set var tools
=============

OVERVIEW
--------
This collection of tools is designed to make it easier to set Nginx variables
using a common interface.  It works by plugging into and extending the features
of the internal rewrite module, and operations performed by this module are
therefore done at the rewrite phase of handling.


ADVANTAGES OF USING THIS MODULE
-------------------------------

- simple interface - you don't have to worry about lots of http script compiling
- it plugs into the rewrite module, so setting (and getting) vars will happen
  in the order you expect based on how they appear in the configuration file
- you do not have to worry about overriding the v->get_handler (useful if
  a variable of a specific name could be set in multiple different ways)


WHEN TO USE THIS AND WHEN TO USE v->get_handler = my_func
---------------------------------------------------------

- if you want a variable to always be generated using a specific function,
    and should not be over-ridden by 'set' functions (e.g. $request_uri, 
    $document_root), then you should use v->get_handler

- if you want to allow a variable to be set using many possible methods,
    including using the 'set' directive, then this module provides an easy way
    for you to do so (if you use the v->get_handler method in this case, you may
    run into problems because the get_handler may over-ride previous uses of the
    set directive)


USAGE
-----

- decide on the type of function you'll need to write

    type                                use when there are these requirements
    ----                                -------------------------------------
    NDK_SET_VAR_BASIC                   0 variable values, no extra data
    NDK_SET_VAR_DATA                    0 variable values, extra data
    NDK_SET_VAR_VALUE                   1 variable value, no extra data
    NDK_SET_VAR_VALUE_DATA              1 variable value, extra data
    NDK_SET_VAR_MULTI_VALUE             2+ variable values, no extra data
    NDK_SET_VAR_MULTI_VALUE_DATA        2+ variable values, extra data
    NDK_SET_VAR_HASH                    the space needed for the result string 
                                        value is known in advance (usually 
                                        used in a hash function)

    NOTE : if none of these generic calling types suit your needs, it is
    easy to extend the list of types in the .c file (and you if you let me know
    I'll add them to the list


- define the filter function with the respective prototype

    type                                prototype
    ----                                ---------
    NDK_SET_VAR_BASIC                   ndk_set_var_pt
    NDK_SET_VAR_DATA                    ndk_set_var_data_pt
    NDK_SET_VAR_VALUE                   ndk_set_var_value_pt
    NDK_SET_VAR_DATA_VALUE              ndk_set_var_value_data_pt
    NDK_SET_VAR_MULTI_VALUE             ndk_set_var_value_pt
    NDK_SET_VAR_MULTI_VALUE_DATA        ndk_set_var_value_data_pt
    NDK_SET_VAR_HASH                    ndk_set_var_hash_pt

    (See ngx_tools_module.h for the prototype definitions.)

    Note : For the multi_value functions, the variable value pointer is to the
    first value (with the others being in an array following it)


to use one of the default setup functions
-----------------------------------------

- define one or multiple ngx_http_var_filter_t's at the global scope, setting :

    type = (one of types above)
    func = function to call
    size = (for multi value)        the number of variable values
           (for hash)               length of buffer to allocate
    data = (for data functions)     additional data (see note below)

- define a configuration directive (see in the .c file for examples), where the
    function is 'ngx_http_set_var' and the 'post' is a pointer your filter definition


to setup in a customized way
----------------------------

- define a configuration directive which has your own specific configuration function

- inside your config function, define one or several ngx_http_var_filter_t's like
    above, and call one of the ngx_http_set_var_..._core functions, passing the 
    variable name and value pointers as appropriate - see examples section

Note : if you're passing extra data to the function, then you will probably want
to use this second method and store the data either in the loc conf, or just
allocate the space for it using one of the ngx_palloc functions.

If the values that will be used for processing are in the same order as in the
config file and there aren't any additional values that are input, then you can
just use the (ngx_str_t *) (cf->args->elts) + 1 as your base for the values or 
possibly not use the _core versions of the functions.


That's it!


FEEDBACK
--------

If you have any comments (good/bad), or have found any bugs, please let me know at:
ngx.eugaia AT gmail DOT com


TODO
----
- add more documentation/examples