1 // SPDX-License-Identifier: (GPL-2.0-or-later 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 */
jsonw_indent(json_writer_t * self)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 */
jsonw_eol(json_writer_t * self)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 */
jsonw_eor(json_writer_t * self)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 */
jsonw_puts(json_writer_t * self,const char * str)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 */
jsonw_new(FILE * f)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 */
jsonw_destroy(json_writer_t ** self_p)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 
jsonw_pretty(json_writer_t * self,bool on)117 void jsonw_pretty(json_writer_t *self, bool on)
118 {
119 	self->pretty = on;
120 }
121 
jsonw_reset(json_writer_t * self)122 void jsonw_reset(json_writer_t *self)
123 {
124 	assert(self->depth == 0);
125 	self->sep = '\0';
126 }
127 
128 /* Basic blocks */
jsonw_begin(json_writer_t * self,int c)129 static void jsonw_begin(json_writer_t *self, int c)
130 {
131 	jsonw_eor(self);
132 	putc(c, self->out);
133 	++self->depth;
134 	self->sep = '\0';
135 }
136 
jsonw_end(json_writer_t * self,int c)137 static void jsonw_end(json_writer_t *self, int c)
138 {
139 	assert(self->depth > 0);
140 
141 	--self->depth;
142 	if (self->sep != '\0')
143 		jsonw_eol(self);
144 	putc(c, self->out);
145 	self->sep = ',';
146 }
147 
148 
149 /* Add a JSON property name */
jsonw_name(json_writer_t * self,const char * name)150 void jsonw_name(json_writer_t *self, const char *name)
151 {
152 	jsonw_eor(self);
153 	jsonw_eol(self);
154 	self->sep = '\0';
155 	jsonw_puts(self, name);
156 	putc(':', self->out);
157 	if (self->pretty)
158 		putc(' ', self->out);
159 }
160 
jsonw_vprintf_enquote(json_writer_t * self,const char * fmt,va_list ap)161 void jsonw_vprintf_enquote(json_writer_t *self, const char *fmt, va_list ap)
162 {
163 	jsonw_eor(self);
164 	putc('"', self->out);
165 	vfprintf(self->out, fmt, ap);
166 	putc('"', self->out);
167 }
168 
jsonw_printf(json_writer_t * self,const char * fmt,...)169 void jsonw_printf(json_writer_t *self, const char *fmt, ...)
170 {
171 	va_list ap;
172 
173 	va_start(ap, fmt);
174 	jsonw_eor(self);
175 	vfprintf(self->out, fmt, ap);
176 	va_end(ap);
177 }
178 
179 /* Collections */
jsonw_start_object(json_writer_t * self)180 void jsonw_start_object(json_writer_t *self)
181 {
182 	jsonw_begin(self, '{');
183 }
184 
jsonw_end_object(json_writer_t * self)185 void jsonw_end_object(json_writer_t *self)
186 {
187 	jsonw_end(self, '}');
188 }
189 
jsonw_start_array(json_writer_t * self)190 void jsonw_start_array(json_writer_t *self)
191 {
192 	jsonw_begin(self, '[');
193 }
194 
jsonw_end_array(json_writer_t * self)195 void jsonw_end_array(json_writer_t *self)
196 {
197 	jsonw_end(self, ']');
198 }
199 
200 /* JSON value types */
jsonw_string(json_writer_t * self,const char * value)201 void jsonw_string(json_writer_t *self, const char *value)
202 {
203 	jsonw_eor(self);
204 	jsonw_puts(self, value);
205 }
206 
jsonw_bool(json_writer_t * self,bool val)207 void jsonw_bool(json_writer_t *self, bool val)
208 {
209 	jsonw_printf(self, "%s", val ? "true" : "false");
210 }
211 
jsonw_null(json_writer_t * self)212 void jsonw_null(json_writer_t *self)
213 {
214 	jsonw_printf(self, "null");
215 }
216 
jsonw_float_fmt(json_writer_t * self,const char * fmt,double num)217 void jsonw_float_fmt(json_writer_t *self, const char *fmt, double num)
218 {
219 	jsonw_printf(self, fmt, num);
220 }
221 
222 #ifdef notused
jsonw_float(json_writer_t * self,double num)223 void jsonw_float(json_writer_t *self, double num)
224 {
225 	jsonw_printf(self, "%g", num);
226 }
227 #endif
228 
jsonw_hu(json_writer_t * self,unsigned short num)229 void jsonw_hu(json_writer_t *self, unsigned short num)
230 {
231 	jsonw_printf(self, "%hu", num);
232 }
233 
jsonw_uint(json_writer_t * self,uint64_t num)234 void jsonw_uint(json_writer_t *self, uint64_t num)
235 {
236 	jsonw_printf(self, "%"PRIu64, num);
237 }
238 
jsonw_lluint(json_writer_t * self,unsigned long long int num)239 void jsonw_lluint(json_writer_t *self, unsigned long long int num)
240 {
241 	jsonw_printf(self, "%llu", num);
242 }
243 
jsonw_int(json_writer_t * self,int64_t num)244 void jsonw_int(json_writer_t *self, int64_t num)
245 {
246 	jsonw_printf(self, "%"PRId64, num);
247 }
248 
249 /* Basic name/value objects */
jsonw_string_field(json_writer_t * self,const char * prop,const char * val)250 void jsonw_string_field(json_writer_t *self, const char *prop, const char *val)
251 {
252 	jsonw_name(self, prop);
253 	jsonw_string(self, val);
254 }
255 
jsonw_bool_field(json_writer_t * self,const char * prop,bool val)256 void jsonw_bool_field(json_writer_t *self, const char *prop, bool val)
257 {
258 	jsonw_name(self, prop);
259 	jsonw_bool(self, val);
260 }
261 
262 #ifdef notused
jsonw_float_field(json_writer_t * self,const char * prop,double val)263 void jsonw_float_field(json_writer_t *self, const char *prop, double val)
264 {
265 	jsonw_name(self, prop);
266 	jsonw_float(self, val);
267 }
268 #endif
269 
jsonw_float_field_fmt(json_writer_t * self,const char * prop,const char * fmt,double val)270 void jsonw_float_field_fmt(json_writer_t *self,
271 			   const char *prop,
272 			   const char *fmt,
273 			   double val)
274 {
275 	jsonw_name(self, prop);
276 	jsonw_float_fmt(self, fmt, val);
277 }
278 
jsonw_uint_field(json_writer_t * self,const char * prop,uint64_t num)279 void jsonw_uint_field(json_writer_t *self, const char *prop, uint64_t num)
280 {
281 	jsonw_name(self, prop);
282 	jsonw_uint(self, num);
283 }
284 
jsonw_hu_field(json_writer_t * self,const char * prop,unsigned short num)285 void jsonw_hu_field(json_writer_t *self, const char *prop, unsigned short num)
286 {
287 	jsonw_name(self, prop);
288 	jsonw_hu(self, num);
289 }
290 
jsonw_lluint_field(json_writer_t * self,const char * prop,unsigned long long int num)291 void jsonw_lluint_field(json_writer_t *self,
292 			const char *prop,
293 			unsigned long long int num)
294 {
295 	jsonw_name(self, prop);
296 	jsonw_lluint(self, num);
297 }
298 
jsonw_int_field(json_writer_t * self,const char * prop,int64_t num)299 void jsonw_int_field(json_writer_t *self, const char *prop, int64_t num)
300 {
301 	jsonw_name(self, prop);
302 	jsonw_int(self, num);
303 }
304 
jsonw_null_field(json_writer_t * self,const char * prop)305 void jsonw_null_field(json_writer_t *self, const char *prop)
306 {
307 	jsonw_name(self, prop);
308 	jsonw_null(self);
309 }
310 
311 #ifdef TEST
main(int argc,char ** argv)312 int main(int argc, char **argv)
313 {
314 	json_writer_t *wr = jsonw_new(stdout);
315 
316 	jsonw_start_object(wr);
317 	jsonw_pretty(wr, true);
318 	jsonw_name(wr, "Vyatta");
319 	jsonw_start_object(wr);
320 	jsonw_string_field(wr, "url", "http://vyatta.com");
321 	jsonw_uint_field(wr, "downloads", 2000000ul);
322 	jsonw_float_field(wr, "stock", 8.16);
323 
324 	jsonw_name(wr, "ARGV");
325 	jsonw_start_array(wr);
326 	while (--argc)
327 		jsonw_string(wr, *++argv);
328 	jsonw_end_array(wr);
329 
330 	jsonw_name(wr, "empty");
331 	jsonw_start_array(wr);
332 	jsonw_end_array(wr);
333 
334 	jsonw_name(wr, "NIL");
335 	jsonw_start_object(wr);
336 	jsonw_end_object(wr);
337 
338 	jsonw_null_field(wr, "my_null");
339 
340 	jsonw_name(wr, "special chars");
341 	jsonw_start_array(wr);
342 	jsonw_string_field(wr, "slash", "/");
343 	jsonw_string_field(wr, "newline", "\n");
344 	jsonw_string_field(wr, "tab", "\t");
345 	jsonw_string_field(wr, "ff", "\f");
346 	jsonw_string_field(wr, "quote", "\"");
347 	jsonw_string_field(wr, "tick", "\'");
348 	jsonw_string_field(wr, "backslash", "\\");
349 	jsonw_end_array(wr);
350 
351 	jsonw_end_object(wr);
352 
353 	jsonw_end_object(wr);
354 	jsonw_destroy(&wr);
355 	return 0;
356 }
357 
358 #endif
359