A Lua library for handling paths when loading data files

Example usage:

local datafile = require("datafile")

local my_template = datafile.open("myapp/my_template.txt", "r")

This will try to find and open myapp/my_template.txt in a series of locations, based on the "opener" plugins found at the datafile.openers sequence, which contain opener functions loaded from the datafile.openers.* modules (you may modify the datafile.openers sequence in an analog fashion to the package.loaders/package.searchers sequence from Lua).

A few default openers are included:

• datafile.openers.luarocks: which tries to determine the LuaRocks context of the running module (only loaded if LuaRocks is detected).
• datafile.openers.caller: tries to find the file based on the path of the caller script.
• datafile.openers.xdg: follows the [freedesktop.org XDG Base Directory Specification](-- http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html)
• datafile.openers.unix: tries traditional Unix paths for data and config files (/etc and dotfiles at the home dir) -- this is an example of a platform-specific opener.
• datafile.openers.windows: tries traditional Windows paths for user and config files. For config files, it tries user configuration first, then system wide. For data/user files, it tries the user directory first, then the public directory.

Note: when installing trough LuaRocks, only files for the relevant platform will be installed.

Opens a file, trying the various loaders.

• file is a relative filename: it is usually prepended by various prefixes as the openers attempt to construct absolute pathnames to find the file.
• mode is the opening mode, as in file:open. If not given, "r" is the default.
• context is an optional hint to be used by the openers. Currently, the following contexts are supported:
  • nil - the default context
  • "config" - this is a configuration file
  • "cache" - a runtime cache file

Some openers may operate only on specific contexts, or ignore the context altogether.

If successful, returns two arguments: the open file handle and its pathname. If failed, returns nil and an error message.

A shorthand function that looks for a file and returns its pathname. The return pathname may be relative.

The input arguments are the same as for datafile.open.

If successful, returns one argument: the pathname, which may be relative. If failed, returns nil and an error message.

• More openers (any Mac-specific paths?)
• Testing

Feedback, pull requests, criticism, contributions, etc. are welcome!