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view libraries/json/json.c @ 154:c8669dde9ce2
Added JSON export function
| author | jbe |
|---|---|
| date | Thu Jul 31 03:01:53 2014 +0200 (2014-07-31) |
| parents | c8c91216255f |
| children | 185e944182cb |
line source
1 #include <lua.h>
2 #include <lauxlib.h>
3 #include <stdlib.h>
4 #include <string.h>
5 #include <math.h>
7 // maximum number of nested JSON values (objects and arrays):
8 // NOTE: The Lua reference states that the stack may typically contain at least
9 // "a few thousand elements". Since every nested level consumes
10 // 3 elements on the Lua stack (the object/array, its shadow table,
11 // a string key or a placeholder), we limit the number of nested levels
12 // to 500. If a stack overflow would still happen in the import function,
13 // this is detected nevertheless and an error is thrown (instead of
14 // returning nil and an error string).
15 #define JSON_MAXDEPTH 500
17 // macros for usage of Lua registry:
18 #define JSON_REGENT char
19 #define JSON_REGPOINTER void *
20 #define json_pushlightref(L, x) lua_pushlightuserdata((L), &json_reference.x)
21 #define json_islightref(L, i, x) (lua_touserdata((L), (i)) == &json_reference.x)
22 #define json_regpointer(x) (&json_registry.x)
23 #define json_regfetchpointer(L, x) lua_rawgetp((L), LUA_REGISTRYINDEX, (x))
24 #define json_regfetch(L, x) json_regfetchpointer(L, json_regpointer(x))
25 #define json_regstore(L, x) lua_rawsetp(L, LUA_REGISTRYINDEX, json_regpointer(x))
27 // generate dummy memory addresses that represent non-modifiable lightuserdata (dummy) objects:
28 static struct {
29 JSON_REGENT nullmark; // magic value to indicate JSON null value in shadow table
30 } json_reference;
32 // generate dummy memory addresses that represent Lua objects
33 // via lightuserdata keys and LUA_REGISTRYINDEX:
34 static struct {
35 JSON_REGENT shadowtbl; // ephemeron table that maps tables to their corresponding shadow table
36 JSON_REGENT unknownmt; // metatable for tables that may be either JSON objects or JSON arrays
37 JSON_REGENT objectmt; // metatable for JSON objects
38 JSON_REGENT arraymt; // metatable for JSON arrays
39 } json_registry;
41 // marks a Lua table as JSON object or JSON array:
42 // (returns its modified argument or a new table if argument is nil)
43 static int json_mark(lua_State *L, JSON_REGPOINTER mt) {
44 // check if argument is nil
45 if (lua_isnoneornil(L, 1)) {
46 // create new table at stack position 1:
47 lua_settop(L, 0);
48 lua_newtable(L);
49 // create shadow table (leaving previously created table on stack position 1):
50 json_regfetch(L, shadowtbl);
51 lua_pushvalue(L, 1);
52 lua_newtable(L);
53 lua_rawset(L, -3);
54 } else {
55 // push shadow table on top of stack:
56 json_regfetch(L, shadowtbl);
57 lua_pushvalue(L, 1);
58 lua_rawget(L, -2);
59 // if shadow table does not exist:
60 if (lua_isnil(L, -1)) {
61 // create shadow table and leave it on top of stack:
62 lua_newtable(L);
63 lua_pushvalue(L, 1);
64 lua_pushvalue(L, -2);
65 lua_rawset(L, -5);
66 }
67 // move elements from original table to shadow table (that's expected on top of stack):
68 for(lua_pushnil(L); lua_next(L, 1); lua_pop(L, 1)) {
69 lua_pushvalue(L, -2);
70 lua_pushnil(L);
71 lua_rawset(L, 1);
72 lua_pushvalue(L, -2);
73 lua_pushvalue(L, -2);
74 lua_rawset(L, -5);
75 }
76 }
77 // discard everything but table to return:
78 lua_settop(L, 1);
79 // set metatable:
80 json_regfetchpointer(L, mt);
81 lua_setmetatable(L, 1);
82 // return table:
83 return 1;
84 }
86 // marks a table as JSON object:
87 // (returns its modified argument or a new table if argument is nil)
88 static int json_object(lua_State *L) {
89 return json_mark(L, json_regpointer(objectmt));
90 }
92 // marks a table as JSON array:
93 // (returns its modified argument or a new table if argument is nil)
94 static int json_array(lua_State *L) {
95 return json_mark(L, json_regpointer(arraymt));
96 }
98 // internal states of JSON parser:
99 #define JSON_STATE_VALUE 0
100 #define JSON_STATE_OBJECT_KEY 1
101 #define JSON_STATE_OBJECT_KEY_TERMINATOR 2
102 #define JSON_STATE_OBJECT_VALUE 3
103 #define JSON_STATE_OBJECT_SEPARATOR 4
104 #define JSON_STATE_ARRAY_VALUE 5
105 #define JSON_STATE_ARRAY_SEPARATOR 6
106 #define JSON_STATE_END 7
108 // special Lua stack indicies for json_import function:
109 #define json_import_objectmt_idx 2
110 #define json_import_arraymt_idx 3
111 #define json_import_shadowtbl_idx 4
112 #define json_import_nullmark_idx 5
114 // decodes a JSON document:
115 static int json_import(lua_State *L) {
116 const char *str; // string to parse
117 size_t total; // total length of string to parse
118 size_t pos = 0; // current position in string to parse
119 size_t level = 0; // nested levels of objects/arrays currently being processed
120 int mode = JSON_STATE_VALUE; // state of parser (i.e. "what's expected next?")
121 char c; // variable to store a single character to be processed
122 luaL_Buffer luabuf; // Lua buffer to decode JSON string values
123 char *cbuf; // C buffer to decode JSON string values
124 size_t writepos; // write position of decoded strings in C buffer
125 size_t arraylen; // variable to temporarily store the array length
126 // stack shall contain one function argument:
127 lua_settop(L, 1);
128 // push objectmt onto stack position 2:
129 json_regfetch(L, objectmt);
130 // push arraymt onto stack position 3:
131 json_regfetch(L, arraymt);
132 // push shadowtbl onto stack position 4:
133 json_regfetch(L, shadowtbl);
134 // push nullmark onto stack position 5:
135 json_pushlightref(L, nullmark);
136 // require string as first argument:
137 str = luaL_checklstring(L, 1, &total);
138 // if string contains a NULL byte, this is a syntax error
139 if (strlen(str) != total) goto json_import_syntax_error;
140 // main loop of parser:
141 json_import_loop:
142 // skip whitespace and store next character in variable 'c':
143 while (c = str[pos],
144 c == ' ' ||
145 c == '\f' ||
146 c == '\n' ||
147 c == '\r' ||
148 c == '\t' ||
149 c == '\v'
150 ) pos++;
151 // switch statement to handle certain (single) characters:
152 switch (c) {
153 // handle end of JSON document:
154 case 0:
155 // if end of JSON document was expected, then return top element of stack as result:
156 if (mode == JSON_STATE_END) return 1;
157 // otherwise, the JSON document was malformed:
158 json_import_unexpected_eof:
159 lua_pushnil(L);
160 if (level == 0) lua_pushliteral(L, "Empty string");
161 else lua_pushliteral(L, "Unexpected end of JSON document");
162 return 2;
163 // new JSON object:
164 case '{':
165 // if a JSON object is not expected here, then return an error:
166 if (
167 mode != JSON_STATE_VALUE &&
168 mode != JSON_STATE_OBJECT_VALUE &&
169 mode != JSON_STATE_ARRAY_VALUE
170 ) goto json_import_syntax_error;
171 // create JSON object on stack:
172 lua_newtable(L);
173 // set metatable of JSON object:
174 lua_pushvalue(L, json_import_objectmt_idx);
175 lua_setmetatable(L, -2);
176 // create internal shadow table on stack:
177 lua_newtable(L);
178 // register internal shadow table:
179 lua_pushvalue(L, -2);
180 lua_pushvalue(L, -2);
181 lua_rawset(L, json_import_shadowtbl_idx);
182 // expect object key (or end of object) to follow:
183 mode = JSON_STATE_OBJECT_KEY;
184 // jump to common code for opening JSON object and JSON array:
185 goto json_import_open;
186 // new JSON array:
187 case '[':
188 // if a JSON array is not expected here, then return an error:
189 if (
190 mode != JSON_STATE_VALUE &&
191 mode != JSON_STATE_OBJECT_VALUE &&
192 mode != JSON_STATE_ARRAY_VALUE
193 ) goto json_import_syntax_error;
194 // create JSON array on stack:
195 lua_newtable(L);
196 // set metatable of JSON array:
197 lua_pushvalue(L, json_import_arraymt_idx);
198 lua_setmetatable(L, -2);
199 // create internal shadow table on stack:
200 lua_newtable(L);
201 // register internal shadow table:
202 lua_pushvalue(L, -2);
203 lua_pushvalue(L, -2);
204 lua_rawset(L, json_import_shadowtbl_idx);
205 // add nil as key (needed to keep stack balance) and as magic to detect arrays:
206 lua_pushnil(L);
207 // expect array value (or end of array) to follow:
208 mode = JSON_STATE_ARRAY_VALUE;
209 // continue with common code for opening JSON object and JSON array:
210 // common code for opening JSON object or JSON array:
211 json_import_open:
212 // limit nested levels:
213 if (level >= JSON_MAXDEPTH) {
214 lua_pushnil(L);
215 lua_pushliteral(L, "Too many nested JSON levels");
216 return 2;
217 }
218 // additional buffer overflow protection:
219 if (!lua_checkstack(L, LUA_MINSTACK))
220 return luaL_error(L, "Caught stack overflow in JSON import function (too many nested levels and stack size too small)");
221 // increment level:
222 level++;
223 // consume input character:
224 pos++;
225 goto json_import_loop;
226 // end of JSON object:
227 case '}':
228 // if end of JSON object is not expected here, then return an error:
229 if (
230 mode != JSON_STATE_OBJECT_KEY &&
231 mode != JSON_STATE_OBJECT_SEPARATOR
232 ) goto json_import_syntax_error;
233 // jump to common code for end of JSON object and JSON array:
234 goto json_import_close;
235 // end of JSON array:
236 case ']':
237 // if end of JSON array is not expected here, then return an error:
238 if (
239 mode != JSON_STATE_ARRAY_VALUE &&
240 mode != JSON_STATE_ARRAY_SEPARATOR
241 ) goto json_import_syntax_error;
242 // pop nil key/magic (that was needed to keep stack balance):
243 lua_pop(L, 1);
244 // continue with common code for end of JSON object and JSON array:
245 // common code for end of JSON object or JSON array:
246 json_import_close:
247 // consume input character:
248 pos++;
249 // pop shadow table:
250 lua_pop(L, 1);
251 // check if nested:
252 if (--level) {
253 // if nested,
254 // check if outer(!) structure is an array or object:
255 if (lua_isnil(L, -2)) {
256 // select array value processing:
257 mode = JSON_STATE_ARRAY_VALUE;
258 } else {
259 // select object value processing:
260 mode = JSON_STATE_OBJECT_VALUE;
261 }
262 // store value in outer structure:
263 goto json_import_process_value;
264 }
265 // if not nested, then expect end of JSON document and continue with loop:
266 mode = JSON_STATE_END;
267 goto json_import_loop;
268 // key terminator:
269 case ':':
270 // if key terminator is not expected here, then return an error:
271 if (mode != JSON_STATE_OBJECT_KEY_TERMINATOR)
272 goto json_import_syntax_error;
273 // consume input character:
274 pos++;
275 // expect object value to follow:
276 mode = JSON_STATE_OBJECT_VALUE;
277 // continue with loop:
278 goto json_import_loop;
279 // value terminator (NOTE: trailing comma at end of value or key-value list is tolerated by this parser)
280 case ',':
281 // branch according to parser state:
282 if (mode == JSON_STATE_OBJECT_SEPARATOR) {
283 // expect an object key to follow:
284 mode = JSON_STATE_OBJECT_KEY;
285 } else if (mode == JSON_STATE_ARRAY_SEPARATOR) {
286 // expect an array value to follow:
287 mode = JSON_STATE_ARRAY_VALUE;
288 } else {
289 // if value terminator is not expected here, then return an error:
290 goto json_import_syntax_error;
291 }
292 // consume input character:
293 pos++;
294 // continue with loop:
295 goto json_import_loop;
296 // string literal:
297 case '"':
298 // consume quote character:
299 pos++;
300 // prepare buffer to decode string (with maximum possible length) and set write position to zero:
301 cbuf = luaL_buffinitsize(L, &luabuf, total-pos);
302 writepos = 0;
303 // loop through the characters until encountering end quote:
304 while ((c = str[pos++]) != '"') {
305 if (c == 0) {
306 // handle unexpected end of JSON document:
307 goto json_import_unexpected_eof;
308 } else if (c < 32 || c == 127) {
309 // do not allow ASCII control characters:
310 // NOTE: illegal UTF-8 sequences and extended control characters are not sanitized
311 // by this parser to allow different encodings than Unicode
312 lua_pushnil(L);
313 lua_pushliteral(L, "Unexpected control character in JSON string");
314 return 2;
315 } else if (c == '\\') {
316 // read next char after backslash escape:
317 c = str[pos++];
318 switch (c) {
319 // unexpected end-of-string:
320 case 0:
321 goto json_import_unexpected_eof;
322 // unescaping of quotation mark, slash, and backslash:
323 case '"':
324 case '/':
325 case '\\':
326 cbuf[writepos++] = c;
327 break;
328 // unescaping of backspace:
329 case 'b': cbuf[writepos++] = '\b'; break;
330 // unescaping of form-feed:
331 case 'f': cbuf[writepos++] = '\f'; break;
332 // unescaping of new-line:
333 case 'n': cbuf[writepos++] = '\n'; break;
334 // unescaping of carriage-return:
335 case 'r': cbuf[writepos++] = '\r'; break;
336 // unescaping of tabulator:
337 case 't': cbuf[writepos++] = '\t'; break;
338 // unescaping of UTF-16 characters
339 case 'u':
340 lua_pushnil(L);
341 lua_pushliteral(L, "JSON unicode escape sequences are not implemented yet"); // TODO
342 return 2;
343 // unexpected escape sequence:
344 default:
345 lua_pushnil(L);
346 lua_pushliteral(L, "Unexpected string escape sequence in JSON document");
347 return 2;
348 }
349 } else {
350 // normal character:
351 cbuf[writepos++] = c;
352 }
353 }
354 // process buffer to Lua string:
355 luaL_pushresultsize(&luabuf, writepos);
356 // continue with processing of decoded string:
357 goto json_import_process_value;
358 }
359 // process values whose type is is not deducible from a single character:
360 if ((c >= '0' && c <= '9') || c == '-' || c == '+') {
361 // for numbers,
362 // use strtod() call to parse a (double precision) floating point number:
363 char *endptr;
364 double numval;
365 numval = strtod(str+pos, &endptr);
366 // catch parsing errors:
367 if (endptr == str+pos) goto json_import_syntax_error;
368 // consume characters that were parsed:
369 pos += endptr - (str+pos);
370 // push parsed (double precision) floating point number on Lua stack:
371 lua_pushnumber(L, numval);
372 } else if (!strncmp(str+pos, "true", 4)) {
373 // consume 4 input characters for "true":
374 pos += 4;
375 // put Lua true value onto stack:
376 lua_pushboolean(L, 1);
377 } else if (!strncmp(str+pos, "false", 5)) {
378 // consume 5 input characters for "false":
379 pos += 5;
380 // put Lua false value onto stack:
381 lua_pushboolean(L, 0);
382 } else if (!strncmp(str+pos, "null", 4)) {
383 // consume 4 input characters for "null":
384 pos += 4;
385 // different behavor for top-level and sub-levels:
386 if (level) {
387 // if sub-level,
388 // push special null-marker onto stack:
389 lua_pushvalue(L, json_import_nullmark_idx);
390 } else {
391 // if top-level,
392 // push nil onto stack:
393 lua_pushnil(L);
394 }
395 } else {
396 // all other cases are a syntax error:
397 goto json_import_syntax_error;
398 }
399 // process a decoded value or key value pair (expected on top of Lua stack):
400 json_import_process_value:
401 switch (mode) {
402 // an object key has been read:
403 case JSON_STATE_OBJECT_KEY:
404 // if an object key is not a string, then this is a syntax error:
405 if (lua_type(L, -1) != LUA_TSTRING) goto json_import_syntax_error;
406 // expect key terminator to follow:
407 mode = JSON_STATE_OBJECT_KEY_TERMINATOR;
408 // continue with loop:
409 goto json_import_loop;
410 // a key value pair has been read:
411 case JSON_STATE_OBJECT_VALUE:
412 // store key value pair in outer shadow table:
413 lua_rawset(L, -3);
414 // expect value terminator (or end of object) to follow:
415 mode = JSON_STATE_OBJECT_SEPARATOR;
416 // continue with loop:
417 goto json_import_loop;
418 // an array value has been read:
419 case JSON_STATE_ARRAY_VALUE:
420 // get current array length:
421 arraylen = lua_rawlen(L, -3);
422 // throw error if array would exceed INT_MAX elements:
423 // TODO: Lua 5.3 may support more elements
424 if (arraylen >= INT_MAX) {
425 lua_pushnil(L);
426 lua_pushfstring(L, "Array exceeded length of %d elements", INT_MAX);
427 }
428 // store value in outer shadow table:
429 lua_rawseti(L, -3, arraylen + 1);
430 // expect value terminator (or end of object) to follow:
431 mode = JSON_STATE_ARRAY_SEPARATOR;
432 // continue with loop
433 goto json_import_loop;
434 // a single value has been read:
435 case JSON_STATE_VALUE:
436 // leave value on top of stack, expect end of JSON document, and continue with loop:
437 mode = JSON_STATE_END;
438 goto json_import_loop;
439 }
440 // syntax error handling (reachable by goto statement):
441 json_import_syntax_error:
442 lua_pushnil(L);
443 lua_pushliteral(L, "Syntax error in JSON document");
444 return 2;
445 }
447 // special Lua stack indicies for json_path function:
448 #define json_path_shadowtbl_idx 1
449 #define json_path_nullmark_idx 2
451 // stack offset of arguments to json_path function:
452 #define json_path_idxshift 2
454 // gets a value or its type from a JSON document (passed as first argument)
455 // using a path (passed as variable number of keys after first argument):
456 static int json_path(lua_State *L, int type_mode) {
457 int stacktop; // stack index of top of stack (after shifting)
458 int idx = 2 + json_path_idxshift; // stack index of current argument to process
459 // insert shadowtbl into stack at position 1 (shifting the arguments):
460 json_regfetch(L, shadowtbl);
461 lua_insert(L, 1);
462 // insert nullmark into stack at position 2 (shifting the arguments):
463 json_pushlightref(L, nullmark);
464 lua_insert(L, 2);
465 // store stack index of top of stack:
466 stacktop = lua_gettop(L);
467 // use first argument as "current value" (stored on top of stack):
468 lua_pushvalue(L, 1 + json_path_idxshift);
469 // process each "path key" (2nd argument and following arguments):
470 while (idx <= stacktop) {
471 // if "current value" (on top of stack) is nil, then the path cannot be walked and nil is returned:
472 if (lua_isnil(L, -1)) return 1;
473 // try to get shadow table of "current value":
474 lua_pushvalue(L, -1);
475 lua_rawget(L, json_path_shadowtbl_idx);
476 if (lua_isnil(L, -1)) {
477 // if no shadow table is found,
478 if (lua_type(L, -1) == LUA_TTABLE) {
479 // and if "current value" is a table,
480 // drop nil from stack:
481 lua_pop(L, 1);
482 // get "next value" using the "path key":
483 lua_pushvalue(L, idx++);
484 lua_gettable(L, -2);
485 } else {
486 // if "current value" is not a table,
487 // then the path cannot be walked and nil (already on top of stack) is returned:
488 return 1;
489 }
490 } else {
491 // if a shadow table is found,
492 // set "current value" to its shadow table:
493 lua_replace(L, -2);
494 // get "next value" using the "path key":
495 lua_pushvalue(L, idx++);
496 lua_rawget(L, -2);
497 }
498 // the "next value" replaces the "current value":
499 lua_replace(L, -2);
500 }
501 if (!type_mode) {
502 // if a value (and not its type) was requested,
503 // check if value is the null-marker, and store nil on top of Lua stack in that case:
504 if (lua_rawequal(L, -1, json_path_nullmark_idx)) lua_pushnil(L);
505 } else {
506 // if the type was requested,
507 // check if value is the null-marker:
508 if (lua_rawequal(L, -1, json_path_nullmark_idx)) {
509 // if yes, store string "null" on top of Lua stack:
510 lua_pushliteral(L, "null");
511 } else {
512 // otherwise,
513 // check if metatable indicates "object" or "array":
514 if (lua_getmetatable(L, -1)) {
515 json_regfetch(L, objectmt);
516 if (lua_rawequal(L, -2, -1)) {
517 // if value has metatable for JSON objects,
518 // return string "object":
519 lua_pushliteral(L, "object");
520 return 1;
521 }
522 json_regfetch(L, arraymt);
523 if (lua_rawequal(L, -3, -1)) {
524 // if value has metatable for JSON arrays,
525 // return string "object":
526 lua_pushliteral(L, "array");
527 return 1;
528 }
529 // remove 3 metatables (one of the value, two for comparison) from stack:
530 lua_pop(L, 3);
531 }
532 // otherwise, get the Lua type:
533 lua_pushstring(L, lua_typename(L, lua_type(L, -1)));
534 }
535 }
536 // return the top most value on the Lua stack:
537 return 1;
538 }
540 // gets a value from a JSON document (passed as first argument)
541 // using a path (passed as variable number of keys after first argument):
542 static int json_get(lua_State *L) {
543 return json_path(L, 0);
544 }
546 // gets a value's type from a JSON document (passed as first argument)
547 // using a path (variable number of keys after first argument):
548 static int json_type(lua_State *L) {
549 return json_path(L, 1);
550 }
552 // checks if a value in a JSON document (first argument) is
553 // explicitly set to null:
554 static int json_isnull(lua_State *L) {
555 const char *jsontype;
556 // call json_type function with variable arguments:
557 lua_pushcfunction(L, json_type);
558 lua_insert(L, 1);
559 lua_call(L, lua_gettop(L) - 1, 1);
560 // return true if result equals to string "null", otherwise return false:
561 jsontype = lua_tostring(L, -1);
562 if (jsontype && !strcmp(jsontype, "null")) lua_pushboolean(L, 1);
563 else lua_pushboolean(L, 0);
564 return 1;
565 }
567 // special Lua stack indicies for json_setnull function:
568 #define json_setnull_unknownmt_idx 3
569 #define json_setnull_objectmt_idx 4
570 #define json_setnull_arraymt_idx 5
571 #define json_setnull_shadowtbl_idx 6
573 // sets a value in a JSON object or JSON array explicitly to null:
574 // NOTE: JSON null is different than absence of a key
575 static int json_setnull(lua_State *L) {
576 // stack shall contain two function arguments:
577 lua_settop(L, 2);
578 // push unknownmt onto stack position 3:
579 json_regfetch(L, unknownmt);
580 // push objectmt onto stack position 4:
581 json_regfetch(L, objectmt);
582 // push arraymt onto stack position 5:
583 json_regfetch(L, arraymt);
584 // push shadowtbl onto stack position 6:
585 json_regfetch(L, shadowtbl);
586 // set metatable if necessary (leaves unknown number of elements on stack):
587 if (
588 !lua_getmetatable(L, 1) || (
589 !lua_rawequal(L, -1, json_setnull_unknownmt_idx) &&
590 !lua_rawequal(L, -1, json_setnull_objectmt_idx) &&
591 !lua_rawequal(L, -1, json_setnull_arraymt_idx)
592 )
593 ) {
594 lua_pushvalue(L, json_setnull_unknownmt_idx);
595 lua_setmetatable(L, 1);
596 }
597 // try to get shadow table:
598 lua_pushvalue(L, 1);
599 lua_rawget(L, json_setnull_shadowtbl_idx);
600 if (lua_isnil(L, -1)) {
601 // if no shadow table is found,
602 // create new shadow table (and leave it on top of stack):
603 lua_newtable(L);
604 // register shadow table:
605 lua_pushvalue(L, 1);
606 lua_pushvalue(L, -2);
607 lua_rawset(L, json_setnull_shadowtbl_idx);
608 }
609 // push key (second argument) and null-marker after shadow table onto stack:
610 lua_pushvalue(L, 2);
611 json_pushlightref(L, nullmark);
612 // store key and null-marker in shadow table:
613 lua_rawset(L, -3);
614 // return nothing:
615 return 0;
616 }
618 // returns the length of a JSON array (or zero for a table without numeric keys):
619 static int json_len(lua_State *L) {
620 // stack shall contain one function argument:
621 lua_settop(L, 1);
622 // try to get corresponding shadow table for first argument:
623 json_regfetch(L, shadowtbl);
624 lua_pushvalue(L, 1);
625 lua_rawget(L, -2);
626 // if shadow table does not exist, return length of argument, else length of shadow table:
627 lua_pushnumber(L, lua_rawlen(L, lua_isnil(L, -1) ? 1 : -1));
628 return 1;
629 }
631 // special Lua stack indicies for json_index function:
632 #define json_index_nullmark_idx 3
633 #define json_index_shadowtbl_idx 4
635 static int json_index(lua_State *L) {
636 // stack shall contain two function arguments:
637 lua_settop(L, 2);
638 // push nullmark onto stack position 3:
639 json_pushlightref(L, nullmark);
640 // push shadowtbl onto stack position 4:
641 json_regfetch(L, shadowtbl);
642 // get corresponding shadow table for first argument:
643 lua_pushvalue(L, 1);
644 lua_rawget(L, json_index_shadowtbl_idx);
645 // throw error if no shadow table was found:
646 if (lua_isnil(L, -1)) return luaL_error(L, "Shadow table not found");
647 // use key passed as second argument to lookup value in shadow table:
648 lua_pushvalue(L, 2);
649 lua_rawget(L, -2);
650 // if value is null-marker, then push nil onto stack:
651 if (lua_rawequal(L, -1, json_index_nullmark_idx)) lua_pushnil(L);
652 // return either looked up value, or nil
653 return 1;
654 }
656 static int json_newindex(lua_State *L) {
657 // stack shall contain three function arguments:
658 lua_settop(L, 3);
659 // get corresponding shadow table for first argument:
660 json_regfetch(L, shadowtbl);
661 lua_pushvalue(L, 1);
662 lua_rawget(L, -2);
663 // throw error if no shadow table was found:
664 if (lua_isnil(L, -1)) return luaL_error(L, "Shadow table not found");
665 // replace first argument with shadow table:
666 lua_replace(L, 1);
667 // reset stack and use second and third argument to write to shadow table:
668 lua_settop(L, 3);
669 lua_rawset(L, 1);
670 // return nothing:
671 return 0;
672 }
674 // special Lua stack indicies for json_pairs_iterfunc function:
675 #define json_pairs_iterfunc_nullmark_idx 3
676 #define json_pairs_iterfunc_shadowtbl_idx 4
678 static int json_pairs_iterfunc(lua_State *L) {
679 // stack shall contain two function arguments:
680 lua_settop(L, 2);
681 // push nullmark onto stack position 3:
682 json_pushlightref(L, nullmark);
683 // push shadowtbl onto stack position 4:
684 json_regfetch(L, shadowtbl);
685 // get corresponding shadow table for first argument:
686 lua_pushvalue(L, 1);
687 lua_rawget(L, json_pairs_iterfunc_shadowtbl_idx);
688 // throw error if no shadow table was found:
689 if (lua_isnil(L, -1)) return luaL_error(L, "Shadow table not found");
690 // get next key value pair from shadow table (using previous key from argument 2)
691 // and return nothing if there is no next pair:
692 lua_pushvalue(L, 2);
693 if (!lua_next(L, -2)) return 0;
694 // replace null-marker with nil:
695 if (lua_rawequal(L, -1, json_pairs_iterfunc_nullmark_idx)) {
696 lua_pop(L, 1);
697 lua_pushnil(L);
698 }
699 // return key and value (or key and nil, if null-marker was found):
700 return 2;
701 }
703 // returns a triple such that 'for key, value in pairs(obj) do ... end'
704 // iterates through all key value pairs (including JSON null keys represented as Lua nil):
705 static int json_pairs(lua_State *L) {
706 // return triple of function json_pairs_iterfunc, first argument, and nil:
707 lua_pushcfunction(L, json_pairs_iterfunc);
708 lua_pushvalue(L, 1);
709 lua_pushnil(L);
710 return 3;
711 }
713 // special Lua stack indicies for json_ipairs_iterfunc function:
714 #define json_ipairs_iterfunc_nullmark_idx 3
715 #define json_ipairs_iterfunc_shadowtbl_idx 4
717 static int json_ipairs_iterfunc(lua_State *L) {
718 lua_Integer idx;
719 // stack shall contain two function arguments:
720 lua_settop(L, 2);
721 // push nullmark onto stack position 3:
722 json_pushlightref(L, nullmark);
723 // push shadowtbl onto stack position 4:
724 json_regfetch(L, shadowtbl);
725 // calculate new index by incrementing second argument:
726 idx = lua_tointeger(L, 2) + 1;
727 // get corresponding shadow table for first argument:
728 lua_pushvalue(L, 1);
729 lua_rawget(L, json_ipairs_iterfunc_shadowtbl_idx);
730 // throw error if no shadow table was found:
731 if (lua_isnil(L, -1)) return luaL_error(L, "Shadow table not found");
732 // do integer lookup in shadow table:
733 lua_rawgeti(L, -1, idx);
734 // return nothing if there was no value:
735 if (lua_isnil(L, -1)) return 0;
736 // return new index and
737 // either the looked up value if it is not equal to the null-marker
738 // or nil instead of null-marker:
739 lua_pushinteger(L, idx);
740 if (lua_rawequal(L, -2, json_ipairs_iterfunc_nullmark_idx)) lua_pushnil(L);
741 else lua_pushvalue(L, -2);
742 return 2;
743 }
745 // returns a triple such that 'for idx, value in ipairs(ary) do ... end'
746 // iterates through all values (including JSON null represented as Lua nil):
747 static int json_ipairs(lua_State *L) {
748 // return triple of function json_ipairs_iterfunc, first argument, and zero:
749 lua_pushcfunction(L, json_ipairs_iterfunc);
750 lua_pushvalue(L, 1);
751 lua_pushinteger(L, 0);
752 return 3;
753 }
755 #define JSON_TABLETYPE_UNKNOWN 0
756 #define JSON_TABLETYPE_OBJECT 1
757 #define JSON_TABLETYPE_ARRAY 2
759 static int json_export(lua_State *L) {
760 lua_Number num;
761 const char *str;
762 unsigned char c;
763 size_t strlen;
764 size_t pos = 0;
765 luaL_Buffer buf;
766 char hexcode[7]; // backslash, character 'u', 4 hex digits, and terminating NULL byte
767 int luatype;
768 int tabletype = JSON_TABLETYPE_UNKNOWN;
769 int needsep = 0;
770 lua_Integer idx;
771 lua_settop(L, 1);
772 switch (lua_type(L, 1)) {
773 case LUA_TNIL:
774 lua_pushliteral(L, "null");
775 return 1;
776 case LUA_TNUMBER:
777 num = lua_tonumber(L, 1);
778 if (isnan(num)) return luaL_error(L, "JSON export not possible for NaN value");
779 if (isinf(num)) return luaL_error(L, "JSON export not possible for infinite numbers");
780 lua_tostring(L, 1);
781 return 1;
782 case LUA_TBOOLEAN:
783 if (lua_toboolean(L, 1)) lua_pushliteral(L, "true");
784 else lua_pushliteral(L, "false");
785 return 1;
786 case LUA_TSTRING:
787 str = lua_tolstring(L, 1, &strlen);
788 luaL_buffinit(L, &buf);
789 luaL_addchar(&buf, '"');
790 while (pos < strlen) {
791 c = str[pos++];
792 if (c == '"') luaL_addstring(&buf, "\\\"");
793 else if (c == '\\') luaL_addstring(&buf, "\\\\");
794 else if (c == 127) luaL_addstring(&buf, "\\u007F");
795 else if (c >= 32) luaL_addchar(&buf, c);
796 else if (c == '\b') luaL_addstring(&buf, "\\b");
797 else if (c == '\f') luaL_addstring(&buf, "\\f");
798 else if (c == '\n') luaL_addstring(&buf, "\\n");
799 else if (c == '\r') luaL_addstring(&buf, "\\r");
800 else if (c == '\t') luaL_addstring(&buf, "\\t");
801 else if (c == '\v') luaL_addstring(&buf, "\\v");
802 else {
803 sprintf(hexcode, "\\u%04X", c);
804 luaL_addstring(&buf, hexcode);
805 }
806 }
807 luaL_addchar(&buf, '"');
808 luaL_pushresult(&buf);
809 return 1;
810 case LUA_TTABLE:
811 if (lua_getmetatable(L, 1)) {
812 json_regfetch(L, objectmt);
813 if (lua_rawequal(L, -2, -1)) {
814 tabletype = JSON_TABLETYPE_OBJECT;
815 } else {
816 json_regfetch(L, arraymt);
817 if (lua_rawequal(L, -3, -1)) tabletype = JSON_TABLETYPE_ARRAY;
818 }
819 }
820 json_regfetch(L, shadowtbl);
821 lua_pushvalue(L, 1);
822 lua_rawget(L, -2);
823 if (!lua_isnil(L, -1)) lua_replace(L, 1);
824 lua_settop(L, 1);
825 if (tabletype == JSON_TABLETYPE_UNKNOWN) {
826 for (lua_pushnil(L); lua_next(L, 1); lua_pop(L, 1)) {
827 luatype = lua_type(L, -2);
828 if (tabletype == JSON_TABLETYPE_UNKNOWN) {
829 if (luatype == LUA_TSTRING) tabletype = JSON_TABLETYPE_OBJECT;
830 else if (luatype == LUA_TNUMBER) tabletype = JSON_TABLETYPE_ARRAY;
831 } else if (
832 (tabletype == JSON_TABLETYPE_OBJECT && luatype == LUA_TNUMBER) ||
833 (tabletype == JSON_TABLETYPE_ARRAY && luatype == LUA_TSTRING)
834 ) {
835 goto json_export_tabletype_error;
836 }
837 }
838 }
839 switch (tabletype) {
840 case JSON_TABLETYPE_OBJECT:
841 lua_settop(L, 3);
842 luaL_buffinit(L, &buf);
843 luaL_addchar(&buf, '{');
844 for (lua_pushnil(L); lua_next(L, 1); ) {
845 if (lua_type(L, -2) == LUA_TSTRING) {
846 lua_replace(L, 3);
847 lua_replace(L, 2);
848 if (needsep) luaL_addchar(&buf, ',');
849 else needsep = 1;
850 lua_pushcfunction(L, json_export);
851 lua_pushvalue(L, 2);
852 lua_call(L, 1, 1);
853 luaL_addvalue(&buf);
854 luaL_addchar(&buf, ':');
855 if (json_islightref(L, 3, nullmark)) {
856 luaL_addstring(&buf, "null");
857 } else {
858 lua_pushcfunction(L, json_export);
859 lua_pushvalue(L, 3);
860 lua_call(L, 1, 1);
861 luaL_addvalue(&buf);
862 }
863 lua_pushvalue(L, 2);
864 } else {
865 lua_pop(L, 1);
866 }
867 }
868 luaL_addchar(&buf, '}');
869 luaL_pushresult(&buf);
870 return 1;
871 case JSON_TABLETYPE_ARRAY:
872 lua_settop(L, 2);
873 luaL_buffinit(L, &buf);
874 luaL_addchar(&buf, '[');
875 for (idx = 1; ; idx++) {
876 lua_rawgeti(L, 1, idx);
877 if (lua_isnil(L, -1)) {
878 lua_pop(L, 1);
879 break;
880 }
881 lua_replace(L, 2);
882 if (needsep) luaL_addchar(&buf, ',');
883 else needsep = 1;
884 lua_pushcfunction(L, json_export);
885 lua_pushvalue(L, 2);
886 lua_call(L, 1, 1);
887 luaL_addvalue(&buf);
888 }
889 luaL_addchar(&buf, ']');
890 luaL_pushresult(&buf);
891 return 1;
892 }
893 json_export_tabletype_error:
894 return luaL_error(L, "JSON export not possible for ambiguous table (cannot decide whether it is an object or array)");
895 }
896 return luaL_error(L, "JSON export not possible for values of type \"%s\"", lua_typename(L, lua_type(L, 1)));
897 }
899 // functions in library module:
900 static const struct luaL_Reg json_module_functions[] = {
901 {"object", json_object},
902 {"array", json_array},
903 {"import", json_import},
904 {"export", json_export},
905 {"get", json_get},
906 {"type", json_type},
907 {"isnull", json_isnull},
908 {"setnull", json_setnull},
909 {NULL, NULL}
910 };
912 // metamethods for JSON objects, JSON arrays, and unknown JSON collections (object or array):
913 static const struct luaL_Reg json_metatable_functions[] = {
914 {"__len", json_len},
915 {"__index", json_index},
916 {"__newindex", json_newindex},
917 {"__pairs", json_pairs},
918 {"__ipairs", json_ipairs},
919 {NULL, NULL}
920 };
922 // initializes json library:
923 int luaopen_json(lua_State *L) {
924 // empty stack:
925 lua_settop(L, 0);
926 // push library module onto stack position 1:
927 lua_newtable(L);
928 // register library functions:
929 luaL_setfuncs(L, json_module_functions, 0);
930 // create and store unknownmt:
931 lua_newtable(L);
932 luaL_setfuncs(L, json_metatable_functions, 0);
933 json_regstore(L, unknownmt);
934 // create and store objectmt:
935 lua_newtable(L);
936 luaL_setfuncs(L, json_metatable_functions, 0);
937 json_regstore(L, objectmt);
938 // create and store arraymt:
939 lua_newtable(L);
940 luaL_setfuncs(L, json_metatable_functions, 0);
941 json_regstore(L, arraymt);
942 // create and store ephemeron table to store shadow tables for each JSON object/array
943 // to allow NULL values returned as nil
944 lua_newtable(L);
945 lua_newtable(L); // metatable for ephemeron table
946 lua_pushliteral(L, "__mode");
947 lua_pushliteral(L, "k");
948 lua_rawset(L, -3);
949 lua_setmetatable(L, -2);
950 json_regstore(L, shadowtbl);
951 // return library module stored on lowest stack position:
952 lua_settop(L, 1);
953 return 1;
954 }