= Lua CJSON 1.0devel Manual = Mark Pulford :revdate: 30th November 2011 Overview -------- Lua CJSON provides fast JSON parsing and encoding support for Lua. .Features - More than 10x to 20x faster than the efficient pure Lua JSON modules. - Full support for JSON with UTF-8, including decoding surrogate pairs. - Optional run-time support for common exceptions to the JSON specification (NaN, Inf,..). .Caveats - UTF-16 and UTF-32 are not supported. - Multi-threading within a single Lua state is not supported. However, this is not a recommended configuration under Lua. Lua CJSON is covered by the MIT license. See the file +LICENSE+ for details. The latest version of this software is available from the http://www.kyne.com.au/~mark/software/lua-cjson.php[Lua CJSON website]. Feel free to email me if you have any patches, suggestions, or comments. Installation Methods -------------------- Lua CJSON requires either http://www.lua.org[Lua] or http://www.luajit.org[LuaJIT] to build. There are 3 build methods available: Make:: POSIX (including Linux, BSD, Mac OSX & Solaris) RPM:: Linux LuaRocks:: POSIX (including Linux, BSD, Mac OSX & Solaris), Windows Build options (#define) ~~~~~~~~~~~~~~~~~~~~~~~ Lua CJSON uses +strtod+(3) and +snprintf+(3) to perform numeric conversion as they are usually well supported, fast and bug free. To ensure JSON encoding/decoding works correctly for locales using comma decimal separators, Lua CJSON may optionally be compiled with one of the following (+#define+): USE_POSIX_USELOCALE:: Thread safe. Supported by Linux and Mac OSX. Recommended where available. USE_POSIX_SETLOCALE:: Works on all ANSI C platforms. Only use with single threaded programs. Also available: USE_INTERNAL_ISINF:: Workaround for Solaris platforms missing isinf(). Make ~~~~ Review and update the included Makefile to suit your platform. Next, build and install the module: [source,sh] make install Or install manually: [source,sh] make cp cjson.so $your_lua_module_directory RPM ~~~ Linux distributions using RPM should be able to create a package via the included RPM spec file. Install the +rpm-build+ package (or similar) then: [source,sh] rpmbuild -tb lua-cjson-1.0devel.tar.gz rpm -Uvh $newly_built_lua_cjson_rpm LuaRocks ~~~~~~~~ http://luarocks.org[LuaRocks] can be used to install and manage Lua modules on a wide range of platforms (including Windows). Extract the Lua CJSON source package into a directory and run: [source,sh] cd lua-cjson-1.0devel luarocks make [NOTE] LuaRocks does not support platform specific configuration for Solaris. On Solaris, you may need to manually uncomment +USE_INTERNAL_ISINF+ in the rockspec before building this module. See the http://luarocks.org/en/Documentation[LuaRocks documentation] for further details. API (Functions) --------------- Synopsis ~~~~~~~~ [source,lua] ------------ require "cjson" -- Or: local cjson = require "cjson" -- Translate Lua value to/from JSON text = cjson.encode(value) value = cjson.decode(text) -- Get and/or set Lua CJSON configuration setting = cjson.refuse_invalid_numbers([setting]) depth = cjson.encode_max_depth([depth]) convert, ratio, safe = cjson.encode_sparse_array([convert[, ratio[, safe]]]) keep = cjson.encode_keep_buffer([keep]) ------------ cjson.decode ~~~~~~~~~~~~ [source,lua] ------------ value = cjson.decode(json_text) ------------ +cjson.decode+ will deserialise any UTF-8 JSON string into a Lua value or table. It may return any of the types that +cjson.encode+ supports. 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 characters 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, _invalid_ numbers (NaN, Infinity, Hexidecimal) will be decoded. This default can be changed with +cjson.refuse_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 when after decoding JSON objects with numeric keys. Each numeric key will be stored as a Lua +string+. Any code assuming type +number+ may break. cjson.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+ Numbers are encoded using the standard Lua number format. Lua CJSON will escape the following characters within each string: - Control characters (ASCII 0 - 31) - Double quote (ASCII 34) - Forward slash (ASCII 47) - Blackslash (ASCII 92) - Delete (ASCII 127) All other characters are passed transparently. Any UTF-8 error checking must be done by the application. Lua CJSON uses a heuristic to determine whether to encode a Lua table as a JSON array or an object. A Lua table which only has positive integers (>0) keys of type +number+ will be encoded as a JSON array. All other tables will be encoded as a JSON object. Missing entries from sparse Lua arrays are encoded as +null+. .Example: Encoding a sparse array [source,lua] cjson.encode({ [3] = "data" }) -- Returns: '[null,null,"data"]' 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. JSON object keys are always strings. +cjson.encode+ can only handle 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 (+[]+). Hence a table must be passed to +cjson.encode+ to generate standards compliant JSON output. By default, the following will generate errors: - Excessively <> - More than 20 nested tables - Invalid numbers (NaN, Infinity) These defaults can be changed with: - +cjson.encode_sparse_array+ - +cjson.encode_max_depth+ - +cjson.refuse_invalid_numbers+ .Example: encoding [source,lua] value = { true, { foo = "bar" } } json_text = cjson.encode(value) -- Returns: '[true,{"foo":"bar"}]' cjson.encode_max_depth ~~~~~~~~~~~~~~~~~~~~~~ [source,lua] ------------ depth = cjson.encode_max_depth([depth]) -- "depth" must be a positive integer (>0). ------------ By default, Lua CJSON will reject data structure with more than 20 nested tables. This check prevents a deeply nested or recursive data structure from crashing the application. .Example: Recursive Lua tables [source,lua] a = {}; b = { a }; a[1] = b Once the maximum table depth has been reached Lua CJSON will throw an error. cjson.encode_number_precision ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ [source,lua] ------------ precision = cjson.encode_number_precision([precision]) -- "precision" must be between 1 and 14 (inclusive) ------------ By default, Lua CJSON will output 14 significant digits when converting a number to text. Reducing number precision to _3_ can improve performance of number heavy JSON conversions by up to 50%. [[sparse_arrays]] cjson.encode_sparse_array ~~~~~~~~~~~~~~~~~~~~~~~~~ [source,lua] ------------ convert, ratio, safe = cjson.encode_sparse_array([convert[, ratio[, safe]]]) -- "convert" must be a boolean. Default: false. -- "ratio" must be a positive integer (>0). Default: 2 -- "safe" must be a positive integer (>0). Default: 10 ------------ Lua CJSON classifies Lua tables into 3 types when encoding as a JSON array. This is determined by the number of values missing for keys up to the maximum index: Normal:: All values are available. Sparse:: At least 1 value is missing. Excessively sparse:: The number of missing values exceed a configured number. Lua CJSON encodes sparse Lua arrays by as JSON arrays using JSON +null+. .Example: Encoding a sparse array [source,lua] cjson.encode({ [3] = "sparse" }) -- Returns: '[null,null,"sparse"]' Lua CJSON checks for excessively sparse arrays when the maximum index is greater an the +safe+ limit and +ratio+ is greater than +0+. An array is _excessively sparse_ when: _maximum_index_ > _item_count_ * +ratio+ By default, attempting to encode excessively sparse arrays will generate an error. If +convert+ is set to +true+, excessively sparse arrays will be converted to a JSON object: .Example: Enabling conversion to a JSON object [source,lua] cjson.encode_sparse_array(true) cjson.encode({ [1000] = "excessively sparse" }) -- Returns: '{"1000":"excessively sparse"}' cjson.keep_encode_buffer ~~~~~~~~~~~~~~~~~~~~~~~~ [source,lua] ------------ keep = cjson.keep_encode_buffer([keep]) -- "keep" must be a boolean ------------ By default, Lua CJSON will reuse the JSON encoding buffer to improve performance. The buffer will grow to the largest size required and is not freed until the Lua CJSON module is garbage collected. Setting this option to +false+ will cause the buffer to be freed after each call to +cjson.encode+. cjson.refuse_invalid_numbers ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ [source,lua] ------------ setting = cjson.refuse_invalid_numbers([setting]) -- "setting" must be on of: -- false, "encode", "decode", "both", true ------------ Lua CJSON considers numbers which are outside the JSON specification to be _invalid_: - Infinity - NaN - Hexadecimal numbers By default Lua CJSON will decode _invalid_ numbers, but will refuse to encode them. This setting can be configured separately for encoding and/or decoding: Enabled:: an error will be generated if an _invalid_ number is found. Disabled (encoding):: NaN and Infinity can be encoded. Disabled (decoding):: All numbers supported by +strtod+(3) will be parsed. API (Variables) --------------- cjson.null ~~~~~~~~~~ Lua CJSON decodes JSON +null+ as a Lua lightuserdata NULL pointer. +cjson.null+ can be used for comparison. cjson.version ~~~~~~~~~~~~~ The version number of the Lua CJSON module in use can be found in +cjson.version+. [sect1] References ---------- - http://tools.ietf.org/html/rfc4627[RFC 4627] - http://www.json.org/[JSON website]