hstore_subs.c

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/*-------------------------------------------------------------------------
 *
 * hstore_subs.c
 *    Subscripting support functions for hstore.
 *
 * This is a great deal simpler than array_subs.c, because the result of
 * subscripting an hstore is just a text string (the value for the key).
 * We do not need to support array slicing notation, nor multiple subscripts.
 * Less obviously, because the subscript result is never a SQL container
 * type, there will never be any nested-assignment scenarios, so we do not
 * need a fetch_old function.  In turn, that means we can drop the
 * check_subscripts function and just let the fetch and assign functions
 * do everything.
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    contrib/hstore/hstore_subs.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "executor/execExpr.h"
#include "hstore.h"
#include "nodes/nodeFuncs.h"
#include "nodes/subscripting.h"
#include "parser/parse_coerce.h"
#include "parser/parse_expr.h"
#include "utils/builtins.h"
 
 
/*
 * Finish parse analysis of a SubscriptingRef expression for hstore.
 *
 * Verify there's just one subscript, coerce it to text,
 * and set the result type of the SubscriptingRef node.
 */
static void
hstore_subscript_transform(SubscriptingRef *sbsref,
                           List *indirection,
                           ParseState *pstate,
                           bool isSlice,
                           bool isAssignment)
{
    A_Indices  *ai;
    Node       *subexpr;
 
    /* We support only single-subscript, non-slice cases */
    if (isSlice || list_length(indirection) != 1)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("hstore allows only one subscript"),
                 parser_errposition(pstate,
                                    exprLocation((Node *) indirection))));
 
    /* Transform the subscript expression to type text */
    ai = linitial_node(A_Indices, indirection);
    Assert(ai->uidx != NULL && ai->lidx == NULL && !ai->is_slice);
 
    subexpr = transformExpr(pstate, ai->uidx, pstate->p_expr_kind);
    /* If it's not text already, try to coerce */
    subexpr = coerce_to_target_type(pstate,
                                    subexpr, exprType(subexpr),
                                    TEXTOID, -1,
                                    COERCION_ASSIGNMENT,
                                    COERCE_IMPLICIT_CAST,
                                    -1);
    if (subexpr == NULL)
        ereport(ERROR,
                (errcode(ERRCODE_DATATYPE_MISMATCH),
                 errmsg("hstore subscript must have type text"),
                 parser_errposition(pstate, exprLocation(ai->uidx))));
 
    /* ... and store the transformed subscript into the SubscriptRef node */
    sbsref->refupperindexpr = list_make1(subexpr);
    sbsref->reflowerindexpr = NIL;
 
    /* Determine the result type of the subscripting operation; always text */
    sbsref->refrestype = TEXTOID;
    sbsref->reftypmod = -1;
}
 
/*
 * Evaluate SubscriptingRef fetch for hstore.
 *
 * Source container is in step's result variable (it's known not NULL, since
 * we set fetch_strict to true), and the subscript expression is in the
 * upperindex[] array.
 */
static void
hstore_subscript_fetch(ExprState *state,
                       ExprEvalStep *op,
                       ExprContext *econtext)
{
    SubscriptingRefState *sbsrefstate = op->d.sbsref.state;
    HStore     *hs;
    text       *key;
    HEntry     *entries;
    int         idx;
    text       *out;
 
    /* Should not get here if source hstore is null */
    Assert(!(*op->resnull));
 
    /* Check for null subscript */
    if (sbsrefstate->upperindexnull[0])
    {
        *op->resnull = true;
        return;
    }
 
    /* OK, fetch/detoast the hstore and subscript */
    hs = DatumGetHStoreP(*op->resvalue);
    key = DatumGetTextPP(sbsrefstate->upperindex[0]);
 
    /* The rest is basically the same as hstore_fetchval() */
    entries = ARRPTR(hs);
    idx = hstoreFindKey(hs, NULL,
                        VARDATA_ANY(key), VARSIZE_ANY_EXHDR(key));
 
    if (idx < 0 || HSTORE_VALISNULL(entries, idx))
    {
        *op->resnull = true;
        return;
    }
 
    out = cstring_to_text_with_len(HSTORE_VAL(entries, STRPTR(hs), idx),
                                   HSTORE_VALLEN(entries, idx));
 
    *op->resvalue = PointerGetDatum(out);
}
 
/*
 * Evaluate SubscriptingRef assignment for hstore.
 *
 * Input container (possibly null) is in result area, replacement value is in
 * SubscriptingRefState's replacevalue/replacenull.
 */
static void
hstore_subscript_assign(ExprState *state,
                        ExprEvalStep *op,
                        ExprContext *econtext)
{
    SubscriptingRefState *sbsrefstate = op->d.sbsref.state;
    text       *key;
    Pairs       p;
    HStore     *out;
 
    /* Check for null subscript */
    if (sbsrefstate->upperindexnull[0])
        ereport(ERROR,
                (errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
                 errmsg("hstore subscript in assignment must not be null")));
 
    /* OK, fetch/detoast the subscript */
    key = DatumGetTextPP(sbsrefstate->upperindex[0]);
 
    /* Create a Pairs entry for subscript + replacement value */
    p.needfree = false;
    p.key = VARDATA_ANY(key);
    p.keylen = hstoreCheckKeyLen(VARSIZE_ANY_EXHDR(key));
 
    if (sbsrefstate->replacenull)
    {
        p.vallen = 0;
        p.isnull = true;
    }
    else
    {
        text       *val = DatumGetTextPP(sbsrefstate->replacevalue);
 
        p.val = VARDATA_ANY(val);
        p.vallen = hstoreCheckValLen(VARSIZE_ANY_EXHDR(val));
        p.isnull = false;
    }
 
    if (*op->resnull)
    {
        /* Just build a one-element hstore (cf. hstore_from_text) */
        out = hstorePairs(&p, 1, p.keylen + p.vallen);
    }
    else
    {
        /*
         * Otherwise, merge the new key into the hstore.  Based on
         * hstore_concat.
         */
        HStore     *hs = DatumGetHStoreP(*op->resvalue);
        int         s1count = HS_COUNT(hs);
        int         outcount = 0;
        int         vsize;
        char       *ps1,
                   *bufd,
                   *pd;
        HEntry     *es1,
                   *ed;
        int         s1idx;
        int         s2idx;
 
        /* Allocate result without considering possibility of duplicate */
        vsize = CALCDATASIZE(s1count + 1, VARSIZE(hs) + p.keylen + p.vallen);
        out = palloc(vsize);
        SET_VARSIZE(out, vsize);
        HS_SETCOUNT(out, s1count + 1);
 
        ps1 = STRPTR(hs);
        bufd = pd = STRPTR(out);
        es1 = ARRPTR(hs);
        ed = ARRPTR(out);
 
        for (s1idx = s2idx = 0; s1idx < s1count || s2idx < 1; ++outcount)
        {
            int         difference;
 
            if (s1idx >= s1count)
                difference = 1;
            else if (s2idx >= 1)
                difference = -1;
            else
            {
                int         s1keylen = HSTORE_KEYLEN(es1, s1idx);
                int         s2keylen = p.keylen;
 
                if (s1keylen == s2keylen)
                    difference = memcmp(HSTORE_KEY(es1, ps1, s1idx),
                                        p.key,
                                        s1keylen);
                else
                    difference = (s1keylen > s2keylen) ? 1 : -1;
            }
 
            if (difference >= 0)
            {
                HS_ADDITEM(ed, bufd, pd, p);
                ++s2idx;
                if (difference == 0)
                    ++s1idx;
            }
            else
            {
                HS_COPYITEM(ed, bufd, pd,
                            HSTORE_KEY(es1, ps1, s1idx),
                            HSTORE_KEYLEN(es1, s1idx),
                            HSTORE_VALLEN(es1, s1idx),
                            HSTORE_VALISNULL(es1, s1idx));
                ++s1idx;
            }
        }
 
        HS_FINALIZE(out, outcount, bufd, pd);
    }
 
    *op->resvalue = PointerGetDatum(out);
    *op->resnull = false;
}
 
/*
 * Set up execution state for an hstore subscript operation.
 */
static void
hstore_exec_setup(const SubscriptingRef *sbsref,
                  SubscriptingRefState *sbsrefstate,
                  SubscriptExecSteps *methods)
{
    /* Assert we are dealing with one subscript */
    Assert(sbsrefstate->numlower == 0);
    Assert(sbsrefstate->numupper == 1);
    /* We can't check upperprovided[0] here, but it must be true */
 
    /* Pass back pointers to appropriate step execution functions */
    methods->sbs_check_subscripts = NULL;
    methods->sbs_fetch = hstore_subscript_fetch;
    methods->sbs_assign = hstore_subscript_assign;
    methods->sbs_fetch_old = NULL;
}
 
/*
 * hstore_subscript_handler
 *      Subscripting handler for hstore.
 */
PG_FUNCTION_INFO_V1(hstore_subscript_handler);
Datum
hstore_subscript_handler(PG_FUNCTION_ARGS)
{
    static const SubscriptRoutines sbsroutines = {
        .transform = hstore_subscript_transform,
        .exec_setup = hstore_exec_setup,
        .fetch_strict = true,   /* fetch returns NULL for NULL inputs */
        .fetch_leakproof = true,    /* fetch returns NULL for bad subscript */
        .store_leakproof = false    /* ... but assignment throws error */
    };
 
    PG_RETURN_POINTER(&sbsroutines);
}