wsutil/wsjsmn.c


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/* wsjsmn.c
 * Utility to check if a payload is json using libjsmn
 *
 * Copyright 2016, Dario Lombardo
 *
 * Wireshark - Network traffic analyzer
 * By Gerald Combs <gerald@wireshark.org>
 * Copyright 1998 Gerald Combs
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 */

#include "wsjsmn.h"

#include <string.h>
#include <wsutil/jsmn.h>
#include <wsutil/str_util.h>
#include <wsutil/unicode-utils.h>
#include "log.h"

gboolean jsmn_is_json(const guint8* buf, const size_t len)
{
        /* We expect no more than 1024 tokens */
        guint max_tokens = 1024;
        jsmntok_t* t;
        jsmn_parser p;
        gboolean ret = TRUE;
        int rcode;

        t = g_new0(jsmntok_t, max_tokens);

        if (!t)
                return FALSE;

        jsmn_init(&p);
        rcode = jsmn_parse(&p, buf, len, t, max_tokens);
        if (rcode < 0) {
                switch (rcode) {
                        case JSMN_ERROR_NOMEM:
                                g_log(LOG_DOMAIN_MAIN, G_LOG_LEVEL_DEBUG, "jsmn: not enough tokens were provided");
                                break;
                        case JSMN_ERROR_INVAL:
                                g_log(LOG_DOMAIN_MAIN, G_LOG_LEVEL_DEBUG, "jsmn: invalid character inside JSON string");
                                break;
                        case JSMN_ERROR_PART:
                                g_log(LOG_DOMAIN_MAIN, G_LOG_LEVEL_DEBUG, "jsmn: the string is not a full JSON packet, "
                                        "more bytes expected");
                                break;
                        default:
                                g_log(LOG_DOMAIN_MAIN, G_LOG_LEVEL_DEBUG, "jsmn: unexpected error");
                                break;
                }
                ret = FALSE;
        }

        g_free(t);

        return ret;
}

int wsjsmn_parse(const char *buf, jsmntok_t *tokens, unsigned int max_tokens)
{
        jsmn_parser p;

        jsmn_init(&p);
        return jsmn_parse(&p, buf, strlen(buf), tokens, max_tokens);
}

gboolean wsjsmn_unescape_json_string(const char *input, char *output)
{
        while (*input) {
                char ch = *input++;

                if (ch == '\\') {
                        ch = *input++;

                        switch (ch) {
                                case '\"':
                                case '\\':
                                case '/':
                                        *output++ = ch;
                                        break;

                                case 'b':
                                        *output++ = '\b';
                                        break;
                                case 'f':
                                        *output++ = '\f';
                                        break;
                                case 'n':
                                        *output++ = '\n';
                                        break;
                                case 'r':
                                        *output++ = '\r';
                                        break;
                                case 't':
                                        *output++ = '\t';
                                        break;

                                case 'u':
                                {
                                        guint32 unicode_hex = 0;
                                        int k;
                                        int bin;

                                        for (k = 0; k < 4; k++) {
                                                unicode_hex <<= 4;

                                                ch = *input++;
                                                bin = ws_xton(ch);
                                                if (bin == -1)
                                                        return FALSE;
                                                unicode_hex |= bin;
                                        }

                                        if ((IS_LEAD_SURROGATE(unicode_hex))) {
                                                guint16 lead_surrogate = unicode_hex;
                                                guint16 trail_surrogate = 0;

                                                if (input[0] != '\\' || input[1] != 'u')
                                                        return FALSE;
                                                input += 2;

                                                for (k = 0; k < 4; k++) {
                                                        trail_surrogate <<= 4;

                                                        ch = *input++;
                                                        bin = ws_xton(ch);
                                                        if (bin == -1)
                                                                return FALSE;
                                                        trail_surrogate |= bin;
                                                }

                                                if ((!IS_TRAIL_SURROGATE(trail_surrogate)))
                                                        return FALSE;

                                                unicode_hex = SURROGATE_VALUE(lead_surrogate,trail_surrogate);

                                        } else if ((IS_TRAIL_SURROGATE(unicode_hex))) {
                                                return FALSE;
                                        }

                                        if (!g_unichar_validate(unicode_hex))
                                                return FALSE;

                                        /* Don't allow NUL byte injection. */
                                        if (unicode_hex == 0)
                                            return FALSE;

                                        /* \uXXXX => 6 bytes, and g_unichar_to_utf8() requires to have output buffer at least 6 bytes -> OK. */
                                        k = g_unichar_to_utf8(unicode_hex, output);
                                        output += k;
                                        break;
                                }

                                default:
                                        return FALSE;
                        }

                } else {
                        *output = ch;
                        output++;
                }
        }

        *output = '\0';
        return TRUE;
}

/*
 * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
 *
 * Local variables:
 * c-basic-offset: 4
 * tab-width: 8
 * indent-tabs-mode: t
 * End:
 *
 * vi: set shiftwidth=4 tabstop=8 noexpandtab:
 * :indentSize=4:tabSize=8:noTabs=false:
 */