C function doesn't return more than one tuple - Mailing list pgsql-general

Hi, I'm trying to develop a C module, but when the query result is
more than one tuple the server crashes.

Here is the code:

#include "postgres.h"
#include "gram.h"
#include "utils/builtins.h"
#include "funcapi.h"
#include "executor/spi.h"
#include "access/heapam.h"
#include "fmgr.h"

extern Datum sqlf(PG_FUNCTION_ARGS);

PG_MODULE_MAGIC;

PG_FUNCTION_INFO_V1(sqlf);

Datum
sqlf(PG_FUNCTION_ARGS)
{

    char            *query = TextDatumGetCString(PG_GETARG_DATUM(0));
    const char      *result="SELECT name FROM people WHERE age>10";
    int             ret,proc;
    int             j,i;

    FuncCallContext *funcctx;
    int call_cntr;
    int max_calls;
    TupleDesc tupdesc;
    TupleDesc tupledesc;
    SPITupleTable   *tuptable;
    AttInMetadata *attinmeta;

    // stuff done only on the first call of the function
    if (SRF_IS_FIRSTCALL()) {
        MemoryContext oldcontext;

        // create a function context for cross-call persistence
        funcctx = SRF_FIRSTCALL_INIT();

        // switch to memory context appropriate for multiple
        // function calls
        oldcontext =
            MemoryContextSwitchTo(funcctx->
                                  multi_call_memory_ctx);

        SPI_connect();
        ret=SPI_execute(result,true,0);
        proc=SPI_processed;

        // total number of tuples to be returned
        funcctx->max_calls = proc;

        if (ret > 0 && SPI_tuptable != NULL){
            tupdesc = SPI_tuptable->tupdesc;
            tuptable = SPI_tuptable;
        }
        tupledesc = BlessTupleDesc(tupdesc);

        MemoryContextSwitchTo(oldcontext);
    }

    // stuff done on every call of the function
    funcctx = SRF_PERCALL_SETUP();

    call_cntr = funcctx->call_cntr;
    max_calls = funcctx->max_calls;
    attinmeta = funcctx->attinmeta;

    j=0;
    if (call_cntr < max_calls) {  // do when there is more left to send

        Datum values[tupdesc->natts];
        bool nulls[tupdesc->natts];
        HeapTuple tuple;
        Datum datum_result;
        bool isnull;

        tuple=tuptable->vals[j];

        for (i = 0; i < tupdesc->natts; i++){
            values[i]=SPI_getbinval(tuple,tupledesc,i+1,&isnull);
            nulls[i]=false;
        }

        // build a tuple
        tuple= heap_form_tuple(tupledesc,values,nulls);

        // make the tuple into a datum
        datum_result = HeapTupleGetDatum(tuple);

        j++;

        SRF_RETURN_NEXT(funcctx, datum_result);
    } else {  // do when there is no more left

        SPI_finish();
        SRF_RETURN_DONE(funcctx);
    }

}