qemu/qobject/json-parser.c

/*
 * JSON Parser
 *
 * Copyright IBM, Corp. 2009
 *
 * Authors:
 *  Anthony Liguori   <aliguori@us.ibm.com>
 *
 * This work is licensed under the terms of the GNU LGPL, version 2.1 or later.
 * See the COPYING.LIB file in the top-level directory.
 *
 */

#include "qemu/osdep.h"
#include "qemu/cutils.h"
#include "qemu/unicode.h"
#include "qapi/error.h"
#include "qemu-common.h"
#include "qapi/qmp/qbool.h"
#include "qapi/qmp/qdict.h"
#include "qapi/qmp/qlist.h"
#include "qapi/qmp/qnull.h"
#include "qapi/qmp/qnum.h"
#include "qapi/qmp/qstring.h"
#include "qapi/qmp/json-parser.h"
#include "qapi/qmp/json-lexer.h"
#include "qapi/qmp/json-streamer.h"

typedef struct JSONParserContext
{
    Error *err;
    JSONToken *current;
    GQueue *buf;
} JSONParserContext;

#define BUG_ON(cond) assert(!(cond))

/**
 * TODO
 *
 * 0) make errors meaningful again
 * 1) add geometry information to tokens
 * 3) should we return a parsed size?
 * 4) deal with premature EOI
 */

static QObject *parse_value(JSONParserContext *ctxt, va_list *ap);

/**
 * Error handler
 */
static void GCC_FMT_ATTR(3, 4) parse_error(JSONParserContext *ctxt,
                                           JSONToken *token, const char *msg, ...)
{
    va_list ap;
    char message[1024];

    if (ctxt->err) {
        return;
    }
    va_start(ap, msg);
    vsnprintf(message, sizeof(message), msg, ap);
    va_end(ap);
    error_setg(&ctxt->err, "JSON parse error, %s", message);
}

static int cvt4hex(const char *s)
{
    int cp, i;

    cp = 0;
    for (i = 0; i < 4; i++) {
        if (!qemu_isxdigit(s[i])) {
            return -1;
        }
        cp <<= 4;
        if (s[i] >= '0' && s[i] <= '9') {
            cp |= s[i] - '0';
        } else if (s[i] >= 'a' && s[i] <= 'f') {
            cp |= 10 + s[i] - 'a';
        } else if (s[i] >= 'A' && s[i] <= 'F') {
            cp |= 10 + s[i] - 'A';
        } else {
            return -1;
        }
    }
    return cp;
}

/**
 * parse_string(): Parse a JSON string
 *
 * From RFC 8259 "The JavaScript Object Notation (JSON) Data
 * Interchange Format":
 *
 *    char = unescaped /
 *        escape (
 *            %x22 /          ; "    quotation mark  U+0022
 *            %x5C /          ; \    reverse solidus U+005C
 *            %x2F /          ; /    solidus         U+002F
 *            %x62 /          ; b    backspace       U+0008
 *            %x66 /          ; f    form feed       U+000C
 *            %x6E /          ; n    line feed       U+000A
 *            %x72 /          ; r    carriage return U+000D
 *            %x74 /          ; t    tab             U+0009
 *            %x75 4HEXDIG )  ; uXXXX                U+XXXX
 *    escape = %x5C              ; \
 *    quotation-mark = %x22      ; "
 *    unescaped = %x20-21 / %x23-5B / %x5D-10FFFF
 *
 * Extensions over RFC 8259:
 * - Extra escape sequence in strings:
 *   0x27 (apostrophe) is recognized after escape, too
 * - Single-quoted strings:
 *   Like double-quoted strings, except they're delimited by %x27
 *   (apostrophe) instead of %x22 (quotation mark), and can't contain
 *   unescaped apostrophe, but can contain unescaped quotation mark.
 *
 * Note:
 * - Encoding is modified UTF-8.
 * - Invalid Unicode characters are rejected.
 * - Control characters \x00..\x1F are rejected by the lexer.
 */
static QString *parse_string(JSONParserContext *ctxt, JSONToken *token)
{
    const char *ptr = token->str;
    QString *str;
    char quote;
    const char *beg;
    int cp, trailing;
    char *end;
    ssize_t len;
    char utf8_buf[5];

    assert(*ptr == '"' || *ptr == '\'');
    quote = *ptr++;
    str = qstring_new();

    while (*ptr != quote) {
        assert(*ptr);
        if (*ptr == '\\') {
            beg = ptr++;
            switch (*ptr++) {
            case '"':
                qstring_append_chr(str, '"');
                break;
            case '\'':
                qstring_append_chr(str, '\'');
                break;
            case '\\':
                qstring_append_chr(str, '\\');
                break;
            case '/':
                qstring_append_chr(str, '/');
                break;
            case 'b':
                qstring_append_chr(str, '\b');
                break;
            case 'f':
                qstring_append_chr(str, '\f');
                break;
            case 'n':
                qstring_append_chr(str, '\n');
                break;
            case 'r':
                qstring_append_chr(str, '\r');
                break;
            case 't':
                qstring_append_chr(str, '\t');
                break;
            case 'u':
                cp = cvt4hex(ptr);
                ptr += 4;

                /* handle surrogate pairs */
                if (cp >= 0xD800 && cp <= 0xDBFF
                    && ptr[0] == '\\' && ptr[1] == 'u') {
                    /* leading surrogate followed by \u */
                    cp = 0x10000 + ((cp & 0x3FF) << 10);
                    trailing = cvt4hex(ptr + 2);
                    if (trailing >= 0xDC00 && trailing <= 0xDFFF) {
                        /* followed by trailing surrogate */
                        cp |= trailing & 0x3FF;
                        ptr += 6;
                    } else {
                        cp = -1; /* invalid */
                    }
                }

                if (mod_utf8_encode(utf8_buf, sizeof(utf8_buf), cp) < 0) {
                    parse_error(ctxt, token,
                                "%.*s is not a valid Unicode character",
                                (int)(ptr - beg), beg);
                    goto out;
                }
                qstring_append(str, utf8_buf);
                break;
            default:
                parse_error(ctxt, token, "invalid escape sequence in string");
                goto out;
            }
        } else {
            cp = mod_utf8_codepoint(ptr, 6, &end);
            if (cp < 0) {
                parse_error(ctxt, token, "invalid UTF-8 sequence in string");
                goto out;
            }
            ptr = end;
            len = mod_utf8_encode(utf8_buf, sizeof(utf8_buf), cp);
            assert(len >= 0);
            qstring_append(str, utf8_buf);
        }
    }

    return str;

out:
    qobject_unref(str);
    return NULL;
}

/* Note: the token object returned by parser_context_peek_token or
 * parser_context_pop_token is deleted as soon as parser_context_pop_token
 * is called again.
 */
static JSONToken *parser_context_pop_token(JSONParserContext *ctxt)
{
    g_free(ctxt->current);
    assert(!g_queue_is_empty(ctxt->buf));
    ctxt->current = g_queue_pop_head(ctxt->buf);
    return ctxt->current;
}

static JSONToken *parser_context_peek_token(JSONParserContext *ctxt)
{
    assert(!g_queue_is_empty(ctxt->buf));
    return g_queue_peek_head(ctxt->buf);
}

/**
 * Parsing rules
 */
static int parse_pair(JSONParserContext *ctxt, QDict *dict, va_list *ap)
{
    QObject *value;
    QString *key = NULL;
    JSONToken *peek, *token;

    peek = parser_context_peek_token(ctxt);
    if (peek == NULL) {
        parse_error(ctxt, NULL, "premature EOI");
        goto out;
    }

    key = qobject_to(QString, parse_value(ctxt, ap));
    if (!key) {
        parse_error(ctxt, peek, "key is not a string in object");
        goto out;
    }

    token = parser_context_pop_token(ctxt);
    if (token == NULL) {
        parse_error(ctxt, NULL, "premature EOI");
        goto out;
    }

    if (token->type != JSON_COLON) {
        parse_error(ctxt, token, "missing : in object pair");
        goto out;
    }

    value = parse_value(ctxt, ap);
    if (value == NULL) {
        parse_error(ctxt, token, "Missing value in dict");
        goto out;
    }

    qdict_put_obj(dict, qstring_get_str(key), value);

    qobject_unref(key);

    return 0;

out:
    qobject_unref(key);

    return -1;
}

static QObject *parse_object(JSONParserContext *ctxt, va_list *ap)
{
    QDict *dict = NULL;
    JSONToken *token, *peek;

    token = parser_context_pop_token(ctxt);
    assert(token && token->type == JSON_LCURLY);

    dict = qdict_new();

    peek = parser_context_peek_token(ctxt);
    if (peek == NULL) {
        parse_error(ctxt, NULL, "premature EOI");
        goto out;
    }

    if (peek->type != JSON_RCURLY) {
        if (parse_pair(ctxt, dict, ap) == -1) {
            goto out;
        }

        token = parser_context_pop_token(ctxt);
        if (token == NULL) {
            parse_error(ctxt, NULL, "premature EOI");
            goto out;
        }

        while (token->type != JSON_RCURLY) {
            if (token->type != JSON_COMMA) {
                parse_error(ctxt, token, "expected separator in dict");
                goto out;
            }

            if (parse_pair(ctxt, dict, ap) == -1) {
                goto out;
            }

            token = parser_context_pop_token(ctxt);
            if (token == NULL) {
                parse_error(ctxt, NULL, "premature EOI");
                goto out;
            }
        }
    } else {
        (void)parser_context_pop_token(ctxt);
    }

    return QOBJECT(dict);

out:
    qobject_unref(dict);
    return NULL;
}

static QObject *parse_array(JSONParserContext *ctxt, va_list *ap)
{
    QList *list = NULL;
    JSONToken *token, *peek;

    token = parser_context_pop_token(ctxt);
    assert(token && token->type == JSON_LSQUARE);

    list = qlist_new();

    peek = parser_context_peek_token(ctxt);
    if (peek == NULL) {
        parse_error(ctxt, NULL, "premature EOI");
        goto out;
    }

    if (peek->type != JSON_RSQUARE) {
        QObject *obj;

        obj = parse_value(ctxt, ap);
        if (obj == NULL) {
            parse_error(ctxt, token, "expecting value");
            goto out;
        }

        qlist_append_obj(list, obj);

        token = parser_context_pop_token(ctxt);
        if (token == NULL) {
            parse_error(ctxt, NULL, "premature EOI");
            goto out;
        }

        while (token->type != JSON_RSQUARE) {
            if (token->type != JSON_COMMA) {
                parse_error(ctxt, token, "expected separator in list");
                goto out;
            }

            obj = parse_value(ctxt, ap);
            if (obj == NULL) {
                parse_error(ctxt, token, "expecting value");
                goto out;
            }

            qlist_append_obj(list, obj);

            token = parser_context_pop_token(ctxt);
            if (token == NULL) {
                parse_error(ctxt, NULL, "premature EOI");
                goto out;
            }
        }
    } else {
        (void)parser_context_pop_token(ctxt);
    }

    return QOBJECT(list);

out:
    qobject_unref(list);
    return NULL;
}

static QObject *parse_keyword(JSONParserContext *ctxt)
{
    JSONToken *token;

    token = parser_context_pop_token(ctxt);
    assert(token && token->type == JSON_KEYWORD);

    if (!strcmp(token->str, "true")) {
        return QOBJECT(qbool_from_bool(true));
    } else if (!strcmp(token->str, "false")) {
        return QOBJECT(qbool_from_bool(false));
    } else if (!strcmp(token->str, "null")) {
        return QOBJECT(qnull());
    }
    parse_error(ctxt, token, "invalid keyword '%s'", token->str);
    return NULL;
}

static QObject *parse_interpolation(JSONParserContext *ctxt, va_list *ap)
{
    JSONToken *token;

    token = parser_context_pop_token(ctxt);
    assert(token && token->type == JSON_INTERP);

    if (!strcmp(token->str, "%p")) {
        return va_arg(*ap, QObject *);
    } else if (!strcmp(token->str, "%i")) {
        return QOBJECT(qbool_from_bool(va_arg(*ap, int)));
    } else if (!strcmp(token->str, "%d")) {
        return QOBJECT(qnum_from_int(va_arg(*ap, int)));
    } else if (!strcmp(token->str, "%ld")) {
        return QOBJECT(qnum_from_int(va_arg(*ap, long)));
    } else if (!strcmp(token->str, "%lld") ||
               !strcmp(token->str, "%I64d")) {
        return QOBJECT(qnum_from_int(va_arg(*ap, long long)));
    } else if (!strcmp(token->str, "%u")) {
        return QOBJECT(qnum_from_uint(va_arg(*ap, unsigned int)));
    } else if (!strcmp(token->str, "%lu")) {
        return QOBJECT(qnum_from_uint(va_arg(*ap, unsigned long)));
    } else if (!strcmp(token->str, "%llu") ||
               !strcmp(token->str, "%I64u")) {
        return QOBJECT(qnum_from_uint(va_arg(*ap, unsigned long long)));
    } else if (!strcmp(token->str, "%s")) {
        return QOBJECT(qstring_from_str(va_arg(*ap, const char *)));
    } else if (!strcmp(token->str, "%f")) {
        return QOBJECT(qnum_from_double(va_arg(*ap, double)));
    }
    parse_error(ctxt, token, "invalid interpolation '%s'", token->str);
    return NULL;
}

static QObject *parse_literal(JSONParserContext *ctxt)
{
    JSONToken *token;

    token = parser_context_pop_token(ctxt);
    assert(token);

    switch (token->type) {
    case JSON_STRING:
        return QOBJECT(parse_string(ctxt, token));
    case JSON_INTEGER: {
        /*
         * Represent JSON_INTEGER as QNUM_I64 if possible, else as
         * QNUM_U64, else as QNUM_DOUBLE.  Note that qemu_strtoi64()
         * and qemu_strtou64() fail with ERANGE when it's not
         * possible.
         *
         * qnum_get_int() will then work for any signed 64-bit
         * JSON_INTEGER, qnum_get_uint() for any unsigned 64-bit
         * integer, and qnum_get_double() both for any JSON_INTEGER
         * and any JSON_FLOAT (with precision loss for integers beyond
         * 53 bits)
         */
        int ret;
        int64_t value;
        uint64_t uvalue;

        ret = qemu_strtoi64(token->str, NULL, 10, &value);
        if (!ret) {
            return QOBJECT(qnum_from_int(value));
        }
        assert(ret == -ERANGE);

        if (token->str[0] != '-') {
            ret = qemu_strtou64(token->str, NULL, 10, &uvalue);
            if (!ret) {
                return QOBJECT(qnum_from_uint(uvalue));
            }
            assert(ret == -ERANGE);
        }
        /* fall through to JSON_FLOAT */
    }
    case JSON_FLOAT:
        /* FIXME dependent on locale; a pervasive issue in QEMU */
        /* FIXME our lexer matches RFC 7159 in forbidding Inf or NaN,
         * but those might be useful extensions beyond JSON */
        return QOBJECT(qnum_from_double(strtod(token->str, NULL)));
    default:
        abort();
    }
}

static QObject *parse_value(JSONParserContext *ctxt, va_list *ap)
{
    JSONToken *token;

    token = parser_context_peek_token(ctxt);
    if (token == NULL) {
        parse_error(ctxt, NULL, "premature EOI");
        return NULL;
    }

    switch (token->type) {
    case JSON_LCURLY:
        return parse_object(ctxt, ap);
    case JSON_LSQUARE:
        return parse_array(ctxt, ap);
    case JSON_INTERP:
        return parse_interpolation(ctxt, ap);
    case JSON_INTEGER:
    case JSON_FLOAT:
    case JSON_STRING:
        return parse_literal(ctxt);
    case JSON_KEYWORD:
        return parse_keyword(ctxt);
    default:
        parse_error(ctxt, token, "expecting value");
        return NULL;
    }
}

QObject *json_parser_parse(GQueue *tokens, va_list *ap, Error **errp)
{
    JSONParserContext ctxt = { .buf = tokens };
    QObject *result;

    result = parse_value(&ctxt, ap);

    error_propagate(errp, ctxt.err);

    while (!g_queue_is_empty(ctxt.buf)) {
        parser_context_pop_token(&ctxt);
    }
    g_free(ctxt.current);
    g_queue_free(ctxt.buf);

    return result;
}