utun2/lib/json_flat.c

#include "json_flat.h"
#include <string.h>

#define SKIP_WS(p, end) while ((p) < (end) && (*(p) == ' ' || *(p) == '\t' || *(p) == '\n' || *(p) == '\r')) (p)++
#define CHECK(p, end)   if ((p) >= (end)) return -1

static int json_read_string(const char** pp, const char* end, char* out, size_t out_sz) {
    const char* p = *pp;
    CHECK(p, end);
    if (*p != '"') return -1; p++;
    size_t n = 0;
    while (p < end && *p != '"') {
        char ch = *p;
        if (*p == '\\') { p++; CHECK(p, end);
            switch (*p) {
                case '"': ch = '"'; break;
                case '\\': ch = '\\'; break;
                case '/': ch = '/'; break;
                case 'n': ch = '\n'; break;
                case 'r': ch = '\r'; break;
                case 't': ch = '\t'; break;
                default: return -1;
            }
        }
        if (out && n < out_sz - 1) out[n++] = ch;
        p++;
    }
    CHECK(p, end); /* closing quote */
    p++;
    if (out && n < out_sz) out[n] = '\0';
    else if (out && out_sz > 0) out[out_sz - 1] = '\0';
    *pp = p;
    return 0;
}

static int json_parse_pair(const char** pp, const char* end,
                            json_flat_cb cb, void* arg) {
    const char* p = *pp;
    SKIP_WS(p, end); CHECK(p, end);
    if (*p == '}') { *pp = p; return 0; }

    char key[128], val[256];
    if (json_read_string(&p, end, key, sizeof(key)) != 0) return -1;
    SKIP_WS(p, end); CHECK(p, end);
    if (*p != ':') return -1; p++;
    SKIP_WS(p, end); CHECK(p, end);
    if (json_read_string(&p, end, val, sizeof(val)) != 0) return -1;

    if (cb && cb(key, val, arg) != 0) { *pp = p; return 1; }

    SKIP_WS(p, end); CHECK(p, end);
    if (*p == ',') p++;

    *pp = p;
    return 0;
}

int json_flat_parse(const char* json, json_flat_cb cb, void* arg) {
    if (!json) return -1;
    const char* p = json, *end = json + strlen(json);
    SKIP_WS(p, end); CHECK(p, end);
    if (*p != '{') return -1; p++;

    for (;;) {
        int rc = json_parse_pair(&p, end, cb, arg);
        if (rc < 0) return -1;
        if (rc > 0) return 0; /* callback stopped */
        SKIP_WS(p, end); CHECK(p, end);
        if (*p == '}') return 0;
    }
}

struct get_ctx { const char* key; char* out; size_t sz; int found; };

static int get_cb(const char* k, const char* v, void* arg) {
    struct get_ctx* g = (struct get_ctx*)arg;
    if (strcmp(k, g->key) == 0) { if (g->out) { size_t vl = strlen(v);
        size_t cp = vl < g->sz - 1 ? vl : g->sz - 1; memcpy(g->out, v, cp); g->out[cp] = '\0'; }
        g->found = 1; return 1; }
    return 0;
}

int json_flat_get(const char* json, const char* key, char* value_out, size_t value_sz) {
    struct get_ctx g = { key, value_out, value_sz, 0 };
    if (json_flat_parse(json, get_cb, &g) != 0) return -1;
    return g.found ? 0 : -1;
}