Consistently use "superuser" instead of "super user"

[pgsql.git] / src / pl / plpython / plpy_exec.c

/*
 * 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 "plpy_elog.h"
#include "plpy_exec.h"
#include "plpy_main.h"
#include "plpy_procedure.h"
#include "plpy_subxactobject.h"
#include "plpython.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
#include "utils/typcache.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_FINALLY();
        {
                Py_XDECREF(plargs);
                Py_XDECREF(plrv);
        }
        PG_END_TRY();

        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 = NULL;
        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_FINALLY();
        {
                PLy_abort_open_subtransactions(save_subxact_level);
        }
        PG_END_TRY();

        /* 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);
        }
}