Update of "Documentation" — dkjson

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David Kolf's JSON module for Lua 5.1/5.2 ========================================

*Version 2.5*

In the default configuration this module writes no global values, not even the module table. Import it using

json = require ("dkjson")

In environments where `require` or a similiar function are not available and you cannot receive the return value of the module, you can set the option `register_global_module_table` to `true`. The module table will then be saved in the global variable with the name given by the option `global_module_name`.

Exported functions and values:

`json.encode (object , state)` --------------------------------

Create a string representing the object. `Object` can be a table, a string, a number, a boolean, `nil`, `json.null` or any object with a function `__tojson` in its metatable. A table can only use strings and numbers as keys and its values have to be valid objects as well. It raises an error for any invalid data types or reference cycles.

`state` is an optional table with the following fields:

- `indent` When `indent` (a boolean) is set, the created string will contain newlines and indentations. Otherwise it will be one long line. - `keyorder` `keyorder` is an array to specify the ordering of keys in the encoded output. If an object has keys which are not in this array they are written after the sorted keys. - `level` This is the initial level of indentation used when `indent` is set. For each level two spaces are added. When absent it is set to 0. - `buffer` `buffer` is an array to store the strings for the result so they can be concatenated at once. When it isn't given, the encode function will create it temporary and will return the concatenated result. - `bufferlen` When `bufferlen` is set, it has to be the index of the last element of `buffer`. - `tables` `tables` is a set to detect reference cycles. It is created temporary when absent. Every table that is currently processed is used as key, the value is `true`. - `exception` When `exception` is given, it will be called whenever the encoder cannot encode a given value. The parameters are `reason`, `value`, `state` and `defaultmessage`. `reason` is either `"reference cycle"`, `"custom encoder failed"` or `"unsupported type"`. `value` is the original value that caused the exception, `state` is this state table, `defaultmessage` is the message of the error that would usually be raised. You can either return `true` and add directly to the buffer or you can return the string directly. To keep raising an error return `nil` and the desired error message. An example implementation for an exception function is given in `json.encodeexception`.

When `state.buffer` was set, the return value will be `true` on success. Without `state.buffer` the return value will be a string.

`json.decode (string , position [, null])` --------------------------------------------

Decode `string` starting at `position` or at 1 if `position` was omitted.

`null` is an optional value to be returned for null values. The default is `nil`, but you could set it to `json.null` or any other value.

The return values are the object or `nil`, the position of the next character that doesn't belong to the object, and in case of errors an error message.

Two metatables are created. Every array or object that is decoded gets a metatable with the `__jsontype` field set to either `array` or `object`. If you want to provide your own metatables use the syntax

json.decode (string, position, null, objectmeta, arraymeta)

To prevent the assigning of metatables pass `nil`:

json.decode (string, position, null, nil)

`<metatable>.__jsonorder` -------------------------

`__jsonorder` can overwrite the `keyorder` for a specific table.

`<metatable>.__jsontype` ------------------------

`__jsontype` can be either `"array"` or `"object"`. This value is only checked for empty tables. (The default for empty tables is `"array"`).

`<metatable>.__tojson (self, state)` ------------------------------------

You can provide your own `__tojson` function in a metatable. In this function you can either add directly to the buffer and return true, or you can return a string. On errors nil and a message should be returned.

`json.null` -----------

You can use this value for setting explicit `null` values.

`json.version` --------------

Set to `"dkjson 2.5"`.

`json.quotestring (string)` ---------------------------

Quote a UTF-8 string and escape critical characters using JSON escape sequences. This function is only necessary when you build your own `__tojson` functions.

`json.addnewline (state)` -------------------------

When `state.indent` is set, add a newline to `state.buffer` and spaces according to `state.level`.

`json.encodeexception (reason, value, state, defaultmessage)` -------------------------------------------------------------

This function can be used as value to the `exception` option. Instead of raising an error this function encodes the error message as a string. This can help to debug malformed input data.

x = json.encode(value, { exception = json.encodeexception })

LPeg support ------------

When the local configuration variable `always_try_using_lpeg` is set, this module tries to load LPeg to replace the `decode` function. The speed increase is significant. You can get the LPeg module at <http://www.inf.puc-rio.br/~roberto/lpeg/>. When LPeg couldn't be loaded, the pure Lua functions stay active.

In case you don't want this module to require LPeg on its own, disable the option `always_try_using_lpeg` in the options section at the top of the module.

In this case you can later load LPeg support using

### `json.use_lpeg ()`

Require the LPeg module and replace the functions `quotestring` and and `decode` with functions that use LPeg patterns. This function returns the module table, so you can load the module using:

json = require "dkjson".use_lpeg()

Alternatively you can use `pcall` so the JSON module still works when LPeg isn't found.

json = require "dkjson" pcall (json.use_lpeg)

### `json.using_lpeg`

This variable is set to `true` when LPeg was loaded successfully.

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Contact -------

You can contact the author by sending an e-mail to 'david' at the domain 'dkolf.de'.

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*Copyright (C) 2010-2014 David Heiko Kolf*

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.