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Integrate the yajl JSON library with Lua.

tag: v2.0

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README
**********************************************************************
* Author  : Brian Maher <maherb at brimworks dot com>
* Library : lua_yajl - Lua 5.1 interface to yajl.
*
* The MIT License
* 
* Copyright (c) 2009 Brian Maher
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
* 
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
* 
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
**********************************************************************

To use this library, you need yajl version 2.x, get it here:
     http://lloyd.github.com/yajl/

To build this library, you need CMake, get it here:
    http://www.cmake.org/cmake/resources/software.html

Loading the library:

    If you built the library as a loadable package
        [local] yajl = require 'yajl'

    If you compiled the package statically into your application, call
    the function "luaopen_yajl(L)". It will create a table with the yajl
    functions and leave it on the stack.

NOTE ON LARGE NUMBERS:

    JSON integers and floating points are handled with the 'double' C
    type, which is normally the native number format for Lua.  We do
    NOT currently do error handling if a number is outside of range,
    instead the number will be truncated as specified by the strtod()
    C function.  At some point in the future perhaps we will add
    support for custom error handlers if a double can not accurately
    represent the JSON number.  (want to write this support!?)

-- yajl functions --

yajl.null

    A light user data object that represents the JSON null value.  We
    use this instead of nil to represent null since Lua tables can not
    have a value of nil (that would delete the key-value pair), and
    nil's can not exist at the end of an array.

If you don't care about streaming, here are two convenience methods:

string = yajl.to_string(lua_obj)

    Translate a lua object into a JSON representation by creating a
    generator and calling the 'value' method with the passed in
    lua_obj and returns the result.  See generator:value() for more
    information about this operation.  Note that information loss
    may happen in certain situations.  For example, empty tables are
    always translated into empty arrays.

lua_obj = yajl.to_value(string)

    Translate a string to a lua object.  This is done in C by running
    code that is essentially the same as this (but faster):

    function to_value(string)
        local result
        local stack = {
            function(val) result = val end
        }
        local obj_key
        local events = {
            value: function(_, val)
                stack[#stack](val)
            end,
            open_array: function()
                local arr = {}
                stack[#stack](arr)
                table.insert(stack, function(val)
                    table.insert(result, val)
                end)
            end,
            open_object: function()
                local obj = {}
                stack[#stack](obj)
                table.insert(stack, function(val)
                    obj[obj_key] = val
                end)
            end,
            object_key: function(_, val)
                obj_key = val
            end,
            close: function()
                stack[#stack] = nil
            end,
        }

        yajl.parser({ events: events })(string)
        return result
    end

parser = yajl.parser {
        allow_comments:  true,
        check_utf8:      false,
        events:          {
            value:       function(events, value, type) ... end,
            open_object: function(events) ... end,
            object_key:  function(events, string) ... end,
            open_array:  function(events) ... end,
            close:       function(events, type) ... end,
        },
    }

    If allow_comments is true, then both // and /* ... */ javascript
    comments are allowed.  If check_utf8 is true, then the parser will
    make sure all input is valid UTF8.

    The results of this function is a parser function:

    parser(string)

        Call it with a string to be parsed.

    The events table has various callback functions that will be
    called when the events happen.  All callbacks are passed the
    events table as the first argument.  Note that the yajl.generator
    conforms to this events interface.  Here is the details of each
    callback function:

    events:value(value, type)

        Called when a JSON string, boolean, integer, double, or null
        is found in the input stream.  The type parameter is one of
        these strings depending on what was found in the input stream:

            "string"  - A JSON string was found.
            "boolean" - A JSON true or false was found.
            "number"  - A JSON number was found.
            "null"    - A JSON null was found.

        Note that nulls are NOT represented as a Lua nil value,
        instead they are the yajl.null value.

    events:open_object()

        An open object brace was found.

    events:object_key(string)

        If defined, instead of calling events:value(string, "string")
        when an object key is found, this method is called instead.

    events:open_array()

        An open array brace was found.

    events:close(type)

        A close array or object brace was found.  Type is the string
        "object" or "array" depending on what type is being
        terminated.

generator = yajl.generator {
        printer: function(string) print(string) end,
        indent:  "\t",
    }

    Create a new generator with the specified printer callback,
    optionally specify a whitespace string to be used for indenting if
    you want "pretty" output.  The printer must be a function that
    takes a single string parameter:

    printer(string)

        The returned value is ignored, string is the text to be
        written to the stream.  Single characters are "printed" to the
        stream, so if writing to a file, be sure it is buffered.

    The returned generator object has the following methods:

    generator = generator:value(lua_object)

        Traverse the lua_object and call the appropriate generator
        methods.  lua_object can be any of these types:

            number/boolean/string - Generates an appropriate JSON
                representation.

            nil/yajl.null - Generates a JSON null representation.

            metatable(lua_object).__gen_json(lua_object, generator) -
                If the lua_object has a metatable with a __gen_json
                function in the metatable, then the work of generating
                a JSON representation is delegated to that function.

            table - If all keys in the table are positive integers,
                generates a JSON array representation with element 1
                being the first element of the array.  Otherwise, it
                is reprsented as a JSON object, and all keys are
                coorced into strings using tostring() lua function.
                The values are recursively traversed in depth first
                fashion.  All keys that begin with two underscores are
                ignored.  An empty table is always treated as an empty
                array.

        All other types are ignored (thread, userdata) unless there is
        an appropriate __gen_json metatable method.

    generator = generator:integer(number)

        Generate an integer JSON representation.

    generator = generator:double(number)

        Generate a floating point JSON representation.

    generator = generator:number(number)

        Generate a number JSON representation.  If the number is
        infinity, we will generate the special 1e+666 number.  If the
        number is NAN (not a number), then we generate -0.  At least
        this way there is minimal information loss (since 1e+666 can
        not be represented in a double, that will be re-encoded as
        infinity).

    generator = generator:string(string)

        Generate a string JSON representation with proper escaping.

    generator = generator:null()

        Generate a null JSON representation.

    generator = generator:boolean(boolean)

        Generate a boolean JSON representation.

    generator = generator:open_object()

        Begin generating a JSON object.  May only be followed with a
        call to generator:close() or generator:string().

    generator = generator:open_array()

        Begin generating an array.

    generator = generator:close()

        End generation of an array or object.
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