json.c

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/*-------------------------------------------------------------------------
 *
 * json.c
 *      JSON data type support.
 *
 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/utils/adt/json.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/htup_details.h"
#include "access/transam.h"
#include "catalog/pg_type.h"
#include "executor/spi.h"
#include "lib/stringinfo.h"
#include "libpq/pqformat.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "parser/parse_coerce.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/date.h"
#include "utils/datetime.h"
#include "utils/lsyscache.h"
#include "utils/json.h"
#include "utils/jsonapi.h"
#include "utils/typcache.h"
#include "utils/syscache.h"

/*
 * 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;

typedef enum                    /* type categories for datum_to_json */
{
    JSONTYPE_NULL,              /* null, so we didn't bother to identify */
    JSONTYPE_BOOL,              /* boolean (built-in types only) */
    JSONTYPE_NUMERIC,           /* numeric (ditto) */
    JSONTYPE_DATE,              /* we use special formatting for datetimes */
    JSONTYPE_TIMESTAMP,
    JSONTYPE_TIMESTAMPTZ,
    JSONTYPE_JSON,              /* JSON itself (and JSONB) */
    JSONTYPE_ARRAY,             /* array */
    JSONTYPE_COMPOSITE,         /* composite */
    JSONTYPE_CAST,              /* something with an explicit cast to JSON */
    JSONTYPE_OTHER              /* all else */
} JsonTypeCategory;

typedef struct JsonAggState
{
    StringInfo  str;
    JsonTypeCategory key_category;
    Oid         key_output_func;
    JsonTypeCategory val_category;
    Oid         val_output_func;
} JsonAggState;

static inline void json_lex(JsonLexContext *lex);
static inline void json_lex_string(JsonLexContext *lex);
static inline void json_lex_number(JsonLexContext *lex, char *s,
                bool *num_err, int *total_len);
static inline void parse_scalar(JsonLexContext *lex, JsonSemAction *sem);
static void parse_object_field(JsonLexContext *lex, JsonSemAction *sem);
static void parse_object(JsonLexContext *lex, JsonSemAction *sem);
static void parse_array_element(JsonLexContext *lex, JsonSemAction *sem);
static void parse_array(JsonLexContext *lex, JsonSemAction *sem);
static void report_parse_error(JsonParseContext ctx, JsonLexContext *lex);
static void report_invalid_token(JsonLexContext *lex);
static int  report_json_context(JsonLexContext *lex);
static char *extract_mb_char(char *s);
static void composite_to_json(Datum composite, StringInfo result,
                  bool use_line_feeds);
static void array_dim_to_json(StringInfo result, int dim, int ndims, int *dims,
                  Datum *vals, bool *nulls, int *valcount,
                  JsonTypeCategory tcategory, Oid outfuncoid,
                  bool use_line_feeds);
static void array_to_json_internal(Datum array, StringInfo result,
                       bool use_line_feeds);
static void json_categorize_type(Oid typoid,
                     JsonTypeCategory *tcategory,
                     Oid *outfuncoid);
static void datum_to_json(Datum val, bool is_null, StringInfo result,
              JsonTypeCategory tcategory, Oid outfuncoid,
              bool key_scalar);
static void add_json(Datum val, bool is_null, StringInfo result,
         Oid val_type, bool key_scalar);
static text *catenate_stringinfo_string(StringInfo buffer, const char *addon);

/* the null action object used for pure validation */
static 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_accept
 *
 * accept the look_ahead token and move the lexer to the next token if the
 * look_ahead token matches the token parameter. In that case, and if required,
 * also hand back the de-escaped lexeme.
 *
 * returns true if the token matched, false otherwise.
 */
static inline bool
lex_accept(JsonLexContext *lex, JsonTokenType token, char **lexeme)
{
    if (lex->token_type == token)
    {
        if (lexeme != NULL)
        {
            if (lex->token_type == JSON_TOKEN_STRING)
            {
                if (lex->strval != NULL)
                    *lexeme = pstrdup(lex->strval->data);
            }
            else
            {
                int         len = (lex->token_terminator - lex->token_start);
                char       *tokstr = palloc(len + 1);

                memcpy(tokstr, lex->token_start, len);
                tokstr[len] = '\0';
                *lexeme = tokstr;
            }
        }
        json_lex(lex);
        return true;
    }
    return false;
}

/*
 * lex_accept
 *
 * move the lexer to the next token if the current look_ahead token matches
 * the parameter token. Otherwise, report an error.
 */
static inline void
lex_expect(JsonParseContext ctx, JsonLexContext *lex, JsonTokenType token)
{
    if (!lex_accept(lex, token, NULL))
        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 = (char *) str + 1;
        dummy_lex.input_length = len - 1;
    }
    else
    {
        dummy_lex.input = (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);
}

/*
 * Input.
 */
Datum
json_in(PG_FUNCTION_ARGS)
{
    char       *json = PG_GETARG_CSTRING(0);
    text       *result = cstring_to_text(json);
    JsonLexContext *lex;

    /* validate it */
    lex = makeJsonLexContext(result, false);
    pg_parse_json(lex, &nullSemAction);

    /* Internal representation is the same as text, for now */
    PG_RETURN_TEXT_P(result);
}

/*
 * Output.
 */
Datum
json_out(PG_FUNCTION_ARGS)
{
    /* we needn't detoast because text_to_cstring will handle that */
    Datum       txt = PG_GETARG_DATUM(0);

    PG_RETURN_CSTRING(TextDatumGetCString(txt));
}

/*
 * Binary send.
 */
Datum
json_send(PG_FUNCTION_ARGS)
{
    text       *t = PG_GETARG_TEXT_PP(0);
    StringInfoData buf;

    pq_begintypsend(&buf);
    pq_sendtext(&buf, VARDATA_ANY(t), VARSIZE_ANY_EXHDR(t));
    PG_RETURN_BYTEA_P(pq_endtypsend(&buf));
}

/*
 * Binary receive.
 */
Datum
json_recv(PG_FUNCTION_ARGS)
{
    StringInfo  buf = (StringInfo) PG_GETARG_POINTER(0);
    char       *str;
    int         nbytes;
    JsonLexContext *lex;

    str = pq_getmsgtext(buf, buf->len - buf->cursor, &nbytes);

    /* Validate it. */
    lex = makeJsonLexContextCstringLen(str, nbytes, false);
    pg_parse_json(lex, &nullSemAction);

    PG_RETURN_TEXT_P(cstring_to_text_with_len(str, nbytes));
}

/*
 * makeJsonLexContext
 *
 * 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.
 *
 * If you already have the json as a text* value, use the first of these
 * functions, otherwise use  makeJsonLexContextCstringLen().
 */
JsonLexContext *
makeJsonLexContext(text *json, bool need_escapes)
{
    return makeJsonLexContextCstringLen(VARDATA_ANY(json),
                                        VARSIZE_ANY_EXHDR(json),
                                        need_escapes);
}

JsonLexContext *
makeJsonLexContextCstringLen(char *json, int len, 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;
    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.
 */
void
pg_parse_json(JsonLexContext *lex, JsonSemAction *sem)
{
    JsonTokenType tok;

    /* get the initial token */
    json_lex(lex);

    tok = lex_peek(lex);

    /* parse by recursive descent */
    switch (tok)
    {
        case JSON_TOKEN_OBJECT_START:
            parse_object(lex, sem);
            break;
        case JSON_TOKEN_ARRAY_START:
            parse_array(lex, sem);
            break;
        default:
            parse_scalar(lex, sem); /* json can be a bare scalar */
    }

    lex_expect(JSON_PARSE_END, lex, JSON_TOKEN_END);

}

/*
 * 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.
 */
int
json_count_array_elements(JsonLexContext *lex)
{
    JsonLexContext copylex;
    int         count;

    /*
     * 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;
    lex_expect(JSON_PARSE_ARRAY_START, &copylex, JSON_TOKEN_ARRAY_START);
    if (lex_peek(&copylex) != JSON_TOKEN_ARRAY_END)
    {
        do
        {
            count++;
            parse_array_element(&copylex, &nullSemAction);
        }
        while (lex_accept(&copylex, JSON_TOKEN_COMMA, NULL));
    }
    lex_expect(JSON_PARSE_ARRAY_NEXT, &copylex, JSON_TOKEN_ARRAY_END);

    return count;
}

/*
 *  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 void
parse_scalar(JsonLexContext *lex, JsonSemAction *sem)
{
    char       *val = NULL;
    json_scalar_action sfunc = sem->scalar;
    char      **valaddr;
    JsonTokenType tok = lex_peek(lex);

    valaddr = sfunc == NULL ? NULL : &val;

    /* a scalar must be a string, a number, true, false, or null */
    switch (tok)
    {
        case JSON_TOKEN_TRUE:
            lex_accept(lex, JSON_TOKEN_TRUE, valaddr);
            break;
        case JSON_TOKEN_FALSE:
            lex_accept(lex, JSON_TOKEN_FALSE, valaddr);
            break;
        case JSON_TOKEN_NULL:
            lex_accept(lex, JSON_TOKEN_NULL, valaddr);
            break;
        case JSON_TOKEN_NUMBER:
            lex_accept(lex, JSON_TOKEN_NUMBER, valaddr);
            break;
        case JSON_TOKEN_STRING:
            lex_accept(lex, JSON_TOKEN_STRING, valaddr);
            break;
        default:
            report_parse_error(JSON_PARSE_VALUE, lex);
    }

    if (sfunc != NULL)
        (*sfunc) (sem->semstate, val, tok);
}

static void
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;
    char      **fnameaddr = NULL;
    JsonTokenType tok;

    if (ostart != NULL || oend != NULL)
        fnameaddr = &fname;

    if (!lex_accept(lex, JSON_TOKEN_STRING, fnameaddr))
        report_parse_error(JSON_PARSE_STRING, lex);

    lex_expect(JSON_PARSE_OBJECT_LABEL, lex, JSON_TOKEN_COLON);

    tok = lex_peek(lex);
    isnull = tok == JSON_TOKEN_NULL;

    if (ostart != NULL)
        (*ostart) (sem->semstate, fname, isnull);

    switch (tok)
    {
        case JSON_TOKEN_OBJECT_START:
            parse_object(lex, sem);
            break;
        case JSON_TOKEN_ARRAY_START:
            parse_array(lex, sem);
            break;
        default:
            parse_scalar(lex, sem);
    }

    if (oend != NULL)
        (*oend) (sem->semstate, fname, isnull);
}

static void
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;

    check_stack_depth();

    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++;

    /* we know this will succeed, just clearing the token */
    lex_expect(JSON_PARSE_OBJECT_START, lex, JSON_TOKEN_OBJECT_START);

    tok = lex_peek(lex);
    switch (tok)
    {
        case JSON_TOKEN_STRING:
            parse_object_field(lex, sem);
            while (lex_accept(lex, JSON_TOKEN_COMMA, NULL))
                parse_object_field(lex, sem);
            break;
        case JSON_TOKEN_OBJECT_END:
            break;
        default:
            /* case of an invalid initial token inside the object */
            report_parse_error(JSON_PARSE_OBJECT_START, lex);
    }

    lex_expect(JSON_PARSE_OBJECT_NEXT, lex, JSON_TOKEN_OBJECT_END);

    lex->lex_level--;

    if (oend != NULL)
        (*oend) (sem->semstate);
}

static void
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);

    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:
            parse_object(lex, sem);
            break;
        case JSON_TOKEN_ARRAY_START:
            parse_array(lex, sem);
            break;
        default:
            parse_scalar(lex, sem);
    }

    if (aend != NULL)
        (*aend) (sem->semstate, isnull);
}

static void
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;

    check_stack_depth();

    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++;

    lex_expect(JSON_PARSE_ARRAY_START, lex, JSON_TOKEN_ARRAY_START);
    if (lex_peek(lex) != JSON_TOKEN_ARRAY_END)
    {

        parse_array_element(lex, sem);

        while (lex_accept(lex, JSON_TOKEN_COMMA, NULL))
            parse_array_element(lex, sem);
    }

    lex_expect(JSON_PARSE_ARRAY_NEXT, lex, JSON_TOKEN_ARRAY_END);

    lex->lex_level--;

    if (aend != NULL)
        (*aend) (sem->semstate);
}

/*
 * Lex one token from the input stream.
 */
static inline void
json_lex(JsonLexContext *lex)
{
    char       *s;
    int         len;

    /* 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;
        ++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 */
                json_lex_string(lex);
                lex->token_type = JSON_TOKEN_STRING;
                break;
            case '-':
                /* Negative number. */
                json_lex_number(lex, s + 1, NULL, NULL);
                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. */
                json_lex_number(lex, s, NULL, NULL);
                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;
                        report_invalid_token(lex);
                    }

                    /*
                     * 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
                            report_invalid_token(lex);
                    }
                    else if (p - s == 5 && memcmp(s, "false", 5) == 0)
                        lex->token_type = JSON_TOKEN_FALSE;
                    else
                        report_invalid_token(lex);

                }
        }                       /* end of switch */
}

/*
 * The next token in the input stream is known to be a string; lex it.
 */
static inline void
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;
            report_invalid_token(lex);
        }
        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;
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                     errmsg("invalid input syntax for type %s", "json"),
                     errdetail("Character with value 0x%02x must be escaped.",
                               (unsigned char) *s),
                     report_json_context(lex)));
        }
        else if (*s == '\\')
        {
            /* OK, we have an escape character. */
            s++;
            len++;
            if (len >= lex->input_length)
            {
                lex->token_terminator = s;
                report_invalid_token(lex);
            }
            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;
                        report_invalid_token(lex);
                    }
                    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_mblen(s);
                        ereport(ERROR,
                                (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                                 errmsg("invalid input syntax for type %s",
                                        "json"),
                                 errdetail("\"\\u\" must be followed by four hexadecimal digits."),
                                 report_json_context(lex)));
                    }
                }
                if (lex->strval != NULL)
                {
                    char        utf8str[5];
                    int         utf8len;

                    if (ch >= 0xd800 && ch <= 0xdbff)
                    {
                        if (hi_surrogate != -1)
                            ereport(ERROR,
                                    (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                                     errmsg("invalid input syntax for type %s",
                                            "json"),
                                     errdetail("Unicode high surrogate must not follow a high surrogate."),
                                     report_json_context(lex)));
                        hi_surrogate = (ch & 0x3ff) << 10;
                        continue;
                    }
                    else if (ch >= 0xdc00 && ch <= 0xdfff)
                    {
                        if (hi_surrogate == -1)
                            ereport(ERROR,
                                    (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                                     errmsg("invalid input syntax for type %s", "json"),
                                     errdetail("Unicode low surrogate must follow a high surrogate."),
                                     report_json_context(lex)));
                        ch = 0x10000 + hi_surrogate + (ch & 0x3ff);
                        hi_surrogate = -1;
                    }

                    if (hi_surrogate != -1)
                        ereport(ERROR,
                                (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                                 errmsg("invalid input syntax for type %s", "json"),
                                 errdetail("Unicode low surrogate must follow a high surrogate."),
                                 report_json_context(lex)));

                    /*
                     * For UTF8, replace the escape sequence by the actual
                     * utf8 character in lex->strval. Do this also for other
                     * encodings if the escape designates an ASCII character,
                     * otherwise raise an error.
                     */

                    if (ch == 0)
                    {
                        /* We can't allow this, since our TEXT type doesn't */
                        ereport(ERROR,
                                (errcode(ERRCODE_UNTRANSLATABLE_CHARACTER),
                                 errmsg("unsupported Unicode escape sequence"),
                                 errdetail("\\u0000 cannot be converted to text."),
                                 report_json_context(lex)));
                    }
                    else if (GetDatabaseEncoding() == PG_UTF8)
                    {
                        unicode_to_utf8(ch, (unsigned char *) utf8str);
                        utf8len = pg_utf_mblen((unsigned char *) utf8str);
                        appendBinaryStringInfo(lex->strval, utf8str, utf8len);
                    }
                    else if (ch <= 0x007f)
                    {
                        /*
                         * This is the only way to designate things like a
                         * form feed character in JSON, so it's useful in all
                         * encodings.
                         */
                        appendStringInfoChar(lex->strval, (char) ch);
                    }
                    else
                    {
                        ereport(ERROR,
                                (errcode(ERRCODE_UNTRANSLATABLE_CHARACTER),
                                 errmsg("unsupported Unicode escape sequence"),
                                 errdetail("Unicode escape values cannot be used for code point values above 007F when the server encoding is not UTF8."),
                                 report_json_context(lex)));
                    }

                }
            }
            else if (lex->strval != NULL)
            {
                if (hi_surrogate != -1)
                    ereport(ERROR,
                            (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                             errmsg("invalid input syntax for type %s",
                                    "json"),
                             errdetail("Unicode low surrogate must follow a high surrogate."),
                             report_json_context(lex)));

                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 error out. */
                        lex->token_terminator = s + pg_mblen(s);
                        ereport(ERROR,
                                (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                                 errmsg("invalid input syntax for type %s",
                                        "json"),
                                 errdetail("Escape sequence \"\\%s\" is invalid.",
                                           extract_mb_char(s)),
                                 report_json_context(lex)));
                }
            }
            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_terminator = s + pg_mblen(s);
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                         errmsg("invalid input syntax for type %s", "json"),
                         errdetail("Escape sequence \"\\%s\" is invalid.",
                                   extract_mb_char(s)),
                         report_json_context(lex)));
            }

        }
        else if (lex->strval != NULL)
        {
            if (hi_surrogate != -1)
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                         errmsg("invalid input syntax for type %s", "json"),
                         errdetail("Unicode low surrogate must follow a high surrogate."),
                         report_json_context(lex)));

            appendStringInfoChar(lex->strval, *s);
        }

    }

    if (hi_surrogate != -1)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                 errmsg("invalid input syntax for type %s", "json"),
                 errdetail("Unicode low surrogate must follow a high surrogate."),
                 report_json_context(lex)));

    /* Hooray, we found the end of the string! */
    lex->prev_token_terminator = lex->token_terminator;
    lex->token_terminator = s + 1;
}

/*
 * 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 void
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)
            report_invalid_token(lex);
    }
}

/*
 * Report a parse error.
 *
 * lex->token_start and lex->token_terminator must identify the current token.
 */
static void
report_parse_error(JsonParseContext ctx, JsonLexContext *lex)
{
    char       *token;
    int         toklen;

    /* Handle case where the input ended prematurely. */
    if (lex->token_start == NULL || lex->token_type == JSON_TOKEN_END)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                 errmsg("invalid input syntax for type %s", "json"),
                 errdetail("The input string ended unexpectedly."),
                 report_json_context(lex)));

    /* Separate out the current token. */
    toklen = lex->token_terminator - lex->token_start;
    token = palloc(toklen + 1);
    memcpy(token, lex->token_start, toklen);
    token[toklen] = '\0';

    /* Complain, with the appropriate detail message. */
    if (ctx == JSON_PARSE_END)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                 errmsg("invalid input syntax for type %s", "json"),
                 errdetail("Expected end of input, but found \"%s\".",
                           token),
                 report_json_context(lex)));
    else
    {
        switch (ctx)
        {
            case JSON_PARSE_VALUE:
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                         errmsg("invalid input syntax for type %s", "json"),
                         errdetail("Expected JSON value, but found \"%s\".",
                                   token),
                         report_json_context(lex)));
                break;
            case JSON_PARSE_STRING:
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                         errmsg("invalid input syntax for type %s", "json"),
                         errdetail("Expected string, but found \"%s\".",
                                   token),
                         report_json_context(lex)));
                break;
            case JSON_PARSE_ARRAY_START:
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                         errmsg("invalid input syntax for type %s", "json"),
                         errdetail("Expected array element or \"]\", but found \"%s\".",
                                   token),
                         report_json_context(lex)));
                break;
            case JSON_PARSE_ARRAY_NEXT:
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                         errmsg("invalid input syntax for type %s", "json"),
                         errdetail("Expected \",\" or \"]\", but found \"%s\".",
                                   token),
                         report_json_context(lex)));
                break;
            case JSON_PARSE_OBJECT_START:
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                         errmsg("invalid input syntax for type %s", "json"),
                         errdetail("Expected string or \"}\", but found \"%s\".",
                                   token),
                         report_json_context(lex)));
                break;
            case JSON_PARSE_OBJECT_LABEL:
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                         errmsg("invalid input syntax for type %s", "json"),
                         errdetail("Expected \":\", but found \"%s\".",
                                   token),
                         report_json_context(lex)));
                break;
            case JSON_PARSE_OBJECT_NEXT:
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                         errmsg("invalid input syntax for type %s", "json"),
                         errdetail("Expected \",\" or \"}\", but found \"%s\".",
                                   token),
                         report_json_context(lex)));
                break;
            case JSON_PARSE_OBJECT_COMMA:
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                         errmsg("invalid input syntax for type %s", "json"),
                         errdetail("Expected string, but found \"%s\".",
                                   token),
                         report_json_context(lex)));
                break;
            default:
                elog(ERROR, "unexpected json parse state: %d", ctx);
        }
    }
}

/*
 * Report an invalid input token.
 *
 * lex->token_start and lex->token_terminator must identify the token.
 */
static void
report_invalid_token(JsonLexContext *lex)
{
    char       *token;
    int         toklen;

    /* Separate out the offending token. */
    toklen = lex->token_terminator - lex->token_start;
    token = palloc(toklen + 1);
    memcpy(token, lex->token_start, toklen);
    token[toklen] = '\0';

    ereport(ERROR,
            (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
             errmsg("invalid input syntax for type %s", "json"),
             errdetail("Token \"%s\" is invalid.", token),
             report_json_context(lex)));
}

/*
 * Report a CONTEXT line for bogus JSON input.
 *
 * lex->token_terminator must be set to identify the spot where we detected
 * the error.  Note that lex->token_start might be NULL, in case we recognized
 * error at EOF.
 *
 * The return value isn't meaningful, but we make it non-void so that this
 * can be invoked inside ereport().
 */
static int
report_json_context(JsonLexContext *lex)
{
    const char *context_start;
    const char *context_end;
    const char *line_start;
    int         line_number;
    char       *ctxt;
    int         ctxtlen;
    const char *prefix;
    const char *suffix;

    /* Choose boundaries for the part of the input we will display */
    context_start = lex->input;
    context_end = lex->token_terminator;
    line_start = context_start;
    line_number = 1;
    for (;;)
    {
        /* Always advance over newlines */
        if (context_start < context_end && *context_start == '\n')
        {
            context_start++;
            line_start = context_start;
            line_number++;
            continue;
        }
        /* Otherwise, done as soon as we are close enough to context_end */
        if (context_end - context_start < 50)
            break;
        /* Advance to next multibyte character */
        if (IS_HIGHBIT_SET(*context_start))
            context_start += pg_mblen(context_start);
        else
            context_start++;
    }

    /*
     * We add "..." to indicate that the excerpt doesn't start at the
     * beginning of the line ... but if we're within 3 characters of the
     * beginning of the line, we might as well just show the whole line.
     */
    if (context_start - line_start <= 3)
        context_start = line_start;

    /* Get a null-terminated copy of the data to present */
    ctxtlen = context_end - context_start;
    ctxt = palloc(ctxtlen + 1);
    memcpy(ctxt, context_start, ctxtlen);
    ctxt[ctxtlen] = '\0';

    /*
     * Show the context, prefixing "..." if not starting at start of line, and
     * suffixing "..." if not ending at end of line.
     */
    prefix = (context_start > line_start) ? "..." : "";
    suffix = (lex->token_type != JSON_TOKEN_END && context_end - lex->input < lex->input_length && *context_end != '\n' && *context_end != '\r') ? "..." : "";

    return errcontext("JSON data, line %d: %s%s%s",
                      line_number, prefix, ctxt, suffix);
}

/*
 * Extract a single, possibly multi-byte char from the input string.
 */
static char *
extract_mb_char(char *s)
{
    char       *res;
    int         len;

    len = pg_mblen(s);
    res = palloc(len + 1);
    memcpy(res, s, len);
    res[len] = '\0';

    return res;
}

/*
 * Determine how we want to print values of a given type in datum_to_json.
 *
 * Given the datatype OID, return its JsonTypeCategory, as well as the type's
 * output function OID.  If the returned category is JSONTYPE_CAST, we
 * return the OID of the type->JSON cast function instead.
 */
static void
json_categorize_type(Oid typoid,
                     JsonTypeCategory *tcategory,
                     Oid *outfuncoid)
{
    bool        typisvarlena;

    /* Look through any domain */
    typoid = getBaseType(typoid);

    *outfuncoid = InvalidOid;

    /*
     * We need to get the output function for everything except date and
     * timestamp types, array and composite types, booleans, and non-builtin
     * types where there's a cast to json.
     */

    switch (typoid)
    {
        case BOOLOID:
            *tcategory = JSONTYPE_BOOL;
            break;

        case INT2OID:
        case INT4OID:
        case INT8OID:
        case FLOAT4OID:
        case FLOAT8OID:
        case NUMERICOID:
            getTypeOutputInfo(typoid, outfuncoid, &typisvarlena);
            *tcategory = JSONTYPE_NUMERIC;
            break;

        case DATEOID:
            *tcategory = JSONTYPE_DATE;
            break;

        case TIMESTAMPOID:
            *tcategory = JSONTYPE_TIMESTAMP;
            break;

        case TIMESTAMPTZOID:
            *tcategory = JSONTYPE_TIMESTAMPTZ;
            break;

        case JSONOID:
        case JSONBOID:
            getTypeOutputInfo(typoid, outfuncoid, &typisvarlena);
            *tcategory = JSONTYPE_JSON;
            break;

        default:
            /* Check for arrays and composites */
            if (OidIsValid(get_element_type(typoid)) || typoid == ANYARRAYOID
                || typoid == RECORDARRAYOID)
                *tcategory = JSONTYPE_ARRAY;
            else if (type_is_rowtype(typoid))   /* includes RECORDOID */
                *tcategory = JSONTYPE_COMPOSITE;
            else
            {
                /* It's probably the general case ... */
                *tcategory = JSONTYPE_OTHER;
                /* but let's look for a cast to json, if it's not built-in */
                if (typoid >= FirstNormalObjectId)
                {
                    Oid         castfunc;
                    CoercionPathType ctype;

                    ctype = find_coercion_pathway(JSONOID, typoid,
                                                  COERCION_EXPLICIT,
                                                  &castfunc);
                    if (ctype == COERCION_PATH_FUNC && OidIsValid(castfunc))
                    {
                        *tcategory = JSONTYPE_CAST;
                        *outfuncoid = castfunc;
                    }
                    else
                    {
                        /* non builtin type with no cast */
                        getTypeOutputInfo(typoid, outfuncoid, &typisvarlena);
                    }
                }
                else
                {
                    /* any other builtin type */
                    getTypeOutputInfo(typoid, outfuncoid, &typisvarlena);
                }
            }
            break;
    }
}

/*
 * Turn a Datum into JSON text, appending the string to "result".
 *
 * tcategory and outfuncoid are from a previous call to json_categorize_type,
 * except that if is_null is true then they can be invalid.
 *
 * If key_scalar is true, the value is being printed as a key, so insist
 * it's of an acceptable type, and force it to be quoted.
 */
static void
datum_to_json(Datum val, bool is_null, StringInfo result,
              JsonTypeCategory tcategory, Oid outfuncoid,
              bool key_scalar)
{
    char       *outputstr;
    text       *jsontext;

    check_stack_depth();

    /* callers are expected to ensure that null keys are not passed in */
    Assert(!(key_scalar && is_null));

    if (is_null)
    {
        appendStringInfoString(result, "null");
        return;
    }

    if (key_scalar &&
        (tcategory == JSONTYPE_ARRAY ||
         tcategory == JSONTYPE_COMPOSITE ||
         tcategory == JSONTYPE_JSON ||
         tcategory == JSONTYPE_CAST))
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("key value must be scalar, not array, composite, or json")));

    switch (tcategory)
    {
        case JSONTYPE_ARRAY:
            array_to_json_internal(val, result, false);
            break;
        case JSONTYPE_COMPOSITE:
            composite_to_json(val, result, false);
            break;
        case JSONTYPE_BOOL:
            outputstr = DatumGetBool(val) ? "true" : "false";
            if (key_scalar)
                escape_json(result, outputstr);
            else
                appendStringInfoString(result, outputstr);
            break;
        case JSONTYPE_NUMERIC:
            outputstr = OidOutputFunctionCall(outfuncoid, val);

            /*
             * Don't call escape_json for a non-key if it's a valid JSON
             * number.
             */
            if (!key_scalar && IsValidJsonNumber(outputstr, strlen(outputstr)))
                appendStringInfoString(result, outputstr);
            else
                escape_json(result, outputstr);
            pfree(outputstr);
            break;
        case JSONTYPE_DATE:
            {
                DateADT     date;
                struct pg_tm tm;
                char        buf[MAXDATELEN + 1];

                date = DatumGetDateADT(val);
                /* Same as date_out(), but forcing DateStyle */
                if (DATE_NOT_FINITE(date))
                    EncodeSpecialDate(date, buf);
                else
                {
                    j2date(date + POSTGRES_EPOCH_JDATE,
                           &(tm.tm_year), &(tm.tm_mon), &(tm.tm_mday));
                    EncodeDateOnly(&tm, USE_XSD_DATES, buf);
                }
                appendStringInfo(result, "\"%s\"", buf);
            }
            break;
        case JSONTYPE_TIMESTAMP:
            {
                Timestamp   timestamp;
                struct pg_tm tm;
                fsec_t      fsec;
                char        buf[MAXDATELEN + 1];

                timestamp = DatumGetTimestamp(val);
                /* Same as timestamp_out(), but forcing DateStyle */
                if (TIMESTAMP_NOT_FINITE(timestamp))
                    EncodeSpecialTimestamp(timestamp, buf);
                else if (timestamp2tm(timestamp, NULL, &tm, &fsec, NULL, NULL) == 0)
                    EncodeDateTime(&tm, fsec, false, 0, NULL, USE_XSD_DATES, buf);
                else
                    ereport(ERROR,
                            (errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
                             errmsg("timestamp out of range")));
                appendStringInfo(result, "\"%s\"", buf);
            }
            break;
        case JSONTYPE_TIMESTAMPTZ:
            {
                TimestampTz timestamp;
                struct pg_tm tm;
                int         tz;
                fsec_t      fsec;
                const char *tzn = NULL;
                char        buf[MAXDATELEN + 1];

                timestamp = DatumGetTimestampTz(val);
                /* Same as timestamptz_out(), but forcing DateStyle */
                if (TIMESTAMP_NOT_FINITE(timestamp))
                    EncodeSpecialTimestamp(timestamp, buf);
                else if (timestamp2tm(timestamp, &tz, &tm, &fsec, &tzn, NULL) == 0)
                    EncodeDateTime(&tm, fsec, true, tz, tzn, USE_XSD_DATES, buf);
                else
                    ereport(ERROR,
                            (errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
                             errmsg("timestamp out of range")));
                appendStringInfo(result, "\"%s\"", buf);
            }
            break;
        case JSONTYPE_JSON:
            /* JSON and JSONB output will already be escaped */
            outputstr = OidOutputFunctionCall(outfuncoid, val);
            appendStringInfoString(result, outputstr);
            pfree(outputstr);
            break;
        case JSONTYPE_CAST:
            /* outfuncoid refers to a cast function, not an output function */
            jsontext = DatumGetTextPP(OidFunctionCall1(outfuncoid, val));
            outputstr = text_to_cstring(jsontext);
            appendStringInfoString(result, outputstr);
            pfree(outputstr);
            pfree(jsontext);
            break;
        default:
            outputstr = OidOutputFunctionCall(outfuncoid, val);
            escape_json(result, outputstr);
            pfree(outputstr);
            break;
    }
}

/*
 * Process a single dimension of an array.
 * If it's the innermost dimension, output the values, otherwise call
 * ourselves recursively to process the next dimension.
 */
static void
array_dim_to_json(StringInfo result, int dim, int ndims, int *dims, Datum *vals,
                  bool *nulls, int *valcount, JsonTypeCategory tcategory,
                  Oid outfuncoid, bool use_line_feeds)
{
    int         i;
    const char *sep;

    Assert(dim < ndims);

    sep = use_line_feeds ? ",\n " : ",";

    appendStringInfoChar(result, '[');

    for (i = 1; i <= dims[dim]; i++)
    {
        if (i > 1)
            appendStringInfoString(result, sep);

        if (dim + 1 == ndims)
        {
            datum_to_json(vals[*valcount], nulls[*valcount], result, tcategory,
                          outfuncoid, false);
            (*valcount)++;
        }
        else
        {
            /*
             * Do we want line feeds on inner dimensions of arrays? For now
             * we'll say no.
             */
            array_dim_to_json(result, dim + 1, ndims, dims, vals, nulls,
                              valcount, tcategory, outfuncoid, false);
        }
    }

    appendStringInfoChar(result, ']');
}

/*
 * Turn an array into JSON.
 */
static void
array_to_json_internal(Datum array, StringInfo result, bool use_line_feeds)
{
    ArrayType  *v = DatumGetArrayTypeP(array);
    Oid         element_type = ARR_ELEMTYPE(v);
    int        *dim;
    int         ndim;
    int         nitems;
    int         count = 0;
    Datum      *elements;
    bool       *nulls;
    int16       typlen;
    bool        typbyval;
    char        typalign;
    JsonTypeCategory tcategory;
    Oid         outfuncoid;

    ndim = ARR_NDIM(v);
    dim = ARR_DIMS(v);
    nitems = ArrayGetNItems(ndim, dim);

    if (nitems <= 0)
    {
        appendStringInfoString(result, "[]");
        return;
    }

    get_typlenbyvalalign(element_type,
                         &typlen, &typbyval, &typalign);

    json_categorize_type(element_type,
                         &tcategory, &outfuncoid);

    deconstruct_array(v, element_type, typlen, typbyval,
                      typalign, &elements, &nulls,
                      &nitems);

    array_dim_to_json(result, 0, ndim, dim, elements, nulls, &count, tcategory,
                      outfuncoid, use_line_feeds);

    pfree(elements);
    pfree(nulls);
}

/*
 * Turn a composite / record into JSON.
 */
static void
composite_to_json(Datum composite, StringInfo result, bool use_line_feeds)
{
    HeapTupleHeader td;
    Oid         tupType;
    int32       tupTypmod;
    TupleDesc   tupdesc;
    HeapTupleData tmptup,
               *tuple;
    int         i;
    bool        needsep = false;
    const char *sep;

    sep = use_line_feeds ? ",\n " : ",";

    td = DatumGetHeapTupleHeader(composite);

    /* Extract rowtype info and find a tupdesc */
    tupType = HeapTupleHeaderGetTypeId(td);
    tupTypmod = HeapTupleHeaderGetTypMod(td);
    tupdesc = lookup_rowtype_tupdesc(tupType, tupTypmod);

    /* Build a temporary HeapTuple control structure */
    tmptup.t_len = HeapTupleHeaderGetDatumLength(td);
    tmptup.t_data = td;
    tuple = &tmptup;

    appendStringInfoChar(result, '{');

    for (i = 0; i < tupdesc->natts; i++)
    {
        Datum       val;
        bool        isnull;
        char       *attname;
        JsonTypeCategory tcategory;
        Oid         outfuncoid;

        if (tupdesc->attrs[i]->attisdropped)
            continue;

        if (needsep)
            appendStringInfoString(result, sep);
        needsep = true;

        attname = NameStr(tupdesc->attrs[i]->attname);
        escape_json(result, attname);
        appendStringInfoChar(result, ':');

        val = heap_getattr(tuple, i + 1, tupdesc, &isnull);

        if (isnull)
        {
            tcategory = JSONTYPE_NULL;
            outfuncoid = InvalidOid;
        }
        else
            json_categorize_type(tupdesc->attrs[i]->atttypid,
                                 &tcategory, &outfuncoid);

        datum_to_json(val, isnull, result, tcategory, outfuncoid, false);
    }

    appendStringInfoChar(result, '}');
    ReleaseTupleDesc(tupdesc);
}

/*
 * Append JSON text for "val" to "result".
 *
 * This is just a thin wrapper around datum_to_json.  If the same type will be
 * printed many times, avoid using this; better to do the json_categorize_type
 * lookups only once.
 */
static void
add_json(Datum val, bool is_null, StringInfo result,
         Oid val_type, bool key_scalar)
{
    JsonTypeCategory tcategory;
    Oid         outfuncoid;

    if (val_type == InvalidOid)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("could not determine input data type")));

    if (is_null)
    {
        tcategory = JSONTYPE_NULL;
        outfuncoid = InvalidOid;
    }
    else
        json_categorize_type(val_type,
                             &tcategory, &outfuncoid);

    datum_to_json(val, is_null, result, tcategory, outfuncoid, key_scalar);
}

/*
 * SQL function array_to_json(row)
 */
extern Datum
array_to_json(PG_FUNCTION_ARGS)
{
    Datum       array = PG_GETARG_DATUM(0);
    StringInfo  result;

    result = makeStringInfo();

    array_to_json_internal(array, result, false);

    PG_RETURN_TEXT_P(cstring_to_text_with_len(result->data, result->len));
}

/*
 * SQL function array_to_json(row, prettybool)
 */
extern Datum
array_to_json_pretty(PG_FUNCTION_ARGS)
{
    Datum       array = PG_GETARG_DATUM(0);
    bool        use_line_feeds = PG_GETARG_BOOL(1);
    StringInfo  result;

    result = makeStringInfo();

    array_to_json_internal(array, result, use_line_feeds);

    PG_RETURN_TEXT_P(cstring_to_text_with_len(result->data, result->len));
}

/*
 * SQL function row_to_json(row)
 */
extern Datum
row_to_json(PG_FUNCTION_ARGS)
{
    Datum       array = PG_GETARG_DATUM(0);
    StringInfo  result;

    result = makeStringInfo();

    composite_to_json(array, result, false);

    PG_RETURN_TEXT_P(cstring_to_text_with_len(result->data, result->len));
}

/*
 * SQL function row_to_json(row, prettybool)
 */
extern Datum
row_to_json_pretty(PG_FUNCTION_ARGS)
{
    Datum       array = PG_GETARG_DATUM(0);
    bool        use_line_feeds = PG_GETARG_BOOL(1);
    StringInfo  result;

    result = makeStringInfo();

    composite_to_json(array, result, use_line_feeds);

    PG_RETURN_TEXT_P(cstring_to_text_with_len(result->data, result->len));
}

/*
 * SQL function to_json(anyvalue)
 */
Datum
to_json(PG_FUNCTION_ARGS)
{
    Datum       val = PG_GETARG_DATUM(0);
    Oid         val_type = get_fn_expr_argtype(fcinfo->flinfo, 0);
    StringInfo  result;
    JsonTypeCategory tcategory;
    Oid         outfuncoid;

    if (val_type == InvalidOid)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("could not determine input data type")));

    json_categorize_type(val_type,
                         &tcategory, &outfuncoid);

    result = makeStringInfo();

    datum_to_json(val, false, result, tcategory, outfuncoid, false);

    PG_RETURN_TEXT_P(cstring_to_text_with_len(result->data, result->len));
}

/*
 * json_agg transition function
 *
 * aggregate input column as a json array value.
 */
Datum
json_agg_transfn(PG_FUNCTION_ARGS)
{
    MemoryContext aggcontext,
                oldcontext;
    JsonAggState *state;
    Datum       val;

    if (!AggCheckCallContext(fcinfo, &aggcontext))
    {
        /* cannot be called directly because of internal-type argument */
        elog(ERROR, "json_agg_transfn called in non-aggregate context");
    }

    if (PG_ARGISNULL(0))
    {
        Oid         arg_type = get_fn_expr_argtype(fcinfo->flinfo, 1);

        if (arg_type == InvalidOid)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("could not determine input data type")));

        /*
         * Make this state object in a context where it will persist for the
         * duration of the aggregate call.  MemoryContextSwitchTo is only
         * needed the first time, as the StringInfo routines make sure they
         * use the right context to enlarge the object if necessary.
         */
        oldcontext = MemoryContextSwitchTo(aggcontext);
        state = (JsonAggState *) palloc(sizeof(JsonAggState));
        state->str = makeStringInfo();
        MemoryContextSwitchTo(oldcontext);

        appendStringInfoChar(state->str, '[');
        json_categorize_type(arg_type, &state->val_category,
                             &state->val_output_func);
    }
    else
    {
        state = (JsonAggState *) PG_GETARG_POINTER(0);
        appendStringInfoString(state->str, ", ");
    }

    /* fast path for NULLs */
    if (PG_ARGISNULL(1))
    {
        datum_to_json((Datum) 0, true, state->str, JSONTYPE_NULL,
                      InvalidOid, false);
        PG_RETURN_POINTER(state);
    }

    val = PG_GETARG_DATUM(1);

    /* add some whitespace if structured type and not first item */
    if (!PG_ARGISNULL(0) &&
        (state->val_category == JSONTYPE_ARRAY ||
         state->val_category == JSONTYPE_COMPOSITE))
    {
        appendStringInfoString(state->str, "\n ");
    }

    datum_to_json(val, false, state->str, state->val_category,
                  state->val_output_func, false);

    /*
     * The transition type for array_agg() is declared to be "internal", which
     * is a pass-by-value type the same size as a pointer.  So we can safely
     * pass the JsonAggState pointer through nodeAgg.c's machinations.
     */
    PG_RETURN_POINTER(state);
}

/*
 * json_agg final function
 */
Datum
json_agg_finalfn(PG_FUNCTION_ARGS)
{
    JsonAggState *state;

    /* cannot be called directly because of internal-type argument */
    Assert(AggCheckCallContext(fcinfo, NULL));

    state = PG_ARGISNULL(0) ?
        NULL :
        (JsonAggState *) PG_GETARG_POINTER(0);

    /* NULL result for no rows in, as is standard with aggregates */
    if (state == NULL)
        PG_RETURN_NULL();

    /* Else return state with appropriate array terminator added */
    PG_RETURN_TEXT_P(catenate_stringinfo_string(state->str, "]"));
}

/*
 * json_object_agg transition function.
 *
 * aggregate two input columns as a single json object value.
 */
Datum
json_object_agg_transfn(PG_FUNCTION_ARGS)
{
    MemoryContext aggcontext,
                oldcontext;
    JsonAggState *state;
    Datum       arg;

    if (!AggCheckCallContext(fcinfo, &aggcontext))
    {
        /* cannot be called directly because of internal-type argument */
        elog(ERROR, "json_object_agg_transfn called in non-aggregate context");
    }

    if (PG_ARGISNULL(0))
    {
        Oid         arg_type;

        /*
         * Make the StringInfo in a context where it will persist for the
         * duration of the aggregate call. Switching context is only needed
         * for this initial step, as the StringInfo routines make sure they
         * use the right context to enlarge the object if necessary.
         */
        oldcontext = MemoryContextSwitchTo(aggcontext);
        state = (JsonAggState *) palloc(sizeof(JsonAggState));
        state->str = makeStringInfo();
        MemoryContextSwitchTo(oldcontext);

        arg_type = get_fn_expr_argtype(fcinfo->flinfo, 1);

        if (arg_type == InvalidOid)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("could not determine data type for argument %d", 1)));

        json_categorize_type(arg_type, &state->key_category,
                             &state->key_output_func);

        arg_type = get_fn_expr_argtype(fcinfo->flinfo, 2);

        if (arg_type == InvalidOid)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("could not determine data type for argument %d", 2)));

        json_categorize_type(arg_type, &state->val_category,
                             &state->val_output_func);

        appendStringInfoString(state->str, "{ ");
    }
    else
    {
        state = (JsonAggState *) PG_GETARG_POINTER(0);
        appendStringInfoString(state->str, ", ");
    }

    /*
     * Note: since json_object_agg() is declared as taking type "any", the
     * parser will not do any type conversion on unknown-type literals (that
     * is, undecorated strings or NULLs).  Such values will arrive here as
     * type UNKNOWN, which fortunately does not matter to us, since
     * unknownout() works fine.
     */

    if (PG_ARGISNULL(1))
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("field name must not be null")));

    arg = PG_GETARG_DATUM(1);

    datum_to_json(arg, false, state->str, state->key_category,
                  state->key_output_func, true);

    appendStringInfoString(state->str, " : ");

    if (PG_ARGISNULL(2))
        arg = (Datum) 0;
    else
        arg = PG_GETARG_DATUM(2);

    datum_to_json(arg, PG_ARGISNULL(2), state->str, state->val_category,
                  state->val_output_func, false);

    PG_RETURN_POINTER(state);
}

/*
 * json_object_agg final function.
 */
Datum
json_object_agg_finalfn(PG_FUNCTION_ARGS)
{
    JsonAggState *state;

    /* cannot be called directly because of internal-type argument */
    Assert(AggCheckCallContext(fcinfo, NULL));

    state = PG_ARGISNULL(0) ? NULL : (JsonAggState *) PG_GETARG_POINTER(0);

    /* NULL result for no rows in, as is standard with aggregates */
    if (state == NULL)
        PG_RETURN_NULL();

    /* Else return state with appropriate object terminator added */
    PG_RETURN_TEXT_P(catenate_stringinfo_string(state->str, " }"));
}

/*
 * Helper function for aggregates: return given StringInfo's contents plus
 * specified trailing string, as a text datum.  We need this because aggregate
 * final functions are not allowed to modify the aggregate state.
 */
static text *
catenate_stringinfo_string(StringInfo buffer, const char *addon)
{
    /* custom version of cstring_to_text_with_len */
    int         buflen = buffer->len;
    int         addlen = strlen(addon);
    text       *result = (text *) palloc(buflen + addlen + VARHDRSZ);

    SET_VARSIZE(result, buflen + addlen + VARHDRSZ);
    memcpy(VARDATA(result), buffer->data, buflen);
    memcpy(VARDATA(result) + buflen, addon, addlen);

    return result;
}

/*
 * SQL function json_build_object(variadic "any")
 */
Datum
json_build_object(PG_FUNCTION_ARGS)
{
    int         nargs = PG_NARGS();
    int         i;
    Datum       arg;
    const char *sep = "";
    StringInfo  result;
    Oid         val_type;

    if (nargs % 2 != 0)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("argument list must have even number of elements"),
                 errhint("The arguments of json_build_object() must consist of alternating keys and values.")));

    result = makeStringInfo();

    appendStringInfoChar(result, '{');

    for (i = 0; i < nargs; i += 2)
    {
        /*
         * Note: since json_build_object() is declared as taking type "any",
         * the parser will not do any type conversion on unknown-type literals
         * (that is, undecorated strings or NULLs).  Such values will arrive
         * here as type UNKNOWN, which fortunately does not matter to us,
         * since unknownout() works fine.
         */
        appendStringInfoString(result, sep);
        sep = ", ";

        /* process key */
        val_type = get_fn_expr_argtype(fcinfo->flinfo, i);

        if (val_type == InvalidOid)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("could not determine data type for argument %d",
                            i + 1)));

        if (PG_ARGISNULL(i))
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("argument %d cannot be null", i + 1),
                     errhint("Object keys should be text.")));

        arg = PG_GETARG_DATUM(i);

        add_json(arg, false, result, val_type, true);

        appendStringInfoString(result, " : ");

        /* process value */
        val_type = get_fn_expr_argtype(fcinfo->flinfo, i + 1);

        if (val_type == InvalidOid)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("could not determine data type for argument %d",
                            i + 2)));

        if (PG_ARGISNULL(i + 1))
            arg = (Datum) 0;
        else
            arg = PG_GETARG_DATUM(i + 1);

        add_json(arg, PG_ARGISNULL(i + 1), result, val_type, false);
    }

    appendStringInfoChar(result, '}');

    PG_RETURN_TEXT_P(cstring_to_text_with_len(result->data, result->len));
}

/*
 * degenerate case of json_build_object where it gets 0 arguments.
 */
Datum
json_build_object_noargs(PG_FUNCTION_ARGS)
{
    PG_RETURN_TEXT_P(cstring_to_text_with_len("{}", 2));
}

/*
 * SQL function json_build_array(variadic "any")
 */
Datum
json_build_array(PG_FUNCTION_ARGS)
{
    int         nargs = PG_NARGS();
    int         i;
    Datum       arg;
    const char *sep = "";
    StringInfo  result;
    Oid         val_type;

    result = makeStringInfo();

    appendStringInfoChar(result, '[');

    for (i = 0; i < nargs; i++)
    {
        /*
         * Note: since json_build_array() is declared as taking type "any",
         * the parser will not do any type conversion on unknown-type literals
         * (that is, undecorated strings or NULLs).  Such values will arrive
         * here as type UNKNOWN, which fortunately does not matter to us,
         * since unknownout() works fine.
         */
        appendStringInfoString(result, sep);
        sep = ", ";

        val_type = get_fn_expr_argtype(fcinfo->flinfo, i);

        if (val_type == InvalidOid)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("could not determine data type for argument %d",
                            i + 1)));

        if (PG_ARGISNULL(i))
            arg = (Datum) 0;
        else
            arg = PG_GETARG_DATUM(i);

        add_json(arg, PG_ARGISNULL(i), result, val_type, false);
    }

    appendStringInfoChar(result, ']');

    PG_RETURN_TEXT_P(cstring_to_text_with_len(result->data, result->len));
}

/*
 * degenerate case of json_build_array where it gets 0 arguments.
 */
Datum
json_build_array_noargs(PG_FUNCTION_ARGS)
{
    PG_RETURN_TEXT_P(cstring_to_text_with_len("[]", 2));
}

/*
 * SQL function json_object(text[])
 *
 * take a one or two dimensional array of text as key/value pairs
 * for a json object.
 */
Datum
json_object(PG_FUNCTION_ARGS)
{
    ArrayType  *in_array = PG_GETARG_ARRAYTYPE_P(0);
    int         ndims = ARR_NDIM(in_array);
    StringInfoData result;
    Datum      *in_datums;
    bool       *in_nulls;
    int         in_count,
                count,
                i;
    text       *rval;
    char       *v;

    switch (ndims)
    {
        case 0:
            PG_RETURN_DATUM(CStringGetTextDatum("{}"));
            break;

        case 1:
            if ((ARR_DIMS(in_array)[0]) % 2)
                ereport(ERROR,
                        (errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
                         errmsg("array must have even number of elements")));
            break;

        case 2:
            if ((ARR_DIMS(in_array)[1]) != 2)
                ereport(ERROR,
                        (errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
                         errmsg("array must have two columns")));
            break;

        default:
            ereport(ERROR,
                    (errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
                     errmsg("wrong number of array subscripts")));
    }

    deconstruct_array(in_array,
                      TEXTOID, -1, false, 'i',
                      &in_datums, &in_nulls, &in_count);

    count = in_count / 2;

    initStringInfo(&result);

    appendStringInfoChar(&result, '{');

    for (i = 0; i < count; ++i)
    {
        if (in_nulls[i * 2])
            ereport(ERROR,
                    (errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
                     errmsg("null value not allowed for object key")));

        v = TextDatumGetCString(in_datums[i * 2]);
        if (i > 0)
            appendStringInfoString(&result, ", ");
        escape_json(&result, v);
        appendStringInfoString(&result, " : ");
        pfree(v);
        if (in_nulls[i * 2 + 1])
            appendStringInfoString(&result, "null");
        else
        {
            v = TextDatumGetCString(in_datums[i * 2 + 1]);
            escape_json(&result, v);
            pfree(v);
        }
    }

    appendStringInfoChar(&result, '}');

    pfree(in_datums);
    pfree(in_nulls);

    rval = cstring_to_text_with_len(result.data, result.len);
    pfree(result.data);

    PG_RETURN_TEXT_P(rval);

}

/*
 * SQL function json_object(text[], text[])
 *
 * take separate key and value arrays of text to construct a json object
 * pairwise.
 */
Datum
json_object_two_arg(PG_FUNCTION_ARGS)
{
    ArrayType  *key_array = PG_GETARG_ARRAYTYPE_P(0);
    ArrayType  *val_array = PG_GETARG_ARRAYTYPE_P(1);
    int         nkdims = ARR_NDIM(key_array);
    int         nvdims = ARR_NDIM(val_array);
    StringInfoData result;
    Datum      *key_datums,
               *val_datums;
    bool       *key_nulls,
               *val_nulls;
    int         key_count,
                val_count,
                i;
    text       *rval;
    char       *v;

    if (nkdims > 1 || nkdims != nvdims)
        ereport(ERROR,
                (errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
                 errmsg("wrong number of array subscripts")));

    if (nkdims == 0)
        PG_RETURN_DATUM(CStringGetTextDatum("{}"));

    deconstruct_array(key_array,
                      TEXTOID, -1, false, 'i',
                      &key_datums, &key_nulls, &key_count);

    deconstruct_array(val_array,
                      TEXTOID, -1, false, 'i',
                      &val_datums, &val_nulls, &val_count);

    if (key_count != val_count)
        ereport(ERROR,
                (errcode(ERRCODE_ARRAY_SUBSCRIPT_ERROR),
                 errmsg("mismatched array dimensions")));

    initStringInfo(&result);

    appendStringInfoChar(&result, '{');

    for (i = 0; i < key_count; ++i)
    {
        if (key_nulls[i])
            ereport(ERROR,
                    (errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
                     errmsg("null value not allowed for object key")));

        v = TextDatumGetCString(key_datums[i]);
        if (i > 0)
            appendStringInfoString(&result, ", ");
        escape_json(&result, v);
        appendStringInfoString(&result, " : ");
        pfree(v);
        if (val_nulls[i])
            appendStringInfoString(&result, "null");
        else
        {
            v = TextDatumGetCString(val_datums[i]);
            escape_json(&result, v);
            pfree(v);
        }
    }

    appendStringInfoChar(&result, '}');

    pfree(key_datums);
    pfree(key_nulls);
    pfree(val_datums);
    pfree(val_nulls);

    rval = cstring_to_text_with_len(result.data, result.len);
    pfree(result.data);

    PG_RETURN_TEXT_P(rval);
}


/*
 * Produce a JSON string literal, properly escaping characters in the text.
 */
void
escape_json(StringInfo buf, const char *str)
{
    const char *p;

    appendStringInfoCharMacro(buf, '"');
    for (p = str; *p; p++)
    {
        switch (*p)
        {
            case '\b':
                appendStringInfoString(buf, "\\b");
                break;
            case '\f':
                appendStringInfoString(buf, "\\f");
                break;
            case '\n':
                appendStringInfoString(buf, "\\n");
                break;
            case '\r':
                appendStringInfoString(buf, "\\r");
                break;
            case '\t':
                appendStringInfoString(buf, "\\t");
                break;
            case '"':
                appendStringInfoString(buf, "\\\"");
                break;
            case '\\':
                appendStringInfoString(buf, "\\\\");
                break;
            default:
                if ((unsigned char) *p < ' ')
                    appendStringInfo(buf, "\\u%04x", (int) *p);
                else
                    appendStringInfoCharMacro(buf, *p);
                break;
        }
    }
    appendStringInfoCharMacro(buf, '"');
}

/*
 * SQL function json_typeof(json) -> text
 *
 * Returns the type of the outermost JSON value as TEXT.  Possible types are
 * "object", "array", "string", "number", "boolean", and "null".
 *
 * Performs a single call to json_lex() to get the first token of the supplied
 * value.  This initial token uniquely determines the value's type.  As our
 * input must already have been validated by json_in() or json_recv(), the
 * initial token should never be JSON_TOKEN_OBJECT_END, JSON_TOKEN_ARRAY_END,
 * JSON_TOKEN_COLON, JSON_TOKEN_COMMA, or JSON_TOKEN_END.
 */
Datum
json_typeof(PG_FUNCTION_ARGS)
{
    text       *json;

    JsonLexContext *lex;
    JsonTokenType tok;
    char       *type;

    json = PG_GETARG_TEXT_PP(0);
    lex = makeJsonLexContext(json, false);

    /* Lex exactly one token from the input and check its type. */
    json_lex(lex);
    tok = lex_peek(lex);
    switch (tok)
    {
        case JSON_TOKEN_OBJECT_START:
            type = "object";
            break;
        case JSON_TOKEN_ARRAY_START:
            type = "array";
            break;
        case JSON_TOKEN_STRING:
            type = "string";
            break;
        case JSON_TOKEN_NUMBER:
            type = "number";
            break;
        case JSON_TOKEN_TRUE:
        case JSON_TOKEN_FALSE:
            type = "boolean";
            break;
        case JSON_TOKEN_NULL:
            type = "null";
            break;
        default:
            elog(ERROR, "unexpected json token: %d", tok);
    }

    PG_RETURN_TEXT_P(cstring_to_text(type));
}