A RESTful Web Service Interface to the ATLAS COOL Database

1. A RESTful Web Service Interface to the ATLAS COOL Database Shaun Roe A RESTful Web Service... (Shaun Roe, Atlas)

2. COOL (see talk by A. Valassi, this conference) COOL: A database schema and API designed to be technology neutral (Oracle/MySQL/SQLite) Data structure is hierarchical: Data entry is to a particular folder, channel and with a specific Interval Of Validity (IOV) and tag. =>These form a unique set of coordinates for the datum or resource. http://lcgapp.cern.ch/doxygen/COOL/COOL_2_6_0/doxygen/html/ Originally in C++, its methods are exposed in Python, in the ‘PyCool’ module. High Voltage values from the Detector Control System of Atlas SemiConductor Tracker A RESTful Web Service... (Shaun Roe, Atlas)

3. REST REpresentational State Transfer A resource is defined by a unique URL What you ‘do’ to that resource is defined by the http method: POST: Create resource GET: Retrieve resource PUT: Update DELETE: Delete resource The reply is given via http codes. The format of the answer that you want can be further defined by http headers noun verb Roy Fielding’s dissertation: http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm e.g. sending a form e.g. A browser normally GETs a web page RESTful ‘404 Not Found…’ ‘Accept: text/html’ A RESTful Web Service... (Shaun Roe, Atlas)

4. Motivation Rewind to 2006… • People want data from Cool on the web! • Solutions: • Use their own SQL from PHP/Python… • Use a shell script to set up environment, then run the Cool api behind some custom code • Use a cron job to generate local html files ..and people want to insert data from the web, too. A RESTful Web Service... (Shaun Roe, Atlas)

5. Aim: Universal Web Service Identify resources with url e.g. http://server/database/schema/dbname/some/folder/path/timespan/0-100/channels/23 Use xml as the data transport format. ‘GET’ retrieves the values ‘POST’ creates the channel in a folder ‘PUT’ updates the channel ‘DELETE’ deletes the channel from the folder Multi-channel uploads/downloads should be possible. DB Modification should be protected. Additional resources to be matched to a url: Database nodelist, folder description, folder payload definition, list of channels in a folder, list of tags; it should be possible to create and delete databases, folders. ‘Accept: text/xml’ A RESTful Web Service... (Shaun Roe, Atlas)

6. Data format: XML <channels server="ATLAS_COOLPROD" schema="ATLAS_COOLOFL_DCS" dbname="COMP200" folder="SCT/DCS/CHANSTAT" since="1226271600000000000" until="1226274125000000000" tag="" version="single”> <channel id="138950656" since="1226270581000000000" until="1226274125000000000"> <value name="LVCHSTAT_RECV">193</value> <value name="STATE">17</value> </channel> <channel id="138950656" since="1226274125000000000" until="1226277728000000000"> <value name="LVCHSTAT_RECV">193</value> <value name="STATE">17</value> </channel> </channels> XML Schema Description Definition of an XSD schema allows validation of data format on upload, or type-ahead and documentation tooltips in an editor: Namespaces? What about JSON ? (see later) JavaScript Object Notation (oXygen editor) A RESTful Web Service... (Shaun Roe, Atlas)

7. Implementation: CherryPy www.cherrypy.org CherryPy is a Python application server. It is very easy to install and use. The ‘Routes’ module (from Ruby) allows automatic or manual mapping of Python classes and methods to URLs: d.connect('folder_payload','/:server/:schema/:dbname/*folderPath/payload',controller=restController,action='folderPayload’) maps this http://myserver.cern.ch/cooldb/ATLAS_COOLPROD/ATLAS_COOL_SCT/DCSP200/SCT/DCS/HV/payload to this def folderPayload(self, server, schema, dbname, folderPath): The http headers and the methods are also available and can be used to route the URL to the appropriate Python method; other modules for security, caching etc are available. A RESTful Web Service... (Shaun Roe, Atlas)

8. Examples, curl http://curl.haxx.se/ Command line examples Create a folder: curl 'http://server/DEVDB10/ATLAS_SCT_COMMCOND_DEV/ACALTEST' -uuser:pwd -F definition=@folderdef.xml -X POST Create channels: curl 'http://server/DEVDB10/ATLAS_SCT_COMMCOND_DEV/ACALTEST/test/gain/channels' -uuser:pwd -F definition=@calib.xml -X POST Insert values: curl 'http://server/DEVDB10/ATLAS_SCT_COMMCOND_DEV/ACALTEST/test/gain/timespan/0-9223372036854775807/channels’ -uuser:pwd -F payload=@calib.xml -X PUT cURL (and libcurl, to use from C, C++, Perl) are standard installations. Other languages have similar libraries: PHP – curl, Java – java.net.url, Python – urllib2 … all are standard installations, so accessing Cool via CherryPy typically does not require any extra setup or libraries. A RESTful Web Service... (Shaun Roe, Atlas)

9. ‘In the wild’ examples /** * @author formica */ public class CherryPyClient { private String name = "user.name"; private String psswd = "mypass"; private String readnodeUrl = "http://server/ATLAS_SCT_COMMCOND_DEV/ROETEST/Branch/Trial1/payload"; private String writenodeUrl = http://server/ATLAS_SCT_COMMCOND_DEV/ROETEST/Branch/Trial1/timespan/0-100; public String coolGetCherryPy() { try { URL url = new URL(this.readnodeUrl); java.net.URLConnectionconn = url.openConnection(); InputStream is = (InputStream) conn.getInputStream(); BufferedReader in = new BufferedReader(newInputStreamReader(is)); String inputLine = in.readLine(); is.close(); return inputLine; } catch (Exception e) { e.printStackTrace(); } return "none"; } Java PHP $header=array('Accept: text/xml'); // $ch = curl_init(); curl_setopt($ch, CURLOPT_HTTPHEADER,$header); curl_setopt($ch, CURLOPT_URL,$url); curl_setopt($ch, CURLOPT_RETURNTRANSFER,1); $format=requested_format(); $http_result = curl_exec($ch); if ($format != 'text/xml'){ $dom=domxml_open_mem($http_result); } curl_close($ch); Python httpHeaders={'Accept':'text/xml'} textData=None request=urllib2.Request(url,textData, httpHeaders) u=urllib2.urlopen(request) xmlDocString = u.read() return xmlDocString A RESTful Web Service... (Shaun Roe, Atlas)

10. Example: Run List Search for runs matching criteria, display results; Uses an ‘Ajax’ request to get the CherryPy XML. XML is inserted directly in the XHTML page, and associated with an XSLT stylesheet to format it as a table eXtensibleStylesheet Language for Transformations Local server side Client-side A RESTful Web Service... (Shaun Roe, Atlas)

11. Plans, conclusion Use of CherryPy allowed rapid development of a web service interface to Cool which greatly simplified conditions access and adheres to ‘RESTful’ principles. It was used during 2008 as the engine for the ‘run list’ query page, for various dcs retrieval services, and for insertion of detector status and calibration data; its adoption is growing as a part of web information collations in the detector subsystems. Future extensions include extra methods for tag viewing, and more flexible output format (e.g. JSON, zipped format…) A RESTful Web Service... (Shaun Roe, Atlas)