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Stuff about DX/GS

Stuff about DX/GS. Overview. Installation of client/server packages 1. Complex installation: pydxs (pydxc) package into …/lib/python2.4/site-packages/ dxs (dxc) into /usr/local/…/dxs/ - holds config file, dataset listings, utility scripts, log dir etc. Client has web content:

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Stuff about DX/GS

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  1. Stuff about DX/GS

  2. Overview

  3. Installation of client/server packages 1 • Complex installation: • pydxs (pydxc) package into …/lib/python2.4/site-packages/ • dxs (dxc) into /usr/local/…/dxs/ - holds config file, dataset listings, utility scripts, log dir etc. • Client has web content: • /srv/www/htdocs/dx/<various> • Requires >15 paths/variables to be set pre-installation.

  4. Installation of client/server packages 2 • Re-using python’s distutils package: • When creating source distribution: python setup.py sdist • When unpacking/building: tar –xvzf …tgz cd … python setup.py install [options] • All complexity of installing in different locations is done in setup.py

  5. Utilities 1 • DateTimeManager.py: • Python utils for date/time objects with: • add(<value>, <unit>) functionality • createList(<start>, <end>, <interval>, <format>) • String formatting of time objects • Simple Calendar support • SessionObject.py • Session management via a python shelve object written to a file.

  6. Utilities 2 • LogManager.py: • Uses python’s logging package

  7. Configuration • Configuration files and vars: • I used *.py config files. Moving towards using python’s ConfigParser • I use UPPER_CASE to show vars are from config file. • In order to allow multiple

  8. Overlap • CSML and DX/GS have overlap: • Date/time funcs • Subset to multiple files/single file rules • File-naming rules • Identify axis etc rules • Feature (GML) analysis – sort of

  9. Error Handling • Server hierarchy based on: • DXError • Error raised may be caught elsewhere in the system. • Administrator will be mailed • Need sensible object to send back to client (I’ve used string for errors). • But still dysfunctional! • CGI uses DEBUG switch to determine if using cgitb module.

  10. DX/GS walk through • DX(GS)Controller class: • def __init__(self, args): - takes a set of arguments controls flow of request. • def _parseArgs(self, args): - parses arguments. They may be selections or actions. • def _checkSecurity(self): - if required, calls security code to check what user is allowed to do. • def _constructSessionObject(self): - constructs a session object (new or saved on server) to store user session info. • def _generateOptions(self): - generate a list of lists containing the next set of options available to user based on existing session object. • def _checkCredit(self): - check user has enough credit to get what they’ve requested. • def _createOutput(self, costOnly=None): - create output file(s).

  11. DX Server Details 1 (old)

  12. DX Server Details 2 (old)

  13. Handling multiple data models in the DX • DX now has standard interfaces (internally) for multiple models: • <DM>DataHandler.py: • openDataFile(…), getVariables(…), getDomain(…), readVariableSubsetIntoMemory(…) • <DM>OutputHandler.py: • writeVariable(…), writeGlobalAttributes(…)

  14. Python style • Creating large packages, makes sense for UML to look like content, hence: • 1 class per module • Class name same as module name, e.g.: • CDMSDataHandler.py holds class “CDMSDataHandler” • Class names begin with capital • Methods being with lower case • Internal only methods prefixed with “_”.

  15. Security Interface • Agnostic to type of security used • Understands concept of roles and users so access could be restricted by either/both. • Can switch on/off • Interface: (roles, token)=validate(username, password, token) (roles, users)=ResourceAccess(<someURI>)

  16. Experience I have • Build cycle for Python Web Service: • Change, build, deploy, test • Web Service testing with command-line clients • Unit testing with: if __name__==“__main__”: • Allows me to test each component • Encourages me to keep interface objects simple

  17. ZSI experience • Change of interface slightly with version 2.0 • Have encoded version specifics: if zsiversion>=2.0: response=response[0][0] • Error catching problem: • Error stack ‘gets lost’ with ZSI unless I define error classes.

  18. Web interface issues • Have traditionally kept Javascript minimal • Ajax paradigm means time to move forward. • CSS should be doing all styling and should be consistent for all NDG web look and feel. • Can we identify third-party libraries to build upon: rico, prototype, x library etc.

  19. Ongoing issues (feedback?) • WSDL never settling down: • Requirements of server interface expanding • Future (WFS/WCS) requirements suggest all should be XML rather than SOAP-Arrays which are currently being used. • Job submission/queuing: • Not an operational solution yesterday – maybe have a basic one (sQimPy).

  20. Things I’d like us to do • Use one python installation across NDG (needs to be CDAT though!?) • Use common GUI styling • Use common code for date/time/data object manipulation • Use common feature identification code

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