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.

Contact

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

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.