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 "utils/builtins.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->argnull[i])
				arg = NULL;
			else
				arg = PLy_input_convert(arginfo, fcinfo->arg[i]);

			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);

			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);
				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);
				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);
				PyDict_SetItemString(pltdata, "new", pytnew);
				Py_DECREF(pytnew);
				pytold = PLy_input_from_tuple(&proc->result_in,
											  tdata->tg_trigtuple,
											  rel_descr);
				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)));

			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);
	}
}