jsonapi.c

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/*-------------------------------------------------------------------------
 *
 * jsonapi.c
 *      JSON parser and lexer interfaces
 *
 * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/common/jsonapi.c
 *
 *-------------------------------------------------------------------------
 */
#ifndef FRONTEND
#include "postgres.h"
#else
#include "postgres_fe.h"
#endif
 
#include "common/jsonapi.h"
#include "mb/pg_wchar.h"
 
#ifndef FRONTEND
#include "miscadmin.h"
#endif
 
/*
 * The context of the parser is maintained by the recursive descent
 * mechanism, but is passed explicitly to the error reporting routine
 * for better diagnostics.
 */
typedef enum                    /* contexts of JSON parser */
{
    JSON_PARSE_VALUE,           /* expecting a value */
    JSON_PARSE_STRING,          /* expecting a string (for a field name) */
    JSON_PARSE_ARRAY_START,     /* saw '[', expecting value or ']' */
    JSON_PARSE_ARRAY_NEXT,      /* saw array element, expecting ',' or ']' */
    JSON_PARSE_OBJECT_START,    /* saw '{', expecting label or '}' */
    JSON_PARSE_OBJECT_LABEL,    /* saw object label, expecting ':' */
    JSON_PARSE_OBJECT_NEXT,     /* saw object value, expecting ',' or '}' */
    JSON_PARSE_OBJECT_COMMA,    /* saw object ',', expecting next label */
    JSON_PARSE_END              /* saw the end of a document, expect nothing */
} JsonParseContext;
 
static inline JsonParseErrorType json_lex_string(JsonLexContext *lex);
static inline JsonParseErrorType json_lex_number(JsonLexContext *lex, char *s,
                                                 bool *num_err, int *total_len);
static inline JsonParseErrorType parse_scalar(JsonLexContext *lex, JsonSemAction *sem);
static JsonParseErrorType parse_object_field(JsonLexContext *lex, JsonSemAction *sem);
static JsonParseErrorType parse_object(JsonLexContext *lex, JsonSemAction *sem);
static JsonParseErrorType parse_array_element(JsonLexContext *lex, JsonSemAction *sem);
static JsonParseErrorType parse_array(JsonLexContext *lex, JsonSemAction *sem);
static JsonParseErrorType report_parse_error(JsonParseContext ctx, JsonLexContext *lex);
 
/* the null action object used for pure validation */
JsonSemAction nullSemAction =
{
    NULL, NULL, NULL, NULL, NULL,
    NULL, NULL, NULL, NULL, NULL
};
 
/* Recursive Descent parser support routines */
 
/*
 * lex_peek
 *
 * what is the current look_ahead token?
*/
static inline JsonTokenType
lex_peek(JsonLexContext *lex)
{
    return lex->token_type;
}
 
/*
 * lex_expect
 *
 * move the lexer to the next token if the current look_ahead token matches
 * the parameter token. Otherwise, report an error.
 */
static inline JsonParseErrorType
lex_expect(JsonParseContext ctx, JsonLexContext *lex, JsonTokenType token)
{
    if (lex_peek(lex) == token)
        return json_lex(lex);
    else
        return report_parse_error(ctx, lex);
}
 
/* chars to consider as part of an alphanumeric token */
#define JSON_ALPHANUMERIC_CHAR(c)  \
    (((c) >= 'a' && (c) <= 'z') || \
     ((c) >= 'A' && (c) <= 'Z') || \
     ((c) >= '0' && (c) <= '9') || \
     (c) == '_' || \
     IS_HIGHBIT_SET(c))
 
/*
 * Utility function to check if a string is a valid JSON number.
 *
 * str is of length len, and need not be null-terminated.
 */
bool
IsValidJsonNumber(const char *str, int len)
{
    bool        numeric_error;
    int         total_len;
    JsonLexContext dummy_lex;
 
    if (len <= 0)
        return false;
 
    /*
     * json_lex_number expects a leading  '-' to have been eaten already.
     *
     * having to cast away the constness of str is ugly, but there's not much
     * easy alternative.
     */
    if (*str == '-')
    {
        dummy_lex.input = unconstify(char *, str) + 1;
        dummy_lex.input_length = len - 1;
    }
    else
    {
        dummy_lex.input = unconstify(char *, str);
        dummy_lex.input_length = len;
    }
 
    json_lex_number(&dummy_lex, dummy_lex.input, &numeric_error, &total_len);
 
    return (!numeric_error) && (total_len == dummy_lex.input_length);
}
 
/*
 * makeJsonLexContextCstringLen
 *
 * lex constructor, with or without StringInfo object for de-escaped lexemes.
 *
 * Without is better as it makes the processing faster, so only make one
 * if really required.
 */
JsonLexContext *
makeJsonLexContextCstringLen(char *json, int len, int encoding, bool need_escapes)
{
    JsonLexContext *lex = palloc0(sizeof(JsonLexContext));
 
    lex->input = lex->token_terminator = lex->line_start = json;
    lex->line_number = 1;
    lex->input_length = len;
    lex->input_encoding = encoding;
    if (need_escapes)
        lex->strval = makeStringInfo();
    return lex;
}
 
/*
 * pg_parse_json
 *
 * Publicly visible entry point for the JSON parser.
 *
 * lex is a lexing context, set up for the json to be processed by calling
 * makeJsonLexContext(). sem is a structure of function pointers to semantic
 * action routines to be called at appropriate spots during parsing, and a
 * pointer to a state object to be passed to those routines.
 */
JsonParseErrorType
pg_parse_json(JsonLexContext *lex, JsonSemAction *sem)
{
    JsonTokenType tok;
    JsonParseErrorType result;
 
    /* get the initial token */
    result = json_lex(lex);
    if (result != JSON_SUCCESS)
        return result;
 
    tok = lex_peek(lex);
 
    /* parse by recursive descent */
    switch (tok)
    {
        case JSON_TOKEN_OBJECT_START:
            result = parse_object(lex, sem);
            break;
        case JSON_TOKEN_ARRAY_START:
            result = parse_array(lex, sem);
            break;
        default:
            result = parse_scalar(lex, sem);    /* json can be a bare scalar */
    }
 
    if (result == JSON_SUCCESS)
        result = lex_expect(JSON_PARSE_END, lex, JSON_TOKEN_END);
 
    return result;
}
 
/*
 * json_count_array_elements
 *
 * Returns number of array elements in lex context at start of array token
 * until end of array token at same nesting level.
 *
 * Designed to be called from array_start routines.
 */
JsonParseErrorType
json_count_array_elements(JsonLexContext *lex, int *elements)
{
    JsonLexContext copylex;
    int         count;
    JsonParseErrorType result;
 
    /*
     * It's safe to do this with a shallow copy because the lexical routines
     * don't scribble on the input. They do scribble on the other pointers
     * etc, so doing this with a copy makes that safe.
     */
    memcpy(&copylex, lex, sizeof(JsonLexContext));
    copylex.strval = NULL;      /* not interested in values here */
    copylex.lex_level++;
 
    count = 0;
    result = lex_expect(JSON_PARSE_ARRAY_START, &copylex,
                        JSON_TOKEN_ARRAY_START);
    if (result != JSON_SUCCESS)
        return result;
    if (lex_peek(&copylex) != JSON_TOKEN_ARRAY_END)
    {
        while (1)
        {
            count++;
            result = parse_array_element(&copylex, &nullSemAction);
            if (result != JSON_SUCCESS)
                return result;
            if (copylex.token_type != JSON_TOKEN_COMMA)
                break;
            result = json_lex(&copylex);
            if (result != JSON_SUCCESS)
                return result;
        }
    }
    result = lex_expect(JSON_PARSE_ARRAY_NEXT, &copylex,
                        JSON_TOKEN_ARRAY_END);
    if (result != JSON_SUCCESS)
        return result;
 
    *elements = count;
    return JSON_SUCCESS;
}
 
/*
 *  Recursive Descent parse routines. There is one for each structural
 *  element in a json document:
 *    - scalar (string, number, true, false, null)
 *    - array  ( [ ] )
 *    - array element
 *    - object ( { } )
 *    - object field
 */
static inline JsonParseErrorType
parse_scalar(JsonLexContext *lex, JsonSemAction *sem)
{
    char       *val = NULL;
    json_scalar_action sfunc = sem->scalar;
    JsonTokenType tok = lex_peek(lex);
    JsonParseErrorType result;
 
    /* a scalar must be a string, a number, true, false, or null */
    if (tok != JSON_TOKEN_STRING && tok != JSON_TOKEN_NUMBER &&
        tok != JSON_TOKEN_TRUE && tok != JSON_TOKEN_FALSE &&
        tok != JSON_TOKEN_NULL)
        return report_parse_error(JSON_PARSE_VALUE, lex);
 
    /* if no semantic function, just consume the token */
    if (sfunc == NULL)
        return json_lex(lex);
 
    /* extract the de-escaped string value, or the raw lexeme */
    if (lex_peek(lex) == JSON_TOKEN_STRING)
    {
        if (lex->strval != NULL)
            val = pstrdup(lex->strval->data);
    }
    else
    {
        int         len = (lex->token_terminator - lex->token_start);
 
        val = palloc(len + 1);
        memcpy(val, lex->token_start, len);
        val[len] = '\0';
    }
 
    /* consume the token */
    result = json_lex(lex);
    if (result != JSON_SUCCESS)
        return result;
 
    /* invoke the callback */
    (*sfunc) (sem->semstate, val, tok);
 
    return JSON_SUCCESS;
}
 
static JsonParseErrorType
parse_object_field(JsonLexContext *lex, JsonSemAction *sem)
{
    /*
     * An object field is "fieldname" : value where value can be a scalar,
     * object or array.  Note: in user-facing docs and error messages, we
     * generally call a field name a "key".
     */
 
    char       *fname = NULL;   /* keep compiler quiet */
    json_ofield_action ostart = sem->object_field_start;
    json_ofield_action oend = sem->object_field_end;
    bool        isnull;
    JsonTokenType tok;
    JsonParseErrorType result;
 
    if (lex_peek(lex) != JSON_TOKEN_STRING)
        return report_parse_error(JSON_PARSE_STRING, lex);
    if ((ostart != NULL || oend != NULL) && lex->strval != NULL)
        fname = pstrdup(lex->strval->data);
    result = json_lex(lex);
    if (result != JSON_SUCCESS)
        return result;
 
    result = lex_expect(JSON_PARSE_OBJECT_LABEL, lex, JSON_TOKEN_COLON);
    if (result != JSON_SUCCESS)
        return result;
 
    tok = lex_peek(lex);
    isnull = tok == JSON_TOKEN_NULL;
 
    if (ostart != NULL)
        (*ostart) (sem->semstate, fname, isnull);
 
    switch (tok)
    {
        case JSON_TOKEN_OBJECT_START:
            result = parse_object(lex, sem);
            break;
        case JSON_TOKEN_ARRAY_START:
            result = parse_array(lex, sem);
            break;
        default:
            result = parse_scalar(lex, sem);
    }
    if (result != JSON_SUCCESS)
        return result;
 
    if (oend != NULL)
        (*oend) (sem->semstate, fname, isnull);
    return JSON_SUCCESS;
}
 
static JsonParseErrorType
parse_object(JsonLexContext *lex, JsonSemAction *sem)
{
    /*
     * an object is a possibly empty sequence of object fields, separated by
     * commas and surrounded by curly braces.
     */
    json_struct_action ostart = sem->object_start;
    json_struct_action oend = sem->object_end;
    JsonTokenType tok;
    JsonParseErrorType result;
 
#ifndef FRONTEND
    check_stack_depth();
#endif
 
    if (ostart != NULL)
        (*ostart) (sem->semstate);
 
    /*
     * Data inside an object is at a higher nesting level than the object
     * itself. Note that we increment this after we call the semantic routine
     * for the object start and restore it before we call the routine for the
     * object end.
     */
    lex->lex_level++;
 
    Assert(lex_peek(lex) == JSON_TOKEN_OBJECT_START);
    result = json_lex(lex);
    if (result != JSON_SUCCESS)
        return result;
 
    tok = lex_peek(lex);
    switch (tok)
    {
        case JSON_TOKEN_STRING:
            result = parse_object_field(lex, sem);
            while (result == JSON_SUCCESS && lex_peek(lex) == JSON_TOKEN_COMMA)
            {
                result = json_lex(lex);
                if (result != JSON_SUCCESS)
                    break;
                result = parse_object_field(lex, sem);
            }
            break;
        case JSON_TOKEN_OBJECT_END:
            break;
        default:
            /* case of an invalid initial token inside the object */
            result = report_parse_error(JSON_PARSE_OBJECT_START, lex);
    }
    if (result != JSON_SUCCESS)
        return result;
 
    result = lex_expect(JSON_PARSE_OBJECT_NEXT, lex, JSON_TOKEN_OBJECT_END);
    if (result != JSON_SUCCESS)
        return result;
 
    lex->lex_level--;
 
    if (oend != NULL)
        (*oend) (sem->semstate);
 
    return JSON_SUCCESS;
}
 
static JsonParseErrorType
parse_array_element(JsonLexContext *lex, JsonSemAction *sem)
{
    json_aelem_action astart = sem->array_element_start;
    json_aelem_action aend = sem->array_element_end;
    JsonTokenType tok = lex_peek(lex);
    JsonParseErrorType result;
 
    bool        isnull;
 
    isnull = tok == JSON_TOKEN_NULL;
 
    if (astart != NULL)
        (*astart) (sem->semstate, isnull);
 
    /* an array element is any object, array or scalar */
    switch (tok)
    {
        case JSON_TOKEN_OBJECT_START:
            result = parse_object(lex, sem);
            break;
        case JSON_TOKEN_ARRAY_START:
            result = parse_array(lex, sem);
            break;
        default:
            result = parse_scalar(lex, sem);
    }
 
    if (result != JSON_SUCCESS)
        return result;
 
    if (aend != NULL)
        (*aend) (sem->semstate, isnull);
 
    return JSON_SUCCESS;
}
 
static JsonParseErrorType
parse_array(JsonLexContext *lex, JsonSemAction *sem)
{
    /*
     * an array is a possibly empty sequence of array elements, separated by
     * commas and surrounded by square brackets.
     */
    json_struct_action astart = sem->array_start;
    json_struct_action aend = sem->array_end;
    JsonParseErrorType result;
 
#ifndef FRONTEND
    check_stack_depth();
#endif
 
    if (astart != NULL)
        (*astart) (sem->semstate);
 
    /*
     * Data inside an array is at a higher nesting level than the array
     * itself. Note that we increment this after we call the semantic routine
     * for the array start and restore it before we call the routine for the
     * array end.
     */
    lex->lex_level++;
 
    result = lex_expect(JSON_PARSE_ARRAY_START, lex, JSON_TOKEN_ARRAY_START);
    if (result == JSON_SUCCESS && lex_peek(lex) != JSON_TOKEN_ARRAY_END)
    {
        result = parse_array_element(lex, sem);
 
        while (result == JSON_SUCCESS && lex_peek(lex) == JSON_TOKEN_COMMA)
        {
            result = json_lex(lex);
            if (result != JSON_SUCCESS)
                break;
            result = parse_array_element(lex, sem);
        }
    }
    if (result != JSON_SUCCESS)
        return result;
 
    result = lex_expect(JSON_PARSE_ARRAY_NEXT, lex, JSON_TOKEN_ARRAY_END);
    if (result != JSON_SUCCESS)
        return result;
 
    lex->lex_level--;
 
    if (aend != NULL)
        (*aend) (sem->semstate);
 
    return JSON_SUCCESS;
}
 
/*
 * Lex one token from the input stream.
 */
JsonParseErrorType
json_lex(JsonLexContext *lex)
{
    char       *s;
    int         len;
    JsonParseErrorType result;
 
    /* Skip leading whitespace. */
    s = lex->token_terminator;
    len = s - lex->input;
    while (len < lex->input_length &&
           (*s == ' ' || *s == '\t' || *s == '\n' || *s == '\r'))
    {
        if (*s++ == '\n')
        {
            ++lex->line_number;
            lex->line_start = s;
        }
        len++;
    }
    lex->token_start = s;
 
    /* Determine token type. */
    if (len >= lex->input_length)
    {
        lex->token_start = NULL;
        lex->prev_token_terminator = lex->token_terminator;
        lex->token_terminator = s;
        lex->token_type = JSON_TOKEN_END;
    }
    else
    {
        switch (*s)
        {
                /* Single-character token, some kind of punctuation mark. */
            case '{':
                lex->prev_token_terminator = lex->token_terminator;
                lex->token_terminator = s + 1;
                lex->token_type = JSON_TOKEN_OBJECT_START;
                break;
            case '}':
                lex->prev_token_terminator = lex->token_terminator;
                lex->token_terminator = s + 1;
                lex->token_type = JSON_TOKEN_OBJECT_END;
                break;
            case '[':
                lex->prev_token_terminator = lex->token_terminator;
                lex->token_terminator = s + 1;
                lex->token_type = JSON_TOKEN_ARRAY_START;
                break;
            case ']':
                lex->prev_token_terminator = lex->token_terminator;
                lex->token_terminator = s + 1;
                lex->token_type = JSON_TOKEN_ARRAY_END;
                break;
            case ',':
                lex->prev_token_terminator = lex->token_terminator;
                lex->token_terminator = s + 1;
                lex->token_type = JSON_TOKEN_COMMA;
                break;
            case ':':
                lex->prev_token_terminator = lex->token_terminator;
                lex->token_terminator = s + 1;
                lex->token_type = JSON_TOKEN_COLON;
                break;
            case '"':
                /* string */
                result = json_lex_string(lex);
                if (result != JSON_SUCCESS)
                    return result;
                lex->token_type = JSON_TOKEN_STRING;
                break;
            case '-':
                /* Negative number. */
                result = json_lex_number(lex, s + 1, NULL, NULL);
                if (result != JSON_SUCCESS)
                    return result;
                lex->token_type = JSON_TOKEN_NUMBER;
                break;
            case '0':
            case '1':
            case '2':
            case '3':
            case '4':
            case '5':
            case '6':
            case '7':
            case '8':
            case '9':
                /* Positive number. */
                result = json_lex_number(lex, s, NULL, NULL);
                if (result != JSON_SUCCESS)
                    return result;
                lex->token_type = JSON_TOKEN_NUMBER;
                break;
            default:
                {
                    char       *p;
 
                    /*
                     * We're not dealing with a string, number, legal
                     * punctuation mark, or end of string.  The only legal
                     * tokens we might find here are true, false, and null,
                     * but for error reporting purposes we scan until we see a
                     * non-alphanumeric character.  That way, we can report
                     * the whole word as an unexpected token, rather than just
                     * some unintuitive prefix thereof.
                     */
                    for (p = s; p - s < lex->input_length - len && JSON_ALPHANUMERIC_CHAR(*p); p++)
                         /* skip */ ;
 
                    /*
                     * We got some sort of unexpected punctuation or an
                     * otherwise unexpected character, so just complain about
                     * that one character.
                     */
                    if (p == s)
                    {
                        lex->prev_token_terminator = lex->token_terminator;
                        lex->token_terminator = s + 1;
                        return JSON_INVALID_TOKEN;
                    }
 
                    /*
                     * We've got a real alphanumeric token here.  If it
                     * happens to be true, false, or null, all is well.  If
                     * not, error out.
                     */
                    lex->prev_token_terminator = lex->token_terminator;
                    lex->token_terminator = p;
                    if (p - s == 4)
                    {
                        if (memcmp(s, "true", 4) == 0)
                            lex->token_type = JSON_TOKEN_TRUE;
                        else if (memcmp(s, "null", 4) == 0)
                            lex->token_type = JSON_TOKEN_NULL;
                        else
                            return JSON_INVALID_TOKEN;
                    }
                    else if (p - s == 5 && memcmp(s, "false", 5) == 0)
                        lex->token_type = JSON_TOKEN_FALSE;
                    else
                        return JSON_INVALID_TOKEN;
                }
        }                       /* end of switch */
    }
 
    return JSON_SUCCESS;
}
 
/*
 * The next token in the input stream is known to be a string; lex it.
 */
static inline JsonParseErrorType
json_lex_string(JsonLexContext *lex)
{
    char       *s;
    int         len;
    int         hi_surrogate = -1;
 
    if (lex->strval != NULL)
        resetStringInfo(lex->strval);
 
    Assert(lex->input_length > 0);
    s = lex->token_start;
    len = lex->token_start - lex->input;
    for (;;)
    {
        s++;
        len++;
        /* Premature end of the string. */
        if (len >= lex->input_length)
        {
            lex->token_terminator = s;
            return JSON_INVALID_TOKEN;
        }
        else if (*s == '"')
            break;
        else if ((unsigned char) *s < 32)
        {
            /* Per RFC4627, these characters MUST be escaped. */
            /* Since *s isn't printable, exclude it from the context string */
            lex->token_terminator = s;
            return JSON_ESCAPING_REQUIRED;
        }
        else if (*s == '\\')
        {
            /* OK, we have an escape character. */
            s++;
            len++;
            if (len >= lex->input_length)
            {
                lex->token_terminator = s;
                return JSON_INVALID_TOKEN;
            }
            else if (*s == 'u')
            {
                int         i;
                int         ch = 0;
 
                for (i = 1; i <= 4; i++)
                {
                    s++;
                    len++;
                    if (len >= lex->input_length)
                    {
                        lex->token_terminator = s;
                        return JSON_INVALID_TOKEN;
                    }
                    else if (*s >= '0' && *s <= '9')
                        ch = (ch * 16) + (*s - '0');
                    else if (*s >= 'a' && *s <= 'f')
                        ch = (ch * 16) + (*s - 'a') + 10;
                    else if (*s >= 'A' && *s <= 'F')
                        ch = (ch * 16) + (*s - 'A') + 10;
                    else
                    {
                        lex->token_terminator = s + pg_encoding_mblen_bounded(lex->input_encoding, s);
                        return JSON_UNICODE_ESCAPE_FORMAT;
                    }
                }
                if (lex->strval != NULL)
                {
                    /*
                     * Combine surrogate pairs.
                     */
                    if (is_utf16_surrogate_first(ch))
                    {
                        if (hi_surrogate != -1)
                            return JSON_UNICODE_HIGH_SURROGATE;
                        hi_surrogate = ch;
                        continue;
                    }
                    else if (is_utf16_surrogate_second(ch))
                    {
                        if (hi_surrogate == -1)
                            return JSON_UNICODE_LOW_SURROGATE;
                        ch = surrogate_pair_to_codepoint(hi_surrogate, ch);
                        hi_surrogate = -1;
                    }
 
                    if (hi_surrogate != -1)
                        return JSON_UNICODE_LOW_SURROGATE;
 
                    /*
                     * Reject invalid cases.  We can't have a value above
                     * 0xFFFF here (since we only accepted 4 hex digits
                     * above), so no need to test for out-of-range chars.
                     */
                    if (ch == 0)
                    {
                        /* We can't allow this, since our TEXT type doesn't */
                        return JSON_UNICODE_CODE_POINT_ZERO;
                    }
 
                    /*
                     * Add the represented character to lex->strval.  In the
                     * backend, we can let pg_unicode_to_server() handle any
                     * required character set conversion; in frontend, we can
                     * only deal with trivial conversions.
                     *
                     * Note: pg_unicode_to_server() will throw an error for a
                     * conversion failure, rather than returning a failure
                     * indication.  That seems OK.
                     */
#ifndef FRONTEND
                    {
                        char        cbuf[MAX_UNICODE_EQUIVALENT_STRING + 1];
 
                        pg_unicode_to_server(ch, (unsigned char *) cbuf);
                        appendStringInfoString(lex->strval, cbuf);
                    }
#else
                    if (lex->input_encoding == PG_UTF8)
                    {
                        /* OK, we can map the code point to UTF8 easily */
                        char        utf8str[5];
                        int         utf8len;
 
                        unicode_to_utf8(ch, (unsigned char *) utf8str);
                        utf8len = pg_utf_mblen((unsigned char *) utf8str);
                        appendBinaryStringInfo(lex->strval, utf8str, utf8len);
                    }
                    else if (ch <= 0x007f)
                    {
                        /* The ASCII range is the same in all encodings */
                        appendStringInfoChar(lex->strval, (char) ch);
                    }
                    else
                        return JSON_UNICODE_HIGH_ESCAPE;
#endif                          /* FRONTEND */
                }
            }
            else if (lex->strval != NULL)
            {
                if (hi_surrogate != -1)
                    return JSON_UNICODE_LOW_SURROGATE;
 
                switch (*s)
                {
                    case '"':
                    case '\\':
                    case '/':
                        appendStringInfoChar(lex->strval, *s);
                        break;
                    case 'b':
                        appendStringInfoChar(lex->strval, '\b');
                        break;
                    case 'f':
                        appendStringInfoChar(lex->strval, '\f');
                        break;
                    case 'n':
                        appendStringInfoChar(lex->strval, '\n');
                        break;
                    case 'r':
                        appendStringInfoChar(lex->strval, '\r');
                        break;
                    case 't':
                        appendStringInfoChar(lex->strval, '\t');
                        break;
                    default:
                        /* Not a valid string escape, so signal error. */
                        lex->token_start = s;
                        lex->token_terminator = s + pg_encoding_mblen_bounded(lex->input_encoding, s);
                        return JSON_ESCAPING_INVALID;
                }
            }
            else if (strchr("\"\\/bfnrt", *s) == NULL)
            {
                /*
                 * Simpler processing if we're not bothered about de-escaping
                 *
                 * It's very tempting to remove the strchr() call here and
                 * replace it with a switch statement, but testing so far has
                 * shown it's not a performance win.
                 */
                lex->token_start = s;
                lex->token_terminator = s + pg_encoding_mblen_bounded(lex->input_encoding, s);
                return JSON_ESCAPING_INVALID;
            }
        }
        else if (lex->strval != NULL)
        {
            if (hi_surrogate != -1)
                return JSON_UNICODE_LOW_SURROGATE;
 
            appendStringInfoChar(lex->strval, *s);
        }
    }
 
    if (hi_surrogate != -1)
        return JSON_UNICODE_LOW_SURROGATE;
 
    /* Hooray, we found the end of the string! */
    lex->prev_token_terminator = lex->token_terminator;
    lex->token_terminator = s + 1;
    return JSON_SUCCESS;
}
 
/*
 * The next token in the input stream is known to be a number; lex it.
 *
 * In JSON, a number consists of four parts:
 *
 * (1) An optional minus sign ('-').
 *
 * (2) Either a single '0', or a string of one or more digits that does not
 *     begin with a '0'.
 *
 * (3) An optional decimal part, consisting of a period ('.') followed by
 *     one or more digits.  (Note: While this part can be omitted
 *     completely, it's not OK to have only the decimal point without
 *     any digits afterwards.)
 *
 * (4) An optional exponent part, consisting of 'e' or 'E', optionally
 *     followed by '+' or '-', followed by one or more digits.  (Note:
 *     As with the decimal part, if 'e' or 'E' is present, it must be
 *     followed by at least one digit.)
 *
 * The 's' argument to this function points to the ostensible beginning
 * of part 2 - i.e. the character after any optional minus sign, or the
 * first character of the string if there is none.
 *
 * If num_err is not NULL, we return an error flag to *num_err rather than
 * raising an error for a badly-formed number.  Also, if total_len is not NULL
 * the distance from lex->input to the token end+1 is returned to *total_len.
 */
static inline JsonParseErrorType
json_lex_number(JsonLexContext *lex, char *s,
                bool *num_err, int *total_len)
{
    bool        error = false;
    int         len = s - lex->input;
 
    /* Part (1): leading sign indicator. */
    /* Caller already did this for us; so do nothing. */
 
    /* Part (2): parse main digit string. */
    if (len < lex->input_length && *s == '0')
    {
        s++;
        len++;
    }
    else if (len < lex->input_length && *s >= '1' && *s <= '9')
    {
        do
        {
            s++;
            len++;
        } while (len < lex->input_length && *s >= '0' && *s <= '9');
    }
    else
        error = true;
 
    /* Part (3): parse optional decimal portion. */
    if (len < lex->input_length && *s == '.')
    {
        s++;
        len++;
        if (len == lex->input_length || *s < '0' || *s > '9')
            error = true;
        else
        {
            do
            {
                s++;
                len++;
            } while (len < lex->input_length && *s >= '0' && *s <= '9');
        }
    }
 
    /* Part (4): parse optional exponent. */
    if (len < lex->input_length && (*s == 'e' || *s == 'E'))
    {
        s++;
        len++;
        if (len < lex->input_length && (*s == '+' || *s == '-'))
        {
            s++;
            len++;
        }
        if (len == lex->input_length || *s < '0' || *s > '9')
            error = true;
        else
        {
            do
            {
                s++;
                len++;
            } while (len < lex->input_length && *s >= '0' && *s <= '9');
        }
    }
 
    /*
     * Check for trailing garbage.  As in json_lex(), any alphanumeric stuff
     * here should be considered part of the token for error-reporting
     * purposes.
     */
    for (; len < lex->input_length && JSON_ALPHANUMERIC_CHAR(*s); s++, len++)
        error = true;
 
    if (total_len != NULL)
        *total_len = len;
 
    if (num_err != NULL)
    {
        /* let the caller handle any error */
        *num_err = error;
    }
    else
    {
        /* return token endpoint */
        lex->prev_token_terminator = lex->token_terminator;
        lex->token_terminator = s;
        /* handle error if any */
        if (error)
            return JSON_INVALID_TOKEN;
    }
 
    return JSON_SUCCESS;
}
 
/*
 * Report a parse error.
 *
 * lex->token_start and lex->token_terminator must identify the current token.
 */
static JsonParseErrorType
report_parse_error(JsonParseContext ctx, JsonLexContext *lex)
{
    /* Handle case where the input ended prematurely. */
    if (lex->token_start == NULL || lex->token_type == JSON_TOKEN_END)
        return JSON_EXPECTED_MORE;
 
    /* Otherwise choose the error type based on the parsing context. */
    switch (ctx)
    {
        case JSON_PARSE_END:
            return JSON_EXPECTED_END;
        case JSON_PARSE_VALUE:
            return JSON_EXPECTED_JSON;
        case JSON_PARSE_STRING:
            return JSON_EXPECTED_STRING;
        case JSON_PARSE_ARRAY_START:
            return JSON_EXPECTED_ARRAY_FIRST;
        case JSON_PARSE_ARRAY_NEXT:
            return JSON_EXPECTED_ARRAY_NEXT;
        case JSON_PARSE_OBJECT_START:
            return JSON_EXPECTED_OBJECT_FIRST;
        case JSON_PARSE_OBJECT_LABEL:
            return JSON_EXPECTED_COLON;
        case JSON_PARSE_OBJECT_NEXT:
            return JSON_EXPECTED_OBJECT_NEXT;
        case JSON_PARSE_OBJECT_COMMA:
            return JSON_EXPECTED_STRING;
    }
 
    /*
     * We don't use a default: case, so that the compiler will warn about
     * unhandled enum values.
     */
    Assert(false);
    return JSON_SUCCESS;        /* silence stupider compilers */
}
 
 
#ifndef FRONTEND
/*
 * Extract the current token from a lexing context, for error reporting.
 */
static char *
extract_token(JsonLexContext *lex)
{
    int         toklen = lex->token_terminator - lex->token_start;
    char       *token = palloc(toklen + 1);
 
    memcpy(token, lex->token_start, toklen);
    token[toklen] = '\0';
    return token;
}
 
/*
 * Construct a detail message for a JSON error.
 *
 * Note that the error message generated by this routine may not be
 * palloc'd, making it unsafe for frontend code as there is no way to
 * know if this can be safery pfree'd or not.
 */
char *
json_errdetail(JsonParseErrorType error, JsonLexContext *lex)
{
    switch (error)
    {
        case JSON_SUCCESS:
            /* fall through to the error code after switch */
            break;
        case JSON_ESCAPING_INVALID:
            return psprintf(_("Escape sequence \"\\%s\" is invalid."),
                            extract_token(lex));
        case JSON_ESCAPING_REQUIRED:
            return psprintf(_("Character with value 0x%02x must be escaped."),
                            (unsigned char) *(lex->token_terminator));
        case JSON_EXPECTED_END:
            return psprintf(_("Expected end of input, but found \"%s\"."),
                            extract_token(lex));
        case JSON_EXPECTED_ARRAY_FIRST:
            return psprintf(_("Expected array element or \"]\", but found \"%s\"."),
                            extract_token(lex));
        case JSON_EXPECTED_ARRAY_NEXT:
            return psprintf(_("Expected \",\" or \"]\", but found \"%s\"."),
                            extract_token(lex));
        case JSON_EXPECTED_COLON:
            return psprintf(_("Expected \":\", but found \"%s\"."),
                            extract_token(lex));
        case JSON_EXPECTED_JSON:
            return psprintf(_("Expected JSON value, but found \"%s\"."),
                            extract_token(lex));
        case JSON_EXPECTED_MORE:
            return _("The input string ended unexpectedly.");
        case JSON_EXPECTED_OBJECT_FIRST:
            return psprintf(_("Expected string or \"}\", but found \"%s\"."),
                            extract_token(lex));
        case JSON_EXPECTED_OBJECT_NEXT:
            return psprintf(_("Expected \",\" or \"}\", but found \"%s\"."),
                            extract_token(lex));
        case JSON_EXPECTED_STRING:
            return psprintf(_("Expected string, but found \"%s\"."),
                            extract_token(lex));
        case JSON_INVALID_TOKEN:
            return psprintf(_("Token \"%s\" is invalid."),
                            extract_token(lex));
        case JSON_UNICODE_CODE_POINT_ZERO:
            return _("\\u0000 cannot be converted to text.");
        case JSON_UNICODE_ESCAPE_FORMAT:
            return _("\"\\u\" must be followed by four hexadecimal digits.");
        case JSON_UNICODE_HIGH_ESCAPE:
            /* note: this case is only reachable in frontend not backend */
            return _("Unicode escape values cannot be used for code point values above 007F when the encoding is not UTF8.");
        case JSON_UNICODE_HIGH_SURROGATE:
            return _("Unicode high surrogate must not follow a high surrogate.");
        case JSON_UNICODE_LOW_SURROGATE:
            return _("Unicode low surrogate must follow a high surrogate.");
    }
 
    /*
     * We don't use a default: case, so that the compiler will warn about
     * unhandled enum values.  But this needs to be here anyway to cover the
     * possibility of an incorrect input.
     */
    elog(ERROR, "unexpected json parse error type: %d", (int) error);
    return NULL;
}
#endif