Pyslet Documentation Release 0.6.20160201 Steve Lay February 02, 2016 Contents 1 What’s New? 1 2 Compatibility 7 3 IMS Global Learning Consortium Specifications 13 4 The Open Data Protocol (OData) 101 5 Hypertext Transfer Protocol (RFC2616) 207 6 Other Supporting Standards 247 7 Welcome to Pyslet 357 Python Module Index 359 i ii CHAPTER 1 What’s New? As part of moving towards PEP-8 compliance a number of name changes are being made to methods and class at- tributes with each release. There is a module, pyslet.pep8, which contains a compatibility class for remapping missing class attribute names to their new forms and generating deprecation warnings, run your code with “python -Wd” to force these warnings to appear. As Pyslet makes the transition to Python 3 some of the old names will go away completely. It is still possible that some previously documented names could now fail (module level functions, function arguments, etc.) but I’ve tried to include wrappers or aliases so please raise an issue on Github if you discover a bug caused by the renaming. I’ll restore any missing old-style names to improve backwards compatibility on request. Finally, in some cases you are encouraged to derive classes from those defined by Pyslet and to override default method implementations. If you have done this using old-style names you will have to update your method names to prevent ambiguity. I have added code to automatically detect most problems and force fatal errors at runtime on construction, the error messages should explain which methods need to be renamed. 1.1 Version Numbering Pyslet version numbers use the check-in date as their last component so you can always tell if one build is newer than another. At the moment there is only one actively maintained branch of the code: version ‘0”. Changes are reported against the versions released to PyPi. ‘XX’ at the end of the version indicates changes that have not yet been released to PyPi but have been committed to the master branch (with tests passing). Not sure which version you are using? Try: from pyslet.info import version print version 1.2 Version 0.6.20160201 Summary of New Features: LTI module rewritten, now suitable for real applications! WSGI-based web-app frame- work built using Pyslet’s DAL MySQL Database connector for Pyslet’s DAL SSL, Certificates and HTTP Basic Authentication HTTP Cookies URNs #3 PEP-8 driven refactoring (ongoing) Added new method decorators to make supporting renamed and redirected methods easier. Added checks for ambigu- ous names in classes likely to have been sub-classed by third-party code. #8 Support for SSL Certificates in HTTP Clients 1 Pyslet Documentation, Release 0.6.20160201 Fixed certificate support in OData and Atom clients. See blog post for further information on how to use certificates: http://swl10.blogspot.co.uk/2014/11/basic-authentication-ssl-and-pyslets.html #9 HTTP client retry strategy Improved HTTP retries with simple Fibonacci-based back-off. Also fixed a bug where, if the first request after a server timed out an idle connection is a POST, the request would fail. #12 bug when using numeric or named parameters in DB API The basic bug is fixed and I’ve also added support for paramstyle ‘format’. #14 content element missing in media-link entries Fixed. Affected atom xml formatted entities only. #15 MySQL implementation of Pyslet’s DAL (ongoing) Changes to the core DAL to deal to better support other DB modules. These included added support for LIMIT clauses to speed up paged access to large entity sets. Implementation of a retry strategy when database commands return OperationalError (e.g., MySQL idle timeouts). An updated connection pool manager and an optional pool cleaner method to clean up idle database connections. #18 Possible bug in parsing AssociationSet names Added a compatibility mode to odata2.csdl to enable the metadata model to optionally accept hyphen or dash characters in simple identifiers using: import pyslet.odata2.csdl as edm edm.set_simple_identifier_re(edm.SIMPLE_IDENTIFIER_COMPATIBILITY_RE) #19 OData Function parameter handling Enabled function parameter passing in OData service operations. Only primitive types are supported but they are now parsed correctly from the query string and coerced to the declared parameter type. Bound functions now receive them as a dictionary of SimpleValue instances. #20 HTTP Basic Authentication Fixed an issue with the OData basic authentication support, in some cases the HTTP client was waiting for a 401 when it could have offered the credentials preemptively. See also the following blog article: http://swl10.blogspot.co.uk/2014/11/basic-authentication-ssl-and-pyslets.html #22 Support for navigation properties in OData expressions Although the code always contained support in general, the mapping to SQL did not previously support the use of table joins in SQL expressions. This release adds support for joins (but not for nested joins). #23 A Framework for WSGI-based LTI Applications Added a new module to make it easier to write WSGI-based applications. Re-factored the existing Basic LTI module to use the new oauthlib and Pyslet’s own OData-inspired data access layer. #24 ESA Sentinel mission compatibility Added the capability to override the metadata used by an OData server to deal with validation issues in some services. Clients can now also be created from an offline copy of the service root document. #26 HTTP client eats memory when downloading large unchunked files Fixed the download buffer which was failing to write out data until an entire chunk (or the entire download) was complete. #29 https connections fail on POST after remote server hangup 2 Chapter 1. What’s New? Pyslet Documentation, Release 0.6.20160201 Partial mitigation with an agressive 2s window in which to start sending a follow-up request when pipelining through https. This is a crude solution and the bug remains open for a more robust solution based around use of the Expect header in HTTP/1.1. #30 HTTP client cleanup thread Added an optional parameter to the HTTP client constructor that creates a cleanup thread to close down idle connec- tions periodically. #31 Removed reliance on Host header in wsgi app class There are a number of ways an application can be attacked using a forged Host header, wsgi now ignores the Host header and uses a new setting for the preferred scheme//host:port. #32 get_certificate_chain Implemented a function to create a complete certificate chain. Implemented using pyOpenSSL with a lot of help from this article #33 Fixed exception: ‘NoneType’ object has no attribute ‘current_thread’ on exit Caused by an overly ambitious __del__ method in SQLEntityContainer. #34 Fixed missing Edm prefix in OData sample code #35 Fixed missing import in rfc5023 (atom protocol) module #36 Fixed incorrect error messages in OData $filter queries #37 Extended comparison operators in OData to include DateTimeOffset values All thanks to @ianwj5int for spotting #38 Python 3 compatibility work I have started revising modules to support Python 3. This is not yet production ready but it is a small impact on existing modules. I have done my best to maintain compatibility, in practice code should continue to work with no changes required. The most likely failure mode is that you may find a unicode string in Python 2 where you expected a plain str. This can have a knock-on effect of promoting data to unicode, e.g., through formatting operations. In general the returned types of methods are just being clarified and unicode values are returned only where they may have been returned previously anyway. However, in the case of the URI attributes in the rfc2396 module the types have changed from str to unicode in this release. This is work in progress but the impact is likely to be minimal at this stage. #40 & #41 Composite keys and Slug headers Key hints were not working properly between the OData client and server implementations, and were not working at all when the key was composite. It is now possible to pass the formatted entity key predicate (including the brackets) as a Slug to the OData server and it will attempt to parse it and use that key where allowed by the underlying data layer. #43 Fixes for Python running on Windows The only substantive changes required were to the way we check for io failures when IOError is raised and the way we handle URI containing non-ASCII characters. Some of the unit tests were also affected due to issues with timing, including the reduced precision of time.time() on Windows-based systems. Untracked enhancements: Added a new module to support HTTP cookies. The HTTP/OData client can now be configured to accept cookies. The default behaviour is to ignore them so this won’t affect existing applications. Added a new module to support URN syntax to provide a better implementation of the IMS LTI vocabularies. Added an optional params dictionary to the OData expression parser to make it much easier to parse parameterized OData queries. 1.2. Version 0.6.20160201 3 Pyslet Documentation, Release 0.6.20160201 Added new methods for creating and executing drop table statements in the DAL. Reworked sample code for the weather data server, included example driver files for mod_wsgi Other fixes: Fixed an issue in the OData client that caused basic key lookup in filtered entity collections to use both a key predicate and a $filter query option. This was causing the filter to be ignored, now the key predicate will be added to the filter rather than the path segment. Fixed the OData DateTime parser to accept (and discard) any time zone specifier given in the literal form as it is now allowed in the ABNF and may therefore be generated by OData servers.