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-----------------------------------------------------------------------------
-- JSON4Lua: JSON encoding / decoding support for the Lua language.
-- json Module.
-- Author: Craig Mason-Jones
-- Homepage: http://json.luaforge.net/
-- Version: 0.9.50
-- This module is released under the MIT License (MIT).
-- Please see LICENCE.txt for details.
--
-- USAGE:
-- This module exposes two functions:
-- encode(o)
-- Returns the table / string / boolean / number / nil / json.null value as a JSON-encoded string.
-- decode(json_string)
-- Returns a Lua object populated with the data encoded in the JSON string json_string.
--
-- REQUIREMENTS:
-- compat-5.1 if using Lua 5.0
--
-- CHANGELOG
-- 0.9.50 Radical performance improvement on decode from Eike Decker. Many thanks!
-- 0.9.40 Changed licence to MIT License (MIT)
-- 0.9.20 Introduction of local Lua functions for private functions (removed _ function prefix).
-- Fixed Lua 5.1 compatibility issues.
-- Introduced json.null to have null values in associative arrays.
-- encode() performance improvement (more than 50%) through table.concat rather than ..
-- Introduced decode ability to ignore /**/ comments in the JSON string.
-- 0.9.10 Fix to array encoding / decoding to correctly manage nil/null values in arrays.
-----------------------------------------------------------------------------
-----------------------------------------------------------------------------
-- Imports and dependencies
-----------------------------------------------------------------------------
local math = require('math')
local string = require("string")
local table = require("table")
local tostring = tostring
local base = _G
-----------------------------------------------------------------------------
-- Module declaration
-----------------------------------------------------------------------------
module("json")
-- Public functions
-- Private functions
local decode_scanArray
local decode_scanComment
local decode_scanConstant
local decode_scanNumber
local decode_scanObject
local decode_scanString
local decode_scanWhitespace
local encodeString
local isArray
local isEncodable
-----------------------------------------------------------------------------
-- PUBLIC FUNCTIONS
-----------------------------------------------------------------------------
--- Encodes an arbitrary Lua object / variable.
-- @param v The Lua object / variable to be JSON encoded.
-- @return String containing the JSON encoding in internal Lua string format (i.e. not unicode)
function encode (v)
-- Handle nil values
if v==nil then
return "null"
end
local vtype = base.type(v)
-- Handle strings
if vtype=='string' then
return '"' .. encodeString(v) .. '"' -- Need to handle encoding in string
end
-- Handle booleans
if vtype=='number' or vtype=='boolean' then
return base.tostring(v)
end
-- Handle tables
if vtype=='table' then
local rval = {}
-- Consider arrays separately
local bArray, maxCount = isArray(v)
if bArray then
for i = 1,maxCount do
table.insert(rval, encode(v[i]))
end
else -- An object, not an array
for i,j in base.pairs(v) do
if isEncodable(i) and isEncodable(j) then
table.insert(rval, '"' .. encodeString(i) .. '":' .. encode(j))
end
end
end
if bArray then
return '[' .. table.concat(rval,',') ..']'
else
return '{' .. table.concat(rval,',') .. '}'
end
end
-- Handle null values
if vtype=='function' and v==null then
return 'null'
end
base.assert(false,'encode attempt to encode unsupported type ' .. vtype .. ':' .. base.tostring(v))
end
--- Decodes a JSON string and returns the decoded value as a Lua data structure / value.
-- @param s The string to scan.
-- @return Lua objectthat was scanned, as a Lua table / string / number / boolean or nil.
function decode(s)
-- Function is re-defined below after token and other items are created.
-- Just defined here for code neatness.
return null
end
--- The null function allows one to specify a null value in an associative array (which is otherwise
-- discarded if you set the value with 'nil' in Lua. Simply set t = { first=json.null }
function null()
return null -- so json.null() will also return null ;-)
end
-----------------------------------------------------------------------------
-- Internal, PRIVATE functions.
-----------------------------------------------------------------------------
--- Encodes a string to be JSON-compatible.
-- This just involves back-quoting inverted commas, back-quotes and newlines, I think ;-)
-- @param s The string to return as a JSON encoded (i.e. backquoted string)
-- @return The string appropriately escaped.
local qrep = {["\\"]="\\\\", ['"']='\\"',['\n']='\\n',['\t']='\\t'}
function encodeString(s)
return tostring(s):gsub('["\\\n\t]',qrep)
end
-- Determines whether the given Lua type is an array or a table / dictionary.
-- We consider any table an array if it has indexes 1..n for its n items, and no
-- other data in the table.
-- I think this method is currently a little 'flaky', but can't think of a good way around it yet...
-- @param t The table to evaluate as an array
-- @return boolean, number True if the table can be represented as an array, false otherwise. If true,
-- the second returned value is the maximum
-- number of indexed elements in the array.
function isArray(t)
-- Next we count all the elements, ensuring that any non-indexed elements are not-encodable
-- (with the possible exception of 'n')
local maxIndex = 0
for k,v in base.pairs(t) do
if (base.type(k)=='number' and math.floor(k)==k and 1<=k) then -- k,v is an indexed pair
if (not isEncodable(v)) then return false end -- All array elements must be encodable
maxIndex = math.max(maxIndex,k)
else
if (k=='n') then
if v ~= table.getn(t) then return false end -- False if n does not hold the number of elements
else -- Else of (k=='n')
if isEncodable(v) then return false end
end -- End of (k~='n')
end -- End of k,v not an indexed pair
end -- End of loop across all pairs
return true, maxIndex
end
--- Determines whether the given Lua object / table / variable can be JSON encoded. The only
-- types that are JSON encodable are: string, boolean, number, nil, table and json.null.
-- In this implementation, all other types are ignored.
-- @param o The object to examine.
-- @return boolean True if the object should be JSON encoded, false if it should be ignored.
function isEncodable(o)
local t = base.type(o)
return (t=='string' or t=='boolean' or t=='number' or t=='nil' or t=='table') or (t=='function' and o==null)
end
-- Radical performance improvement for decode from Eike Decker!
do
local type = base.type
local error = base.error
local assert = base.assert
local print = base.print
local tonumber = base.tonumber
-- initialize some values to be used in decoding function
-- initializes a table to contain a byte=>table mapping
-- the table contains tokens (byte values) as keys and maps them on other
-- token tables (mostly, the boolean value 'true' is used to indicate termination
-- of a token sequence)
-- the token table's purpose is, that it allows scanning a sequence of bytes
-- until something interesting has been found (e.g. a token that is not expected)
-- name is a descriptor for the table to be printed in error messages
local function init_token_table (tt)
local struct = {}
local value
function struct:link(other_tt)
value = other_tt
return struct
end
function struct:to(chars)
for i=1,#chars do
tt[chars:byte(i)] = value
end
return struct
end
return function (name)
tt.name = name
return struct
end
end
-- keep "named" byte values at hands
local
c_esc,
c_e,
c_l,
c_r,
c_u,
c_f,
c_a,
c_s,
c_slash = ("\\elrufas/"):byte(1,9)
-- token tables - tt_doublequote_string = strDoubleQuot, tt_singlequote_string = strSingleQuot
local
tt_object_key,
tt_object_colon,
tt_object_value,
tt_doublequote_string,
tt_singlequote_string,
tt_array_value,
tt_array_seperator,
tt_numeric,
tt_boolean,
tt_null,
tt_comment_start,
tt_comment_middle,
tt_ignore --< tt_ignore is special - marked tokens will be tt_ignored
= {},{},{},{},{},{},{},{},{},{},{},{},{}
-- strings to be used in certain token tables
local strchars = "" -- all valid string characters (all except newlines)
local allchars = "" -- all characters that are valid in comments
--local escapechar = {}
for i=0,0xff do
local c = string.char(i)
if c~="\n" and c~="\r" then strchars = strchars .. c end
allchars = allchars .. c
--escapechar[i] = "\\" .. string.char(i)
end
--[[
charstounescape = "\"\'\\bfnrt/";
unescapechars = "\"'\\\b\f\n\r\t\/";
for i=1,#charstounescape do
escapechar[ charstounescape:byte(i) ] = unescapechars:sub(i,i)
end
]]--
-- obj key reader, expects the end of the object or a quoted string as key
init_token_table (tt_object_key) "object (' or \" or } or , expected)"
:link(tt_singlequote_string) :to "'"
:link(tt_doublequote_string) :to '"'
:link(true) :to "}"
:link(tt_object_key) :to ","
:link(tt_comment_start) :to "/"
:link(tt_ignore) :to " \t\r\n"
-- after the key, a colon is expected (or comment)
init_token_table (tt_object_colon) "object (: expected)"
:link(tt_object_value) :to ":"
:link(tt_comment_start) :to "/"
:link(tt_ignore) :to" \t\r\n"
-- as values, anything is possible, numbers, arrays, objects, boolean, null, strings
init_token_table (tt_object_value) "object ({ or [ or ' or \" or number or boolean or null expected)"
:link(tt_object_key) :to "{"
:link(tt_array_seperator) :to "["
:link(tt_singlequote_string) :to "'"
:link(tt_doublequote_string) :to '"'
:link(tt_numeric) :to "0123456789.-"
:link(tt_boolean) :to "tf"
:link(tt_null) :to "n"
:link(tt_comment_start) :to "/"
:link(tt_ignore) :to " \t\r\n"
-- token tables for reading strings
init_token_table (tt_doublequote_string) "double quoted string"
:link(tt_ignore) :to (strchars)
:link(c_esc) :to "\\"
:link(true) :to '"'
init_token_table (tt_singlequote_string) "single quoted string"
:link(tt_ignore) :to (strchars)
:link(c_esc) :to "\\"
:link(true) :to "'"
-- array reader that expects termination of the array or a comma that indicates the next value
init_token_table (tt_array_value) "array (, or ] expected)"
:link(tt_array_seperator) :to ","
:link(true) :to "]"
:link(tt_comment_start) :to "/"
:link(tt_ignore) :to " \t\r\n"
-- a value, pretty similar to tt_object_value
init_token_table (tt_array_seperator) "array ({ or [ or ' or \" or number or boolean or null expected)"
:link(tt_object_key) :to "{"
:link(tt_array_seperator) :to "["
:link(tt_singlequote_string) :to "'"
:link(tt_doublequote_string) :to '"'
:link(tt_comment_start) :to "/"
:link(tt_numeric) :to "0123456789.-"
:link(tt_boolean) :to "tf"
:link(tt_null) :to "n"
:link(tt_ignore) :to " \t\r\n"
-- valid number tokens
init_token_table (tt_numeric) "number"
:link(tt_ignore) :to "0123456789.-Ee"
-- once a comment has been started with /, a * is expected
init_token_table (tt_comment_start) "comment start (* expected)"
:link(tt_comment_middle) :to "*"
-- now everything is allowed, watch out for * though. The next char is then checked manually
init_token_table (tt_comment_middle) "comment end"
:link(tt_ignore) :to (allchars)
:link(true) :to "*"
function decode (js_string)
local pos = 1 -- position in the string
-- read the next byte value
local function next_byte () pos = pos + 1 return js_string:byte(pos-1) end
-- in case of error, report the location using line numbers
local function location ()
local n = ("\n"):byte()
local line,lpos = 1,0
for i=1,pos do
if js_string:byte(i) == n then
line,lpos = line + 1,1
else
lpos = lpos + 1
end
end
return "Line "..line.." character "..lpos
end
-- debug func
--local function status (str)
-- print(str.." ("..s:sub(math.max(1,p-10),p+10)..")")
--end
-- read the next token, according to the passed token table
local function next_token (tok)
while pos <= #js_string do
local b = js_string:byte(pos)
local t = tok[b]
if not t then
error("Unexpected character at "..location()..": "..
string.char(b).." ("..b..") when reading "..tok.name.."\nContext: \n"..
js_string:sub(math.max(1,pos-30),pos+30).."\n"..(" "):rep(pos+math.min(-1,30-pos)).."^")
end
pos = pos + 1
if t~=tt_ignore then return t end
end
error("unexpected termination of JSON while looking for "..tok.name)
end
-- read a string, double and single quoted ones
local function read_string (tok)
local start = pos
--local returnString = {}
repeat
local t = next_token(tok)
if t == c_esc then
--table.insert(returnString, js_string:sub(start, pos-2))
--table.insert(returnString, escapechar[ js_string:byte(pos) ])
pos = pos + 1
--start = pos
end -- jump over escaped chars, no matter what
until t == true
return (base.loadstring("return " .. js_string:sub(start-1, pos-1) ) ())
-- We consider the situation where no escaped chars were encountered separately,
-- and use the fastest possible return in this case.
--if 0 == #returnString then
-- return js_string:sub(start,pos-2)
--else
-- table.insert(returnString, js_string:sub(start,pos-2))
-- return table.concat(returnString,"");
--end
--return js_string:sub(start,pos-2)
end
local function read_num ()
local start = pos
while pos <= #js_string do
local b = js_string:byte(pos)
if not tt_numeric[b] then break end
pos = pos + 1
end
return tonumber(js_string:sub(start-1,pos-1))
end
-- read_bool and read_null are both making an assumption that I have not tested:
-- I would expect that the string extraction is more expensive than actually
-- making manual comparision of the byte values
local function read_bool ()
pos = pos + 3
local a,b,c,d = js_string:byte(pos-3,pos)
if a == c_r and b == c_u and c == c_e then return true end
pos = pos + 1
if a ~= c_a or b ~= c_l or c ~= c_s or d ~= c_e then
error("Invalid boolean: "..js_string:sub(math.max(1,pos-5),pos+5))
end
return false
end
-- same as read_bool: only last
local function read_null ()
pos = pos + 3
local u,l1,l2 = js_string:byte(pos-3,pos-1)
if u == c_u and l1 == c_l and l2 == c_l then return nil end
error("Invalid value (expected null):"..js_string:sub(pos-4,pos-1)..
" ("..js_string:byte(pos-1).."="..js_string:sub(pos-1,pos-1).." / "..c_l..")")
end
local read_object_value,read_object_key,read_array,read_value,read_comment
-- read a value depending on what token was returned, might require info what was used (in case of comments)
function read_value (t,fromt)
if t == tt_object_key then return read_object_key({}) end
if t == tt_array_seperator then return read_array({}) end
if t == tt_singlequote_string or
t == tt_doublequote_string then return read_string(t) end
if t == tt_numeric then return read_num() end
if t == tt_boolean then return read_bool() end
if t == tt_null then return read_null() end
if t == tt_comment_start then return read_value(read_comment(fromt)) end
error("unexpected termination - "..js_string:sub(math.max(1,pos-10),pos+10))
end
-- read comments until something noncomment like surfaces, using the token reader which was
-- used when stumbling over this comment
function read_comment (fromt)
while true do
next_token(tt_comment_start)
while true do
local t = next_token(tt_comment_middle)
if next_byte() == c_slash then
local t = next_token(fromt)
if t~= tt_comment_start then return t end
break
end
end
end
end
-- read arrays, empty array expected as o arg
function read_array (o,i)
--if not i then status "arr open" end
i = i or 1
-- loop until ...
while true do
o[i] = read_value(next_token(tt_array_seperator),tt_array_seperator)
local t = next_token(tt_array_value)
if t == tt_comment_start then
t = read_comment(tt_array_value)
end
if t == true then -- ... we found a terminator token
--status "arr close"
return o
end
i = i + 1
end
end
-- object value reading
function read_object_value (o)
local t = next_token(tt_object_value)
return read_value(t,tt_object_value)
end
-- object key reading, might also terminate the object
function read_object_key (o)
while true do
local t = next_token(tt_object_key)
if t == tt_comment_start then
t = read_comment(tt_object_key)
end
if t == true then return o end
if t == tt_object_key then return read_object_key(o) end
local k = read_string(t)
if next_token(tt_object_colon) == tt_comment_start then
t = read_comment(tt_object_colon)
end
local v = read_object_value(o)
o[k] = v
end
end
-- now let's read data from our string and pretend it's an object value
local r = read_object_value()
if pos<=#js_string then
-- not sure about what to do with dangling characters
--error("Dangling characters in JSON code ("..location()..")")
end
return r
end
end
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