json.c

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/* Parse JSON files using the JSMN parser. */

/*
 * Copyright (c) 2014, Intel Corporation
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 * this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
*/

#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include "jsmn.h"
#include "json.h"
#include <linux/kernel.h>


static char *mapfile(const char *fn, size_t *size)
{
    unsigned ps = sysconf(_SC_PAGESIZE);
    struct stat st;
    char *map = NULL;
    int err;
    int fd = open(fn, O_RDONLY);

    if (fd < 0 && verbose > 0 && fn) {
        pr_err("Error opening events file '%s': %s\n", fn,
                strerror(errno));
    }

    if (fd < 0)
        return NULL;
    err = fstat(fd, &st);
    if (err < 0)
        goto out;
    *size = st.st_size;
    map = mmap(NULL,
           (st.st_size + ps - 1) & ~(ps - 1),
           PROT_READ|PROT_WRITE, MAP_PRIVATE, fd, 0);
    if (map == MAP_FAILED)
        map = NULL;
out:
    close(fd);
    return map;
}

static void unmapfile(char *map, size_t size)
{
    unsigned ps = sysconf(_SC_PAGESIZE);
    munmap(map, roundup(size, ps));
}

/*
 * Parse json file using jsmn. Return array of tokens,
 * and mapped file. Caller needs to free array.
 */
jsmntok_t *parse_json(const char *fn, char **map, size_t *size, int *len)
{
    jsmn_parser parser;
    jsmntok_t *tokens;
    jsmnerr_t res;
    unsigned sz;

    *map = mapfile(fn, size);
    if (!*map)
        return NULL;
    /* Heuristic */
    sz = *size * 16;
    tokens = malloc(sz);
    if (!tokens)
        goto error;
    jsmn_init(&parser);
    res = jsmn_parse(&parser, *map, *size, tokens,
             sz / sizeof(jsmntok_t));
    if (res != JSMN_SUCCESS) {
        pr_err("%s: json error %s\n", fn, jsmn_strerror(res));
        goto error_free;
    }
    if (len)
        *len = parser.toknext;
    return tokens;
error_free:
    free(tokens);
error:
    unmapfile(*map, *size);
    return NULL;
}

void free_json(char *map, size_t size, jsmntok_t *tokens)
{
    free(tokens);
    unmapfile(map, size);
}

static int countchar(char *map, char c, int end)
{
    int i;
    int count = 0;
    for (i = 0; i < end; i++)
        if (map[i] == c)
            count++;
    return count;
}

/* Return line number of a jsmn token */
int json_line(char *map, jsmntok_t *t)
{
    return countchar(map, '\n', t->start) + 1;
}

static const char * const jsmn_types[] = {
    [JSMN_PRIMITIVE] = "primitive",
    [JSMN_ARRAY] = "array",
    [JSMN_OBJECT] = "object",
    [JSMN_STRING] = "string"
};

#define LOOKUP(a, i) ((i) < (sizeof(a)/sizeof(*(a))) ? ((a)[i]) : "?")

/* Return type name of a jsmn token */
const char *json_name(jsmntok_t *t)
{
    return LOOKUP(jsmn_types, t->type);
}

int json_len(jsmntok_t *t)
{
    return t->end - t->start;
}

/* Is string t equal to s? */
int json_streq(char *map, jsmntok_t *t, const char *s)
{
    unsigned len = json_len(t);
    return len == strlen(s) && !strncasecmp(map + t->start, s, len);
}