lib/json_writer.c

   1 /* SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause) */
   2 /*
   3  * Simple streaming JSON writer
   4  *
   5  * This takes care of the annoying bits of JSON syntax like the commas
   6  * after elements
   7  *
   8  * Authors:     Stephen Hemminger <stephen@networkplumber.org>
   9  */
  10
  11 #include <stdio.h>
  12 #include <stdbool.h>
  13 #include <stdarg.h>
  14 #include <assert.h>
  15 #include <malloc.h>
  16 #include <inttypes.h>
  17 #include <stdint.h>
  18
  19 #include "json_writer.h"
  20
  21 struct json_writer {
  22         FILE            *out;   /* output file */
  23         unsigned        depth;  /* nesting */
  24         bool            pretty; /* optional whitepace */
  25         char            sep;    /* either nul or comma */
  26 };
  27
  28 /* indentation for pretty print */
  29 static void jsonw_indent(json_writer_t *self)
  30 {
  31         unsigned i;
  32         for (i = 0; i < self->depth; ++i)
  33                 fputs("    ", self->out);
  34 }
  35
  36 /* end current line and indent if pretty printing */
  37 static void jsonw_eol(json_writer_t *self)
  38 {
  39         if (!self->pretty)
  40                 return;
  41
  42         putc('\n', self->out);
  43         jsonw_indent(self);
  44 }
  45
  46 /* If current object is not empty print a comma */
  47 static void jsonw_eor(json_writer_t *self)
  48 {
  49         if (self->sep != '\0')
  50                 putc(self->sep, self->out);
  51         self->sep = ',';
  52 }
  53
  54
  55 /* Output JSON encoded string */
  56 /* Handles C escapes, does not do Unicode */
  57 static void jsonw_puts(json_writer_t *self, const char *str)
  58 {
  59         putc('"', self->out);
  60         for (; *str; ++str)
  61                 switch (*str) {
  62                 case '\t':
  63                         fputs("\\t", self->out);
  64                         break;
  65                 case '\n':
  66                         fputs("\\n", self->out);
  67                         break;
  68                 case '\r':
  69                         fputs("\\r", self->out);
  70                         break;
  71                 case '\f':
  72                         fputs("\\f", self->out);
  73                         break;
  74                 case '\b':
  75                         fputs("\\b", self->out);
  76                         break;
  77                 case '\\':
  78                         fputs("\\n", self->out);
  79                         break;
  80                 case '"':
  81                         fputs("\\\"", self->out);
  82                         break;
  83                 case '\'':
  84                         fputs("\\\'", self->out);
  85                         break;
  86                 default:
  87                         putc(*str, self->out);
  88                 }
  89         putc('"', self->out);
  90 }
  91
  92 /* Create a new JSON stream */
  93 json_writer_t *jsonw_new(FILE *f)
  94 {
  95         json_writer_t *self = malloc(sizeof(*self));
  96         if (self) {
  97                 self->out = f;
  98                 self->depth = 0;
  99                 self->pretty = false;
 100                 self->sep = '\0';
 101         }
 102         return self;
 103 }
 104
 105 /* End output to JSON stream */
 106 void jsonw_destroy(json_writer_t **self_p)
 107 {
 108         json_writer_t *self = *self_p;
 109
 110         assert(self->depth == 0);
 111         fputs("\n", self->out);
 112         fflush(self->out);
 113         free(self);
 114         *self_p = NULL;
 115 }
 116
 117 void jsonw_pretty(json_writer_t *self, bool on)
 118 {
 119         self->pretty = on;
 120 }
 121
 122 /* Basic blocks */
 123 static void jsonw_begin(json_writer_t *self, int c)
 124 {
 125         jsonw_eor(self);
 126         putc(c, self->out);
 127         ++self->depth;
 128         self->sep = '\0';
 129 }
 130
 131 static void jsonw_end(json_writer_t *self, int c)
 132 {
 133         assert(self->depth > 0);
 134
 135         --self->depth;
 136         if (self->sep != '\0')
 137                 jsonw_eol(self);
 138         putc(c, self->out);
 139         self->sep = ',';
 140 }
 141
 142
 143 /* Add a JSON property name */
 144 void jsonw_name(json_writer_t *self, const char *name)
 145 {
 146         jsonw_eor(self);
 147         jsonw_eol(self);
 148         self->sep = '\0';
 149         jsonw_puts(self, name);
 150         putc(':', self->out);
 151         if (self->pretty)
 152                 putc(' ', self->out);
 153 }
 154
 155 __attribute__((format(printf, 2, 3)))
 156 void jsonw_printf(json_writer_t *self, const char *fmt, ...)
 157 {
 158         va_list ap;
 159
 160         va_start(ap, fmt);
 161         jsonw_eor(self);
 162         vfprintf(self->out, fmt, ap);
 163         va_end(ap);
 164 }
 165
 166 /* Collections */
 167 void jsonw_start_object(json_writer_t *self)
 168 {
 169         jsonw_begin(self, '{');
 170 }
 171
 172 void jsonw_end_object(json_writer_t *self)
 173 {
 174         jsonw_end(self, '}');
 175 }
 176
 177 void jsonw_start_array(json_writer_t *self)
 178 {
 179         jsonw_begin(self, '[');
 180         if (self->pretty)
 181                 putc(' ', self->out);
 182 }
 183
 184 void jsonw_end_array(json_writer_t *self)
 185 {
 186         if (self->pretty && self->sep)
 187                 putc(' ', self->out);
 188         self->sep = '\0';
 189         jsonw_end(self, ']');
 190 }
 191
 192 /* JSON value types */
 193 void jsonw_string(json_writer_t *self, const char *value)
 194 {
 195         jsonw_eor(self);
 196         jsonw_puts(self, value);
 197 }
 198
 199 void jsonw_bool(json_writer_t *self, bool val)
 200 {
 201         jsonw_printf(self, "%s", val ? "true" : "false");
 202 }
 203
 204 void jsonw_null(json_writer_t *self)
 205 {
 206         jsonw_printf(self, "null");
 207 }
 208
 209 void jsonw_float(json_writer_t *self, double num)
 210 {
 211         jsonw_printf(self, "%g", num);
 212 }
 213
 214 void jsonw_hu(json_writer_t *self, unsigned short num)
 215 {
 216         jsonw_printf(self, "%hu", num);
 217 }
 218
 219 void jsonw_uint(json_writer_t *self, unsigned int num)
 220 {
 221         jsonw_printf(self, "%u", num);
 222 }
 223
 224 void jsonw_u64(json_writer_t *self, uint64_t num)
 225 {
 226         jsonw_printf(self, "%"PRIu64, num);
 227 }
 228
 229 void jsonw_xint(json_writer_t *self, uint64_t num)
 230 {
 231         jsonw_printf(self, "%"PRIx64, num);
 232 }
 233
 234 void jsonw_luint(json_writer_t *self, unsigned long num)
 235 {
 236         jsonw_printf(self, "%lu", num);
 237 }
 238
 239 void jsonw_lluint(json_writer_t *self, unsigned long long num)
 240 {
 241         jsonw_printf(self, "%llu", num);
 242 }
 243
 244 void jsonw_int(json_writer_t *self, int num)
 245 {
 246         jsonw_printf(self, "%d", num);
 247 }
 248
 249 void jsonw_s64(json_writer_t *self, int64_t num)
 250 {
 251         jsonw_printf(self, "%"PRId64, num);
 252 }
 253
 254 /* Basic name/value objects */
 255 void jsonw_string_field(json_writer_t *self, const char *prop, const char *val)
 256 {
 257         jsonw_name(self, prop);
 258         jsonw_string(self, val);
 259 }
 260
 261 void jsonw_bool_field(json_writer_t *self, const char *prop, bool val)
 262 {
 263         jsonw_name(self, prop);
 264         jsonw_bool(self, val);
 265 }
 266
 267 void jsonw_float_field(json_writer_t *self, const char *prop, double val)
 268 {
 269         jsonw_name(self, prop);
 270         jsonw_float(self, val);
 271 }
 272
 273 void jsonw_uint_field(json_writer_t *self, const char *prop, unsigned int num)
 274 {
 275         jsonw_name(self, prop);
 276         jsonw_uint(self, num);
 277 }
 278
 279 void jsonw_u64_field(json_writer_t *self, const char *prop, uint64_t num)
 280 {
 281         jsonw_name(self, prop);
 282         jsonw_u64(self, num);
 283 }
 284
 285 void jsonw_xint_field(json_writer_t *self, const char *prop, uint64_t num)
 286 {
 287         jsonw_name(self, prop);
 288         jsonw_xint(self, num);
 289 }
 290
 291 void jsonw_hu_field(json_writer_t *self, const char *prop, unsigned short num)
 292 {
 293         jsonw_name(self, prop);
 294         jsonw_hu(self, num);
 295 }
 296
 297 void jsonw_luint_field(json_writer_t *self,
 298                         const char *prop,
 299                         unsigned long num)
 300 {
 301         jsonw_name(self, prop);
 302         jsonw_luint(self, num);
 303 }
 304
 305 void jsonw_lluint_field(json_writer_t *self,
 306                         const char *prop,
 307                         unsigned long long num)
 308 {
 309         jsonw_name(self, prop);
 310         jsonw_lluint(self, num);
 311 }
 312
 313 void jsonw_int_field(json_writer_t *self, const char *prop, int num)
 314 {
 315         jsonw_name(self, prop);
 316         jsonw_int(self, num);
 317 }
 318
 319 void jsonw_s64_field(json_writer_t *self, const char *prop, int64_t num)
 320 {
 321         jsonw_name(self, prop);
 322         jsonw_s64(self, num);
 323 }
 324
 325 void jsonw_null_field(json_writer_t *self, const char *prop)
 326 {
 327         jsonw_name(self, prop);
 328         jsonw_null(self);
 329 }
 330
 331 #ifdef TEST
 332 int main(int argc, char **argv)
 333 {
 334         json_writer_t *wr = jsonw_new(stdout);
 335
 336         jsonw_start_object(wr);
 337         jsonw_pretty(wr, true);
 338         jsonw_name(wr, "Vyatta");
 339         jsonw_start_object(wr);
 340         jsonw_string_field(wr, "url", "http://vyatta.com");
 341         jsonw_uint_field(wr, "downloads", 2000000ul);
 342         jsonw_float_field(wr, "stock", 8.16);
 343
 344         jsonw_name(wr, "ARGV");
 345         jsonw_start_array(wr);
 346         while (--argc)
 347                 jsonw_string(wr, *++argv);
 348         jsonw_end_array(wr);
 349
 350         jsonw_name(wr, "empty");
 351         jsonw_start_array(wr);
 352         jsonw_end_array(wr);
 353
 354         jsonw_name(wr, "NIL");
 355         jsonw_start_object(wr);
 356         jsonw_end_object(wr);
 357
 358         jsonw_null_field(wr, "my_null");
 359
 360         jsonw_name(wr, "special chars");
 361         jsonw_start_array(wr);
 362         jsonw_string_field(wr, "slash", "/");
 363         jsonw_string_field(wr, "newline", "\n");
 364         jsonw_string_field(wr, "tab", "\t");
 365         jsonw_string_field(wr, "ff", "\f");
 366         jsonw_string_field(wr, "quote", "\"");
 367         jsonw_string_field(wr, "tick", "\'");
 368         jsonw_string_field(wr, "backslash", "\\");
 369         jsonw_end_array(wr);
 370
 371         jsonw_end_object(wr);
 372
 373         jsonw_end_object(wr);
 374         jsonw_destroy(&wr);
 375         return 0;
 376 }
 377
 378 #endif