nodemcu-firmware/app/cjson/manual.txt

= Lua CJSON 2.1devel Manual =
Mark Pulford <mark@kyne.com.au>
:revdate: 1st March 2012

Overview
--------

The Lua CJSON module provides JSON support for Lua.

*Features*::
- Fast, standards compliant encoding/parsing routines
- Full support for JSON with UTF-8, including decoding surrogate pairs
- Optional run-time support for common exceptions to the JSON
  specification (infinity, NaN,..)
- No dependencies on other libraries

*Caveats*::
- UTF-16 and UTF-32 are not supported

Lua CJSON is covered by the MIT license. Review the file +LICENSE+ for
details.

API (Functions)
---------------

Synopsis
~~~~~~~~

[source,lua]
------------

-- Translate Lua value to/from JSON
text = cjson.encode(value)
value = cjson.decode(text)


Module Instantiation
~~~~~~~~~~~~~~~~~~~~

decode
~~~~~~

[source,lua]
------------
value = cjson.decode(json_text)
------------

+cjson.decode+ will deserialise any UTF-8 JSON string into a Lua value
or table.

UTF-16 and UTF-32 JSON strings are not supported.

+cjson.decode+ requires that any NULL (ASCII 0) and double quote (ASCII
34) characters are escaped within strings. All escape codes will be
decoded and other bytes will be passed transparently. UTF-8 characters
are not validated during decoding and should be checked elsewhere if
required.

JSON +null+ will be converted to a NULL +lightuserdata+ value. This can
be compared with +cjson.null+ for convenience.

By default, numbers incompatible with the JSON specification (infinity,
NaN, hexadecimal) can be decoded. This default can be changed with
<<decode_invalid_numbers,+cjson.decode_invalid_numbers+>>.

.Example: Decoding
[source,lua]
json_text = '[ true, { "foo": "bar" } ]'
value = cjson.decode(json_text)
-- Returns: { true, { foo = "bar" } }

[CAUTION]
Care must be taken after decoding JSON objects with numeric keys. Each
numeric key will be stored as a Lua +string+. Any subsequent code
assuming type +number+ may break.


[[encode]]
encode
~~~~~~

[source,lua]
------------
json_text = cjson.encode(value)
------------

+cjson.encode+ will serialise a Lua value into a string containing the
JSON representation.

+cjson.encode+ supports the following types:

- +boolean+
- +lightuserdata+ (NULL value only)
- +nil+
- +number+
- +string+
- +table+

The remaining Lua types will generate an error:

- +function+
- +lightuserdata+ (non-NULL values)
- +thread+
- +userdata+

By default, numbers are encoded with 14 significant digits. Refer to
<<encode_number_precision,+cjson.encode_number_precision+>> for details.

Lua CJSON will escape the following characters within each UTF-8 string:

- Control characters (ASCII 0 - 31)
- Double quote (ASCII 34)
- Forward slash (ASCII 47)
- Blackslash (ASCII 92)
- Delete (ASCII 127)

All other bytes are passed transparently.

[CAUTION]
=========
Lua CJSON will successfully encode/decode binary strings, but this is
technically not supported by JSON and may not be compatible with other
JSON libraries. To ensure the output is valid JSON, applications should
ensure all Lua strings passed to +cjson.encode+ are UTF-8.

Base64 is commonly used to encode binary data as the most efficient
encoding under UTF-8 can only reduce the encoded size by a further
&#126;8%. Lua Base64 routines can be found in the
http://w3.impa.br/%7Ediego/software/luasocket/[LuaSocket] and
http://www.tecgraf.puc-rio.br/%7Elhf/ftp/lua/#lbase64[lbase64] packages.
=========

Lua CJSON uses a heuristic to determine whether to encode a Lua table as
a JSON array or an object. A Lua table with only positive integer keys
of type +number+ will be encoded as a JSON array. All other tables will
be encoded as a JSON object.

Lua CJSON does not use metamethods when serialising tables.

- +rawget+ is used to iterate over Lua arrays
- +next+ is used to iterate over Lua objects

Lua arrays with missing entries (_sparse arrays_) may optionally be
encoded in several different ways. Refer to
<<encode_sparse_array,+cjson.encode_sparse_array+>> for details.

JSON object keys are always strings. Hence +cjson.encode+ only supports
table keys which are type +number+ or +string+. All other types will
generate an error.

[NOTE]
Standards compliant JSON must be encapsulated in either an object (+{}+)
or an array (+[]+). If strictly standards compliant JSON is desired, a
table must be passed to +cjson.encode+.

By default, encoding the following Lua values will generate errors:

- Numbers incompatible with the JSON specification (infinity, NaN)
- Tables nested more than 1000 levels deep
- Excessively sparse Lua arrays

.Example: Encoding
[source,lua]
value = { true, { foo = "bar" } }
json_text = cjson.encode(value)
-- Returns: '[true,{"foo":"bar"}]'

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