plpy_exec.c

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/*
 * executing Python code
 *
 * src/pl/plpython/plpy_exec.c
 */

#include "postgres.h"

#include "access/htup_details.h"
#include "access/xact.h"
#include "catalog/pg_type.h"
#include "commands/trigger.h"
#include "executor/spi.h"
#include "funcapi.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
#include "utils/typcache.h"

#include "plpython.h"

#include "plpy_exec.h"

#include "plpy_elog.h"
#include "plpy_main.h"
#include "plpy_procedure.h"
#include "plpy_subxactobject.h"


/* saved state for a set-returning function */
typedef struct PLySRFState
{
    PyObject   *iter;           /* Python iterator producing results */
    PLySavedArgs *savedargs;    /* function argument values */
    MemoryContextCallback callback; /* for releasing refcounts when done */
} PLySRFState;

static PyObject *PLy_function_build_args(FunctionCallInfo fcinfo, PLyProcedure *proc);
static PLySavedArgs *PLy_function_save_args(PLyProcedure *proc);
static void PLy_function_restore_args(PLyProcedure *proc, PLySavedArgs *savedargs);
static void PLy_function_drop_args(PLySavedArgs *savedargs);
static void PLy_global_args_push(PLyProcedure *proc);
static void PLy_global_args_pop(PLyProcedure *proc);
static void plpython_srf_cleanup_callback(void *arg);
static void plpython_return_error_callback(void *arg);

static PyObject *PLy_trigger_build_args(FunctionCallInfo fcinfo, PLyProcedure *proc,
                                        HeapTuple *rv);
static HeapTuple PLy_modify_tuple(PLyProcedure *proc, PyObject *pltd,
                                  TriggerData *tdata, HeapTuple otup);
static void plpython_trigger_error_callback(void *arg);

static PyObject *PLy_procedure_call(PLyProcedure *proc, const char *kargs, PyObject *vargs);
static void PLy_abort_open_subtransactions(int save_subxact_level);


/* function subhandler */
Datum
PLy_exec_function(FunctionCallInfo fcinfo, PLyProcedure *proc)
{
    bool        is_setof = proc->is_setof;
    Datum       rv;
    PyObject   *volatile plargs = NULL;
    PyObject   *volatile plrv = NULL;
    FuncCallContext *volatile funcctx = NULL;
    PLySRFState *volatile srfstate = NULL;
    ErrorContextCallback plerrcontext;

    /*
     * If the function is called recursively, we must push outer-level
     * arguments into the stack.  This must be immediately before the PG_TRY
     * to ensure that the corresponding pop happens.
     */
    PLy_global_args_push(proc);

    PG_TRY();
    {
        if (is_setof)
        {
            /* First Call setup */
            if (SRF_IS_FIRSTCALL())
            {
                funcctx = SRF_FIRSTCALL_INIT();
                srfstate = (PLySRFState *)
                    MemoryContextAllocZero(funcctx->multi_call_memory_ctx,
                                           sizeof(PLySRFState));
                /* Immediately register cleanup callback */
                srfstate->callback.func = plpython_srf_cleanup_callback;
                srfstate->callback.arg = (void *) srfstate;
                MemoryContextRegisterResetCallback(funcctx->multi_call_memory_ctx,
                                                   &srfstate->callback);
                funcctx->user_fctx = (void *) srfstate;
            }
            /* Every call setup */
            funcctx = SRF_PERCALL_SETUP();
            Assert(funcctx != NULL);
            srfstate = (PLySRFState *) funcctx->user_fctx;
            Assert(srfstate != NULL);
        }

        if (srfstate == NULL || srfstate->iter == NULL)
        {
            /*
             * Non-SETOF function or first time for SETOF function: build
             * args, then actually execute the function.
             */
            plargs = PLy_function_build_args(fcinfo, proc);
            plrv = PLy_procedure_call(proc, "args", plargs);
            Assert(plrv != NULL);
        }
        else
        {
            /*
             * Second or later call for a SETOF function: restore arguments in
             * globals dict to what they were when we left off.  We must do
             * this in case multiple evaluations of the same SETOF function
             * are interleaved.  It's a bit annoying, since the iterator may
             * not look at the arguments at all, but we have no way to know
             * that.  Fortunately this isn't terribly expensive.
             */
            if (srfstate->savedargs)
                PLy_function_restore_args(proc, srfstate->savedargs);
            srfstate->savedargs = NULL; /* deleted by restore_args */
        }

        /*
         * If it returns a set, call the iterator to get the next return item.
         * We stay in the SPI context while doing this, because PyIter_Next()
         * calls back into Python code which might contain SPI calls.
         */
        if (is_setof)
        {
            if (srfstate->iter == NULL)
            {
                /* first time -- do checks and setup */
                ReturnSetInfo *rsi = (ReturnSetInfo *) fcinfo->resultinfo;

                if (!rsi || !IsA(rsi, ReturnSetInfo) ||
                    (rsi->allowedModes & SFRM_ValuePerCall) == 0)
                {
                    ereport(ERROR,
                            (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                             errmsg("unsupported set function return mode"),
                             errdetail("PL/Python set-returning functions only support returning one value per call.")));
                }
                rsi->returnMode = SFRM_ValuePerCall;

                /* Make iterator out of returned object */
                srfstate->iter = PyObject_GetIter(plrv);

                Py_DECREF(plrv);
                plrv = NULL;

                if (srfstate->iter == NULL)
                    ereport(ERROR,
                            (errcode(ERRCODE_DATATYPE_MISMATCH),
                             errmsg("returned object cannot be iterated"),
                             errdetail("PL/Python set-returning functions must return an iterable object.")));
            }

            /* Fetch next from iterator */
            plrv = PyIter_Next(srfstate->iter);
            if (plrv == NULL)
            {
                /* Iterator is exhausted or error happened */
                bool        has_error = (PyErr_Occurred() != NULL);

                Py_DECREF(srfstate->iter);
                srfstate->iter = NULL;

                if (has_error)
                    PLy_elog(ERROR, "error fetching next item from iterator");

                /* Pass a null through the data-returning steps below */
                Py_INCREF(Py_None);
                plrv = Py_None;
            }
            else
            {
                /*
                 * This won't be last call, so save argument values.  We do
                 * this again each time in case the iterator is changing those
                 * values.
                 */
                srfstate->savedargs = PLy_function_save_args(proc);
            }
        }

        /*
         * Disconnect from SPI manager and then create the return values datum
         * (if the input function does a palloc for it this must not be
         * allocated in the SPI memory context because SPI_finish would free
         * it).
         */
        if (SPI_finish() != SPI_OK_FINISH)
            elog(ERROR, "SPI_finish failed");

        plerrcontext.callback = plpython_return_error_callback;
        plerrcontext.previous = error_context_stack;
        error_context_stack = &plerrcontext;

        /*
         * For a procedure or function declared to return void, the Python
         * return value must be None. For void-returning functions, we also
         * treat a None return value as a special "void datum" rather than
         * NULL (as is the case for non-void-returning functions).
         */
        if (proc->result.typoid == VOIDOID)
        {
            if (plrv != Py_None)
            {
                if (proc->is_procedure)
                    ereport(ERROR,
                            (errcode(ERRCODE_DATATYPE_MISMATCH),
                             errmsg("PL/Python procedure did not return None")));
                else
                    ereport(ERROR,
                            (errcode(ERRCODE_DATATYPE_MISMATCH),
                             errmsg("PL/Python function with return type \"void\" did not return None")));
            }

            fcinfo->isnull = false;
            rv = (Datum) 0;
        }
        else if (plrv == Py_None &&
                 srfstate && srfstate->iter == NULL)
        {
            /*
             * In a SETOF function, the iteration-ending null isn't a real
             * value; don't pass it through the input function, which might
             * complain.
             */
            fcinfo->isnull = true;
            rv = (Datum) 0;
        }
        else
        {
            /* Normal conversion of result */
            rv = PLy_output_convert(&proc->result, plrv,
                                    &fcinfo->isnull);
        }
    }
    PG_CATCH();
    {
        /* Pop old arguments from the stack if they were pushed above */
        PLy_global_args_pop(proc);

        Py_XDECREF(plargs);
        Py_XDECREF(plrv);

        /*
         * If there was an error within a SRF, the iterator might not have
         * been exhausted yet.  Clear it so the next invocation of the
         * function will start the iteration again.  (This code is probably
         * unnecessary now; plpython_srf_cleanup_callback should take care of
         * cleanup.  But it doesn't hurt anything to do it here.)
         */
        if (srfstate)
        {
            Py_XDECREF(srfstate->iter);
            srfstate->iter = NULL;
            /* And drop any saved args; we won't need them */
            if (srfstate->savedargs)
                PLy_function_drop_args(srfstate->savedargs);
            srfstate->savedargs = NULL;
        }

        PG_RE_THROW();
    }
    PG_END_TRY();

    error_context_stack = plerrcontext.previous;

    /* Pop old arguments from the stack if they were pushed above */
    PLy_global_args_pop(proc);

    Py_XDECREF(plargs);
    Py_DECREF(plrv);

    if (srfstate)
    {
        /* We're in a SRF, exit appropriately */
        if (srfstate->iter == NULL)
        {
            /* Iterator exhausted, so we're done */
            SRF_RETURN_DONE(funcctx);
        }
        else if (fcinfo->isnull)
            SRF_RETURN_NEXT_NULL(funcctx);
        else
            SRF_RETURN_NEXT(funcctx, rv);
    }

    /* Plain function, just return the Datum value (possibly null) */
    return rv;
}

/* trigger subhandler
 *
 * the python function is expected to return Py_None if the tuple is
 * acceptable and unmodified.  Otherwise it should return a PyString
 * object who's value is SKIP, or MODIFY.  SKIP means don't perform
 * this action.  MODIFY means the tuple has been modified, so update
 * tuple and perform action.  SKIP and MODIFY assume the trigger fires
 * BEFORE the event and is ROW level.  postgres expects the function
 * to take no arguments and return an argument of type trigger.
 */
HeapTuple
PLy_exec_trigger(FunctionCallInfo fcinfo, PLyProcedure *proc)
{
    HeapTuple   rv = NULL;
    PyObject   *volatile plargs = NULL;
    PyObject   *volatile plrv = NULL;
    TriggerData *tdata;
    TupleDesc   rel_descr;

    Assert(CALLED_AS_TRIGGER(fcinfo));
    tdata = (TriggerData *) fcinfo->context;

    /*
     * Input/output conversion for trigger tuples.  We use the result and
     * result_in fields to store the tuple conversion info.  We do this over
     * again on each call to cover the possibility that the relation's tupdesc
     * changed since the trigger was last called.  The PLy_xxx_setup_func
     * calls should only happen once, but PLy_input_setup_tuple and
     * PLy_output_setup_tuple are responsible for not doing repetitive work.
     */
    rel_descr = RelationGetDescr(tdata->tg_relation);
    if (proc->result.typoid != rel_descr->tdtypeid)
        PLy_output_setup_func(&proc->result, proc->mcxt,
                              rel_descr->tdtypeid,
                              rel_descr->tdtypmod,
                              proc);
    if (proc->result_in.typoid != rel_descr->tdtypeid)
        PLy_input_setup_func(&proc->result_in, proc->mcxt,
                             rel_descr->tdtypeid,
                             rel_descr->tdtypmod,
                             proc);
    PLy_output_setup_tuple(&proc->result, rel_descr, proc);
    PLy_input_setup_tuple(&proc->result_in, rel_descr, proc);

    PG_TRY();
    {
        int         rc PG_USED_FOR_ASSERTS_ONLY;

        rc = SPI_register_trigger_data(tdata);
        Assert(rc >= 0);

        plargs = PLy_trigger_build_args(fcinfo, proc, &rv);
        plrv = PLy_procedure_call(proc, "TD", plargs);

        Assert(plrv != NULL);

        /*
         * Disconnect from SPI manager
         */
        if (SPI_finish() != SPI_OK_FINISH)
            elog(ERROR, "SPI_finish failed");

        /*
         * return of None means we're happy with the tuple
         */
        if (plrv != Py_None)
        {
            char       *srv;

            if (PyString_Check(plrv))
                srv = PyString_AsString(plrv);
            else if (PyUnicode_Check(plrv))
                srv = PLyUnicode_AsString(plrv);
            else
            {
                ereport(ERROR,
                        (errcode(ERRCODE_DATA_EXCEPTION),
                         errmsg("unexpected return value from trigger procedure"),
                         errdetail("Expected None or a string.")));
                srv = NULL;     /* keep compiler quiet */
            }

            if (pg_strcasecmp(srv, "SKIP") == 0)
                rv = NULL;
            else if (pg_strcasecmp(srv, "MODIFY") == 0)
            {
                TriggerData *tdata = (TriggerData *) fcinfo->context;

                if (TRIGGER_FIRED_BY_INSERT(tdata->tg_event) ||
                    TRIGGER_FIRED_BY_UPDATE(tdata->tg_event))
                    rv = PLy_modify_tuple(proc, plargs, tdata, rv);
                else
                    ereport(WARNING,
                            (errmsg("PL/Python trigger function returned \"MODIFY\" in a DELETE trigger -- ignored")));
            }
            else if (pg_strcasecmp(srv, "OK") != 0)
            {
                /*
                 * accept "OK" as an alternative to None; otherwise, raise an
                 * error
                 */
                ereport(ERROR,
                        (errcode(ERRCODE_DATA_EXCEPTION),
                         errmsg("unexpected return value from trigger procedure"),
                         errdetail("Expected None, \"OK\", \"SKIP\", or \"MODIFY\".")));
            }
        }
    }
    PG_CATCH();
    {
        Py_XDECREF(plargs);
        Py_XDECREF(plrv);

        PG_RE_THROW();
    }
    PG_END_TRY();

    Py_DECREF(plargs);
    Py_DECREF(plrv);

    return rv;
}

/* helper functions for Python code execution */

static PyObject *
PLy_function_build_args(FunctionCallInfo fcinfo, PLyProcedure *proc)
{
    PyObject   *volatile arg = NULL;
    PyObject   *volatile args = NULL;
    int         i;

    PG_TRY();
    {
        args = PyList_New(proc->nargs);
        if (!args)
            return NULL;

        for (i = 0; i < proc->nargs; i++)
        {
            PLyDatumToOb *arginfo = &proc->args[i];

            if (fcinfo->args[i].isnull)
                arg = NULL;
            else
                arg = PLy_input_convert(arginfo, fcinfo->args[i].value);

            if (arg == NULL)
            {
                Py_INCREF(Py_None);
                arg = Py_None;
            }

            if (PyList_SetItem(args, i, arg) == -1)
                PLy_elog(ERROR, "PyList_SetItem() failed, while setting up arguments");

            if (proc->argnames && proc->argnames[i] &&
                PyDict_SetItemString(proc->globals, proc->argnames[i], arg) == -1)
                PLy_elog(ERROR, "PyDict_SetItemString() failed, while setting up arguments");
            arg = NULL;
        }

        /* Set up output conversion for functions returning RECORD */
        if (proc->result.typoid == RECORDOID)
        {
            TupleDesc   desc;

            if (get_call_result_type(fcinfo, NULL, &desc) != TYPEFUNC_COMPOSITE)
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("function returning record called in context "
                                "that cannot accept type record")));

            /* cache the output conversion functions */
            PLy_output_setup_record(&proc->result, desc, proc);
        }
    }
    PG_CATCH();
    {
        Py_XDECREF(arg);
        Py_XDECREF(args);

        PG_RE_THROW();
    }
    PG_END_TRY();

    return args;
}

/*
 * Construct a PLySavedArgs struct representing the current values of the
 * procedure's arguments in its globals dict.  This can be used to restore
 * those values when exiting a recursive call level or returning control to a
 * set-returning function.
 *
 * This would not be necessary except for an ancient decision to make args
 * available via the proc's globals :-( ... but we're stuck with that now.
 */
static PLySavedArgs *
PLy_function_save_args(PLyProcedure *proc)
{
    PLySavedArgs *result;

    /* saved args are always allocated in procedure's context */
    result = (PLySavedArgs *)
        MemoryContextAllocZero(proc->mcxt,
                               offsetof(PLySavedArgs, namedargs) +
                               proc->nargs * sizeof(PyObject *));
    result->nargs = proc->nargs;

    /* Fetch the "args" list */
    result->args = PyDict_GetItemString(proc->globals, "args");
    Py_XINCREF(result->args);

    /* Fetch all the named arguments */
    if (proc->argnames)
    {
        int         i;

        for (i = 0; i < result->nargs; i++)
        {
            if (proc->argnames[i])
            {
                result->namedargs[i] = PyDict_GetItemString(proc->globals,
                                                            proc->argnames[i]);
                Py_XINCREF(result->namedargs[i]);
            }
        }
    }

    return result;
}

/*
 * Restore procedure's arguments from a PLySavedArgs struct,
 * then free the struct.
 */
static void
PLy_function_restore_args(PLyProcedure *proc, PLySavedArgs *savedargs)
{
    /* Restore named arguments into their slots in the globals dict */
    if (proc->argnames)
    {
        int         i;

        for (i = 0; i < savedargs->nargs; i++)
        {
            if (proc->argnames[i] && savedargs->namedargs[i])
            {
                PyDict_SetItemString(proc->globals, proc->argnames[i],
                                     savedargs->namedargs[i]);
                Py_DECREF(savedargs->namedargs[i]);
            }
        }
    }

    /* Restore the "args" object, too */
    if (savedargs->args)
    {
        PyDict_SetItemString(proc->globals, "args", savedargs->args);
        Py_DECREF(savedargs->args);
    }

    /* And free the PLySavedArgs struct */
    pfree(savedargs);
}

/*
 * Free a PLySavedArgs struct without restoring the values.
 */
static void
PLy_function_drop_args(PLySavedArgs *savedargs)
{
    int         i;

    /* Drop references for named args */
    for (i = 0; i < savedargs->nargs; i++)
    {
        Py_XDECREF(savedargs->namedargs[i]);
    }

    /* Drop ref to the "args" object, too */
    Py_XDECREF(savedargs->args);

    /* And free the PLySavedArgs struct */
    pfree(savedargs);
}

/*
 * Save away any existing arguments for the given procedure, so that we can
 * install new values for a recursive call.  This should be invoked before
 * doing PLy_function_build_args().
 *
 * NB: caller must ensure that PLy_global_args_pop gets invoked once, and
 * only once, per successful completion of PLy_global_args_push.  Otherwise
 * we'll end up out-of-sync between the actual call stack and the contents
 * of proc->argstack.
 */
static void
PLy_global_args_push(PLyProcedure *proc)
{
    /* We only need to push if we are already inside some active call */
    if (proc->calldepth > 0)
    {
        PLySavedArgs *node;

        /* Build a struct containing current argument values */
        node = PLy_function_save_args(proc);

        /*
         * Push the saved argument values into the procedure's stack.  Once we
         * modify either proc->argstack or proc->calldepth, we had better
         * return without the possibility of error.
         */
        node->next = proc->argstack;
        proc->argstack = node;
    }
    proc->calldepth++;
}

/*
 * Pop old arguments when exiting a recursive call.
 *
 * Note: the idea here is to adjust the proc's callstack state before doing
 * anything that could possibly fail.  In event of any error, we want the
 * callstack to look like we've done the pop.  Leaking a bit of memory is
 * tolerable.
 */
static void
PLy_global_args_pop(PLyProcedure *proc)
{
    Assert(proc->calldepth > 0);
    /* We only need to pop if we were already inside some active call */
    if (proc->calldepth > 1)
    {
        PLySavedArgs *ptr = proc->argstack;

        /* Pop the callstack */
        Assert(ptr != NULL);
        proc->argstack = ptr->next;
        proc->calldepth--;

        /* Restore argument values, then free ptr */
        PLy_function_restore_args(proc, ptr);
    }
    else
    {
        /* Exiting call depth 1 */
        Assert(proc->argstack == NULL);
        proc->calldepth--;

        /*
         * We used to delete the named arguments (but not "args") from the
         * proc's globals dict when exiting the outermost call level for a
         * function.  This seems rather pointless though: nothing can see the
         * dict until the function is called again, at which time we'll
         * overwrite those dict entries.  So don't bother with that.
         */
    }
}

/*
 * Memory context deletion callback for cleaning up a PLySRFState.
 * We need this in case execution of the SRF is terminated early,
 * due to error or the caller simply not running it to completion.
 */
static void
plpython_srf_cleanup_callback(void *arg)
{
    PLySRFState *srfstate = (PLySRFState *) arg;

    /* Release refcount on the iter, if we still have one */
    Py_XDECREF(srfstate->iter);
    srfstate->iter = NULL;
    /* And drop any saved args; we won't need them */
    if (srfstate->savedargs)
        PLy_function_drop_args(srfstate->savedargs);
    srfstate->savedargs = NULL;
}

static void
plpython_return_error_callback(void *arg)
{
    PLyExecutionContext *exec_ctx = PLy_current_execution_context();

    if (exec_ctx->curr_proc &&
        !exec_ctx->curr_proc->is_procedure)
        errcontext("while creating return value");
}

static PyObject *
PLy_trigger_build_args(FunctionCallInfo fcinfo, PLyProcedure *proc, HeapTuple *rv)
{
    TriggerData *tdata = (TriggerData *) fcinfo->context;
    TupleDesc   rel_descr = RelationGetDescr(tdata->tg_relation);
    PyObject   *pltname,
               *pltevent,
               *pltwhen,
               *pltlevel,
               *pltrelid,
               *plttablename,
               *plttableschema;
    PyObject   *pltargs,
               *pytnew,
               *pytold;
    PyObject   *volatile pltdata = NULL;
    char       *stroid;

    PG_TRY();
    {
        pltdata = PyDict_New();
        if (!pltdata)
            return NULL;

        pltname = PyString_FromString(tdata->tg_trigger->tgname);
        PyDict_SetItemString(pltdata, "name", pltname);
        Py_DECREF(pltname);

        stroid = DatumGetCString(DirectFunctionCall1(oidout,
                                                     ObjectIdGetDatum(tdata->tg_relation->rd_id)));
        pltrelid = PyString_FromString(stroid);
        PyDict_SetItemString(pltdata, "relid", pltrelid);
        Py_DECREF(pltrelid);
        pfree(stroid);

        stroid = SPI_getrelname(tdata->tg_relation);
        plttablename = PyString_FromString(stroid);
        PyDict_SetItemString(pltdata, "table_name", plttablename);
        Py_DECREF(plttablename);
        pfree(stroid);

        stroid = SPI_getnspname(tdata->tg_relation);
        plttableschema = PyString_FromString(stroid);
        PyDict_SetItemString(pltdata, "table_schema", plttableschema);
        Py_DECREF(plttableschema);
        pfree(stroid);

        if (TRIGGER_FIRED_BEFORE(tdata->tg_event))
            pltwhen = PyString_FromString("BEFORE");
        else if (TRIGGER_FIRED_AFTER(tdata->tg_event))
            pltwhen = PyString_FromString("AFTER");
        else if (TRIGGER_FIRED_INSTEAD(tdata->tg_event))
            pltwhen = PyString_FromString("INSTEAD OF");
        else
        {
            elog(ERROR, "unrecognized WHEN tg_event: %u", tdata->tg_event);
            pltwhen = NULL;     /* keep compiler quiet */
        }
        PyDict_SetItemString(pltdata, "when", pltwhen);
        Py_DECREF(pltwhen);

        if (TRIGGER_FIRED_FOR_ROW(tdata->tg_event))
        {
            pltlevel = PyString_FromString("ROW");
            PyDict_SetItemString(pltdata, "level", pltlevel);
            Py_DECREF(pltlevel);

            /*
             * Note: In BEFORE trigger, stored generated columns are not
             * computed yet, so don't make them accessible in NEW row.
             */

            if (TRIGGER_FIRED_BY_INSERT(tdata->tg_event))
            {
                pltevent = PyString_FromString("INSERT");

                PyDict_SetItemString(pltdata, "old", Py_None);
                pytnew = PLy_input_from_tuple(&proc->result_in,
                                              tdata->tg_trigtuple,
                                              rel_descr,
                                              !TRIGGER_FIRED_BEFORE(tdata->tg_event));
                PyDict_SetItemString(pltdata, "new", pytnew);
                Py_DECREF(pytnew);
                *rv = tdata->tg_trigtuple;
            }
            else if (TRIGGER_FIRED_BY_DELETE(tdata->tg_event))
            {
                pltevent = PyString_FromString("DELETE");

                PyDict_SetItemString(pltdata, "new", Py_None);
                pytold = PLy_input_from_tuple(&proc->result_in,
                                              tdata->tg_trigtuple,
                                              rel_descr,
                                              true);
                PyDict_SetItemString(pltdata, "old", pytold);
                Py_DECREF(pytold);
                *rv = tdata->tg_trigtuple;
            }
            else if (TRIGGER_FIRED_BY_UPDATE(tdata->tg_event))
            {
                pltevent = PyString_FromString("UPDATE");

                pytnew = PLy_input_from_tuple(&proc->result_in,
                                              tdata->tg_newtuple,
                                              rel_descr,
                                              !TRIGGER_FIRED_BEFORE(tdata->tg_event));
                PyDict_SetItemString(pltdata, "new", pytnew);
                Py_DECREF(pytnew);
                pytold = PLy_input_from_tuple(&proc->result_in,
                                              tdata->tg_trigtuple,
                                              rel_descr,
                                              true);
                PyDict_SetItemString(pltdata, "old", pytold);
                Py_DECREF(pytold);
                *rv = tdata->tg_newtuple;
            }
            else
            {
                elog(ERROR, "unrecognized OP tg_event: %u", tdata->tg_event);
                pltevent = NULL;    /* keep compiler quiet */
            }

            PyDict_SetItemString(pltdata, "event", pltevent);
            Py_DECREF(pltevent);
        }
        else if (TRIGGER_FIRED_FOR_STATEMENT(tdata->tg_event))
        {
            pltlevel = PyString_FromString("STATEMENT");
            PyDict_SetItemString(pltdata, "level", pltlevel);
            Py_DECREF(pltlevel);

            PyDict_SetItemString(pltdata, "old", Py_None);
            PyDict_SetItemString(pltdata, "new", Py_None);
            *rv = NULL;

            if (TRIGGER_FIRED_BY_INSERT(tdata->tg_event))
                pltevent = PyString_FromString("INSERT");
            else if (TRIGGER_FIRED_BY_DELETE(tdata->tg_event))
                pltevent = PyString_FromString("DELETE");
            else if (TRIGGER_FIRED_BY_UPDATE(tdata->tg_event))
                pltevent = PyString_FromString("UPDATE");
            else if (TRIGGER_FIRED_BY_TRUNCATE(tdata->tg_event))
                pltevent = PyString_FromString("TRUNCATE");
            else
            {
                elog(ERROR, "unrecognized OP tg_event: %u", tdata->tg_event);
                pltevent = NULL;    /* keep compiler quiet */
            }

            PyDict_SetItemString(pltdata, "event", pltevent);
            Py_DECREF(pltevent);
        }
        else
            elog(ERROR, "unrecognized LEVEL tg_event: %u", tdata->tg_event);

        if (tdata->tg_trigger->tgnargs)
        {
            /*
             * all strings...
             */
            int         i;
            PyObject   *pltarg;

            pltargs = PyList_New(tdata->tg_trigger->tgnargs);
            if (!pltargs)
            {
                Py_DECREF(pltdata);
                return NULL;
            }
            for (i = 0; i < tdata->tg_trigger->tgnargs; i++)
            {
                pltarg = PyString_FromString(tdata->tg_trigger->tgargs[i]);

                /*
                 * stolen, don't Py_DECREF
                 */
                PyList_SetItem(pltargs, i, pltarg);
            }
        }
        else
        {
            Py_INCREF(Py_None);
            pltargs = Py_None;
        }
        PyDict_SetItemString(pltdata, "args", pltargs);
        Py_DECREF(pltargs);
    }
    PG_CATCH();
    {
        Py_XDECREF(pltdata);
        PG_RE_THROW();
    }
    PG_END_TRY();

    return pltdata;
}

/*
 * Apply changes requested by a MODIFY return from a trigger function.
 */
static HeapTuple
PLy_modify_tuple(PLyProcedure *proc, PyObject *pltd, TriggerData *tdata,
                 HeapTuple otup)
{
    HeapTuple   rtup;
    PyObject   *volatile plntup;
    PyObject   *volatile plkeys;
    PyObject   *volatile plval;
    Datum      *volatile modvalues;
    bool       *volatile modnulls;
    bool       *volatile modrepls;
    ErrorContextCallback plerrcontext;

    plerrcontext.callback = plpython_trigger_error_callback;
    plerrcontext.previous = error_context_stack;
    error_context_stack = &plerrcontext;

    plntup = plkeys = plval = NULL;
    modvalues = NULL;
    modnulls = NULL;
    modrepls = NULL;

    PG_TRY();
    {
        TupleDesc   tupdesc;
        int         nkeys,
                    i;

        if ((plntup = PyDict_GetItemString(pltd, "new")) == NULL)
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_OBJECT),
                     errmsg("TD[\"new\"] deleted, cannot modify row")));
        Py_INCREF(plntup);
        if (!PyDict_Check(plntup))
            ereport(ERROR,
                    (errcode(ERRCODE_DATATYPE_MISMATCH),
                     errmsg("TD[\"new\"] is not a dictionary")));

        plkeys = PyDict_Keys(plntup);
        nkeys = PyList_Size(plkeys);

        tupdesc = RelationGetDescr(tdata->tg_relation);

        modvalues = (Datum *) palloc0(tupdesc->natts * sizeof(Datum));
        modnulls = (bool *) palloc0(tupdesc->natts * sizeof(bool));
        modrepls = (bool *) palloc0(tupdesc->natts * sizeof(bool));

        for (i = 0; i < nkeys; i++)
        {
            PyObject   *platt;
            char       *plattstr;
            int         attn;
            PLyObToDatum *att;

            platt = PyList_GetItem(plkeys, i);
            if (PyString_Check(platt))
                plattstr = PyString_AsString(platt);
            else if (PyUnicode_Check(platt))
                plattstr = PLyUnicode_AsString(platt);
            else
            {
                ereport(ERROR,
                        (errcode(ERRCODE_DATATYPE_MISMATCH),
                         errmsg("TD[\"new\"] dictionary key at ordinal position %d is not a string", i)));
                plattstr = NULL;    /* keep compiler quiet */
            }
            attn = SPI_fnumber(tupdesc, plattstr);
            if (attn == SPI_ERROR_NOATTRIBUTE)
                ereport(ERROR,
                        (errcode(ERRCODE_UNDEFINED_COLUMN),
                         errmsg("key \"%s\" found in TD[\"new\"] does not exist as a column in the triggering row",
                                plattstr)));
            if (attn <= 0)
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("cannot set system attribute \"%s\"",
                                plattstr)));
            if (TupleDescAttr(tupdesc, attn - 1)->attgenerated)
                ereport(ERROR,
                        (errcode(ERRCODE_E_R_I_E_TRIGGER_PROTOCOL_VIOLATED),
                         errmsg("cannot set generated column \"%s\"",
                                plattstr)));

            plval = PyDict_GetItem(plntup, platt);
            if (plval == NULL)
                elog(FATAL, "Python interpreter is probably corrupted");

            Py_INCREF(plval);

            /* We assume proc->result is set up to convert tuples properly */
            att = &proc->result.u.tuple.atts[attn - 1];

            modvalues[attn - 1] = PLy_output_convert(att,
                                                     plval,
                                                     &modnulls[attn - 1]);
            modrepls[attn - 1] = true;

            Py_DECREF(plval);
            plval = NULL;
        }

        rtup = heap_modify_tuple(otup, tupdesc, modvalues, modnulls, modrepls);
    }
    PG_CATCH();
    {
        Py_XDECREF(plntup);
        Py_XDECREF(plkeys);
        Py_XDECREF(plval);

        if (modvalues)
            pfree(modvalues);
        if (modnulls)
            pfree(modnulls);
        if (modrepls)
            pfree(modrepls);

        PG_RE_THROW();
    }
    PG_END_TRY();

    Py_DECREF(plntup);
    Py_DECREF(plkeys);

    pfree(modvalues);
    pfree(modnulls);
    pfree(modrepls);

    error_context_stack = plerrcontext.previous;

    return rtup;
}

static void
plpython_trigger_error_callback(void *arg)
{
    PLyExecutionContext *exec_ctx = PLy_current_execution_context();

    if (exec_ctx->curr_proc)
        errcontext("while modifying trigger row");
}

/* execute Python code, propagate Python errors to the backend */
static PyObject *
PLy_procedure_call(PLyProcedure *proc, const char *kargs, PyObject *vargs)
{
    PyObject   *rv;
    int volatile save_subxact_level = list_length(explicit_subtransactions);

    PyDict_SetItemString(proc->globals, kargs, vargs);

    PG_TRY();
    {
#if PY_VERSION_HEX >= 0x03020000
        rv = PyEval_EvalCode(proc->code,
                             proc->globals, proc->globals);
#else
        rv = PyEval_EvalCode((PyCodeObject *) proc->code,
                             proc->globals, proc->globals);
#endif

        /*
         * Since plpy will only let you close subtransactions that you
         * started, you cannot *unnest* subtransactions, only *nest* them
         * without closing.
         */
        Assert(list_length(explicit_subtransactions) >= save_subxact_level);
    }
    PG_CATCH();
    {
        PLy_abort_open_subtransactions(save_subxact_level);
        PG_RE_THROW();
    }
    PG_END_TRY();

    PLy_abort_open_subtransactions(save_subxact_level);

    /* If the Python code returned an error, propagate it */
    if (rv == NULL)
        PLy_elog(ERROR, NULL);

    return rv;
}

/*
 * Abort lingering subtransactions that have been explicitly started
 * by plpy.subtransaction().start() and not properly closed.
 */
static void
PLy_abort_open_subtransactions(int save_subxact_level)
{
    Assert(save_subxact_level >= 0);

    while (list_length(explicit_subtransactions) > save_subxact_level)
    {
        PLySubtransactionData *subtransactiondata;

        Assert(explicit_subtransactions != NIL);

        ereport(WARNING,
                (errmsg("forcibly aborting a subtransaction that has not been exited")));

        RollbackAndReleaseCurrentSubTransaction();

        subtransactiondata = (PLySubtransactionData *) linitial(explicit_subtransactions);
        explicit_subtransactions = list_delete_first(explicit_subtransactions);

        MemoryContextSwitchTo(subtransactiondata->oldcontext);
        CurrentResourceOwner = subtransactiondata->oldowner;
        pfree(subtransactiondata);
    }
}