1--
2-- json.lua
3--
4-- Copyright (c) 2020 rxi
5--
6-- Permission is hereby granted, free of charge, to any person obtaining a copy of
7-- this software and associated documentation files (the "Software"), to deal in
8-- the Software without restriction, including without limitation the rights to
9-- use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
10-- of the Software, and to permit persons to whom the Software is furnished to do
11-- so, subject to the following conditions:
12--
13-- The above copyright notice and this permission notice shall be included in all
14-- copies or substantial portions of the Software.
15--
16-- THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17-- IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18-- FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
19-- AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20-- LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
21-- OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
22-- SOFTWARE.
23--
24
25local json = { _version = "0.1.2" }
26
27-------------------------------------------------------------------------------
28-- Encode
29-------------------------------------------------------------------------------
30
31local encode
32
33local escape_char_map = {
34 [ "\\" ] = "\\",
35 [ "\"" ] = "\"",
36 [ "\b" ] = "b",
37 [ "\f" ] = "f",
38 [ "\n" ] = "n",
39 [ "\r" ] = "r",
40 [ "\t" ] = "t",
41}
42
43local escape_char_map_inv = { [ "/" ] = "/" }
44for k, v in pairs(escape_char_map) do
45 escape_char_map_inv[v] = k
46end
47
48local function escape_char(c)
49 return "\\" .. (escape_char_map[c] or string.format("u%04x", c:byte()))
50end
51
52local function encode_nil(val)
53 return "null"
54end
55
56local function encode_table(val, stack)
57 local res = {}
58 stack = stack or {}
59
60 -- Circular reference?
61 if stack[val] then error("circular reference") end
62
63 stack[val] = true
64
65 if rawget(val, 1) ~= nil or next(val) == nil then
66 -- Treat as array -- check keys are valid and it is not sparse
67 local n = 0
68 for k in pairs(val) do
69 if type(k) ~= "number" then
70 error("invalid table: mixed or invalid key types")
71 end
72 n = n + 1
73 end
74 if n ~= #val then
75 error("invalid table: sparse array")
76 end
77 -- Encode
78 for i, v in ipairs(val) do
79 table.insert(res, encode(v, stack))
80 end
81 stack[val] = nil
82 return "[" .. table.concat(res, ",") .. "]"
83
84 else
85 -- Treat as an object
86 for k, v in pairs(val) do
87 if type(k) ~= "string" then
88 error("invalid table: mixed or invalid key types")
89 end
90 table.insert(res, encode(k, stack) .. ":" .. encode(v, stack))
91 end
92 stack[val] = nil
93 return "{" .. table.concat(res, ",") .. "}"
94 end
95end
96
97local function encode_string(val)
98 return '"' .. val:gsub('[%z\1-\31\\"]', escape_char) .. '"'
99end
100
101local function encode_number(val)
102 -- Check for NaN, -inf and inf
103 if val ~= val or val <= -math.huge or val >= math.huge then
104 error("unexpected number value '" .. tostring(val) .. "'")
105 end
106 return string.format("%.14g", val)
107end
108
109local type_func_map = {
110 [ "nil" ] = encode_nil,
111 [ "table" ] = encode_table,
112 [ "string" ] = encode_string,
113 [ "number" ] = encode_number,
114 [ "boolean" ] = tostring,
115}
116
117encode = function(val, stack)
118 local t = type(val)
119 local f = type_func_map[t]
120 if f then
121 return f(val, stack)
122 end
123 error("unexpected type '" .. t .. "'")
124end
125
126function json.encode(val)
127 return ( encode(val) )
128end
129
130-------------------------------------------------------------------------------
131-- Decode
132-------------------------------------------------------------------------------
133
134local parse
135
136local function create_set(...)
137 local res = {}
138 for i = 1, select("#", ...) do
139 res[ select(i, ...) ] = true
140 end
141 return res
142end
143
144local space_chars = create_set(" ", "\t", "\r", "\n")
145local delim_chars = create_set(" ", "\t", "\r", "\n", "]", "}", ",")
146local escape_chars = create_set("\\", "/", '"', "b", "f", "n", "r", "t", "u")
147local literals = create_set("true", "false", "null")
148
149local literal_map = {
150 [ "true" ] = true,
151 [ "false" ] = false,
152 [ "null" ] = nil,
153}
154
155local function next_char(str, idx, set, negate)
156 for i = idx, #str do
157 if set[str:sub(i, i)] ~= negate then
158 return i
159 end
160 end
161 return #str + 1
162end
163
164local function decode_error(str, idx, msg)
165 local line_count = 1
166 local col_count = 1
167 for i = 1, idx - 1 do
168 col_count = col_count + 1
169 if str:sub(i, i) == "\n" then
170 line_count = line_count + 1
171 col_count = 1
172 end
173 end
174 error( string.format("%s at line %d col %d", msg, line_count, col_count) )
175end
176
177local function codepoint_to_utf8(n)
178 -- http://scripts.sil.org/cms/scripts/page.php?site_id=nrsi&id=iws-appendixa
179 local f = math.floor
180 if n <= 0x7f then
181 return string.char(n)
182 elseif n <= 0x7ff then
183 return string.char(f(n / 64) + 192, n % 64 + 128)
184 elseif n <= 0xffff then
185 return string.char(f(n / 4096) + 224, f(n % 4096 / 64) + 128, n % 64 + 128)
186 elseif n <= 0x10ffff then
187 return string.char(f(n / 262144) + 240, f(n % 262144 / 4096) + 128,
188 f(n % 4096 / 64) + 128, n % 64 + 128)
189 end
190 error( string.format("invalid unicode codepoint '%x'", n) )
191end
192
193local function parse_unicode_escape(s)
194 local n1 = tonumber( s:sub(1, 4), 16 )
195 local n2 = tonumber( s:sub(7, 10), 16 )
196 -- Surrogate pair?
197 if n2 then
198 return codepoint_to_utf8((n1 - 0xd800) * 0x400 + (n2 - 0xdc00) + 0x10000)
199 else
200 return codepoint_to_utf8(n1)
201 end
202end
203
204local function parse_string(str, i)
205 local res = ""
206 local j = i + 1
207 local k = j
208
209 while j <= #str do
210 local x = str:byte(j)
211
212 if x < 32 then
213 decode_error(str, j, "control character in string")
214
215 elseif x == 92 then -- `\`: Escape
216 res = res .. str:sub(k, j - 1)
217 j = j + 1
218 local c = str:sub(j, j)
219 if c == "u" then
220 local hex = str:match("^[dD][89aAbB]%x%x\\u%x%x%x%x", j + 1)
221 or str:match("^%x%x%x%x", j + 1)
222 or decode_error(str, j - 1, "invalid unicode escape in string")
223 res = res .. parse_unicode_escape(hex)
224 j = j + #hex
225 else
226 if not escape_chars[c] then
227 decode_error(str, j - 1, "invalid escape char '" .. c .. "' in string")
228 end
229 res = res .. escape_char_map_inv[c]
230 end
231 k = j + 1
232
233 elseif x == 34 then -- `"`: End of string
234 res = res .. str:sub(k, j - 1)
235 return res, j + 1
236 end
237
238 j = j + 1
239 end
240
241 decode_error(str, i, "expected closing quote for string")
242end
243
244local function parse_number(str, i)
245 local x = next_char(str, i, delim_chars)
246 local s = str:sub(i, x - 1)
247 local n = tonumber(s)
248 if not n then
249 decode_error(str, i, "invalid number '" .. s .. "'")
250 end
251 return n, x
252end
253
254local function parse_literal(str, i)
255 local x = next_char(str, i, delim_chars)
256 local word = str:sub(i, x - 1)
257 if not literals[word] then
258 decode_error(str, i, "invalid literal '" .. word .. "'")
259 end
260 return literal_map[word], x
261end
262
263local function parse_array(str, i)
264 local res = {}
265 local n = 1
266 i = i + 1
267 while 1 do
268 local x
269 i = next_char(str, i, space_chars, true)
270 -- Empty / end of array?
271 if str:sub(i, i) == "]" then
272 i = i + 1
273 break
274 end
275 -- Read token
276 x, i = parse(str, i)
277 res[n] = x
278 n = n + 1
279 -- Next token
280 i = next_char(str, i, space_chars, true)
281 local chr = str:sub(i, i)
282 i = i + 1
283 if chr == "]" then break end
284 if chr ~= "," then decode_error(str, i, "expected ']' or ','") end
285 end
286 return res, i
287end
288
289local function parse_object(str, i)
290 local res = {}
291 i = i + 1
292 while 1 do
293 local key, val
294 i = next_char(str, i, space_chars, true)
295 -- Empty / end of object?
296 if str:sub(i, i) == "}" then
297 i = i + 1
298 break
299 end
300 -- Read key
301 if str:sub(i, i) ~= '"' then
302 decode_error(str, i, "expected string for key")
303 end
304 key, i = parse(str, i)
305 -- Read ':' delimiter
306 i = next_char(str, i, space_chars, true)
307 if str:sub(i, i) ~= ":" then
308 decode_error(str, i, "expected ':' after key")
309 end
310 i = next_char(str, i + 1, space_chars, true)
311 -- Read value
312 val, i = parse(str, i)
313 -- Set
314 res[key] = val
315 -- Next token
316 i = next_char(str, i, space_chars, true)
317 local chr = str:sub(i, i)
318 i = i + 1
319 if chr == "}" then break end
320 if chr ~= "," then decode_error(str, i, "expected '}' or ','") end
321 end
322 return res, i
323end
324
325local char_func_map = {
326 [ '"' ] = parse_string,
327 [ "0" ] = parse_number,
328 [ "1" ] = parse_number,
329 [ "2" ] = parse_number,
330 [ "3" ] = parse_number,
331 [ "4" ] = parse_number,
332 [ "5" ] = parse_number,
333 [ "6" ] = parse_number,
334 [ "7" ] = parse_number,
335 [ "8" ] = parse_number,
336 [ "9" ] = parse_number,
337 [ "-" ] = parse_number,
338 [ "t" ] = parse_literal,
339 [ "f" ] = parse_literal,
340 [ "n" ] = parse_literal,
341 [ "[" ] = parse_array,
342 [ "{" ] = parse_object,
343}
344
345parse = function(str, idx)
346 local chr = str:sub(idx, idx)
347 local f = char_func_map[chr]
348 if f then
349 return f(str, idx)
350 end
351 decode_error(str, idx, "unexpected character '" .. chr .. "'")
352end
353
354function json.decode(str)
355 if type(str) ~= "string" then
356 error("expected argument of type string, got " .. type(str))
357 end
358 local res, idx = parse(str, next_char(str, 1, space_chars, true))
359 idx = next_char(str, idx, space_chars, true)
360 if idx <= #str then
361 decode_error(str, idx, "trailing garbage")
362 end
363 return res
364end
365
366return json