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view libraries/json/json.c @ 151:6d2bb696f736
Simplified C macros for Lua registry handling in JSON library (using lua_rawgetp API function)
| author | jbe |
|---|---|
| date | Thu Jul 31 00:44:17 2014 +0200 (2014-07-31) |
| parents | 35fb4f92a887 |
| children | 7b5c13fdc2ec |
line source
1 #include <lua.h>
2 #include <lauxlib.h>
3 #include <stdlib.h>
4 #include <string.h>
6 // maximum number of nested JSON values (objects and arrays):
7 // NOTE: The Lua reference states that the stack may typically contain at least
8 // "a few thousand elements". Since every nested level consumes
9 // 3 elements on the Lua stack (the object/array, its shadow table,
10 // a string key or a placeholder), we limit the number of nested levels
11 // to 500. If a stack overflow would still happen in the import function,
12 // this is detected nevertheless and an error is thrown (instead of
13 // returning nil and an error string).
14 #define JSON_MAXDEPTH 500
16 // macros for usage of Lua registry:
17 #define JSON_REGENT char
18 #define JSON_REGPOINTER void *
19 #define json_pushlightref(L, x) lua_pushlightuserdata((L), &json_reference.x)
20 #define json_regpointer(x) (&json_registry.x)
21 #define json_regfetchpointer(L, x) lua_rawgetp((L), LUA_REGISTRYINDEX, (x))
22 #define json_regfetch(L, x) json_regfetchpointer(L, json_regpointer(x))
23 #define json_regstore(L, x) lua_rawsetp(L, LUA_REGISTRYINDEX, json_regpointer(x))
25 // generate dummy memory addresses that represent non-modifiable lightuserdata (dummy) objects:
26 static struct {
27 JSON_REGENT nullmark; // magic value to indicate JSON null value in shadow table
28 } json_reference;
31 // generate dummy memory addresses that represent Lua objects
32 // via lightuserdata keys and LUA_REGISTRYINDEX:
33 static struct {
34 JSON_REGENT shadowtbl; // ephemeron table that maps tables to their corresponding shadow table
35 JSON_REGENT unknownmt; // metatable for tables that may be either JSON objects or JSON arrays
36 JSON_REGENT objectmt; // metatable for JSON objects
37 JSON_REGENT arraymt; // metatable for JSON arrays
38 } json_registry;
40 // marks a Lua table as JSON object or JSON array:
41 // (returns its modified argument or a new table if argument is nil)
42 static int json_mark(lua_State *L, JSON_REGPOINTER mt) {
43 // check if argument is nil
44 if (lua_isnoneornil(L, 1)) {
45 // create new table at stack position 1:
46 lua_settop(L, 0);
47 lua_newtable(L);
48 // create shadow table (leaving previously created table on stack position 1):
49 json_regfetch(L, shadowtbl);
50 lua_pushvalue(L, 1);
51 lua_newtable(L);
52 lua_rawset(L, -3);
53 } else {
54 // push shadow table on top of stack:
55 json_regfetch(L, shadowtbl);
56 lua_pushvalue(L, 1);
57 lua_rawget(L, -2);
58 // if shadow table does not exist:
59 if (lua_isnil(L, -1)) {
60 // create shadow table and leave it on top of stack:
61 lua_newtable(L);
62 lua_pushvalue(L, 1);
63 lua_pushvalue(L, -2);
64 lua_rawset(L, -5);
65 }
66 // move elements from original table to shadow table (that's expected on top of stack):
67 for(lua_pushnil(L); lua_next(L, 1); lua_pop(L, 1)) {
68 lua_pushvalue(L, -2);
69 lua_pushnil(L);
70 lua_rawset(L, 1);
71 lua_pushvalue(L, -2);
72 lua_pushvalue(L, -2);
73 lua_rawset(L, -5);
74 }
75 }
76 // discard everything but table to return:
77 lua_settop(L, 1);
78 // set metatable:
79 json_regfetchpointer(L, mt);
80 lua_setmetatable(L, 1);
81 // return table:
82 return 1;
83 }
85 // marks a table as JSON object:
86 // (returns its modified argument or a new table if argument is nil)
87 static int json_object(lua_State *L) {
88 return json_mark(L, json_regpointer(objectmt));
89 }
91 // marks a table as JSON array:
92 // (returns its modified argument or a new table if argument is nil)
93 static int json_array(lua_State *L) {
94 return json_mark(L, json_regpointer(arraymt));
95 }
97 // internal states of JSON parser:
98 #define JSON_STATE_VALUE 0
99 #define JSON_STATE_OBJECT_KEY 1
100 #define JSON_STATE_OBJECT_KEY_TERMINATOR 2
101 #define JSON_STATE_OBJECT_VALUE 3
102 #define JSON_STATE_OBJECT_SEPARATOR 4
103 #define JSON_STATE_ARRAY_VALUE 5
104 #define JSON_STATE_ARRAY_SEPARATOR 6
105 #define JSON_STATE_END 7
107 // special Lua stack indicies for json_import function:
108 #define json_import_objectmt_idx 2
109 #define json_import_arraymt_idx 3
110 #define json_import_shadowtbl_idx 4
111 #define json_import_nullmark_idx 5
113 // decodes a JSON document:
114 static int json_import(lua_State *L) {
115 const char *str; // string to parse
116 size_t total; // total length of string to parse
117 size_t pos = 0; // current position in string to parse
118 size_t level = 0; // nested levels of objects/arrays currently being processed
119 int mode = JSON_STATE_VALUE; // state of parser (i.e. "what's expected next?")
120 char c; // variable to store a single character to be processed
121 luaL_Buffer luabuf; // Lua buffer to decode JSON string values
122 char *cbuf; // C buffer to decode JSON string values
123 size_t writepos; // write position of decoded strings in C buffer
124 // stack shall contain one function argument:
125 lua_settop(L, 1);
126 // push objectmt onto stack position 2:
127 json_regfetch(L, objectmt);
128 // push arraymt onto stack position 3:
129 json_regfetch(L, arraymt);
130 // push shadowtbl onto stack position 4:
131 json_regfetch(L, shadowtbl);
132 // push nullmark onto stack position 5:
133 json_pushlightref(L, nullmark);
134 // require string as first argument:
135 str = luaL_checklstring(L, 1, &total);
136 // if string contains a NULL byte, this is a syntax error
137 if (strlen(str) != total) goto json_import_syntax_error;
138 // main loop of parser:
139 json_import_loop:
140 // skip whitespace and store next character in variable 'c':
141 while (c = str[pos],
142 c == ' ' ||
143 c == '\f' ||
144 c == '\n' ||
145 c == '\r' ||
146 c == '\t' ||
147 c == '\v'
148 ) pos++;
149 // switch statement to handle certain (single) characters:
150 switch (c) {
151 // handle end of JSON document:
152 case 0:
153 // if end of JSON document was expected, then return top element of stack as result:
154 if (mode == JSON_STATE_END) return 1;
155 // otherwise, the JSON document was malformed:
156 json_import_unexpected_eof:
157 lua_pushnil(L);
158 if (level == 0) lua_pushliteral(L, "Empty string");
159 else lua_pushliteral(L, "Unexpected end of JSON document");
160 return 2;
161 // new JSON object:
162 case '{':
163 // if a JSON object is not expected here, then return an error:
164 if (
165 mode != JSON_STATE_VALUE &&
166 mode != JSON_STATE_OBJECT_VALUE &&
167 mode != JSON_STATE_ARRAY_VALUE
168 ) goto json_import_syntax_error;
169 // create JSON object on stack:
170 lua_newtable(L);
171 // set metatable of JSON object:
172 lua_pushvalue(L, json_import_objectmt_idx);
173 lua_setmetatable(L, -2);
174 // create internal shadow table on stack:
175 lua_newtable(L);
176 // register internal shadow table:
177 lua_pushvalue(L, -2);
178 lua_pushvalue(L, -2);
179 lua_rawset(L, json_import_shadowtbl_idx);
180 // expect object key (or end of object) to follow:
181 mode = JSON_STATE_OBJECT_KEY;
182 // jump to common code for opening JSON object and JSON array:
183 goto json_import_open;
184 // new JSON array:
185 case '[':
186 // if a JSON array is not expected here, then return an error:
187 if (
188 mode != JSON_STATE_VALUE &&
189 mode != JSON_STATE_OBJECT_VALUE &&
190 mode != JSON_STATE_ARRAY_VALUE
191 ) goto json_import_syntax_error;
192 // create JSON array on stack:
193 lua_newtable(L);
194 // set metatable of JSON array:
195 lua_pushvalue(L, json_import_arraymt_idx);
196 lua_setmetatable(L, -2);
197 // create internal shadow table on stack:
198 lua_newtable(L);
199 // register internal shadow table:
200 lua_pushvalue(L, -2);
201 lua_pushvalue(L, -2);
202 lua_rawset(L, json_import_shadowtbl_idx);
203 // add nil as key (needed to keep stack balance) and as magic to detect arrays:
204 lua_pushnil(L);
205 // expect array value (or end of array) to follow:
206 mode = JSON_STATE_ARRAY_VALUE;
207 // continue with common code for opening JSON object and JSON array:
208 // common code for opening JSON object or JSON array:
209 json_import_open:
210 // limit nested levels:
211 if (level >= JSON_MAXDEPTH) {
212 lua_pushnil(L);
213 lua_pushliteral(L, "Too many nested JSON levels");
214 return 2;
215 }
216 // additional buffer overflow protection:
217 if (!lua_checkstack(L, LUA_MINSTACK))
218 return luaL_error(L, "Caught stack overflow in JSON import function (too many nested levels and stack size too small)");
219 // increment level:
220 level++;
221 // consume input character:
222 pos++;
223 goto json_import_loop;
224 // end of JSON object:
225 case '}':
226 // if end of JSON object is not expected here, then return an error:
227 if (
228 mode != JSON_STATE_OBJECT_KEY &&
229 mode != JSON_STATE_OBJECT_SEPARATOR
230 ) goto json_import_syntax_error;
231 // jump to common code for end of JSON object and JSON array:
232 goto json_import_close;
233 // end of JSON array:
234 case ']':
235 // if end of JSON array is not expected here, then return an error:
236 if (
237 mode != JSON_STATE_ARRAY_VALUE &&
238 mode != JSON_STATE_ARRAY_SEPARATOR
239 ) goto json_import_syntax_error;
240 // pop nil key/magic (that was needed to keep stack balance):
241 lua_pop(L, 1);
242 // continue with common code for end of JSON object and JSON array:
243 // common code for end of JSON object or JSON array:
244 json_import_close:
245 // consume input character:
246 pos++;
247 // pop shadow table:
248 lua_pop(L, 1);
249 // check if nested:
250 if (--level) {
251 // if nested,
252 // check if outer(!) structure is an array or object:
253 if (lua_isnil(L, -2)) {
254 // select array value processing:
255 mode = JSON_STATE_ARRAY_VALUE;
256 } else {
257 // select object value processing:
258 mode = JSON_STATE_OBJECT_VALUE;
259 }
260 // store value in outer structure:
261 goto json_import_process_value;
262 }
263 // if not nested, then expect end of JSON document and continue with loop:
264 mode = JSON_STATE_END;
265 goto json_import_loop;
266 // key terminator:
267 case ':':
268 // if key terminator is not expected here, then return an error:
269 if (mode != JSON_STATE_OBJECT_KEY_TERMINATOR)
270 goto json_import_syntax_error;
271 // consume input character:
272 pos++;
273 // expect object value to follow:
274 mode = JSON_STATE_OBJECT_VALUE;
275 // continue with loop:
276 goto json_import_loop;
277 // value terminator (NOTE: trailing comma at end of value or key-value list is tolerated by this parser)
278 case ',':
279 // branch according to parser state:
280 if (mode == JSON_STATE_OBJECT_SEPARATOR) {
281 // expect an object key to follow:
282 mode = JSON_STATE_OBJECT_KEY;
283 } else if (mode == JSON_STATE_ARRAY_SEPARATOR) {
284 // expect an array value to follow:
285 mode = JSON_STATE_ARRAY_VALUE;
286 } else {
287 // if value terminator is not expected here, then return an error:
288 goto json_import_syntax_error;
289 }
290 // consume input character:
291 pos++;
292 // continue with loop:
293 goto json_import_loop;
294 // string literal:
295 case '"':
296 // consume quote character:
297 pos++;
298 // prepare buffer to decode string (with maximum possible length) and set write position to zero:
299 cbuf = luaL_buffinitsize(L, &luabuf, total-pos);
300 writepos = 0;
301 // loop through the characters until encountering end quote:
302 while ((c = str[pos++]) != '"') {
303 if (c == 0) {
304 // handle unexpected end of JSON document:
305 goto json_import_unexpected_eof;
306 } else if (c < 32 || c == 127) {
307 // do not allow ASCII control characters:
308 // NOTE: illegal UTF-8 sequences and extended control characters are not sanitized
309 // by this parser to allow different encodings than Unicode
310 lua_pushnil(L);
311 lua_pushliteral(L, "Unexpected control character in JSON string");
312 return 2;
313 } else if (c == '\\') {
314 // read next char after backslash escape:
315 c = str[pos++];
316 switch (c) {
317 // unexpected end-of-string:
318 case 0:
319 goto json_import_unexpected_eof;
320 // unescaping of quotation mark, slash, and backslash:
321 case '"':
322 case '/':
323 case '\\':
324 cbuf[writepos++] = c;
325 break;
326 // unescaping of backspace:
327 case 'b': cbuf[writepos++] = '\b'; break;
328 // unescaping of form-feed:
329 case 'f': cbuf[writepos++] = '\f'; break;
330 // unescaping of new-line:
331 case 'n': cbuf[writepos++] = '\n'; break;
332 // unescaping of carriage-return:
333 case 'r': cbuf[writepos++] = '\r'; break;
334 // unescaping of tabulator:
335 case 't': cbuf[writepos++] = '\t'; break;
336 // unescaping of UTF-16 characters
337 case 'u':
338 lua_pushnil(L);
339 lua_pushliteral(L, "JSON unicode escape sequences are not implemented yet"); // TODO
340 return 2;
341 // unexpected escape sequence:
342 default:
343 lua_pushnil(L);
344 lua_pushliteral(L, "Unexpected string escape sequence in JSON document");
345 return 2;
346 }
347 } else {
348 // normal character:
349 cbuf[writepos++] = c;
350 }
351 }
352 // process buffer to Lua string:
353 luaL_pushresultsize(&luabuf, writepos);
354 // continue with processing of decoded string:
355 goto json_import_process_value;
356 }
357 // process values whose type is is not deducible from a single character:
358 if ((c >= '0' && c <= '9') || c == '-' || c == '+') {
359 // for numbers,
360 // use strtod() call to parse a (double precision) floating point number:
361 char *endptr;
362 double numval;
363 numval = strtod(str+pos, &endptr);
364 // catch parsing errors:
365 if (endptr == str+pos) goto json_import_syntax_error;
366 // consume characters that were parsed:
367 pos += endptr - (str+pos);
368 // push parsed (double precision) floating point number on Lua stack:
369 lua_pushnumber(L, numval);
370 } else if (!strncmp(str+pos, "true", 4)) {
371 // consume 4 input characters for "true":
372 pos += 4;
373 // put Lua true value onto stack:
374 lua_pushboolean(L, 1);
375 } else if (!strncmp(str+pos, "false", 5)) {
376 // consume 5 input characters for "false":
377 pos += 5;
378 // put Lua false value onto stack:
379 lua_pushboolean(L, 0);
380 } else if (!strncmp(str+pos, "null", 4)) {
381 // consume 4 input characters for "null":
382 pos += 4;
383 // put special null-marker onto stack:
384 lua_pushvalue(L, json_import_nullmark_idx);
385 } else {
386 // all other cases are a syntax error:
387 goto json_import_syntax_error;
388 }
389 // process a decoded value or key value pair (expected on top of Lua stack):
390 json_import_process_value:
391 switch (mode) {
392 // an object key has been read:
393 case JSON_STATE_OBJECT_KEY:
394 // if an object key is not a string, then this is a syntax error:
395 if (lua_type(L, -1) != LUA_TSTRING) goto json_import_syntax_error;
396 // expect key terminator to follow:
397 mode = JSON_STATE_OBJECT_KEY_TERMINATOR;
398 // continue with loop:
399 goto json_import_loop;
400 // a key value pair has been read:
401 case JSON_STATE_OBJECT_VALUE:
402 // store key value pair in outer shadow table:
403 lua_rawset(L, -3);
404 // expect value terminator (or end of object) to follow:
405 mode = JSON_STATE_OBJECT_SEPARATOR;
406 // continue with loop:
407 goto json_import_loop;
408 // an array value has been read:
409 case JSON_STATE_ARRAY_VALUE:
410 // store value in outer shadow table:
411 lua_rawseti(L, -3, lua_rawlen(L, -3) + 1);
412 // expect value terminator (or end of object) to follow:
413 mode = JSON_STATE_ARRAY_SEPARATOR;
414 // continue with loop
415 goto json_import_loop;
416 // a single value has been read:
417 case JSON_STATE_VALUE:
418 // leave value on top of stack, expect end of JSON document, and continue with loop:
419 mode = JSON_STATE_END;
420 goto json_import_loop;
421 }
422 // syntax error handling (reachable by goto statement):
423 json_import_syntax_error:
424 lua_pushnil(L);
425 lua_pushliteral(L, "Syntax error in JSON document");
426 return 2;
427 }
429 // special Lua stack indicies for json_path function:
430 #define json_path_shadowtbl_idx 1
431 #define json_path_nullmark_idx 2
433 // stack offset of arguments to json_path function:
434 #define json_path_idxshift 2
436 // gets a value or its type from a JSON document (passed as first argument)
437 // using a path (passed as variable number of keys after first argument):
438 static int json_path(lua_State *L, int type_mode) {
439 int stacktop; // stack index of top of stack (after shifting)
440 int idx = 2 + json_path_idxshift; // stack index of current argument to process
441 // insert shadowtbl into stack at position 1 (shifting the arguments):
442 json_regfetch(L, shadowtbl);
443 lua_insert(L, 1);
444 // insert nullmark into stack at position 2 (shifting the arguments):
445 json_pushlightref(L, nullmark);
446 lua_insert(L, 2);
447 // store stack index of top of stack:
448 stacktop = lua_gettop(L);
449 // use first argument as "current value" (stored on top of stack):
450 lua_pushvalue(L, 1 + json_path_idxshift);
451 // process each "path key" (2nd argument and following arguments):
452 while (idx <= stacktop) {
453 // if "current value" (on top of stack) is nil, then the path cannot be walked and nil is returned:
454 if (lua_isnil(L, -1)) return 1;
455 // try to get shadow table of "current value":
456 lua_pushvalue(L, -1);
457 lua_rawget(L, json_path_shadowtbl_idx);
458 if (lua_isnil(L, -1)) {
459 // if no shadow table is found,
460 if (lua_type(L, -1) == LUA_TTABLE) {
461 // and if "current value" is a table,
462 // drop nil from stack:
463 lua_pop(L, 1);
464 // get "next value" using the "path key":
465 lua_pushvalue(L, idx++);
466 lua_gettable(L, -2);
467 } else {
468 // if "current value" is not a table,
469 // then the path cannot be walked and nil (already on top of stack) is returned:
470 return 1;
471 }
472 } else {
473 // if a shadow table is found,
474 // set "current value" to its shadow table:
475 lua_replace(L, -2);
476 // get "next value" using the "path key":
477 lua_pushvalue(L, idx++);
478 lua_rawget(L, -2);
479 }
480 // the "next value" replaces the "current value":
481 lua_replace(L, -2);
482 }
483 if (!type_mode) {
484 // if a value (and not its type) was requested,
485 // check if value is the null-marker, and store nil on top of Lua stack in that case:
486 if (lua_rawequal(L, -1, json_path_nullmark_idx)) lua_pushnil(L);
487 } else {
488 // if the type was requested,
489 // check if value is the null-marker:
490 if (lua_rawequal(L, -1, json_path_nullmark_idx)) {
491 // if yes, store string "null" on top of Lua stack:
492 lua_pushliteral(L, "null");
493 } else {
494 // otherwise,
495 // check if metatable indicates "object" or "array":
496 if (lua_getmetatable(L, -1)) {
497 json_regfetch(L, objectmt);
498 if (lua_rawequal(L, -2, -1)) {
499 // if value has metatable for JSON objects,
500 // return string "object":
501 lua_pushliteral(L, "object");
502 return 1;
503 }
504 json_regfetch(L, arraymt);
505 if (lua_rawequal(L, -3, -1)) {
506 // if value has metatable for JSON arrays,
507 // return string "object":
508 lua_pushliteral(L, "array");
509 return 1;
510 }
511 // remove 3 metatables (one of the value, two for comparison) from stack:
512 lua_pop(L, 3);
513 }
514 // otherwise, get the Lua type:
515 lua_pushstring(L, lua_typename(L, lua_type(L, -1)));
516 }
517 }
518 // return the top most value on the Lua stack:
519 return 1;
520 }
522 // gets a value from a JSON document (passed as first argument)
523 // using a path (passed as variable number of keys after first argument):
524 static int json_get(lua_State *L) {
525 return json_path(L, 0);
526 }
528 // gets a value's type from a JSON document (passed as first argument)
529 // using a path (variable number of keys after first argument):
530 static int json_type(lua_State *L) {
531 return json_path(L, 1);
532 }
534 // checks if a value in a JSON document (first argument) is
535 // explicitly set to null:
536 static int json_isnull(lua_State *L) {
537 const char *jsontype;
538 // call json_type function with variable arguments:
539 lua_pushcfunction(L, json_type);
540 lua_insert(L, 1);
541 lua_call(L, lua_gettop(L) - 1, 1);
542 // return true if result equals to string "null", otherwise return false:
543 jsontype = lua_tostring(L, -1);
544 if (jsontype && !strcmp(jsontype, "null")) lua_pushboolean(L, 1);
545 else lua_pushboolean(L, 0);
546 return 1;
547 }
549 // special Lua stack indicies for json_setnull function:
550 #define json_setnull_unknownmt_idx 3
551 #define json_setnull_objectmt_idx 4
552 #define json_setnull_arraymt_idx 5
553 #define json_setnull_shadowtbl_idx 6
555 // sets a value in a JSON object or JSON array explicitly to null:
556 // NOTE: JSON null is different than absence of a key
557 static int json_setnull(lua_State *L) {
558 // stack shall contain two function arguments:
559 lua_settop(L, 2);
560 // push unknownmt onto stack position 3:
561 json_regfetch(L, unknownmt);
562 // push objectmt onto stack position 4:
563 json_regfetch(L, objectmt);
564 // push arraymt onto stack position 5:
565 json_regfetch(L, arraymt);
566 // push shadowtbl onto stack position 6:
567 json_regfetch(L, shadowtbl);
568 // set metatable if necessary (leaves unknown number of elements on stack):
569 if (
570 !lua_getmetatable(L, 1) || (
571 !lua_rawequal(L, -1, json_setnull_unknownmt_idx) &&
572 !lua_rawequal(L, -1, json_setnull_objectmt_idx) &&
573 !lua_rawequal(L, -1, json_setnull_arraymt_idx)
574 )
575 ) {
576 lua_pushvalue(L, json_setnull_unknownmt_idx);
577 lua_setmetatable(L, 1);
578 }
579 // try to get shadow table:
580 lua_pushvalue(L, 1);
581 lua_rawget(L, json_setnull_shadowtbl_idx);
582 if (lua_isnil(L, -1)) {
583 // if no shadow table is found,
584 // create new shadow table (and leave it on top of stack):
585 lua_newtable(L);
586 // register shadow table:
587 lua_pushvalue(L, 1);
588 lua_pushvalue(L, -2);
589 lua_rawset(L, json_setnull_shadowtbl_idx);
590 }
591 // push key (second argument) and null-marker after shadow table onto stack:
592 lua_pushvalue(L, 2);
593 json_pushlightref(L, nullmark);
594 // store key and null-marker in shadow table:
595 lua_rawset(L, -3);
596 // return nothing:
597 return 0;
598 }
600 // returns the length of a JSON array (or zero for a table without numeric keys):
601 static int json_len(lua_State *L) {
602 // stack shall contain one function argument:
603 lua_settop(L, 1);
604 // try to get corresponding shadow table for first argument:
605 json_regfetch(L, shadowtbl);
606 lua_pushvalue(L, 1);
607 lua_rawget(L, -2);
608 // if shadow table does not exist, return length of argument, else length of shadow table:
609 lua_pushnumber(L, lua_rawlen(L, lua_isnil(L, -1) ? 1 : -1));
610 return 1;
611 }
613 // special Lua stack indicies for json_index function:
614 #define json_index_nullmark_idx 3
615 #define json_index_shadowtbl_idx 4
617 static int json_index(lua_State *L) {
618 // stack shall contain two function arguments:
619 lua_settop(L, 2);
620 // push nullmark onto stack position 3:
621 json_pushlightref(L, nullmark);
622 // push shadowtbl onto stack position 4:
623 json_regfetch(L, shadowtbl);
624 // get corresponding shadow table for first argument:
625 lua_pushvalue(L, 1);
626 lua_rawget(L, json_index_shadowtbl_idx);
627 // throw error if no shadow table was found:
628 if (lua_isnil(L, -1)) return luaL_error(L, "Shadow table not found");
629 // use key passed as second argument to lookup value in shadow table:
630 lua_pushvalue(L, 2);
631 lua_rawget(L, -2);
632 // if value is null-marker, then push nil onto stack:
633 if (lua_rawequal(L, -1, json_index_nullmark_idx)) lua_pushnil(L);
634 // return either looked up value, or nil
635 return 1;
636 }
638 static int json_newindex(lua_State *L) {
639 // stack shall contain three function arguments:
640 lua_settop(L, 3);
641 // get corresponding shadow table for first argument:
642 json_regfetch(L, shadowtbl);
643 lua_pushvalue(L, 1);
644 lua_rawget(L, -2);
645 // throw error if no shadow table was found:
646 if (lua_isnil(L, -1)) return luaL_error(L, "Shadow table not found");
647 // replace first argument with shadow table:
648 lua_replace(L, 1);
649 // reset stack and use second and third argument to write to shadow table:
650 lua_settop(L, 3);
651 lua_rawset(L, 1);
652 // return nothing:
653 return 0;
654 }
656 // special Lua stack indicies for json_pairs_iterfunc function:
657 #define json_pairs_iterfunc_nullmark_idx 3
658 #define json_pairs_iterfunc_shadowtbl_idx 4
660 static int json_pairs_iterfunc(lua_State *L) {
661 // stack shall contain two function arguments:
662 lua_settop(L, 2);
663 // push nullmark onto stack position 3:
664 json_pushlightref(L, nullmark);
665 // push shadowtbl onto stack position 4:
666 json_regfetch(L, shadowtbl);
667 // get corresponding shadow table for first argument:
668 lua_pushvalue(L, 1);
669 lua_rawget(L, json_pairs_iterfunc_shadowtbl_idx);
670 // throw error if no shadow table was found:
671 if (lua_isnil(L, -1)) return luaL_error(L, "Shadow table not found");
672 // get next key value pair from shadow table (using previous key from argument 2)
673 // and return nothing if there is no next pair:
674 lua_pushvalue(L, 2);
675 if (!lua_next(L, -2)) return 0;
676 // replace null-marker with nil:
677 if (lua_rawequal(L, -1, json_pairs_iterfunc_nullmark_idx)) {
678 lua_pop(L, 1);
679 lua_pushnil(L);
680 }
681 // return key and value (or key and nil, if null-marker was found):
682 return 2;
683 }
685 // returns a triple such that 'for key, value in pairs(obj) do ... end'
686 // iterates through all key value pairs (including JSON null keys represented as Lua nil):
687 static int json_pairs(lua_State *L) {
688 // return triple of function json_pairs_iterfunc, first argument, and nil:
689 lua_pushcfunction(L, json_pairs_iterfunc);
690 lua_pushvalue(L, 1);
691 lua_pushnil(L);
692 return 3;
693 }
695 // special Lua stack indicies for json_ipairs_iterfunc function:
696 #define json_ipairs_iterfunc_nullmark_idx 3
697 #define json_ipairs_iterfunc_shadowtbl_idx 4
699 static int json_ipairs_iterfunc(lua_State *L) {
700 int idx;
701 // stack shall contain two function arguments:
702 lua_settop(L, 2);
703 // push nullmark onto stack position 3:
704 json_pushlightref(L, nullmark);
705 // push shadowtbl onto stack position 4:
706 json_regfetch(L, shadowtbl);
707 // calculate new index by incrementing second argument:
708 idx = lua_tointeger(L, 2) + 1;
709 // get corresponding shadow table for first argument:
710 lua_pushvalue(L, 1);
711 lua_rawget(L, json_ipairs_iterfunc_shadowtbl_idx);
712 // throw error if no shadow table was found:
713 if (lua_isnil(L, -1)) return luaL_error(L, "Shadow table not found");
714 // do integer lookup in shadow table:
715 lua_rawgeti(L, -1, idx);
716 // return nothing if there was no value:
717 if (lua_isnil(L, -1)) return 0;
718 // return new index and
719 // either the looked up value if it is not equal to the null-marker
720 // or nil instead of null-marker:
721 lua_pushinteger(L, idx);
722 if (lua_rawequal(L, -2, json_ipairs_iterfunc_nullmark_idx)) lua_pushnil(L);
723 else lua_pushvalue(L, -2);
724 return 2;
725 }
727 // returns a triple such that 'for idx, value in ipairs(ary) do ... end'
728 // iterates through all values (including JSON null represented as Lua nil):
729 static int json_ipairs(lua_State *L) {
730 // return triple of function json_ipairs_iterfunc, first argument, and zero:
731 lua_pushcfunction(L, json_ipairs_iterfunc);
732 lua_pushvalue(L, 1);
733 lua_pushinteger(L, 0);
734 return 3;
735 }
737 // functions in library module:
738 static const struct luaL_Reg json_module_functions[] = {
739 {"object", json_object},
740 {"array", json_array},
741 {"import", json_import},
742 {"get", json_get},
743 {"type", json_type},
744 {"isnull", json_isnull},
745 {"setnull", json_setnull},
746 {NULL, NULL}
747 };
749 // metamethods for JSON objects, JSON arrays, and unknown JSON collections (object or array):
750 static const struct luaL_Reg json_metatable_functions[] = {
751 {"__len", json_len},
752 {"__index", json_index},
753 {"__newindex", json_newindex},
754 {"__pairs", json_pairs},
755 {"__ipairs", json_ipairs},
756 {NULL, NULL}
757 };
759 // initializes json library:
760 int luaopen_json(lua_State *L) {
761 // empty stack:
762 lua_settop(L, 0);
763 // push library module onto stack position 1:
764 lua_newtable(L);
765 // register library functions:
766 luaL_setfuncs(L, json_module_functions, 0);
767 // create and store unknownmt:
768 lua_newtable(L);
769 luaL_setfuncs(L, json_metatable_functions, 0);
770 json_regstore(L, unknownmt);
771 // create and store objectmt:
772 lua_newtable(L);
773 luaL_setfuncs(L, json_metatable_functions, 0);
774 json_regstore(L, objectmt);
775 // create and store arraymt:
776 lua_newtable(L);
777 luaL_setfuncs(L, json_metatable_functions, 0);
778 json_regstore(L, arraymt);
779 // create and store ephemeron table to store shadow tables for each JSON object/array
780 // to allow NULL values returned as nil
781 lua_newtable(L);
782 lua_newtable(L); // metatable for ephemeron table
783 lua_pushliteral(L, "__mode");
784 lua_pushliteral(L, "k");
785 lua_rawset(L, -3);
786 lua_setmetatable(L, -2);
787 json_regstore(L, shadowtbl);
788 // return library module stored on lowest stack position:
789 lua_settop(L, 1);
790 return 1;
791 }