Abstract

The mod_lua module for the Apache HTTP Server is lacking a strong and comprehensive binding to the APR. APR and APR-util provide many useful facilities, which should be made available to mod_lua scripts, as currently the only facilities exported are reading and writing keys in APR tables. Bindings to APR, APR-util (and mod_dbd) could give efficient database access, directory access facilities, XML parsing and socket access, to list but a few things.

About Me

I am Peter Cawley, a student from England. In October 2009, I'll be starting the Maths and Computer Science course at Keble college, Oxford*. This is my first year applying for GSoC, but I have previously participated in the GHOP contest, where I completed 15 tasks for the Drupal project and then was chosen as their grand prize winner. Like 99% of web developers, I have used Apache httpd, and contributing to such a behemoth is an exciting prospect. I have done alot of work with Lua, including identifying bugs in the Lua source code (i, ii, iii) and I've dabbled slightly with using mod_lua (i, ii, iii). I'm also fluent in C++, so understanding and extending the C codebase of mod_lua should not be an issue.

* This university place is conditional upon A-level results, which come out in August 2009. I am still eligible for GSoC (having explicitly checked with LH).

Other commitments

While GSoC will be my only "job" as such over the summer (assuming I'm accepted), I do have eight A-level exams:

• A-level physics practical exam (PHB6): May 18th
• A-level further mathematics written paper (D2): June 1st
• A-level computing written papers (CPT4 and CPT5): June 4th
• A-level mathematics written paper (C4): June 15th
• A-level physics written paper (PHB5): June 16th
• A-level further mathematics written paper (FP2): June 19th
• Advanced extension award mathematics paper (AEA): June 24th

Project break-down

I have identified the following areas where useful APR functionality can be made visible to Lua:

• Environment access (apr_env_*); Lua provides os.getenv() in its standard libraries, but only supports the get operation, not set or delete.
• File information (apr_stat, apr_file_*_set); Lua provides file I/O functions already, but does not support querying and setting file information like permissions, modified time and attributes.
• Directory iteration (apr_dir_*); at the moment, an external library (LuaFileSystem) is required to perform any kind of directory iteration. Inspiration for the directory API should be taken from here to make it familiar to existing Lua coders.
• Network access (apr_socket_*); at the moment, an external library (LuaSocket, or a higher-level library like LuaCURL) is required to get network access. The APR socket functions should be made visible to Lua in a similar API to that used by the low-level parts of LuaSocket, with the idea being that then the higher level parts of LuaSocket (which provide HTTP, FTP and SMTP protocol layers) could be re-used without modification.
• Improved APR table binding; currently, __index and __newindex metamethods are provided to allow the reading and writing of individual keys in an APR table. Additional metamethods like __len and __pairs (which is not a core metamethod, but would be called by a standard modification to the pairs function) are required to bring an APR table closer to a native Lua table.
• User and group IDs (apr_[ug]id_*); Lua has no builtin acess to user and group information.
• Hashing (apr_md[45]_*); at the moment, an external library like MD5 (or an inefficient pure Lua implementation) is currently required to compute MD5 hashes.
• Base64 encoding (apr_base64_*); at the moment, base 64 support can only be found in external libraries like LuaSocket, or as a slow pure Lua implementation.
• Enhancded date and time handling (apr_date_parse_*, apr_time_*); the Lua standard libraries contain minimal time support, but the APR has much more comprehensive support.
• Database access (apr_dbd_* / mod_dbd); the current standard for database access in Lua is the LuaSQL module. Using DBD would yield more efficient database access due to pooled connections, as well as giving mod_lua access to exactly the same database drivers as the rest of httpd.
• URI construction and parsing (apr_uri_*); Lua standard libraries do not provide this, but LuaSocket's URL sublibrary does.
• XML parsing (apr_xml_*); There are a number of options for XML parsing in Lua, some of which are pure Lua implementations (and hence likely not as well tested as APR's parser) and some which involve bringing in an external library.

As noted, some of the functionality which would be provided by an enhanced binding to the APR can already be found in existing Lua libraries, so initially it might seem redundant to provide these features via the APR. On the contrary, I think that it would be beneficial to provide a binding to the APR to provide these features. If something is possible using pure Lua, then doing through the APR instead would likely be faster (while Lua is fast, C is faster) and the code in the APR has likely been through alot more testing than some hacked together Lua code. If something is possible by pulling in an external library, then that can bring its own issues - such libraries would have to be compiled, and in shared hosting contexts, Lua's DLL/SO loading capabilities may be neutered for security reasons. Furthermore, having a more comprehensive out-of-the-box library for mod_lua would be useful for users who want to start coding and not have to pull in external libraries to perform "trivial" tasks.

The first phase of my project would be to write the aforementioned bindings to the APR, doing so in the Lua "style" where possible. The second phase would be documenting this binding so that developers are aware of its functionality. The third phase would be writing some (small) sample pages which make use of this functionality.

As the APR is a portable (i.e. cross-platform) library, it makes sense to develop and test on at least 2 different platforms. Therefore, my work will be done on:

• Win32 (Vista), using prebuilt Apache 2.2.9
• Linux, using svn-head Apache (2.3.x)

Contact

Website: www.corsix.org
Email: [email protected]