1#include <stdio.h>
2#include <string.h>
3#include "../jsmn.h"
4
5/*
6 * A small example of jsmn parsing when JSON structure is known and number of
7 * tokens is predictable.
8 */
9
10const char *JSON_STRING =
11	"{\"user\": \"johndoe\", \"admin\": false, \"uid\": 1000,\n  "
12	"\"groups\": [\"users\", \"wheel\", \"audio\", \"video\"]}";
13
14static int jsoneq(const char *json, jsmntok_t *tok, const char *s) {
15	if (tok->type == JSMN_STRING && (int) strlen(s) == tok->end - tok->start &&
16			strncmp(json + tok->start, s, tok->end - tok->start) == 0) {
17		return 0;
18	}
19	return -1;
20}
21
22int main() {
23	int i;
24	int r;
25	jsmn_parser p;
26	jsmntok_t t[128]; /* We expect no more than 128 tokens */
27
28	jsmn_init(&p);
29	r = jsmn_parse(&p, JSON_STRING, strlen(JSON_STRING), t, sizeof(t)/sizeof(t[0]));
30	if (r < 0) {
31		printf("Failed to parse JSON: %d\n", r);
32		return 1;
33	}
34
35	/* Assume the top-level element is an object */
36	if (r < 1 || t[0].type != JSMN_OBJECT) {
37		printf("Object expected\n");
38		return 1;
39	}
40
41	/* Loop over all keys of the root object */
42	for (i = 1; i < r; i++) {
43		if (jsoneq(JSON_STRING, &t[i], "user") == 0) {
44			/* We may use strndup() to fetch string value */
45			printf("- User: %.*s\n", t[i+1].end-t[i+1].start,
46					JSON_STRING + t[i+1].start);
47			i++;
48		} else if (jsoneq(JSON_STRING, &t[i], "admin") == 0) {
49			/* We may additionally check if the value is either "true" or "false" */
50			printf("- Admin: %.*s\n", t[i+1].end-t[i+1].start,
51					JSON_STRING + t[i+1].start);
52			i++;
53		} else if (jsoneq(JSON_STRING, &t[i], "uid") == 0) {
54			/* We may want to do strtol() here to get numeric value */
55			printf("- UID: %.*s\n", t[i+1].end-t[i+1].start,
56					JSON_STRING + t[i+1].start);
57			i++;
58		} else if (jsoneq(JSON_STRING, &t[i], "groups") == 0) {
59			int j;
60			printf("- Groups:\n");
61			if (t[i+1].type != JSMN_ARRAY) {
62				continue; /* We expect groups to be an array of strings */
63			}
64			for (j = 0; j < t[i+1].size; j++) {
65				jsmntok_t *g = &t[i+j+2];
66				printf("  * %.*s\n", g->end - g->start, JSON_STRING + g->start);
67			}
68			i += t[i+1].size + 1;
69		} else {
70			printf("Unexpected key: %.*s\n", t[i].end-t[i].start,
71					JSON_STRING + t[i].start);
72		}
73	}
74	return 0;
75}
76