jsonpath.c

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/*-------------------------------------------------------------------------
 *
 * jsonpath.c
 *   Input/output and supporting routines for jsonpath
 *
 * jsonpath expression is a chain of path items.  First path item is $, $var,
 * literal or arithmetic expression.  Subsequent path items are accessors
 * (.key, .*, [subscripts], [*]), filters (? (predicate)) and methods (.type(),
 * .size() etc).
 *
 * For instance, structure of path items for simple expression:
 *
 *      $.a[*].type()
 *
 * is pretty evident:
 *
 *      $ => .a => [*] => .type()
 *
 * Some path items such as arithmetic operations, predicates or array
 * subscripts may comprise subtrees.  For instance, more complex expression
 *
 *      ($.a + $[1 to 5, 7] ? (@ > 3).double()).type()
 *
 * have following structure of path items:
 *
 *            +  =>  .type()
 *        ___/ \___
 *       /         \
 *      $ => .a     $  =>  []  =>   ?  =>  .double()
 *                        _||_      |
 *                       /    \     >
 *                      to    to   / \
 *                     / \    /   @   3
 *                    1   5  7
 *
 * Binary encoding of jsonpath constitutes a sequence of 4-bytes aligned
 * variable-length path items connected by links.  Every item has a header
 * consisting of item type (enum JsonPathItemType) and offset of next item
 * (zero means no next item).  After the header, item may have payload
 * depending on item type.  For instance, payload of '.key' accessor item is
 * length of key name and key name itself.  Payload of '>' arithmetic operator
 * item is offsets of right and left operands.
 *
 * So, binary representation of sample expression above is:
 * (bottom arrows are next links, top lines are argument links)
 *
 *                                _____
 *       _____                ___/____ \                __
 *    _ /_    \         _____/__/____ \ \      __    _ /_ \
 *   / /  \    \       /    /  /     \ \ \    /  \  / /  \ \
 * +(LR)  $ .a  $  [](* to *, * to *) 1 5 7 ?(A)  >(LR)   @ 3 .double() .type()
 * |      |  ^  |  ^|                        ^|                   ^        ^
 * |      |__|  |__||________________________||___________________|        |
 * |_______________________________________________________________________|
 *
 * Copyright (c) 2019-2020, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *  src/backend/utils/adt/jsonpath.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "funcapi.h"
#include "lib/stringinfo.h"
#include "libpq/pqformat.h"
#include "miscadmin.h"
#include "utils/builtins.h"
#include "utils/json.h"
#include "utils/jsonpath.h"


static Datum jsonPathFromCstring(char *in, int len);
static char *jsonPathToCstring(StringInfo out, JsonPath *in,
                               int estimated_len);
static int  flattenJsonPathParseItem(StringInfo buf, JsonPathParseItem *item,
                                     int nestingLevel, bool insideArraySubscript);
static void alignStringInfoInt(StringInfo buf);
static int32 reserveSpaceForItemPointer(StringInfo buf);
static void printJsonPathItem(StringInfo buf, JsonPathItem *v, bool inKey,
                              bool printBracketes);
static int  operationPriority(JsonPathItemType op);


/**************************** INPUT/OUTPUT ********************************/

/*
 * jsonpath type input function
 */
Datum
jsonpath_in(PG_FUNCTION_ARGS)
{
    char       *in = PG_GETARG_CSTRING(0);
    int         len = strlen(in);

    return jsonPathFromCstring(in, len);
}

/*
 * jsonpath type recv function
 *
 * The type is sent as text in binary mode, so this is almost the same
 * as the input function, but it's prefixed with a version number so we
 * can change the binary format sent in future if necessary. For now,
 * only version 1 is supported.
 */
Datum
jsonpath_recv(PG_FUNCTION_ARGS)
{
    StringInfo  buf = (StringInfo) PG_GETARG_POINTER(0);
    int         version = pq_getmsgint(buf, 1);
    char       *str;
    int         nbytes;

    if (version == JSONPATH_VERSION)
        str = pq_getmsgtext(buf, buf->len - buf->cursor, &nbytes);
    else
        elog(ERROR, "unsupported jsonpath version number: %d", version);

    return jsonPathFromCstring(str, nbytes);
}

/*
 * jsonpath type output function
 */
Datum
jsonpath_out(PG_FUNCTION_ARGS)
{
    JsonPath   *in = PG_GETARG_JSONPATH_P(0);

    PG_RETURN_CSTRING(jsonPathToCstring(NULL, in, VARSIZE(in)));
}

/*
 * jsonpath type send function
 *
 * Just send jsonpath as a version number, then a string of text
 */
Datum
jsonpath_send(PG_FUNCTION_ARGS)
{
    JsonPath   *in = PG_GETARG_JSONPATH_P(0);
    StringInfoData buf;
    StringInfoData jtext;
    int         version = JSONPATH_VERSION;

    initStringInfo(&jtext);
    (void) jsonPathToCstring(&jtext, in, VARSIZE(in));

    pq_begintypsend(&buf);
    pq_sendint8(&buf, version);
    pq_sendtext(&buf, jtext.data, jtext.len);
    pfree(jtext.data);

    PG_RETURN_BYTEA_P(pq_endtypsend(&buf));
}

/*
 * Converts C-string to a jsonpath value.
 *
 * Uses jsonpath parser to turn string into an AST, then
 * flattenJsonPathParseItem() does second pass turning AST into binary
 * representation of jsonpath.
 */
static Datum
jsonPathFromCstring(char *in, int len)
{
    JsonPathParseResult *jsonpath = parsejsonpath(in, len);
    JsonPath   *res;
    StringInfoData buf;

    initStringInfo(&buf);
    enlargeStringInfo(&buf, 4 * len /* estimation */ );

    appendStringInfoSpaces(&buf, JSONPATH_HDRSZ);

    if (!jsonpath)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                 errmsg("invalid input syntax for type %s: \"%s\"", "jsonpath",
                        in)));

    flattenJsonPathParseItem(&buf, jsonpath->expr, 0, false);

    res = (JsonPath *) buf.data;
    SET_VARSIZE(res, buf.len);
    res->header = JSONPATH_VERSION;
    if (jsonpath->lax)
        res->header |= JSONPATH_LAX;

    PG_RETURN_JSONPATH_P(res);
}

/*
 * Converts jsonpath value to a C-string.
 *
 * If 'out' argument is non-null, the resulting C-string is stored inside the
 * StringBuffer.  The resulting string is always returned.
 */
static char *
jsonPathToCstring(StringInfo out, JsonPath *in, int estimated_len)
{
    StringInfoData buf;
    JsonPathItem v;

    if (!out)
    {
        out = &buf;
        initStringInfo(out);
    }
    enlargeStringInfo(out, estimated_len);

    if (!(in->header & JSONPATH_LAX))
        appendBinaryStringInfo(out, "strict ", 7);

    jspInit(&v, in);
    printJsonPathItem(out, &v, false, true);

    return out->data;
}

/*
 * Recursive function converting given jsonpath parse item and all its
 * children into a binary representation.
 */
static int
flattenJsonPathParseItem(StringInfo buf, JsonPathParseItem *item,
                         int nestingLevel, bool insideArraySubscript)
{
    /* position from beginning of jsonpath data */
    int32       pos = buf->len - JSONPATH_HDRSZ;
    int32       chld;
    int32       next;
    int         argNestingLevel = 0;

    check_stack_depth();
    CHECK_FOR_INTERRUPTS();

    appendStringInfoChar(buf, (char) (item->type));

    /*
     * We align buffer to int32 because a series of int32 values often goes
     * after the header, and we want to read them directly by dereferencing
     * int32 pointer (see jspInitByBuffer()).
     */
    alignStringInfoInt(buf);

    /*
     * Reserve space for next item pointer.  Actual value will be recorded
     * later, after next and children items processing.
     */
    next = reserveSpaceForItemPointer(buf);

    switch (item->type)
    {
        case jpiString:
        case jpiVariable:
        case jpiKey:
            appendBinaryStringInfo(buf, (char *) &item->value.string.len,
                                   sizeof(item->value.string.len));
            appendBinaryStringInfo(buf, item->value.string.val,
                                   item->value.string.len);
            appendStringInfoChar(buf, '\0');
            break;
        case jpiNumeric:
            appendBinaryStringInfo(buf, (char *) item->value.numeric,
                                   VARSIZE(item->value.numeric));
            break;
        case jpiBool:
            appendBinaryStringInfo(buf, (char *) &item->value.boolean,
                                   sizeof(item->value.boolean));
            break;
        case jpiAnd:
        case jpiOr:
        case jpiEqual:
        case jpiNotEqual:
        case jpiLess:
        case jpiGreater:
        case jpiLessOrEqual:
        case jpiGreaterOrEqual:
        case jpiAdd:
        case jpiSub:
        case jpiMul:
        case jpiDiv:
        case jpiMod:
        case jpiStartsWith:
            {
                /*
                 * First, reserve place for left/right arg's positions, then
                 * record both args and sets actual position in reserved
                 * places.
                 */
                int32       left = reserveSpaceForItemPointer(buf);
                int32       right = reserveSpaceForItemPointer(buf);

                chld = !item->value.args.left ? pos :
                    flattenJsonPathParseItem(buf, item->value.args.left,
                                             nestingLevel + argNestingLevel,
                                             insideArraySubscript);
                *(int32 *) (buf->data + left) = chld - pos;

                chld = !item->value.args.right ? pos :
                    flattenJsonPathParseItem(buf, item->value.args.right,
                                             nestingLevel + argNestingLevel,
                                             insideArraySubscript);
                *(int32 *) (buf->data + right) = chld - pos;
            }
            break;
        case jpiLikeRegex:
            {
                int32       offs;

                appendBinaryStringInfo(buf,
                                       (char *) &item->value.like_regex.flags,
                                       sizeof(item->value.like_regex.flags));
                offs = reserveSpaceForItemPointer(buf);
                appendBinaryStringInfo(buf,
                                       (char *) &item->value.like_regex.patternlen,
                                       sizeof(item->value.like_regex.patternlen));
                appendBinaryStringInfo(buf, item->value.like_regex.pattern,
                                       item->value.like_regex.patternlen);
                appendStringInfoChar(buf, '\0');

                chld = flattenJsonPathParseItem(buf, item->value.like_regex.expr,
                                                nestingLevel,
                                                insideArraySubscript);
                *(int32 *) (buf->data + offs) = chld - pos;
            }
            break;
        case jpiFilter:
            argNestingLevel++;
            /* FALLTHROUGH */
        case jpiIsUnknown:
        case jpiNot:
        case jpiPlus:
        case jpiMinus:
        case jpiExists:
        case jpiDatetime:
            {
                int32       arg = reserveSpaceForItemPointer(buf);

                chld = !item->value.arg ? pos :
                    flattenJsonPathParseItem(buf, item->value.arg,
                                             nestingLevel + argNestingLevel,
                                             insideArraySubscript);
                *(int32 *) (buf->data + arg) = chld - pos;
            }
            break;
        case jpiNull:
            break;
        case jpiRoot:
            break;
        case jpiAnyArray:
        case jpiAnyKey:
            break;
        case jpiCurrent:
            if (nestingLevel <= 0)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("@ is not allowed in root expressions")));
            break;
        case jpiLast:
            if (!insideArraySubscript)
                ereport(ERROR,
                        (errcode(ERRCODE_SYNTAX_ERROR),
                         errmsg("LAST is allowed only in array subscripts")));
            break;
        case jpiIndexArray:
            {
                int32       nelems = item->value.array.nelems;
                int         offset;
                int         i;

                appendBinaryStringInfo(buf, (char *) &nelems, sizeof(nelems));

                offset = buf->len;

                appendStringInfoSpaces(buf, sizeof(int32) * 2 * nelems);

                for (i = 0; i < nelems; i++)
                {
                    int32      *ppos;
                    int32       topos;
                    int32       frompos =
                    flattenJsonPathParseItem(buf,
                                             item->value.array.elems[i].from,
                                             nestingLevel, true) - pos;

                    if (item->value.array.elems[i].to)
                        topos = flattenJsonPathParseItem(buf,
                                                         item->value.array.elems[i].to,
                                                         nestingLevel, true) - pos;
                    else
                        topos = 0;

                    ppos = (int32 *) &buf->data[offset + i * 2 * sizeof(int32)];

                    ppos[0] = frompos;
                    ppos[1] = topos;
                }
            }
            break;
        case jpiAny:
            appendBinaryStringInfo(buf,
                                   (char *) &item->value.anybounds.first,
                                   sizeof(item->value.anybounds.first));
            appendBinaryStringInfo(buf,
                                   (char *) &item->value.anybounds.last,
                                   sizeof(item->value.anybounds.last));
            break;
        case jpiType:
        case jpiSize:
        case jpiAbs:
        case jpiFloor:
        case jpiCeiling:
        case jpiDouble:
        case jpiKeyValue:
            break;
        default:
            elog(ERROR, "unrecognized jsonpath item type: %d", item->type);
    }

    if (item->next)
    {
        chld = flattenJsonPathParseItem(buf, item->next, nestingLevel,
                                        insideArraySubscript) - pos;
        *(int32 *) (buf->data + next) = chld;
    }

    return pos;
}

/*
 * Align StringInfo to int by adding zero padding bytes
 */
static void
alignStringInfoInt(StringInfo buf)
{
    switch (INTALIGN(buf->len) - buf->len)
    {
        case 3:
            appendStringInfoCharMacro(buf, 0);
            /* FALLTHROUGH */
        case 2:
            appendStringInfoCharMacro(buf, 0);
            /* FALLTHROUGH */
        case 1:
            appendStringInfoCharMacro(buf, 0);
            /* FALLTHROUGH */
        default:
            break;
    }
}

/*
 * Reserve space for int32 JsonPathItem pointer.  Now zero pointer is written,
 * actual value will be recorded at '(int32 *) &buf->data[pos]' later.
 */
static int32
reserveSpaceForItemPointer(StringInfo buf)
{
    int32       pos = buf->len;
    int32       ptr = 0;

    appendBinaryStringInfo(buf, (char *) &ptr, sizeof(ptr));

    return pos;
}

/*
 * Prints text representation of given jsonpath item and all its children.
 */
static void
printJsonPathItem(StringInfo buf, JsonPathItem *v, bool inKey,
                  bool printBracketes)
{
    JsonPathItem elem;
    int         i;

    check_stack_depth();
    CHECK_FOR_INTERRUPTS();

    switch (v->type)
    {
        case jpiNull:
            appendStringInfoString(buf, "null");
            break;
        case jpiKey:
            if (inKey)
                appendStringInfoChar(buf, '.');
            escape_json(buf, jspGetString(v, NULL));
            break;
        case jpiString:
            escape_json(buf, jspGetString(v, NULL));
            break;
        case jpiVariable:
            appendStringInfoChar(buf, '$');
            escape_json(buf, jspGetString(v, NULL));
            break;
        case jpiNumeric:
            appendStringInfoString(buf,
                                   DatumGetCString(DirectFunctionCall1(numeric_out,
                                                                       NumericGetDatum(jspGetNumeric(v)))));
            break;
        case jpiBool:
            if (jspGetBool(v))
                appendBinaryStringInfo(buf, "true", 4);
            else
                appendBinaryStringInfo(buf, "false", 5);
            break;
        case jpiAnd:
        case jpiOr:
        case jpiEqual:
        case jpiNotEqual:
        case jpiLess:
        case jpiGreater:
        case jpiLessOrEqual:
        case jpiGreaterOrEqual:
        case jpiAdd:
        case jpiSub:
        case jpiMul:
        case jpiDiv:
        case jpiMod:
        case jpiStartsWith:
            if (printBracketes)
                appendStringInfoChar(buf, '(');
            jspGetLeftArg(v, &elem);
            printJsonPathItem(buf, &elem, false,
                              operationPriority(elem.type) <=
                              operationPriority(v->type));
            appendStringInfoChar(buf, ' ');
            appendStringInfoString(buf, jspOperationName(v->type));
            appendStringInfoChar(buf, ' ');
            jspGetRightArg(v, &elem);
            printJsonPathItem(buf, &elem, false,
                              operationPriority(elem.type) <=
                              operationPriority(v->type));
            if (printBracketes)
                appendStringInfoChar(buf, ')');
            break;
        case jpiLikeRegex:
            if (printBracketes)
                appendStringInfoChar(buf, '(');

            jspInitByBuffer(&elem, v->base, v->content.like_regex.expr);
            printJsonPathItem(buf, &elem, false,
                              operationPriority(elem.type) <=
                              operationPriority(v->type));

            appendBinaryStringInfo(buf, " like_regex ", 12);

            escape_json(buf, v->content.like_regex.pattern);

            if (v->content.like_regex.flags)
            {
                appendBinaryStringInfo(buf, " flag \"", 7);

                if (v->content.like_regex.flags & JSP_REGEX_ICASE)
                    appendStringInfoChar(buf, 'i');
                if (v->content.like_regex.flags & JSP_REGEX_DOTALL)
                    appendStringInfoChar(buf, 's');
                if (v->content.like_regex.flags & JSP_REGEX_MLINE)
                    appendStringInfoChar(buf, 'm');
                if (v->content.like_regex.flags & JSP_REGEX_WSPACE)
                    appendStringInfoChar(buf, 'x');
                if (v->content.like_regex.flags & JSP_REGEX_QUOTE)
                    appendStringInfoChar(buf, 'q');

                appendStringInfoChar(buf, '"');
            }

            if (printBracketes)
                appendStringInfoChar(buf, ')');
            break;
        case jpiPlus:
        case jpiMinus:
            if (printBracketes)
                appendStringInfoChar(buf, '(');
            appendStringInfoChar(buf, v->type == jpiPlus ? '+' : '-');
            jspGetArg(v, &elem);
            printJsonPathItem(buf, &elem, false,
                              operationPriority(elem.type) <=
                              operationPriority(v->type));
            if (printBracketes)
                appendStringInfoChar(buf, ')');
            break;
        case jpiFilter:
            appendBinaryStringInfo(buf, "?(", 2);
            jspGetArg(v, &elem);
            printJsonPathItem(buf, &elem, false, false);
            appendStringInfoChar(buf, ')');
            break;
        case jpiNot:
            appendBinaryStringInfo(buf, "!(", 2);
            jspGetArg(v, &elem);
            printJsonPathItem(buf, &elem, false, false);
            appendStringInfoChar(buf, ')');
            break;
        case jpiIsUnknown:
            appendStringInfoChar(buf, '(');
            jspGetArg(v, &elem);
            printJsonPathItem(buf, &elem, false, false);
            appendBinaryStringInfo(buf, ") is unknown", 12);
            break;
        case jpiExists:
            appendBinaryStringInfo(buf, "exists (", 8);
            jspGetArg(v, &elem);
            printJsonPathItem(buf, &elem, false, false);
            appendStringInfoChar(buf, ')');
            break;
        case jpiCurrent:
            Assert(!inKey);
            appendStringInfoChar(buf, '@');
            break;
        case jpiRoot:
            Assert(!inKey);
            appendStringInfoChar(buf, '$');
            break;
        case jpiLast:
            appendBinaryStringInfo(buf, "last", 4);
            break;
        case jpiAnyArray:
            appendBinaryStringInfo(buf, "[*]", 3);
            break;
        case jpiAnyKey:
            if (inKey)
                appendStringInfoChar(buf, '.');
            appendStringInfoChar(buf, '*');
            break;
        case jpiIndexArray:
            appendStringInfoChar(buf, '[');
            for (i = 0; i < v->content.array.nelems; i++)
            {
                JsonPathItem from;
                JsonPathItem to;
                bool        range = jspGetArraySubscript(v, &from, &to, i);

                if (i)
                    appendStringInfoChar(buf, ',');

                printJsonPathItem(buf, &from, false, false);

                if (range)
                {
                    appendBinaryStringInfo(buf, " to ", 4);
                    printJsonPathItem(buf, &to, false, false);
                }
            }
            appendStringInfoChar(buf, ']');
            break;
        case jpiAny:
            if (inKey)
                appendStringInfoChar(buf, '.');

            if (v->content.anybounds.first == 0 &&
                v->content.anybounds.last == PG_UINT32_MAX)
                appendBinaryStringInfo(buf, "**", 2);
            else if (v->content.anybounds.first == v->content.anybounds.last)
            {
                if (v->content.anybounds.first == PG_UINT32_MAX)
                    appendStringInfo(buf, "**{last}");
                else
                    appendStringInfo(buf, "**{%u}",
                                     v->content.anybounds.first);
            }
            else if (v->content.anybounds.first == PG_UINT32_MAX)
                appendStringInfo(buf, "**{last to %u}",
                                 v->content.anybounds.last);
            else if (v->content.anybounds.last == PG_UINT32_MAX)
                appendStringInfo(buf, "**{%u to last}",
                                 v->content.anybounds.first);
            else
                appendStringInfo(buf, "**{%u to %u}",
                                 v->content.anybounds.first,
                                 v->content.anybounds.last);
            break;
        case jpiType:
            appendBinaryStringInfo(buf, ".type()", 7);
            break;
        case jpiSize:
            appendBinaryStringInfo(buf, ".size()", 7);
            break;
        case jpiAbs:
            appendBinaryStringInfo(buf, ".abs()", 6);
            break;
        case jpiFloor:
            appendBinaryStringInfo(buf, ".floor()", 8);
            break;
        case jpiCeiling:
            appendBinaryStringInfo(buf, ".ceiling()", 10);
            break;
        case jpiDouble:
            appendBinaryStringInfo(buf, ".double()", 9);
            break;
        case jpiDatetime:
            appendBinaryStringInfo(buf, ".datetime(", 10);
            if (v->content.arg)
            {
                jspGetArg(v, &elem);
                printJsonPathItem(buf, &elem, false, false);
            }
            appendStringInfoChar(buf, ')');
            break;
        case jpiKeyValue:
            appendBinaryStringInfo(buf, ".keyvalue()", 11);
            break;
        default:
            elog(ERROR, "unrecognized jsonpath item type: %d", v->type);
    }

    if (jspGetNext(v, &elem))
        printJsonPathItem(buf, &elem, true, true);
}

const char *
jspOperationName(JsonPathItemType type)
{
    switch (type)
    {
        case jpiAnd:
            return "&&";
        case jpiOr:
            return "||";
        case jpiEqual:
            return "==";
        case jpiNotEqual:
            return "!=";
        case jpiLess:
            return "<";
        case jpiGreater:
            return ">";
        case jpiLessOrEqual:
            return "<=";
        case jpiGreaterOrEqual:
            return ">=";
        case jpiPlus:
        case jpiAdd:
            return "+";
        case jpiMinus:
        case jpiSub:
            return "-";
        case jpiMul:
            return "*";
        case jpiDiv:
            return "/";
        case jpiMod:
            return "%";
        case jpiStartsWith:
            return "starts with";
        case jpiLikeRegex:
            return "like_regex";
        case jpiType:
            return "type";
        case jpiSize:
            return "size";
        case jpiKeyValue:
            return "keyvalue";
        case jpiDouble:
            return "double";
        case jpiAbs:
            return "abs";
        case jpiFloor:
            return "floor";
        case jpiCeiling:
            return "ceiling";
        case jpiDatetime:
            return "datetime";
        default:
            elog(ERROR, "unrecognized jsonpath item type: %d", type);
            return NULL;
    }
}

static int
operationPriority(JsonPathItemType op)
{
    switch (op)
    {
        case jpiOr:
            return 0;
        case jpiAnd:
            return 1;
        case jpiEqual:
        case jpiNotEqual:
        case jpiLess:
        case jpiGreater:
        case jpiLessOrEqual:
        case jpiGreaterOrEqual:
        case jpiStartsWith:
            return 2;
        case jpiAdd:
        case jpiSub:
            return 3;
        case jpiMul:
        case jpiDiv:
        case jpiMod:
            return 4;
        case jpiPlus:
        case jpiMinus:
            return 5;
        default:
            return 6;
    }
}

/******************* Support functions for JsonPath *************************/

/*
 * Support macros to read stored values
 */

#define read_byte(v, b, p) do {         \
    (v) = *(uint8*)((b) + (p));         \
    (p) += 1;                           \
} while(0)                              \

#define read_int32(v, b, p) do {        \
    (v) = *(uint32*)((b) + (p));        \
    (p) += sizeof(int32);               \
} while(0)                              \

#define read_int32_n(v, b, p, n) do {   \
    (v) = (void *)((b) + (p));          \
    (p) += sizeof(int32) * (n);         \
} while(0)                              \

/*
 * Read root node and fill root node representation
 */
void
jspInit(JsonPathItem *v, JsonPath *js)
{
    Assert((js->header & ~JSONPATH_LAX) == JSONPATH_VERSION);
    jspInitByBuffer(v, js->data, 0);
}

/*
 * Read node from buffer and fill its representation
 */
void
jspInitByBuffer(JsonPathItem *v, char *base, int32 pos)
{
    v->base = base + pos;

    read_byte(v->type, base, pos);
    pos = INTALIGN((uintptr_t) (base + pos)) - (uintptr_t) base;
    read_int32(v->nextPos, base, pos);

    switch (v->type)
    {
        case jpiNull:
        case jpiRoot:
        case jpiCurrent:
        case jpiAnyArray:
        case jpiAnyKey:
        case jpiType:
        case jpiSize:
        case jpiAbs:
        case jpiFloor:
        case jpiCeiling:
        case jpiDouble:
        case jpiKeyValue:
        case jpiLast:
            break;
        case jpiKey:
        case jpiString:
        case jpiVariable:
            read_int32(v->content.value.datalen, base, pos);
            /* FALLTHROUGH */
        case jpiNumeric:
        case jpiBool:
            v->content.value.data = base + pos;
            break;
        case jpiAnd:
        case jpiOr:
        case jpiAdd:
        case jpiSub:
        case jpiMul:
        case jpiDiv:
        case jpiMod:
        case jpiEqual:
        case jpiNotEqual:
        case jpiLess:
        case jpiGreater:
        case jpiLessOrEqual:
        case jpiGreaterOrEqual:
        case jpiStartsWith:
            read_int32(v->content.args.left, base, pos);
            read_int32(v->content.args.right, base, pos);
            break;
        case jpiLikeRegex:
            read_int32(v->content.like_regex.flags, base, pos);
            read_int32(v->content.like_regex.expr, base, pos);
            read_int32(v->content.like_regex.patternlen, base, pos);
            v->content.like_regex.pattern = base + pos;
            break;
        case jpiNot:
        case jpiExists:
        case jpiIsUnknown:
        case jpiPlus:
        case jpiMinus:
        case jpiFilter:
        case jpiDatetime:
            read_int32(v->content.arg, base, pos);
            break;
        case jpiIndexArray:
            read_int32(v->content.array.nelems, base, pos);
            read_int32_n(v->content.array.elems, base, pos,
                         v->content.array.nelems * 2);
            break;
        case jpiAny:
            read_int32(v->content.anybounds.first, base, pos);
            read_int32(v->content.anybounds.last, base, pos);
            break;
        default:
            elog(ERROR, "unrecognized jsonpath item type: %d", v->type);
    }
}

void
jspGetArg(JsonPathItem *v, JsonPathItem *a)
{
    Assert(v->type == jpiFilter ||
           v->type == jpiNot ||
           v->type == jpiIsUnknown ||
           v->type == jpiExists ||
           v->type == jpiPlus ||
           v->type == jpiMinus ||
           v->type == jpiDatetime);

    jspInitByBuffer(a, v->base, v->content.arg);
}

bool
jspGetNext(JsonPathItem *v, JsonPathItem *a)
{
    if (jspHasNext(v))
    {
        Assert(v->type == jpiString ||
               v->type == jpiNumeric ||
               v->type == jpiBool ||
               v->type == jpiNull ||
               v->type == jpiKey ||
               v->type == jpiAny ||
               v->type == jpiAnyArray ||
               v->type == jpiAnyKey ||
               v->type == jpiIndexArray ||
               v->type == jpiFilter ||
               v->type == jpiCurrent ||
               v->type == jpiExists ||
               v->type == jpiRoot ||
               v->type == jpiVariable ||
               v->type == jpiLast ||
               v->type == jpiAdd ||
               v->type == jpiSub ||
               v->type == jpiMul ||
               v->type == jpiDiv ||
               v->type == jpiMod ||
               v->type == jpiPlus ||
               v->type == jpiMinus ||
               v->type == jpiEqual ||
               v->type == jpiNotEqual ||
               v->type == jpiGreater ||
               v->type == jpiGreaterOrEqual ||
               v->type == jpiLess ||
               v->type == jpiLessOrEqual ||
               v->type == jpiAnd ||
               v->type == jpiOr ||
               v->type == jpiNot ||
               v->type == jpiIsUnknown ||
               v->type == jpiType ||
               v->type == jpiSize ||
               v->type == jpiAbs ||
               v->type == jpiFloor ||
               v->type == jpiCeiling ||
               v->type == jpiDouble ||
               v->type == jpiDatetime ||
               v->type == jpiKeyValue ||
               v->type == jpiStartsWith);

        if (a)
            jspInitByBuffer(a, v->base, v->nextPos);
        return true;
    }

    return false;
}

void
jspGetLeftArg(JsonPathItem *v, JsonPathItem *a)
{
    Assert(v->type == jpiAnd ||
           v->type == jpiOr ||
           v->type == jpiEqual ||
           v->type == jpiNotEqual ||
           v->type == jpiLess ||
           v->type == jpiGreater ||
           v->type == jpiLessOrEqual ||
           v->type == jpiGreaterOrEqual ||
           v->type == jpiAdd ||
           v->type == jpiSub ||
           v->type == jpiMul ||
           v->type == jpiDiv ||
           v->type == jpiMod ||
           v->type == jpiStartsWith);

    jspInitByBuffer(a, v->base, v->content.args.left);
}

void
jspGetRightArg(JsonPathItem *v, JsonPathItem *a)
{
    Assert(v->type == jpiAnd ||
           v->type == jpiOr ||
           v->type == jpiEqual ||
           v->type == jpiNotEqual ||
           v->type == jpiLess ||
           v->type == jpiGreater ||
           v->type == jpiLessOrEqual ||
           v->type == jpiGreaterOrEqual ||
           v->type == jpiAdd ||
           v->type == jpiSub ||
           v->type == jpiMul ||
           v->type == jpiDiv ||
           v->type == jpiMod ||
           v->type == jpiStartsWith);

    jspInitByBuffer(a, v->base, v->content.args.right);
}

bool
jspGetBool(JsonPathItem *v)
{
    Assert(v->type == jpiBool);

    return (bool) *v->content.value.data;
}

Numeric
jspGetNumeric(JsonPathItem *v)
{
    Assert(v->type == jpiNumeric);

    return (Numeric) v->content.value.data;
}

char *
jspGetString(JsonPathItem *v, int32 *len)
{
    Assert(v->type == jpiKey ||
           v->type == jpiString ||
           v->type == jpiVariable);

    if (len)
        *len = v->content.value.datalen;
    return v->content.value.data;
}

bool
jspGetArraySubscript(JsonPathItem *v, JsonPathItem *from, JsonPathItem *to,
                     int i)
{
    Assert(v->type == jpiIndexArray);

    jspInitByBuffer(from, v->base, v->content.array.elems[i].from);

    if (!v->content.array.elems[i].to)
        return false;

    jspInitByBuffer(to, v->base, v->content.array.elems[i].to);

    return true;
}