSplus, and other tools written at various fusion labs [7], [8],
are powerful and reasonably flexible. However, an X-windows user needs to know
many details such as operating-specific command- and file-syntax, directory
names and environmental variables. This can confuse a user unfamiliar with the
operating system of the data-serving computer. Additionally, the use of
X-windows may require setting additional parameters, such as the TCP/IP address
of the X-window "DISPLAY," number of colors, security settings, etc. Accessing
data from a Web browser requires much less knowledge in general.
World Wide Web browsers,
such as Internet Explorer or Netscape, are familiar to today's researchers.
While there can be installation-specific incompatibilities when using a
browser, such as special fonts, plug-ins, and screen resolution, basic
functions such as making menu selections, entering data into fields, and the
display of images, will operate similarly on most computers, regardless of
operating system. Web browser access allows, but does not require, the use of a
username and password.
Because of the ease-of-use of these tools, there is a
growing and appreciative user base at PPPL.
The Web-based tools for
NSTX may be accessed from http://nstx.pppl.gov/nstx/Software/WebTools/.
A. Treesearch - Searches
MDSplus node names or their contents for text strings.
B. Logbook - standard and
custom SQL queries to find shots by date, database entries by user, etc.
C. MDSshotSearch – searches
signals within a range of shot numbers for data within user-specified limits.
Lists shot numbers found and the minimum and maximum of the signal.
D. MDSplots – plots MDSplus
signals with options to use "Scope" files as inputs and to overlay shots (see
Fig. 1).
Fig. 1 Web page for MDSplots. Users fill in fields and make
selections with the mouse to see plots of experimental data in any Web browser.
E. MDSlist – like MDSplots,
but a table of numbers is displayed, suitable for importing into a spreadsheet.
F. Web Traverser –
Traverses an MDSplus data tree hierarchy and plots signals (written in Java)
[9].
G. Dbaccess – View and plot
information from MS-SQL databases derived from MDSplus data.
H. Shot Listing – lists the
shots associated with particular experimental proposals (XPs), and lists shot
ranges for each run day.
Some of the most
frequently asked questions about the NSTX data stored in MDSplus involve
determining the node names for signals of interest and determining shots that
satisfy certain criteria. SignalLabels, TreeSearch, Logbook, MDSshotSearch, the
Web Traverser, and Dbaccess.asp make it easy to find signal names and shots of
interest.
Both the Logbook and
DBaccess application query an MS-SQL database containing experimental
parameters and comments for each shot. Dbaccess uses an active server page
(ASP) to generate up-to-date lists of tables and data items.
The MDSplots,
TreeSearch, MDSshots, and MDSlist are written in simple HTML, but connect
through TCP/IP sockets to Perl [10] scripts that in turn make IDL Remote
Procedure Calls (RPC's). MDSplots allows MDSplus "Scope" setup files
as an input, or accepts individual MDSplus node names, and allows the user to
overlay data from several shots. TreeSearch searches MDSplus nodes, with
various options, and displays node and tag names that satisfy the search
criteria. MDSshots lists shots that satisfy certain criteria, such as those
with greater than, or less than, a certain value for common parameters, or from
user-specified MDSplus node names.
IV. Design Details of
the MDSplots Web tool
The data flow of the MDSplots Web Tool is shown in Fig. 2.
Fig. 2 Data flow of the MDSplots page and the Perl server.
The input fields on the Web page are part of an HTML form. When the user hits the "Send" button on the Web page, field names and inputted data are sent to the host computer. A Perl script, whose functions are listed in the boxes in Fig. 2, needs to be running on the host computer, and have made a connection to the correct socket. The Perl script then stays in a loop with a limited number of commands including "forking" a separate subprocess for each set of inputs. The commands in each forked process may take several minutes, but inputs from other Web browsers can be processed concurrently by the main loop. Within a forked process, a unique portable network graphics (PNG) file name is created (based on the PID of the process), and another unique file name to act as a lock. Commands are piped to a newly-spawned IDL process which end with an IDL command to delete the lockfile. The Perl script then waits for the lockfile to be deleted by the IDL process after it has created the PNG file. When the lockfile ceases to exist, the Perl script sends the newly-created PNG file back to the Web browser that initiated the request.
The NCSA Web page entitled "Writing secure CGI scripts" [11] states:
Any time that a program is interacting with a networked client, there is the possibility of that client attacking the program to gain unauthorized access. Even the most innocent looking script can be very dangerous to the integrity of your system.
Two distinct security concerns require different policies and practices. Of primary importance is preventing unauthorized access to system functions. These include access to passwords and other private data and the ability to modify or destroy experimental data or source code. Protecting experimental data from unauthorized or incorrect use is a secondary concern. While the only way to be sure a computer is secure is to make it inaccessible from the outside, security concerns can be managed by following established practices.
The flexibility of Perl allows for the execution of operating system commands, such as those for deleting files. The –T switch in Perl enables "taint" checking. The basic principle of taint checking is "to mark as tainted anything that comes from outside the program, including command line arguments, environmental variables and file input. Tainted data may not be used directly or indirectly in any operation that invokes a subshell, or in any operation that modifies files, directories, or processes" [10].
The Perl script we use passes commands based on user inputs to an IDL server. These commands can include filenames entered on the Web page. This necessitates additional checks. The Perl script explicitly checks all input strings and eliminates characters that would allow the Perl script or the IDL process to access the Unix shell or to execute other dangerous commands. The contents of the filenames entered are not displayed or executed; they are only read by specific IDL code.
"Buffer overflows" were by far the most frequent form of security vulnerability for remotely accessible networks in the 1990's [12]. An example of this is when program inputs exceed the input buffer sizes of the program and the remaining characters somehow become executable code. The Web applications described here were tested with a variety of large buffer sizes, and no vulnerabilities or unexpected behavior were evident. IDL always does explicit bounds checking, unlike the C programming language. If the scripts supporting our Web applications were compromised, any damage would be contained, since they do not execute with system priveledges.
PPPL has a firewall between its internal computers and the Internet. By default, a user must have a SecurID Badge, and enter a username, Secure ID Pin and a number from the badge (which changes every minute). Some of our Web pages require this form of authentication and some are open to anyone.
The use of Web browsers is well understood by most
computer users. The Web tools described here for locating and displaying
MDSplus data were developed with no more effort than traditional
X-windows/Motif applications and have increased accessibility to the data for
many researchers. The Web tools that do not use Java do not have some of the
features of the corresponding X-windows tools, such as using the mouse for
panning and zooming, but require the users to know far fewer details. Security
concerns are more complex with Web applications, but by following some
relatively simple established practices, we feel we have struck a good balance
between security and accessibility.
Acknowledgment
The authors thank Tom Fredian and Josh
Stillerman from MIT for support with MDSplus issues, Stan Kaye and Dennis
Mueller for guidance on user requirements for NSTX, and Steve Davis with
guidance on security.
References
[1] Kaye et al., The physics design of the National Spherical Torus Experiment. Fusion Technology, 36, July 1999, p. 16, or http://nstx.pppl.gov/index.shtml.
[2] W. Davis, P. Roney, T. Carroll, T. Gibney, D. Mastrovito, "The Use of MDSplus on NSTX at PPPL." Presented at the 3rd IAEA TCM on Control, Data Acquisition, and Remote Participation for Fusion Research, Padova, Italy (2001), Fusion Eng. Des., in press.
[3] P. Roney, K. Tindall, S. Davis, "Computer
and Network Infrastructure of NSTX" these proceedings.
[4] J.A. Stillerman, T.W. Fredian, K.A. Klare,
G. Manduchi, "MDSplus Data Acquisition System."Review of Scientific Instruments, 68 (1) January, 1997, p. 939.
[5]
Tree Data Interface (TDI) Language. http://www.mdsplus.org/tdi/tdi_tutorial
[6] IDL – The Interactive Data Language http://www.rsinc.com/idl/
[7] J. Schachter, Q. Peng, D.P. Schissel, "Data analysis software tools for enhanced collaboration at the DIII-D National Fusion Facility," Fusion Engineering Design 48 (2000) 91-98.
[8] FAS User's Guide, http://nstx.pppl.gov/nstx/Software/fas/index page.
[9] G. Manduchi, C. Taliercio, A. Luchetta, "The Java interface of MDSplus: towards a unified approach for local and remote data access," Fusion Engineering Design 48 (2000) 163-170.
[10] L. Wall, T. Christiansen, and J. Orwant, Programming Perl, 3rd ed. Sebastopol, CA: O'Reilly, 2000, pp. 559.
[11] Writing secure CGI scripts. http://hoohoo.ncsa.uiuc.edu/cgi/security page.
[12] C. Cowan, P. Wagle, C. Pu, S. Beattie, J. Walpole, "Buffer overflows: Attacks and Defenses for the Vulnerability of the Decade" Proceedings of DARPA Information Survivability Conference and Expo (DISCEX), http://schafercorp-ballston.com/discex To appear at SANS 2000, http://www.sans.org/newlook/events/sans2000.htm. For a copy, see http://immunix.org/documentation page.