lib/json.c

   1 /*
   2  * Copyright (c) 2009 Nicira Networks.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at:
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 #include <config.h>
  18
  19 #include "json.h"
  20
  21 #include <assert.h>
  22 #include <ctype.h>
  23 #include <errno.h>
  24 #include <float.h>
  25 #include <limits.h>
  26 #include <math.h>
  27 #include <string.h>
  28
  29 #include "dynamic-string.h"
  30 #include "hash.h"
  31 #include "shash.h"
  32 #include "unicode.h"
  33 #include "util.h"
  34
  35 /* The type of a JSON token. */
  36 enum json_token_type {
  37     T_EOF = 0,
  38     T_BEGIN_ARRAY = '[',
  39     T_END_ARRAY = ']',
  40     T_BEGIN_OBJECT = '{',
  41     T_END_OBJECT = '}',
  42     T_NAME_SEPARATOR = ':',
  43     T_VALUE_SEPARATOR = ',',
  44     T_FALSE = UCHAR_MAX + 1,
  45     T_NULL,
  46     T_TRUE,
  47     T_INTEGER,
  48     T_REAL,
  49     T_STRING
  50 };
  51
  52 /* A JSON token.
  53  *
  54  * RFC 4627 doesn't define a lexical structure for JSON but I believe this to
  55  * be compliant with the standard.
  56  */
  57 struct json_token {
  58     enum json_token_type type;
  59     union {
  60         double real;
  61         long long int integer;
  62         const char *string;
  63     } u;
  64 };
  65
  66 enum json_lex_state {
  67     JSON_LEX_START,             /* Not inside a token. */
  68     JSON_LEX_NUMBER,            /* Reading a number. */
  69     JSON_LEX_KEYWORD,           /* Reading a keyword. */
  70     JSON_LEX_STRING,            /* Reading a quoted string. */
  71     JSON_LEX_ESCAPE             /* In a quoted string just after a "\". */
  72 };
  73
  74 enum json_parse_state {
  75     JSON_PARSE_START,           /* Beginning of input. */
  76     JSON_PARSE_END,             /* End of input. */
  77
  78     /* Objects. */
  79     JSON_PARSE_OBJECT_INIT,     /* Expecting '}' or an object name. */
  80     JSON_PARSE_OBJECT_NAME,     /* Expecting an object name. */
  81     JSON_PARSE_OBJECT_COLON,    /* Expecting ':'. */
  82     JSON_PARSE_OBJECT_VALUE,    /* Expecting an object value. */
  83     JSON_PARSE_OBJECT_NEXT,     /* Expecting ',' or '}'. */
  84
  85     /* Arrays. */
  86     JSON_PARSE_ARRAY_INIT,      /* Expecting ']' or a value. */
  87     JSON_PARSE_ARRAY_VALUE,     /* Expecting a value. */
  88     JSON_PARSE_ARRAY_NEXT       /* Expecting ',' or ']'. */
  89 };
  90
  91 struct json_parser_node {
  92     struct json *json;
  93 };
  94
  95 /* A JSON parser. */
  96 struct json_parser {
  97     int flags;
  98
  99     /* Lexical analysis. */
 100     enum json_lex_state lex_state;
 101     struct ds buffer;           /* Buffer for accumulating token text. */
 102
 103     /* Parsing. */
 104     enum json_parse_state parse_state;
 105 #define JSON_MAX_HEIGHT 1000
 106     struct json_parser_node *stack;
 107     size_t height, allocated_height;
 108     char *member_name;
 109
 110     /* Parse status. */
 111     bool done;
 112     char *error;                /* Error message, if any, null if none yet. */
 113 };
 114
 115 static struct json *json_create(enum json_type type);
 116 static void json_parser_input(struct json_parser *, struct json_token *);
 117
 118 static void json_error(struct json_parser *p, const char *format, ...)
 119     PRINTF_FORMAT(2, 3);
 120 \f
 121 const char *
 122 json_type_to_string(enum json_type type)
 123 {
 124     switch (type) {
 125     case JSON_NULL:
 126         return "null";
 127
 128     case JSON_FALSE:
 129         return "false";
 130
 131     case JSON_TRUE:
 132         return "true";
 133
 134     case JSON_OBJECT:
 135         return "object";
 136
 137     case JSON_ARRAY:
 138         return "array";
 139
 140     case JSON_INTEGER:
 141     case JSON_REAL:
 142         return "number";
 143
 144     case JSON_STRING:
 145         return "string";
 146
 147     case JSON_N_TYPES:
 148     default:
 149         return "<invalid>";
 150     }
 151 }
 152 \f
 153 /* Functions for manipulating struct json. */
 154
 155 struct json *
 156 json_null_create(void)
 157 {
 158     return json_create(JSON_NULL);
 159 }
 160
 161 struct json *
 162 json_boolean_create(bool b)
 163 {
 164     return json_create(b ? JSON_TRUE : JSON_FALSE);
 165 }
 166
 167 struct json *
 168 json_string_create_nocopy(char *s)
 169 {
 170     struct json *json = json_create(JSON_STRING);
 171     json->u.string = s;
 172     return json;
 173 }
 174
 175 struct json *
 176 json_string_create(const char *s)
 177 {
 178     return json_string_create_nocopy(xstrdup(s));
 179 }
 180
 181 struct json *
 182 json_array_create_empty(void)
 183 {
 184     struct json *json = json_create(JSON_ARRAY);
 185     json->u.array.elems = NULL;
 186     json->u.array.n = 0;
 187     json->u.array.n_allocated = 0;
 188     return json;
 189 }
 190
 191 void
 192 json_array_add(struct json *array_, struct json *element)
 193 {
 194     struct json_array *array = json_array(array_);
 195     if (array->n >= array->n_allocated) {
 196         array->elems = x2nrealloc(array->elems, &array->n_allocated,
 197                                   sizeof *array->elems);
 198     }
 199     array->elems[array->n++] = element;
 200 }
 201
 202 void
 203 json_array_trim(struct json *array_)
 204 {
 205     struct json_array *array = json_array(array_);
 206     if (array->n < array->n_allocated){
 207         array->n_allocated = array->n;
 208         array->elems = xrealloc(array->elems, array->n * sizeof *array->elems);
 209     }
 210 }
 211
 212 struct json *
 213 json_array_create(struct json **elements, size_t n)
 214 {
 215     struct json *json = json_create(JSON_ARRAY);
 216     json->u.array.elems = elements;
 217     json->u.array.n = n;
 218     json->u.array.n_allocated = n;
 219     return json;
 220 }
 221
 222 struct json *
 223 json_array_create_2(struct json *elem0, struct json *elem1)
 224 {
 225     struct json **elems = xmalloc(2 * sizeof *elems);
 226     elems[0] = elem0;
 227     elems[1] = elem1;
 228     return json_array_create(elems, 2);
 229 }
 230
 231 struct json *
 232 json_array_create_3(struct json *elem0, struct json *elem1, struct json *elem2)
 233 {
 234     struct json **elems = xmalloc(3 * sizeof *elems);
 235     elems[0] = elem0;
 236     elems[1] = elem1;
 237     elems[2] = elem2;
 238     return json_array_create(elems, 3);
 239 }
 240
 241 struct json *
 242 json_object_create(void)
 243 {
 244     struct json *json = json_create(JSON_OBJECT);
 245     json->u.object = xmalloc(sizeof *json->u.object);
 246     shash_init(json->u.object);
 247     return json;
 248 }
 249
 250 struct json *
 251 json_integer_create(long long int integer)
 252 {
 253     struct json *json = json_create(JSON_INTEGER);
 254     json->u.integer = integer;
 255     return json;
 256 }
 257
 258 struct json *
 259 json_real_create(double real)
 260 {
 261     struct json *json = json_create(JSON_REAL);
 262     json->u.real = real;
 263     return json;
 264 }
 265
 266 void
 267 json_object_put(struct json *json, const char *name, struct json *value)
 268 {
 269     shash_add(json->u.object, name, value);
 270 }
 271
 272 void
 273 json_object_put_string(struct json *json, const char *name, const char *value)
 274 {
 275     json_object_put(json, name, json_string_create(value));
 276 }
 277
 278 const char *
 279 json_string(const struct json *json)
 280 {
 281     assert(json->type == JSON_STRING);
 282     return json->u.string;
 283 }
 284
 285 struct json_array *
 286 json_array(const struct json *json)
 287 {
 288     assert(json->type == JSON_ARRAY);
 289     return (struct json_array *) &json->u.array;
 290 }
 291
 292 struct shash *
 293 json_object(const struct json *json)
 294 {
 295     assert(json->type == JSON_OBJECT);
 296     return (struct shash *) json->u.object;
 297 }
 298
 299 bool
 300 json_boolean(const struct json *json)
 301 {
 302     assert(json->type == JSON_TRUE || json->type == JSON_FALSE);
 303     return json->type == JSON_TRUE;
 304 }
 305
 306 double
 307 json_real(const struct json *json)
 308 {
 309     assert(json->type == JSON_REAL || json->type == JSON_INTEGER);
 310     return json->type == JSON_REAL ? json->u.real : json->u.integer;
 311 }
 312
 313 int64_t
 314 json_integer(const struct json *json)
 315 {
 316     assert(json->type == JSON_INTEGER);
 317     return json->u.integer;
 318 }
 319 \f
 320 static void json_destroy_object(struct shash *object);
 321 static void json_destroy_array(struct json_array *array);
 322
 323 /* Frees 'json' and everything it points to, recursively. */
 324 void
 325 json_destroy(struct json *json)
 326 {
 327     if (json) {
 328         switch (json->type) {
 329         case JSON_OBJECT:
 330             json_destroy_object(json->u.object);
 331             break;
 332
 333         case JSON_ARRAY:
 334             json_destroy_array(&json->u.array);
 335             break;
 336
 337         case JSON_STRING:
 338             free(json->u.string);
 339             break;
 340
 341         case JSON_NULL:
 342         case JSON_FALSE:
 343         case JSON_TRUE:
 344         case JSON_INTEGER:
 345         case JSON_REAL:
 346             break;
 347
 348         case JSON_N_TYPES:
 349             NOT_REACHED();
 350         }
 351         free(json);
 352     }
 353 }
 354
 355 static void
 356 json_destroy_object(struct shash *object)
 357 {
 358     struct shash_node *node, *next;
 359
 360     SHASH_FOR_EACH_SAFE (node, next, object) {
 361         struct json *value = node->data;
 362
 363         json_destroy(value);
 364         shash_delete(object, node);
 365     }
 366     shash_destroy(object);
 367     free(object);
 368 }
 369
 370 static void
 371 json_destroy_array(struct json_array *array)
 372 {
 373     size_t i;
 374
 375     for (i = 0; i < array->n; i++) {
 376         json_destroy(array->elems[i]);
 377     }
 378     free(array->elems);
 379 }
 380 \f
 381 static struct json *json_clone_object(const struct shash *object);
 382 static struct json *json_clone_array(const struct json_array *array);
 383
 384 /* Returns a deep copy of 'json'. */
 385 struct json *
 386 json_clone(const struct json *json)
 387 {
 388     switch (json->type) {
 389     case JSON_OBJECT:
 390         return json_clone_object(json->u.object);
 391
 392     case JSON_ARRAY:
 393         return json_clone_array(&json->u.array);
 394
 395     case JSON_STRING:
 396         return json_string_create(json->u.string);
 397
 398     case JSON_NULL:
 399     case JSON_FALSE:
 400     case JSON_TRUE:
 401         return json_create(json->type);
 402
 403     case JSON_INTEGER:
 404         return json_integer_create(json->u.integer);
 405
 406     case JSON_REAL:
 407         return json_real_create(json->u.real);
 408
 409     case JSON_N_TYPES:
 410     default:
 411         NOT_REACHED();
 412     }
 413 }
 414
 415 static struct json *
 416 json_clone_object(const struct shash *object)
 417 {
 418     struct shash_node *node;
 419     struct json *json;
 420
 421     json = json_object_create();
 422     SHASH_FOR_EACH (node, object) {
 423         struct json *value = node->data;
 424         json_object_put(json, node->name, json_clone(value));
 425     }
 426     return json;
 427 }
 428
 429 static struct json *
 430 json_clone_array(const struct json_array *array)
 431 {
 432     struct json **elems;
 433     size_t i;
 434
 435     elems = xmalloc(array->n * sizeof *elems);
 436     for (i = 0; i < array->n; i++) {
 437         elems[i] = json_clone(array->elems[i]);
 438     }
 439     return json_array_create(elems, array->n);
 440 }
 441 \f
 442 static size_t
 443 json_hash_object(const struct shash *object, size_t basis)
 444 {
 445     const struct shash_node **nodes;
 446     size_t n, i;
 447
 448     nodes = shash_sort(object);
 449     n = shash_count(object);
 450     for (i = 0; i < n; i++) {
 451         const struct shash_node *node = nodes[i];
 452         basis = hash_string(node->name, basis);
 453         basis = json_hash(node->data, basis);
 454     }
 455     return basis;
 456 }
 457
 458 static size_t
 459 json_hash_array(const struct json_array *array, size_t basis)
 460 {
 461     size_t i;
 462
 463     basis = hash_int(array->n, basis);
 464     for (i = 0; i < array->n; i++) {
 465         basis = json_hash(array->elems[i], basis);
 466     }
 467     return basis;
 468 }
 469
 470 size_t
 471 json_hash(const struct json *json, size_t basis)
 472 {
 473     switch (json->type) {
 474     case JSON_OBJECT:
 475         return json_hash_object(json->u.object, basis);
 476
 477     case JSON_ARRAY:
 478         return json_hash_array(&json->u.array, basis);
 479
 480     case JSON_STRING:
 481         return hash_string(json->u.string, basis);
 482
 483     case JSON_NULL:
 484     case JSON_FALSE:
 485     case JSON_TRUE:
 486         return hash_int(json->type << 8, basis);
 487
 488     case JSON_INTEGER:
 489         return hash_int(json->u.integer, basis);
 490
 491     case JSON_REAL:
 492         return hash_double(json->u.real, basis);
 493
 494     case JSON_N_TYPES:
 495     default:
 496         NOT_REACHED();
 497     }
 498 }
 499
 500 static bool
 501 json_equal_object(const struct shash *a, const struct shash *b)
 502 {
 503     struct shash_node *node;
 504
 505     if (shash_count(a) != shash_count(b)) {
 506         return false;
 507     }
 508
 509     SHASH_FOR_EACH (node, a) {
 510         if (!shash_find(b, node->name)) {
 511             return false;
 512         }
 513     }
 514
 515     return true;
 516 }
 517
 518 static bool
 519 json_equal_array(const struct json_array *a, const struct json_array *b)
 520 {
 521     size_t i;
 522
 523     if (a->n != b->n) {
 524         return false;
 525     }
 526
 527     for (i = 0; i < a->n; i++) {
 528         if (!json_equal(a->elems[i], b->elems[i])) {
 529             return false;
 530         }
 531     }
 532
 533     return true;
 534 }
 535
 536 bool
 537 json_equal(const struct json *a, const struct json *b)
 538 {
 539     if (a->type != b->type) {
 540         return false;
 541     }
 542
 543     switch (a->type) {
 544     case JSON_OBJECT:
 545         return json_equal_object(a->u.object, b->u.object);
 546
 547     case JSON_ARRAY:
 548         return json_equal_array(&a->u.array, &b->u.array);
 549
 550     case JSON_STRING:
 551         return !strcmp(a->u.string, b->u.string);
 552
 553     case JSON_NULL:
 554     case JSON_FALSE:
 555     case JSON_TRUE:
 556         return true;
 557
 558     case JSON_INTEGER:
 559         return a->u.integer == b->u.integer;
 560
 561     case JSON_REAL:
 562         return a->u.real == b->u.real;
 563
 564     case JSON_N_TYPES:
 565     default:
 566         NOT_REACHED();
 567     }
 568 }
 569 \f
 570 /* Lexical analysis. */
 571
 572 static void
 573 json_lex_keyword(struct json_parser *p)
 574 {
 575     struct json_token token;
 576     const char *s;
 577
 578     s = ds_cstr(&p->buffer);
 579     if (!strcmp(s, "false")) {
 580         token.type = T_FALSE;
 581     } else if (!strcmp(s, "true")) {
 582         token.type = T_TRUE;
 583     } else if (!strcmp(s, "null")) {
 584         token.type = T_NULL;
 585     } else {
 586         json_error(p, "invalid keyword '%s'", s);
 587         return;
 588     }
 589     json_parser_input(p, &token);
 590 }
 591
 592 static void
 593 json_lex_number(struct json_parser *p)
 594 {
 595     const char *cp = ds_cstr(&p->buffer);
 596     unsigned long long int significand = 0;
 597     int sig_digits = 0;
 598     bool imprecise = false;
 599     bool negative = false;
 600     int pow10 = 0;
 601
 602     /* Leading minus sign. */
 603     if (*cp == '-') {
 604         negative = true;
 605         cp++;
 606     }
 607
 608     /* At least one integer digit, but 0 may not be used as a leading digit for
 609      * a longer number. */
 610     significand = 0;
 611     sig_digits = 0;
 612     if (*cp == '0') {
 613         cp++;
 614         if (isdigit(*cp)) {
 615             json_error(p, "leading zeros not allowed");
 616             return;
 617         }
 618     } else if (isdigit(*cp)) {
 619         do {
 620             if (significand <= ULLONG_MAX / 10) {
 621                 significand = significand * 10 + (*cp - '0');
 622                 sig_digits++;
 623             } else {
 624                 pow10++;
 625                 if (*cp != '0') {
 626                     imprecise = true;
 627                 }
 628             }
 629             cp++;
 630         } while (isdigit(*cp));
 631     } else {
 632         json_error(p, "'-' must be followed by digit");
 633         return;
 634     }
 635
 636     /* Optional fraction. */
 637     if (*cp == '.') {
 638         cp++;
 639         if (!isdigit(*cp)) {
 640             json_error(p, "decimal point must be followed by digit");
 641             return;
 642         }
 643         do {
 644             if (significand <= ULLONG_MAX / 10) {
 645                 significand = significand * 10 + (*cp - '0');
 646                 sig_digits++;
 647                 pow10--;
 648             } else if (*cp != '0') {
 649                 imprecise = true;
 650             }
 651             cp++;
 652         } while (isdigit(*cp));
 653     }
 654
 655     /* Optional exponent. */
 656     if (*cp == 'e' || *cp == 'E') {
 657         bool negative_exponent = false;
 658         int exponent;
 659
 660         cp++;
 661         if (*cp == '+') {
 662             cp++;
 663         } else if (*cp == '-') {
 664             negative_exponent = true;
 665             cp++;
 666         }
 667
 668         if (!isdigit(*cp)) {
 669             json_error(p, "exponent must contain at least one digit");
 670             return;
 671         }
 672
 673         exponent = 0;
 674         do {
 675             if (exponent >= INT_MAX / 10) {
 676                 json_error(p, "exponent outside valid range");
 677                 return;
 678             }
 679             exponent = exponent * 10 + (*cp - '0');
 680             cp++;
 681         } while (isdigit(*cp));
 682
 683         if (negative_exponent) {
 684             pow10 -= exponent;
 685         } else {
 686             pow10 += exponent;
 687         }
 688     }
 689
 690     if (*cp != '\0') {
 691         json_error(p, "syntax error in number");
 692         return;
 693     }
 694
 695     /* Figure out number.
 696      *
 697      * We suppress negative zeros as a matter of policy. */
 698     if (!significand) {
 699         struct json_token token;
 700         token.type = T_INTEGER;
 701         token.u.integer = 0;
 702         json_parser_input(p, &token);
 703         return;
 704     }
 705
 706     if (!imprecise) {
 707         while (pow10 > 0 && significand < ULLONG_MAX / 10) {
 708             significand *= 10;
 709             sig_digits++;
 710             pow10--;
 711         }
 712         while (pow10 < 0 && significand % 10 == 0) {
 713             significand /= 10;
 714             sig_digits--;
 715             pow10++;
 716         }
 717         if (pow10 == 0
 718             && significand <= (negative
 719                                ? (unsigned long long int) LLONG_MAX + 1
 720                                : LLONG_MAX)) {
 721             struct json_token token;
 722             token.type = T_INTEGER;
 723             token.u.integer = negative ? -significand : significand;
 724             json_parser_input(p, &token);
 725             return;
 726         }
 727     }
 728
 729     if (pow10 + sig_digits <= DBL_MAX_10_EXP) {
 730         struct json_token token;
 731         token.type = T_REAL;
 732         token.u.real = significand * pow(10.0, pow10);
 733         if (token.u.real <= DBL_MAX) {
 734             if (negative && token.u.real) {
 735                 token.u.real = -token.u.real;
 736             }
 737             json_parser_input(p, &token);
 738             return;
 739         }
 740     }
 741     json_error(p, "number outside valid range");
 742 }
 743
 744 static bool
 745 json_lex_4hex(struct json_parser *p, const char *cp, int *valuep)
 746 {
 747     int value, i;
 748
 749     value = 0;
 750     for (i = 0; i < 4; i++) {
 751         unsigned char c = *cp++;
 752         if (!isxdigit(c)) {
 753             json_error(p, "malformed \\u escape");
 754             return false;
 755         }
 756         value = (value << 4) | hexit_value(c);
 757     }
 758     if (!value) {
 759         json_error(p, "null bytes not supported in quoted strings");
 760         return false;
 761     }
 762     *valuep = value;
 763     return true;
 764 }
 765
 766 static const char *
 767 json_lex_unicode(struct json_parser *p, const char *cp, struct ds *s)
 768 {
 769     int c0, c1;
 770
 771     if (!json_lex_4hex(p, cp, &c0)) {
 772         return NULL;
 773     }
 774     cp += 4;
 775     if (!uc_is_leading_surrogate(c0)) {
 776         ds_put_utf8(s, c0);
 777         return cp;
 778     }
 779
 780     if (*cp++ != '\\' || *cp++ != 'u') {
 781         json_error(p, "malformed escaped surrogate pair");
 782         return NULL;
 783     }
 784
 785     if (!json_lex_4hex(p, cp, &c1)) {
 786         return NULL;
 787     }
 788     cp += 4;
 789     if (!uc_is_trailing_surrogate(c1)) {
 790         json_error(p, "second half of escaped surrogate pair is not "
 791                    "trailing surrogate");
 792         return NULL;
 793     }
 794
 795     ds_put_utf8(s, utf16_decode_surrogate_pair(c0, c1));
 796     return cp;
 797 }
 798
 799 static void
 800 json_lex_string(struct json_parser *p)
 801 {
 802     struct json_token token;
 803     const char *cp;
 804     struct ds s;
 805
 806     cp = ds_cstr(&p->buffer);
 807     if (!strchr(cp, '\\')) {
 808         token.type = T_STRING;
 809         token.u.string = cp;
 810         json_parser_input(p, &token);
 811         return;
 812     }
 813
 814     ds_init(&s);
 815     ds_reserve(&s, strlen(cp));
 816     while (*cp != '\0') {
 817         if (*cp != '\\') {
 818             ds_put_char(&s, *cp++);
 819             continue;
 820         }
 821
 822         cp++;
 823         switch (*cp++) {
 824         case '"': case '\\': case '/':
 825             ds_put_char(&s, cp[-1]);
 826             break;
 827
 828         case 'b':
 829             ds_put_char(&s, '\b');
 830             break;
 831
 832         case 'f':
 833             ds_put_char(&s, '\f');
 834             break;
 835
 836         case 'n':
 837             ds_put_char(&s, '\n');
 838             break;
 839
 840         case 'r':
 841             ds_put_char(&s, '\r');
 842             break;
 843
 844         case 't':
 845             ds_put_char(&s, '\t');
 846             break;
 847
 848         case 'u':
 849             cp = json_lex_unicode(p, cp, &s);
 850             if (!cp) {
 851                 goto exit;
 852             }
 853             break;
 854
 855         default:
 856             json_error(p, "bad escape \\%c", cp[-1]);
 857             goto exit;
 858         }
 859     }
 860
 861     token.type = T_STRING;
 862     token.u.string = ds_cstr(&s);
 863     json_parser_input(p, &token);
 864
 865 exit:
 866     ds_destroy(&s);
 867     return;
 868 }
 869
 870 static bool
 871 json_lex_input(struct json_parser *p, int c)
 872 {
 873     struct json_token token;
 874
 875     switch (p->lex_state) {
 876     case JSON_LEX_START:
 877         switch (c) {
 878         case ' ': case '\t': case '\n': case '\r':
 879             /* Nothing to do. */
 880             return true;
 881
 882         case 'a': case 'b': case 'c': case 'd': case 'e':
 883         case 'f': case 'g': case 'h': case 'i': case 'j':
 884         case 'k': case 'l': case 'm': case 'n': case 'o':
 885         case 'p': case 'q': case 'r': case 's': case 't':
 886         case 'u': case 'v': case 'w': case 'x': case 'y':
 887         case 'z':
 888             p->lex_state = JSON_LEX_KEYWORD;
 889             break;
 890
 891         case '[': case '{': case ']': case '}': case ':': case ',':
 892             token.type = c;
 893             json_parser_input(p, &token);
 894             return true;
 895
 896         case '-':
 897         case '0': case '1': case '2': case '3': case '4':
 898         case '5': case '6': case '7': case '8': case '9':
 899             p->lex_state = JSON_LEX_NUMBER;
 900             break;
 901
 902         case '"':
 903             p->lex_state = JSON_LEX_STRING;
 904             return true;
 905
 906         default:
 907             if (isprint(c)) {
 908                 json_error(p, "invalid character '%c'", c);
 909             } else {
 910                 json_error(p, "invalid character U+%04x", c);
 911             }
 912             return true;
 913         }
 914         break;
 915
 916     case JSON_LEX_KEYWORD:
 917         if (!isalpha((unsigned char) c)) {
 918             json_lex_keyword(p);
 919             return false;
 920         }
 921         break;
 922
 923     case JSON_LEX_NUMBER:
 924         if (!strchr(".0123456789eE-+", c)) {
 925             json_lex_number(p);
 926             return false;
 927         }
 928         break;
 929
 930     case JSON_LEX_STRING:
 931         if (c == '\\') {
 932             p->lex_state = JSON_LEX_ESCAPE;
 933         } else if (c == '"') {
 934             json_lex_string(p);
 935             return true;
 936         } else if (c < 0x20) {
 937             json_error(p, "U+%04X must be escaped in quoted string", c);
 938             return true;
 939         }
 940         break;
 941
 942     case JSON_LEX_ESCAPE:
 943         p->lex_state = JSON_LEX_STRING;
 944         break;
 945
 946     default:
 947         abort();
 948     }
 949     ds_put_char(&p->buffer, c);
 950     return true;
 951 }
 952 \f
 953 /* Parsing. */
 954
 955 /* Parses 'string' as a JSON object or array and returns a newly allocated
 956  * 'struct json'.  The caller must free the returned structure with
 957  * json_destroy() when it is no longer needed.
 958  *
 959  * 'string' must be encoded in UTF-8.
 960  *
 961  * If 'string' is valid JSON, then the returned 'struct json' will be either an
 962  * object (JSON_OBJECT) or an array (JSON_ARRAY).
 963  *
 964  * If 'string' is not valid JSON, then the returned 'struct json' will be a
 965  * string (JSON_STRING) that describes the particular error encountered during
 966  * parsing.  (This is an acceptable means of error reporting because at its top
 967  * level JSON must be either an object or an array; a bare string is not
 968  * valid.) */
 969 struct json *
 970 json_from_string(const char *string)
 971 {
 972     struct json_parser *p = json_parser_create(JSPF_TRAILER);
 973     json_parser_feed(p, string, strlen(string));
 974     return json_parser_finish(p);
 975 }
 976
 977 /* Reads the file named 'file_name', parses its contents as a JSON object or
 978  * array, and returns a newly allocated 'struct json'.  The caller must free
 979  * the returned structure with json_destroy() when it is no longer needed.
 980  *
 981  * The file must be encoded in UTF-8.
 982  *
 983  * See json_from_string() for return value semantics.
 984  */
 985 struct json *
 986 json_from_file(const char *file_name)
 987 {
 988     struct json_parser *p;
 989     struct json *json;
 990     FILE *stream;
 991
 992     /* Open file. */
 993     stream = fopen(file_name, "r");
 994     if (!stream) {
 995         return json_string_create_nocopy(
 996             xasprintf("error opening \"%s\": %s", file_name, strerror(errno)));
 997     }
 998
 999     /* Read and parse file. */
1000     p = json_parser_create(JSPF_TRAILER);
1001     for (;;) {
1002         char buffer[BUFSIZ];
1003         size_t n;
1004
1005         n = fread(buffer, 1, sizeof buffer, stream);
1006         if (!n || json_parser_feed(p, buffer, n) != n) {
1007             break;
1008         }
1009     }
1010     json = json_parser_finish(p);
1011
1012     /* Close file and check for I/O errors. */
1013     if (ferror(stream)) {
1014         json_destroy(json);
1015         json = json_string_create_nocopy(
1016             xasprintf("error reading \"%s\": %s", file_name, strerror(errno)));
1017     }
1018     fclose(stream);
1019
1020     return json;
1021 }
1022
1023 struct json_parser *
1024 json_parser_create(int flags)
1025 {
1026     struct json_parser *p = xzalloc(sizeof *p);
1027     p->flags = flags;
1028     return p;
1029 }
1030
1031 size_t
1032 json_parser_feed(struct json_parser *p, const char *input, size_t n)
1033 {
1034     size_t i;
1035     for (i = 0; !p->done && i < n; ) {
1036         if (json_lex_input(p, input[i])) {
1037             i++;
1038         }
1039     }
1040     return i;
1041 }
1042
1043 bool
1044 json_parser_is_done(const struct json_parser *p)
1045 {
1046     return p->done;
1047 }
1048
1049 struct json *
1050 json_parser_finish(struct json_parser *p)
1051 {
1052     struct json *json;
1053
1054     switch (p->lex_state) {
1055     case JSON_LEX_START:
1056         break;
1057
1058     case JSON_LEX_STRING:
1059     case JSON_LEX_ESCAPE:
1060         json_error(p, "unexpected end of input in quoted string");
1061         break;
1062
1063     case JSON_LEX_NUMBER:
1064     case JSON_LEX_KEYWORD:
1065         json_lex_input(p, ' ');
1066         break;
1067     }
1068
1069     if (p->parse_state == JSON_PARSE_START) {
1070         json_error(p, "empty input stream");
1071     } else if (p->parse_state != JSON_PARSE_END) {
1072         json_error(p, "unexpected end of input");
1073     }
1074
1075     if (!p->error) {
1076         assert(p->height == 1);
1077         assert(p->stack[0].json != NULL);
1078         json = p->stack[--p->height].json;
1079     } else {
1080         json = json_string_create_nocopy(p->error);
1081         p->error = NULL;
1082     }
1083
1084     json_parser_abort(p);
1085
1086     return json;
1087 }
1088
1089 void
1090 json_parser_abort(struct json_parser *p)
1091 {
1092     if (p) {
1093         ds_destroy(&p->buffer);
1094         if (p->height) {
1095             json_destroy(p->stack[0].json);
1096         }
1097         free(p->stack);
1098         free(p->member_name);
1099         free(p->error);
1100         free(p);
1101     }
1102 }
1103
1104 static struct json_parser_node *
1105 json_parser_top(struct json_parser *p)
1106 {
1107     return &p->stack[p->height - 1];
1108 }
1109
1110 static void
1111 json_parser_put_value(struct json_parser *p, struct json *value)
1112 {
1113     struct json_parser_node *node = json_parser_top(p);
1114     if (node->json->type == JSON_OBJECT) {
1115         json_object_put(node->json, p->member_name, value);
1116         free(p->member_name);
1117         p->member_name = NULL;
1118     } else if (node->json->type == JSON_ARRAY) {
1119         json_array_add(node->json, value);
1120     } else {
1121         NOT_REACHED();
1122     }
1123 }
1124
1125 static struct json_parser_node *
1126 json_parser_push(struct json_parser *p,
1127                  struct json *new_json, enum json_parse_state new_state)
1128 {
1129     if (p->height < JSON_MAX_HEIGHT) {
1130         struct json_parser_node *node;
1131
1132         if (p->height >= p->allocated_height) {
1133             p->stack = x2nrealloc(p->stack, &p->allocated_height,
1134                                   sizeof *p->stack);
1135         }
1136
1137         if (p->height > 0) {
1138             json_parser_put_value(p, new_json);
1139         }
1140
1141         node = &p->stack[p->height++];
1142         node->json = new_json;
1143         p->parse_state = new_state;
1144         return node;
1145     } else {
1146         json_error(p, "input exceeds maximum nesting depth %d",
1147                    JSON_MAX_HEIGHT);
1148         return NULL;
1149     }
1150 }
1151
1152 static void
1153 json_parser_push_object(struct json_parser *p)
1154 {
1155     json_parser_push(p, json_object_create(), JSON_PARSE_OBJECT_INIT);
1156 }
1157
1158 static void
1159 json_parser_push_array(struct json_parser *p)
1160 {
1161     json_parser_push(p, json_array_create_empty(), JSON_PARSE_ARRAY_INIT);
1162 }
1163
1164 static void
1165 json_parse_value(struct json_parser *p, struct json_token *token,
1166                  enum json_parse_state next_state)
1167 {
1168     struct json *value;
1169
1170     switch (token->type) {
1171     case T_FALSE:
1172         value = json_boolean_create(false);
1173         break;
1174
1175     case T_NULL:
1176         value = json_null_create();
1177         break;
1178
1179     case T_TRUE:
1180         value = json_boolean_create(true);
1181         break;
1182
1183     case '{':
1184         json_parser_push_object(p);
1185         return;
1186
1187     case '[':
1188         json_parser_push_array(p);
1189         return;
1190
1191     case T_INTEGER:
1192         value = json_integer_create(token->u.integer);
1193         break;
1194
1195     case T_REAL:
1196         value = json_real_create(token->u.real);
1197         break;
1198
1199     case T_STRING:
1200         value = json_string_create(token->u.string);
1201         break;
1202
1203     case T_EOF:
1204     case '}':
1205     case ']':
1206     case ':':
1207     case ',':
1208     default:
1209         json_error(p, "syntax error expecting value");
1210         return;
1211     }
1212
1213     json_parser_put_value(p, value);
1214     p->parse_state = next_state;
1215 }
1216
1217 static void
1218 json_parser_pop(struct json_parser *p)
1219 {
1220     struct json_parser_node *node;
1221
1222     /* Conserve memory. */
1223     node = json_parser_top(p);
1224     if (node->json->type == JSON_ARRAY) {
1225         json_array_trim(node->json);
1226     }
1227
1228     /* Pop off the top-of-stack. */
1229     if (p->height == 1) {
1230         p->parse_state = JSON_PARSE_END;
1231         if (!(p->flags & JSPF_TRAILER)) {
1232             p->done = true;
1233         }
1234     } else {
1235         p->height--;
1236         node = json_parser_top(p);
1237         if (node->json->type == JSON_ARRAY) {
1238             p->parse_state = JSON_PARSE_ARRAY_NEXT;
1239         } else if (node->json->type == JSON_OBJECT) {
1240             p->parse_state = JSON_PARSE_OBJECT_NEXT;
1241         } else {
1242             NOT_REACHED();
1243         }
1244     }
1245 }
1246
1247 static void
1248 json_parser_input(struct json_parser *p, struct json_token *token)
1249 {
1250     switch (p->parse_state) {
1251     case JSON_PARSE_START:
1252         if (token->type == '{') {
1253             json_parser_push_object(p);
1254         } else if (token->type == '[') {
1255             json_parser_push_array(p);
1256         } else {
1257             json_error(p, "syntax error at beginning of input");
1258         }
1259         break;
1260
1261     case JSON_PARSE_END:
1262         json_error(p, "trailing garbage at end of input");
1263         break;
1264
1265     case JSON_PARSE_OBJECT_INIT:
1266         if (token->type == '}') {
1267             json_parser_pop(p);
1268             break;
1269         }
1270         /* Fall through. */
1271     case JSON_PARSE_OBJECT_NAME:
1272         if (token->type == T_STRING) {
1273             p->member_name = xstrdup(token->u.string);
1274             p->parse_state = JSON_PARSE_OBJECT_COLON;
1275         } else {
1276             json_error(p, "syntax error parsing object expecting string");
1277         }
1278         break;
1279
1280     case JSON_PARSE_OBJECT_COLON:
1281         if (token->type == ':') {
1282             p->parse_state = JSON_PARSE_OBJECT_VALUE;
1283         } else {
1284             json_error(p, "syntax error parsing object expecting ':'");
1285         }
1286         break;
1287
1288     case JSON_PARSE_OBJECT_VALUE:
1289         json_parse_value(p, token, JSON_PARSE_OBJECT_NEXT);
1290         break;
1291
1292     case JSON_PARSE_OBJECT_NEXT:
1293         if (token->type == ',') {
1294             p->parse_state = JSON_PARSE_OBJECT_NAME;
1295         } else if (token->type == '}') {
1296             json_parser_pop(p);
1297         } else {
1298             json_error(p, "syntax error expecting '}' or ','");
1299         }
1300         break;
1301
1302     case JSON_PARSE_ARRAY_INIT:
1303         if (token->type == ']') {
1304             json_parser_pop(p);
1305             break;
1306         }
1307         /* Fall through. */
1308     case JSON_PARSE_ARRAY_VALUE:
1309         json_parse_value(p, token, JSON_PARSE_ARRAY_NEXT);
1310         break;
1311
1312     case JSON_PARSE_ARRAY_NEXT:
1313         if (token->type == ',') {
1314             p->parse_state = JSON_PARSE_ARRAY_VALUE;
1315         } else if (token->type == ']') {
1316             json_parser_pop(p);
1317         } else {
1318             json_error(p, "syntax error expecting ']' or ','");
1319         }
1320         break;
1321
1322     default:
1323         abort();
1324     }
1325
1326     p->lex_state = JSON_LEX_START;
1327     ds_clear(&p->buffer);
1328 }
1329
1330 static struct json *
1331 json_create(enum json_type type)
1332 {
1333     struct json *json = xmalloc(sizeof *json);
1334     json->type = type;
1335     return json;
1336 }
1337
1338 static void
1339 json_error(struct json_parser *p, const char *format, ...)
1340 {
1341     if (!p->error) {
1342         va_list args;
1343
1344         va_start(args, format);
1345         p->error = xvasprintf(format, args);
1346         va_end(args);
1347
1348         p->done = true;
1349     }
1350 }
1351 \f
1352 #define SPACES_PER_LEVEL 2
1353
1354 struct json_serializer {
1355     struct ds ds;
1356     int depth;
1357     int flags;
1358 };
1359
1360 static void json_to_ds(const struct json *, struct json_serializer *);
1361 static void json_object_to_ds(const struct shash *object,
1362                               struct json_serializer *);
1363 static void json_array_to_ds(const struct json_array *,
1364                              struct json_serializer *);
1365 static void json_string_to_ds(const char *string, struct ds *);
1366
1367 /* Converts 'json' to a string in JSON format, encoded in UTF-8, and returns
1368  * that string.  The caller is responsible for freeing the returned string,
1369  * with free(), when it is no longer needed.
1370  *
1371  * If 'flags' contains JSSF_PRETTY, the output is pretty-printed with each
1372  * nesting level introducing an additional indentation.  Otherwise, the
1373  * returned string does not contain any new-line characters.
1374  *
1375  * If 'flags' contains JSSF_SORT, members of objects in the output are sorted
1376  * in bytewise lexicographic order for reproducibility.  Otherwise, members of
1377  * objects are output in an indeterminate order.
1378  *
1379  * The returned string is valid JSON only if 'json' represents an array or an
1380  * object, since a bare literal does not satisfy the JSON grammar. */
1381 char *
1382 json_to_string(const struct json *json, int flags)
1383 {
1384     struct json_serializer s;
1385     ds_init(&s.ds);
1386     s.depth = 0;
1387     s.flags = flags;
1388     json_to_ds(json, &s);
1389     return ds_steal_cstr(&s.ds);
1390 }
1391
1392 static void
1393 json_to_ds(const struct json *json, struct json_serializer *s)
1394 {
1395     struct ds *ds = &s->ds;
1396
1397     switch (json->type) {
1398     case JSON_NULL:
1399         ds_put_cstr(ds, "null");
1400         break;
1401
1402     case JSON_FALSE:
1403         ds_put_cstr(ds, "false");
1404         break;
1405
1406     case JSON_TRUE:
1407         ds_put_cstr(ds, "true");
1408         break;
1409
1410     case JSON_OBJECT:
1411         json_object_to_ds(json->u.object, s);
1412         break;
1413
1414     case JSON_ARRAY:
1415         json_array_to_ds(&json->u.array, s);
1416         break;
1417
1418     case JSON_INTEGER:
1419         ds_put_format(ds, "%lld", json->u.integer);
1420         break;
1421
1422     case JSON_REAL:
1423         ds_put_format(ds, "%.*g", DBL_DIG, json->u.real);
1424         break;
1425
1426     case JSON_STRING:
1427         json_string_to_ds(json->u.string, ds);
1428         break;
1429
1430     case JSON_N_TYPES:
1431     default:
1432         NOT_REACHED();
1433     }
1434 }
1435
1436 static void
1437 indent_line(struct json_serializer *s)
1438 {
1439     if (s->flags & JSSF_PRETTY) {
1440         ds_put_char(&s->ds, '\n');
1441         ds_put_char_multiple(&s->ds, ' ', SPACES_PER_LEVEL * s->depth);
1442     }
1443 }
1444
1445 static void
1446 json_object_member_to_ds(size_t i, const struct shash_node *node,
1447                          struct json_serializer *s)
1448 {
1449     struct ds *ds = &s->ds;
1450
1451     if (i) {
1452         ds_put_char(ds, ',');
1453         indent_line(s);
1454     }
1455
1456     json_string_to_ds(node->name, ds);
1457     ds_put_char(ds, ':');
1458     if (s->flags & JSSF_PRETTY) {
1459         ds_put_char(ds, ' ');
1460     }
1461     json_to_ds(node->data, s);
1462 }
1463
1464 static void
1465 json_object_to_ds(const struct shash *object, struct json_serializer *s)
1466 {
1467     struct ds *ds = &s->ds;
1468
1469     ds_put_char(ds, '{');
1470
1471     s->depth++;
1472     indent_line(s);
1473
1474     if (s->flags & JSSF_SORT) {
1475         const struct shash_node **nodes;
1476         size_t n, i;
1477
1478         nodes = shash_sort(object);
1479         n = shash_count(object);
1480         for (i = 0; i < n; i++) {
1481             json_object_member_to_ds(i, nodes[i], s);
1482         }
1483         free(nodes);
1484     } else {
1485         struct shash_node *node;
1486         size_t i;
1487
1488         i = 0;
1489         SHASH_FOR_EACH (node, object) {
1490             json_object_member_to_ds(i++, node, s);
1491         }
1492     }
1493
1494     ds_put_char(ds, '}');
1495     s->depth--;
1496 }
1497
1498 static void
1499 json_array_to_ds(const struct json_array *array, struct json_serializer *s)
1500 {
1501     struct ds *ds = &s->ds;
1502     size_t i;
1503
1504     ds_put_char(ds, '[');
1505     s->depth++;
1506
1507     if (array->n > 0) {
1508         indent_line(s);
1509
1510         for (i = 0; i < array->n; i++) {
1511             if (i) {
1512                 ds_put_char(ds, ',');
1513                 indent_line(s);
1514             }
1515             json_to_ds(array->elems[i], s);
1516         }
1517     }
1518
1519     s->depth--;
1520     ds_put_char(ds, ']');
1521 }
1522
1523 static void
1524 json_string_to_ds(const char *string, struct ds *ds)
1525 {
1526     uint8_t c;
1527
1528     ds_put_char(ds, '"');
1529     while ((c = *string++) != '\0') {
1530         switch (c) {
1531         case '"':
1532             ds_put_cstr(ds, "\\\"");
1533             break;
1534
1535         case '\\':
1536             ds_put_cstr(ds, "\\\\");
1537             break;
1538
1539         case '\b':
1540             ds_put_cstr(ds, "\\b");
1541             break;
1542
1543         case '\f':
1544             ds_put_cstr(ds, "\\f");
1545             break;
1546
1547         case '\n':
1548             ds_put_cstr(ds, "\\n");
1549             break;
1550
1551         case '\r':
1552             ds_put_cstr(ds, "\\r");
1553             break;
1554
1555         case '\t':
1556             ds_put_cstr(ds, "\\t");
1557             break;
1558
1559         default:
1560             if (c >= 32) {
1561                 ds_put_char(ds, c);
1562             } else {
1563                 ds_put_format(ds, "\\u%04x", c);
1564             }
1565             break;
1566         }
1567     }
1568     ds_put_char(ds, '"');
1569 }