lib/json_writer.c

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