json.c

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/*-------------------------------------------------------------------------
 *
 * json.c
 *      JSON data type support.
 *
 * Portions Copyright (c) 1996-2023, 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 "catalog/pg_proc.h"
#include "catalog/pg_type.h"
#include "common/hashfn.h"
#include "funcapi.h"
#include "libpq/pqformat.h"
#include "miscadmin.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/date.h"
#include "utils/datetime.h"
#include "utils/json.h"
#include "utils/jsonfuncs.h"
#include "utils/lsyscache.h"
#include "utils/typcache.h"
 
 
/*
 * Support for fast key uniqueness checking.
 *
 * We maintain a hash table of used keys in JSON objects for fast detection
 * of duplicates.
 */
/* Common context for key uniqueness check */
typedef struct HTAB *JsonUniqueCheckState;  /* hash table for key names */
 
/* Hash entry for JsonUniqueCheckState */
typedef struct JsonUniqueHashEntry
{
    const char *key;
    int         key_len;
    int         object_id;
} JsonUniqueHashEntry;
 
/* Stack element for key uniqueness check during JSON parsing */
typedef struct JsonUniqueStackEntry
{
    struct JsonUniqueStackEntry *parent;
    int         object_id;
} JsonUniqueStackEntry;
 
/* Context struct for key uniqueness check during JSON parsing */
typedef struct JsonUniqueParsingState
{
    JsonLexContext *lex;
    JsonUniqueCheckState check;
    JsonUniqueStackEntry *stack;
    int         id_counter;
    bool        unique;
} JsonUniqueParsingState;
 
/* Context struct for key uniqueness check during JSON building */
typedef struct JsonUniqueBuilderState
{
    JsonUniqueCheckState check; /* unique check */
    StringInfoData skipped_keys;    /* skipped keys with NULL values */
    MemoryContext mcxt;         /* context for saving skipped keys */
} JsonUniqueBuilderState;
 
 
/* State struct for JSON aggregation */
typedef struct JsonAggState
{
    StringInfo  str;
    JsonTypeCategory key_category;
    Oid         key_output_func;
    JsonTypeCategory val_category;
    Oid         val_output_func;
    JsonUniqueBuilderState unique_check;
} JsonAggState;
 
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 datum_to_json_internal(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);
 
/*
 * Input.
 */
Datum
json_in(PG_FUNCTION_ARGS)
{
    char       *json = PG_GETARG_CSTRING(0);
    text       *result = cstring_to_text(json);
    JsonLexContext lex;
 
    /* validate it */
    makeJsonLexContext(&lex, result, false);
    if (!pg_parse_json_or_errsave(&lex, &nullSemAction, fcinfo->context))
        PG_RETURN_NULL();
 
    /* Internal representation is the same as text */
    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. */
    makeJsonLexContextCstringLen(&lex, str, nbytes, GetDatabaseEncoding(),
                                 false);
    pg_parse_json_or_ereport(&lex, &nullSemAction);
 
    PG_RETURN_TEXT_P(cstring_to_text_with_len(str, nbytes));
}
 
/*
 * 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_internal(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:
            {
                char        buf[MAXDATELEN + 1];
 
                JsonEncodeDateTime(buf, val, DATEOID, NULL);
                appendStringInfo(result, "\"%s\"", buf);
            }
            break;
        case JSONTYPE_TIMESTAMP:
            {
                char        buf[MAXDATELEN + 1];
 
                JsonEncodeDateTime(buf, val, TIMESTAMPOID, NULL);
                appendStringInfo(result, "\"%s\"", buf);
            }
            break;
        case JSONTYPE_TIMESTAMPTZ:
            {
                char        buf[MAXDATELEN + 1];
 
                JsonEncodeDateTime(buf, val, TIMESTAMPTZOID, NULL);
                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;
    }
}
 
/*
 * Encode 'value' of datetime type 'typid' into JSON string in ISO format using
 * optionally preallocated buffer 'buf'.  Optional 'tzp' determines time-zone
 * offset (in seconds) in which we want to show timestamptz.
 */
char *
JsonEncodeDateTime(char *buf, Datum value, Oid typid, const int *tzp)
{
    if (!buf)
        buf = palloc(MAXDATELEN + 1);
 
    switch (typid)
    {
        case DATEOID:
            {
                DateADT     date;
                struct pg_tm tm;
 
                date = DatumGetDateADT(value);
 
                /* 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);
                }
            }
            break;
        case TIMEOID:
            {
                TimeADT     time = DatumGetTimeADT(value);
                struct pg_tm tt,
                           *tm = &tt;
                fsec_t      fsec;
 
                /* Same as time_out(), but forcing DateStyle */
                time2tm(time, tm, &fsec);
                EncodeTimeOnly(tm, fsec, false, 0, USE_XSD_DATES, buf);
            }
            break;
        case TIMETZOID:
            {
                TimeTzADT  *time = DatumGetTimeTzADTP(value);
                struct pg_tm tt,
                           *tm = &tt;
                fsec_t      fsec;
                int         tz;
 
                /* Same as timetz_out(), but forcing DateStyle */
                timetz2tm(time, tm, &fsec, &tz);
                EncodeTimeOnly(tm, fsec, true, tz, USE_XSD_DATES, buf);
            }
            break;
        case TIMESTAMPOID:
            {
                Timestamp   timestamp;
                struct pg_tm tm;
                fsec_t      fsec;
 
                timestamp = DatumGetTimestamp(value);
                /* 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")));
            }
            break;
        case TIMESTAMPTZOID:
            {
                TimestampTz timestamp;
                struct pg_tm tm;
                int         tz;
                fsec_t      fsec;
                const char *tzn = NULL;
 
                timestamp = DatumGetTimestampTz(value);
 
                /*
                 * If a time zone is specified, we apply the time-zone shift,
                 * convert timestamptz to pg_tm as if it were without a time
                 * zone, and then use the specified time zone for converting
                 * the timestamp into a string.
                 */
                if (tzp)
                {
                    tz = *tzp;
                    timestamp -= (TimestampTz) tz * USECS_PER_SEC;
                }
 
                /* Same as timestamptz_out(), but forcing DateStyle */
                if (TIMESTAMP_NOT_FINITE(timestamp))
                    EncodeSpecialTimestamp(timestamp, buf);
                else if (timestamp2tm(timestamp, tzp ? NULL : &tz, &tm, &fsec,
                                      tzp ? NULL : &tzn, NULL) == 0)
                {
                    if (tzp)
                        tm.tm_isdst = 1;    /* set time-zone presence flag */
 
                    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")));
            }
            break;
        default:
            elog(ERROR, "unknown jsonb value datetime type oid %u", typid);
            return NULL;
    }
 
    return buf;
}
 
/*
 * 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_internal(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, false,
                         &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;
        Form_pg_attribute att = TupleDescAttr(tupdesc, i);
 
        if (att->attisdropped)
            continue;
 
        if (needsep)
            appendStringInfoString(result, sep);
        needsep = true;
 
        attname = NameStr(att->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(att->atttypid, false, &tcategory,
                                 &outfuncoid);
 
        datum_to_json_internal(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, false,
                             &tcategory, &outfuncoid);
 
    datum_to_json_internal(val, is_null, result, tcategory, outfuncoid,
                           key_scalar);
}
 
/*
 * SQL function array_to_json(row)
 */
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)
 */
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)
 */
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)
 */
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));
}
 
/*
 * Is the given type immutable when coming out of a JSON context?
 *
 * At present, datetimes are all considered mutable, because they
 * depend on timezone.  XXX we should also drill down into objects
 * and arrays, but do not.
 */
bool
to_json_is_immutable(Oid typoid)
{
    JsonTypeCategory tcategory;
    Oid         outfuncoid;
 
    json_categorize_type(typoid, false, &tcategory, &outfuncoid);
 
    switch (tcategory)
    {
        case JSONTYPE_BOOL:
        case JSONTYPE_JSON:
        case JSONTYPE_JSONB:
        case JSONTYPE_NULL:
            return true;
 
        case JSONTYPE_DATE:
        case JSONTYPE_TIMESTAMP:
        case JSONTYPE_TIMESTAMPTZ:
            return false;
 
        case JSONTYPE_ARRAY:
            return false;       /* TODO recurse into elements */
 
        case JSONTYPE_COMPOSITE:
            return false;       /* TODO recurse into fields */
 
        case JSONTYPE_NUMERIC:
        case JSONTYPE_CAST:
        case JSONTYPE_OTHER:
            return func_volatile(outfuncoid) == PROVOLATILE_IMMUTABLE;
    }
 
    return false;               /* not reached */
}
 
/*
 * 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);
    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, false,
                         &tcategory, &outfuncoid);
 
    PG_RETURN_DATUM(datum_to_json(val, tcategory, outfuncoid));
}
 
/*
 * Turn a Datum into JSON text.
 *
 * tcategory and outfuncoid are from a previous call to json_categorize_type.
 */
Datum
datum_to_json(Datum val, JsonTypeCategory tcategory, Oid outfuncoid)
{
    StringInfo  result = makeStringInfo();
 
    datum_to_json_internal(val, false, result, tcategory, outfuncoid,
                           false);
 
    return PointerGetDatum(cstring_to_text_with_len(result->data, result->len));
}
 
/*
 * json_agg transition function
 *
 * aggregate input column as a json array value.
 */
static Datum
json_agg_transfn_worker(FunctionCallInfo fcinfo, bool absent_on_null)
{
    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, false, &state->val_category,
                             &state->val_output_func);
    }
    else
    {
        state = (JsonAggState *) PG_GETARG_POINTER(0);
    }
 
    if (absent_on_null && PG_ARGISNULL(1))
        PG_RETURN_POINTER(state);
 
    if (state->str->len > 1)
        appendStringInfoString(state->str, ", ");
 
    /* fast path for NULLs */
    if (PG_ARGISNULL(1))
    {
        datum_to_json_internal((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->str->len > 1 &&
        (state->val_category == JSONTYPE_ARRAY ||
         state->val_category == JSONTYPE_COMPOSITE))
    {
        appendStringInfoString(state->str, "\n ");
    }
 
    datum_to_json_internal(val, false, state->str, state->val_category,
                           state->val_output_func, false);
 
    /*
     * The transition type for json_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 aggregate function
 */
Datum
json_agg_transfn(PG_FUNCTION_ARGS)
{
    return json_agg_transfn_worker(fcinfo, false);
}
 
/*
 * json_agg_strict aggregate function
 */
Datum
json_agg_strict_transfn(PG_FUNCTION_ARGS)
{
    return json_agg_transfn_worker(fcinfo, true);
}
 
/*
 * 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, "]"));
}
 
/* Functions implementing hash table for key uniqueness check */
static uint32
json_unique_hash(const void *key, Size keysize)
{
    const JsonUniqueHashEntry *entry = (JsonUniqueHashEntry *) key;
    uint32      hash = hash_bytes_uint32(entry->object_id);
 
    hash ^= hash_bytes((const unsigned char *) entry->key, entry->key_len);
 
    return DatumGetUInt32(hash);
}
 
static int
json_unique_hash_match(const void *key1, const void *key2, Size keysize)
{
    const JsonUniqueHashEntry *entry1 = (const JsonUniqueHashEntry *) key1;
    const JsonUniqueHashEntry *entry2 = (const JsonUniqueHashEntry *) key2;
 
    if (entry1->object_id != entry2->object_id)
        return entry1->object_id > entry2->object_id ? 1 : -1;
 
    if (entry1->key_len != entry2->key_len)
        return entry1->key_len > entry2->key_len ? 1 : -1;
 
    return strncmp(entry1->key, entry2->key, entry1->key_len);
}
 
/*
 * Uniqueness detection support.
 *
 * In order to detect uniqueness during building or parsing of a JSON
 * object, we maintain a hash table of key names already seen.
 */
static void
json_unique_check_init(JsonUniqueCheckState *cxt)
{
    HASHCTL     ctl;
 
    memset(&ctl, 0, sizeof(ctl));
    ctl.keysize = sizeof(JsonUniqueHashEntry);
    ctl.entrysize = sizeof(JsonUniqueHashEntry);
    ctl.hcxt = CurrentMemoryContext;
    ctl.hash = json_unique_hash;
    ctl.match = json_unique_hash_match;
 
    *cxt = hash_create("json object hashtable",
                       32,
                       &ctl,
                       HASH_ELEM | HASH_CONTEXT | HASH_FUNCTION | HASH_COMPARE);
}
 
static void
json_unique_builder_init(JsonUniqueBuilderState *cxt)
{
    json_unique_check_init(&cxt->check);
    cxt->mcxt = CurrentMemoryContext;
    cxt->skipped_keys.data = NULL;
}
 
static bool
json_unique_check_key(JsonUniqueCheckState *cxt, const char *key, int object_id)
{
    JsonUniqueHashEntry entry;
    bool        found;
 
    entry.key = key;
    entry.key_len = strlen(key);
    entry.object_id = object_id;
 
    (void) hash_search(*cxt, &entry, HASH_ENTER, &found);
 
    return !found;
}
 
/*
 * On-demand initialization of a throwaway StringInfo.  This is used to
 * read a key name that we don't need to store in the output object, for
 * duplicate key detection when the value is NULL.
 */
static StringInfo
json_unique_builder_get_throwawaybuf(JsonUniqueBuilderState *cxt)
{
    StringInfo  out = &cxt->skipped_keys;
 
    if (!out->data)
    {
        MemoryContext oldcxt = MemoryContextSwitchTo(cxt->mcxt);
 
        initStringInfo(out);
        MemoryContextSwitchTo(oldcxt);
    }
    else
        /* Just reset the string to empty */
        out->len = 0;
 
    return out;
}
 
/*
 * json_object_agg transition function.
 *
 * aggregate two input columns as a single json object value.
 */
static Datum
json_object_agg_transfn_worker(FunctionCallInfo fcinfo,
                               bool absent_on_null, bool unique_keys)
{
    MemoryContext aggcontext,
                oldcontext;
    JsonAggState *state;
    StringInfo  out;
    Datum       arg;
    bool        skip;
    int         key_offset;
 
    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 and dynahash 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();
        if (unique_keys)
            json_unique_builder_init(&state->unique_check);
        else
            memset(&state->unique_check, 0, sizeof(state->unique_check));
        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, false, &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, false, &state->val_category,
                             &state->val_output_func);
 
        appendStringInfoString(state->str, "{ ");
    }
    else
    {
        state = (JsonAggState *) PG_GETARG_POINTER(0);
    }
 
    /*
     * 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_NULL_VALUE_NOT_ALLOWED),
                 errmsg("null value not allowed for object key")));
 
    /* Skip null values if absent_on_null */
    skip = absent_on_null && PG_ARGISNULL(2);
 
    if (skip)
    {
        /*
         * We got a NULL value and we're not storing those; if we're not
         * testing key uniqueness, we're done.  If we are, use the throwaway
         * buffer to store the key name so that we can check it.
         */
        if (!unique_keys)
            PG_RETURN_POINTER(state);
 
        out = json_unique_builder_get_throwawaybuf(&state->unique_check);
    }
    else
    {
        out = state->str;
 
        /*
         * Append comma delimiter only if we have already output some fields
         * after the initial string "{ ".
         */
        if (out->len > 2)
            appendStringInfoString(out, ", ");
    }
 
    arg = PG_GETARG_DATUM(1);
 
    key_offset = out->len;
 
    datum_to_json_internal(arg, false, out, state->key_category,
                           state->key_output_func, true);
 
    if (unique_keys)
    {
        const char *key = &out->data[key_offset];
 
        if (!json_unique_check_key(&state->unique_check.check, key, 0))
            ereport(ERROR,
                    errcode(ERRCODE_DUPLICATE_JSON_OBJECT_KEY_VALUE),
                    errmsg("duplicate JSON object key value: %s", key));
 
        if (skip)
            PG_RETURN_POINTER(state);
    }
 
    appendStringInfoString(state->str, " : ");
 
    if (PG_ARGISNULL(2))
        arg = (Datum) 0;
    else
        arg = PG_GETARG_DATUM(2);
 
    datum_to_json_internal(arg, PG_ARGISNULL(2), state->str,
                           state->val_category,
                           state->val_output_func, false);
 
    PG_RETURN_POINTER(state);
}
 
/*
 * json_object_agg aggregate function
 */
Datum
json_object_agg_transfn(PG_FUNCTION_ARGS)
{
    return json_object_agg_transfn_worker(fcinfo, false, false);
}
 
/*
 * json_object_agg_strict aggregate function
 */
Datum
json_object_agg_strict_transfn(PG_FUNCTION_ARGS)
{
    return json_object_agg_transfn_worker(fcinfo, true, false);
}
 
/*
 * json_object_agg_unique aggregate function
 */
Datum
json_object_agg_unique_transfn(PG_FUNCTION_ARGS)
{
    return json_object_agg_transfn_worker(fcinfo, false, true);
}
 
/*
 * json_object_agg_unique_strict aggregate function
 */
Datum
json_object_agg_unique_strict_transfn(PG_FUNCTION_ARGS)
{
    return json_object_agg_transfn_worker(fcinfo, true, true);
}
 
/*
 * 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;
}
 
Datum
json_build_object_worker(int nargs, const Datum *args, const bool *nulls, const Oid *types,
                         bool absent_on_null, bool unique_keys)
{
    int         i;
    const char *sep = "";
    StringInfo  result;
    JsonUniqueBuilderState unique_check;
 
    if (nargs % 2 != 0)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("argument list must have even number of elements"),
        /* translator: %s is a SQL function name */
                 errhint("The arguments of %s must consist of alternating keys and values.",
                         "json_build_object()")));
 
    result = makeStringInfo();
 
    appendStringInfoChar(result, '{');
 
    if (unique_keys)
        json_unique_builder_init(&unique_check);
 
    for (i = 0; i < nargs; i += 2)
    {
        StringInfo  out;
        bool        skip;
        int         key_offset;
 
        /* Skip null values if absent_on_null */
        skip = absent_on_null && nulls[i + 1];
 
        if (skip)
        {
            /* If key uniqueness check is needed we must save skipped keys */
            if (!unique_keys)
                continue;
 
            out = json_unique_builder_get_throwawaybuf(&unique_check);
        }
        else
        {
            appendStringInfoString(result, sep);
            sep = ", ";
            out = result;
        }
 
        /* process key */
        if (nulls[i])
            ereport(ERROR,
                    (errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
                     errmsg("null value not allowed for object key")));
 
        /* save key offset before appending it */
        key_offset = out->len;
 
        add_json(args[i], false, out, types[i], true);
 
        if (unique_keys)
        {
            /* check key uniqueness after key appending */
            const char *key = &out->data[key_offset];
 
            if (!json_unique_check_key(&unique_check.check, key, 0))
                ereport(ERROR,
                        errcode(ERRCODE_DUPLICATE_JSON_OBJECT_KEY_VALUE),
                        errmsg("duplicate JSON object key value: %s", key));
 
            if (skip)
                continue;
        }
 
        appendStringInfoString(result, " : ");
 
        /* process value */
        add_json(args[i + 1], nulls[i + 1], result, types[i + 1], false);
    }
 
    appendStringInfoChar(result, '}');
 
    return PointerGetDatum(cstring_to_text_with_len(result->data, result->len));
}
 
/*
 * SQL function json_build_object(variadic "any")
 */
Datum
json_build_object(PG_FUNCTION_ARGS)
{
    Datum      *args;
    bool       *nulls;
    Oid        *types;
 
    /* build argument values to build the object */
    int         nargs = extract_variadic_args(fcinfo, 0, true,
                                              &args, &types, &nulls);
 
    if (nargs < 0)
        PG_RETURN_NULL();
 
    PG_RETURN_DATUM(json_build_object_worker(nargs, args, nulls, types, false, false));
}
 
/*
 * 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));
}
 
Datum
json_build_array_worker(int nargs, const Datum *args, const bool *nulls, const Oid *types,
                        bool absent_on_null)
{
    int         i;
    const char *sep = "";
    StringInfo  result;
 
    result = makeStringInfo();
 
    appendStringInfoChar(result, '[');
 
    for (i = 0; i < nargs; i++)
    {
        if (absent_on_null && nulls[i])
            continue;
 
        appendStringInfoString(result, sep);
        sep = ", ";
        add_json(args[i], nulls[i], result, types[i], false);
    }
 
    appendStringInfoChar(result, ']');
 
    return PointerGetDatum(cstring_to_text_with_len(result->data, result->len));
}
 
/*
 * SQL function json_build_array(variadic "any")
 */
Datum
json_build_array(PG_FUNCTION_ARGS)
{
    Datum      *args;
    bool       *nulls;
    Oid        *types;
 
    /* build argument values to build the object */
    int         nargs = extract_variadic_args(fcinfo, 0, true,
                                              &args, &types, &nulls);
 
    if (nargs < 0)
        PG_RETURN_NULL();
 
    PG_RETURN_DATUM(json_build_array_worker(nargs, args, nulls, types, false));
}
 
/*
 * 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_builtin(in_array, TEXTOID, &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_builtin(key_array, TEXTOID, &key_datums, &key_nulls, &key_count);
    deconstruct_array_builtin(val_array, TEXTOID, &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, '"');
}
 
/* Semantic actions for key uniqueness check */
static JsonParseErrorType
json_unique_object_start(void *_state)
{
    JsonUniqueParsingState *state = _state;
    JsonUniqueStackEntry *entry;
 
    if (!state->unique)
        return JSON_SUCCESS;
 
    /* push object entry to stack */
    entry = palloc(sizeof(*entry));
    entry->object_id = state->id_counter++;
    entry->parent = state->stack;
    state->stack = entry;
 
    return JSON_SUCCESS;
}
 
static JsonParseErrorType
json_unique_object_end(void *_state)
{
    JsonUniqueParsingState *state = _state;
    JsonUniqueStackEntry *entry;
 
    if (!state->unique)
        return JSON_SUCCESS;
 
    entry = state->stack;
    state->stack = entry->parent;   /* pop object from stack */
    pfree(entry);
    return JSON_SUCCESS;
}
 
static JsonParseErrorType
json_unique_object_field_start(void *_state, char *field, bool isnull)
{
    JsonUniqueParsingState *state = _state;
    JsonUniqueStackEntry *entry;
 
    if (!state->unique)
        return JSON_SUCCESS;
 
    /* find key collision in the current object */
    if (json_unique_check_key(&state->check, field, state->stack->object_id))
        return JSON_SUCCESS;
 
    state->unique = false;
 
    /* pop all objects entries */
    while ((entry = state->stack))
    {
        state->stack = entry->parent;
        pfree(entry);
    }
    return JSON_SUCCESS;
}
 
/* Validate JSON text and additionally check key uniqueness */
bool
json_validate(text *json, bool check_unique_keys, bool throw_error)
{
    JsonLexContext lex;
    JsonSemAction uniqueSemAction = {0};
    JsonUniqueParsingState state;
    JsonParseErrorType result;
 
    makeJsonLexContext(&lex, json, check_unique_keys);
 
    if (check_unique_keys)
    {
        state.lex = &lex;
        state.stack = NULL;
        state.id_counter = 0;
        state.unique = true;
        json_unique_check_init(&state.check);
 
        uniqueSemAction.semstate = &state;
        uniqueSemAction.object_start = json_unique_object_start;
        uniqueSemAction.object_field_start = json_unique_object_field_start;
        uniqueSemAction.object_end = json_unique_object_end;
    }
 
    result = pg_parse_json(&lex, check_unique_keys ? &uniqueSemAction : &nullSemAction);
 
    if (result != JSON_SUCCESS)
    {
        if (throw_error)
            json_errsave_error(result, &lex, NULL);
 
        return false;           /* invalid json */
    }
 
    if (check_unique_keys && !state.unique)
    {
        if (throw_error)
            ereport(ERROR,
                    (errcode(ERRCODE_DUPLICATE_JSON_OBJECT_KEY_VALUE),
                     errmsg("duplicate JSON object key value")));
 
        return false;           /* not unique keys */
    }
 
    if (check_unique_keys)
        freeJsonLexContext(&lex);
 
    return true;                /* ok */
}
 
/*
 * 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 = PG_GETARG_TEXT_PP(0);
    JsonLexContext lex;
    char       *type;
    JsonParseErrorType result;
 
    /* Lex exactly one token from the input and check its type. */
    makeJsonLexContext(&lex, json, false);
    result = json_lex(&lex);
    if (result != JSON_SUCCESS)
        json_errsave_error(result, &lex, NULL);
 
    switch (lex.token_type)
    {
        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", lex.token_type);
    }
 
    PG_RETURN_TEXT_P(cstring_to_text(type));
}