A RESTful Web Service Interface to the ATLAS COOL Database Shaun Roe 1A RESTful Web Service... (Shaun Roe, Atlas)CHEP'09 Prague

COOL (see talk by A. Valassi, this conference) 2A RESTful Web Service... (Shaun Roe, Atlas) ml/ CHEP'09 Prague COOL: A database schema and API designed to be technology neutral (Oracle/MySQL/SQLite) Data structure is hierarchical: folderchannel IOVtag Data entry is to a particular folder, channel and with a specific Interval Of Validity (IOV) and tag. resource =>These form a unique set of coordinates for the datum or resource. 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

URL A resource is defined by a unique URL http method 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 REST CHEP'09 PragueA RESTful Web Service... (Shaun Roe, Atlas)3 REpresentational State Transfer REpresentational State Transfer noun verb e.g. sending a form e.g. A browser normally GETs a web page ‘404 Not Found…’ ‘Accept: text/html’ Roy Fielding’s dissertation: RESTful

Motivation CHEP'09 PragueA RESTful Web Service... (Shaun Roe, Atlas)4 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.

Aim: Universal Web Service CHEP'09 PragueA RESTful Web Service... (Shaun Roe, Atlas)5 Identify resources with url e.g. 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’

Data format: XML CHEP'09 PragueA RESTful Web Service... (Shaun Roe, Atlas)6 What about JSON ? (see later) Definition of an XSD schema allows validation of data format on upload, or type-ahead and documentation tooltips in an editor: Namespaces? (oXygen editor) XML Schema Description JavaScript Object Notation

Implementation: CherryPy CHEP'09 PragueA RESTful Web Service... (Shaun Roe, Atlas)7 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=restCont roller,action='folderPayload’) def folderPayload(self, server, schema, dbname, folderPath): maps this to this 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.

Examples, curl CHEP'09 PragueA RESTful Web Service... (Shaun Roe, Atlas)8 Command line examples Create a folder: curl ' -u user:pwd -F -X POST Create channels: curl ' /channels' -u user:pwd -F -X POST Insert values: curl ' /timespan/ /channels’ -u user:pwd -F -X PUT accessing Cool via CherryPy typically does not require any extra setup or libraries. 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.

‘In the wild’ examples CHEP'09 PragueA RESTful Web Service... (Shaun Roe, Atlas)9 /** formica */ public class CherryPyClient { private String name = "user.name"; private String psswd = "mypass"; private String readnodeUrl = " private String writenodeUrl = public String coolGetCherryPy() { try { URL url = new URL(this.readnodeUrl); java.net.URLConnection conn = url.openConnection(); InputStream is = (InputStream) conn.getInputStream(); BufferedReader in = new BufferedReader(new InputStreamReader(is)); String inputLine = in.readLine(); is.close(); return inputLine; } catch (Exception e) { e.printStackTrace(); } return "none"; } $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); $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); Java PHP httpHeaders={'Accept':'text/xml'} textData=None request=urllib2.Request(url,textData, httpHeaders) u=urllib2.urlopen(request) xmlDocString = u.read() return xmlDocString httpHeaders={'Accept':'text/xml'} textData=None request=urllib2.Request(url,textData, httpHeaders) u=urllib2.urlopen(request) xmlDocString = u.read() return xmlDocString Python

eXtensible Stylesheet Language for Transformations Example: Run List CHEP'09 PragueA RESTful Web Service... (Shaun Roe, Atlas)10 Search for runs matching criteria, display results; Uses an ‘Ajax’ request to get the CherryPy XML. Client-side Local server side XML is inserted directly in the XHTML page, and associated with an XSLT stylesheet to format it as a table

Plans, conclusion CHEP'09 PragueA RESTful Web Service... (Shaun Roe, Atlas)11 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…)